bolted joints integrity management guidelines

Guidelines for the management ofthe integrity of bolted jointsfor pressurised systems

2nd edition

IPAn IP Publication

GUIDELINES FOR THEMANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS

FOR PRESSURISED SYSTEMS

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GUIDELINES FOR THEMANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS

FOR PRESSURISED SYSTEMS

June 2007Second edition

Published byENERGY INSTITUTE, LONDON

The Energy Institute is a professional membership body incorporated by Royal Charter 2003Registered charity number 1097899

Endorsed byOil & Gas UK, HSE OSD and the ECITB

The Energy Institute gratefully acknowledges the financial contributions towards the scientific andtechnical programme from the following companies:

BG GroupBHP Billiton LimitedBP Exploration Operating Co LtdBP Oil UK LtdChevronConocoPhillips LtdENIExxonMobil International LtdKuwait Petroleum International LtdMaersk Oil North Sea UK Limited

Murco Petroleum LtdNexenSaudi AramcoShell UK Oil Products LimitedShell U.K. Exploration and Production LtdStatoil (U.K.) LimitedTalisman Energy (UK) LtdTotal E&P UK plcTotal UK Limited

Copyright © 2007 by the Energy Institute, London:The Energy Institute is a professional membership body incorporated by Royal Charter 2003.Registered charity number 1097899, EnglandAll rights reserved

No part of this book may be reproduced by any means, or transmitted or translated into a machine language withoutthe written permission of the publisher.

The information contained in this publication is provided as guidance only and while every reasonable care has beentaken to ensure the accuracy of its contents, the Energy Institute cannot accept any responsibility for any action taken,or not taken, on the basis of this information. The Energy Institute shall not be liable to any person for any loss ordamage which may arise from the use of any of the information contained in any of its publications.

The above disclaimer is not intended to restrict or exclude liability for death or personal injury caused by ownnegligence.

ISBN 978 0 85293 461 6Published by the Energy Institute

Further copies can be obtained from Portland Customer Services, Commerce Way,Whitehall Industrial Estate, Colchester CO2 8HP, UK. Tel: +44 (0) 1206 796 351email: [email protected]

Electronic access to EI and IP publications is available via our website, www.energyinstpubs.org.uk.Documents can be purchased online as downloadable pdfs or on an annual subscription for single users andcompanies. For more information, contact the EI Publications Team,e: [email protected]

IV

CONTENTS

Foreword

Acknowledgements

1 Introduction

2 Bolted joint technology and practice2.1 Overview2.2 Types of bolted joints2.3 Bolted pipe joint components2.4 Principles of joint assembly and disassembly2.5 Controlled tightening of joints2.6 Bolted joint reliability2.7 Integrity testing

3 Criticality assessment3.1 Introduction3.2 Assessing the risks with bolted joints

4 Training and competence4.1 Introduction4.2 Competence management4.3 Training4.4 Ongoing competence4.5 Training in engineering construction skills (TECSkills)4.6 Vocational qualifications4.7 Independent accreditation organisations

5 Records, data management and tagging5.1 Joint identification5.2 Records and data management5.3 Review

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Contents Cont....

6 Management of leaks6.1 Introduction6.2 Engineering risk assessment of leaks6.3 Stages at which leaks occur6.4 Corrective actions6.5 Definition and detection of leaks6.6 Managing leaks and repairs6.7 Learning from leaks

7 In-service inspection7.1 Introduction7.2 Risk assessment7.3 Degradation mechanisms7.4 Inspection techniques7.5 Defect mitigation measures

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FOREWORD

The first edition of this publication was commissioned by the upstream oil and gas industry as part of anHSE/industry drive to reduce the incidence of hydrocarbon releases. Leaking joints have been the main cause ofhydrocarbon releases on UK Continental Shelf offshore installations. Similar concerns exist for many onshorefacilities handling petroleum and other dangerous substances.

In 2005, the UKOOA (now Oil & Gas UK) led Installation Integrity Working Group (IIWG) requested that theEnergy Institute manage the review and revision of the UKOOA/IP Guidelines for the management of integrity ofbolted pipe joints, first published in June 2002. This project required the formation of a cross-industry Work Group(WG), which included some members that also contributed to the first edition. Other members were drawn from theparent IIWG, consultants and from the industry training organisation, ECITB.

This updated publication supports the principles of the IIWG in making available good practice on key integrityissues and is referenced in Oil and Gas UK Hydrocarbon Release Reduction Toolkit, which itself is referenced inthe Oil and Gas UK Asset Integrity Toolkit.

During the review process, the WG elected to widen the scope to include bolted joints used within pressurisedsystems and not just pipe joints as is the case for the first edition, and to ensure that the publication is applicable bothto onshore facilities as well as offshore oil and gas installations.

This publication provides guidance only and is intended to improve knowledge of good practice which should assistoperators to develop their own management systems for bolted pipe joints. While every reasonable care has beentaken to ensure the accuracy and relevance of its contents, the Energy Institute, its sponsoring companies, sectionwriters and the WG members listed in the Acknowledgements who have contributed to its preparation, cannot acceptany responsibility for any action taken, or not taken, on the basis of this information. The Energy Institute shall notbe liable to any person for any loss or damage which may arise from the use of any of the information contained inany of its publications.

This publication will be reviewed in the future and it would be of considerable assistance for any subsequent revisionif users would send comments or suggestions for improvements to:

The Technical Department,Energy Institute,61 New Cavendish Street,LondonW1G 7ARe: [email protected]

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ACKNOWLEDGEMENTS

As Work Group members, the Institute wishes to record its appreciation of the work carried out by the following:Sub Group Champions, who have managed the coordination and compilation of designated sections throughleadership of their respective volunteer sub-groups and through providing authorship expertise:

Stuart Brooks BP Exploration Operating Company Ltd.Rod Corbet RotaboltAnderson Foster Total E&P UK plcJim MacRae Nexen Petroleum UK Ltd.Robert Noble Hydratight

Sub Group members, who have provided valued input into their designated sections:

Blair Barclay ECITBKeith Dunnett CNR InternationalBill Eccles Bolt Science (Hytorc)Alan Gardner ConsultantTim Jervis Shell Exploration & ProductionGary Milne HydratightPhillip Roberts Shell Exploration & ProductionRavi Sharma HSEMike Shearer Lloyds Register EMEALawrence Turner Shell Exploration & ProductionMark Williams Klinger UK LtdPat Wright RGB Ltd.

Assistance was also provided by the following other Work Group members:

Gwyn Ashby Mitsui BabcockPeter Barker Marathon OilArunesh Bose Lloyds Register EMEAMartin Carter BHP BillitonKevin Fraser IMESNorrie Hewie Hess CorporationGavin Smith Novus SealingRoy Smith HytorcJan Webjorn Verax

Liaison with other organisations was provided by:

EEMUA Andrew PearsonIMechE Pressure Systems Group Chris Boocock

Oil & Gas UK (formerly UKOOA) Bob Kyle

Technical authorship and editing:

Phil Smith ODL

The revision/review project was coordinated and managed by Keith Hart FEI, Energy Institute, Upstream TechnicalManager.

The Institute also wishes to recognise the contribution made by those who have provided comments on the Draftdocument which was issued during an industry consultation period.

1

INTRODUCTION

A bolted joint is one of many critical components of apressurised system. Dependent upon the contents andpressure of the system, leakage or failure of a boltedjoint can have potentially catastrophic consequences. Tomeet this challenge, every operator of pressurisedsystems should have in place a system to positively andactively manage the integrity of bolted joints. It isexpected that such a system will be built around theprinciple of continuous improvement (see Figure 1.1).

This document describes the principles and goodpractice for the establishment of a management system

for bolted joints in pressurised systems. Individually thesections of this document provide details of what isconsidered good practice in the key areas of ensuringjoint integrity. Together they provide the framework fora management system.

This document is not intended as a design guide forbolted joints, but as a guide to how to manage jointsduring construction and commissioning phases andthrough their operational life. It provides a frameworkto achieve this based on working with a correctlydesigned joint.

Figure 1.1: Essential elements of a management system

The following are considered essential elements ofa management system which must be applied to ensurethat the system is implemented and remains effective:

— OwnershipThere should be an identified owner of themanagement system, responsible not only for itsimplementation and ongoing maintenance, but alsofor communicating its aims and objectivesthroughout the organisation. The owner shouldstate the expectations for the system and monitor itseffectiveness.

— Technology and PracticeGood practice with regard to selection and controlof assembly, tightening and assurance of boltedjoints should be applied. Understanding of thetheory and practice of bolted joints anddevelopment of appropriate procedures should beencouraged throughout the organisation.

— Criticality AssessmentThe range of services, pressures and conditionswhich bolted joints experience varies considerably.Each joint should undergo a criticality assessmentwhich will determine the levels of inspection,assembly control, tightening technique, testing,assurance and in-service inspection relevant to thejoint.

— Training and CompetenceEveryone with an influence on joint integrity in theorganisation should be aware of the managementsystem, its objectives, expectations and effects onproject planning and day-to-day working. Goodawareness needs to be maintained. Any staffworking on bolted joints should be appropriatelytrained and competent.

— Records, Data Management and TaggingThe certainty of achieving joint integrity increasesif historical data exist on the activities carried out

in the past, ideally from original construction of thejoint, linked to the design specification of the joint.Providing and recording traceable data encouragesbest practice at the time of the activity, and willprovide useful planning data for the next time thejoint is disturbed.

In-service InspectionLearning from both positive performance andincidents is important. A management systemshould include the means for gathering relevantdata on joints which are successful and those thathave incidents or leakage issues. These should becollected by everyone involved in bolted joints, andperiodically reviewed and analysed to establishtrends, issues and improvement opportunities.

Management of LeaksThe objective of a correctly designed and installedbolted joint is to provide a long-term tight seal andprevent ingress or egress of fluids through the joint.However, leaks can occur and managing theinvestigation and repair of the leak is essential toavoid recurrence. It can also provide useful data forprevention on other projects.

Analysis, Learning and ImprovementAnalysis of leakage and inspection data coupledwith formal reviews of the management systemshould occur at agreed intervals by the owner andusers. Results obtained from commissioning,incident analysis and in-service inspections shouldbe used to generate ideas for continuousimprovement.

Easily monitored but meaningful performancestandards should be put in place at launch toquantify the contribution being made by themanagement system and evaluate user satisfaction.Feedback on good practice in integrity issues andcauses and solutions to incidents should beprovided both internally and to industry tocontribute to continuous improvement.

BOLTED JOINT TECHNOLOGYAND PRACTICE

2.1 OVERVIEW

This section gives a brief outline of how joints work andprovides guidance on the safe and efficient assemblyand disassembly of flanged joints and clamps. It alsodiscusses basic proposals for integrity testing. Thescope of these Guidelines covers all pressure-containingjoints including pipelines, pressure vessels such asreactors and heat exchangers, associated valves andother pressure-containing equipment. Due to operatingconditions with heat exchangers and reactors,particularly temperature gradients, different metal jointcomponents and thermal and pressure cycling, a higherlevel of control and assurance of bolt load is generallyrequired compared to, for example, piping jointssubjected to static pressure only. The principles set outare generic in nature and not exclusive to pressurecontainment applications; they can be applied to boltedjoints subjected to other service conditions such asfatigue, vibration and structural loading.

The flanged joint is deceptively simple yet, incommon with the welded joint, its integrity relies on anumber of parameters including the basic design,structural and metallurgical quality of its componentsand achieving the required design clamp force onassembly. Important to meeting these assembled designobjectives is the selection of suitable installationprocedures and tools that are applied by competentoperators.

The importance of planning the joint assembly,preparation of all components, procedures, tooling andensuring application of the correct methodology isessential.

Pipework and pressure systems are designed tomeet varying operational conditions. In order to avoidfailure, it is very important that the relevant pipingspecifications for materials and components are adheredto in full.

There are many types of bolted joint and only someof the more commonly used are mentioned here but asmentioned previously, the basic reliability parametersand procedures applied are the same for all.

2.2 TYPES OF BOLTED JOINTS

2.2.1 Flange joints

The most common type of joint is made up of two pipeflanges to ASME B16.5 design code, between which agasket is compressed by the installed bolting. Similararrangements are used for other codes such as API 6A,BS 1560 and MSS SP 44. The piping materialspecification will detail the codes and materials toconstruct the facility.

The principle of a bolted joint is based on thebolting delivering sufficient joint compression andgasket seating stress to withstand maximum servicepressure and forces. This is when the bolting is undertensile load as illustrated in Figure 2.1. For integrity aminimum level of operational gasket seating stress mustbe maintained throughout joint service, therefore thedesign bolt load/compression target on installationshould allow for creep, relaxation, uncertainty overservice loadings and the tolerances of components andtools used.

GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS

Possibleflangebending or"rotation"

OperatingGasketStress

Figure 2.1: Working principle of bolted flange joints

2.2.2 Compact flanges

Various types of compact flanges have been developedby specialist manufacturers. Some use gasketarrangements similar to the metallic ring joint whereasothers use metal to metal, gasketless contact and thejoint becomes a static entity with minimal flangerotation potential. Such compact flanges tend to becharacterised by the sealing area being positioned closerto the pipe bore thereby reducing bolt and working loadeccentricity and subsequent end load on the bolts. Thisis a preferred bolted joint design feature and can resultin smaller, lighter flange sizes and a reduction in boltdiameter, quantity or strength grade. The designphilosophy can vary from type to type so themanufacturer should always be consulted for advice onjoint sealing, design bolt tension and installationprocedures.

Hub

Clamp

Figure 2.2: Clamped connector

2.2.3 Clamped connectors

Clamped connectors (see Figure 2.2) use a split clampto join the pipe. Hubs at the ends of the pipe havetapered shoulders sloping towards the joint and theclamps have tapered faces, which form a wedgingaction to close the two hubs together. The hubs haveinternal sloping faces which bear on taper ring gaskets,causing them to be distorted elastically and form a seal.

2.3 BOLTED PIPE JOINT COMPONENTS

2.3.1 Flanges and clamped connectors

Like pipes, flanges and clamped connectors operateunder varying conditions of temperature and pressure.The most critical area on a flange or clamped connectoris its sealing face, on which the gasket or seal ring seatsto form a pressure retaining seal (see Figure 2.3 onpage 7). It is therefore imperative that the sealing face'ssurface finish complies with the design specification orthe manufacturer's recommendations. It must beprotected at all times and free from damage, grease andprotective coatings.

On ASME B16.5 type flanges, the nut seating areaat the back of the flange must be clean and of a smoothfinish to reduce friction unless stated in themanufacturer's specification. Flanges, blinds and flangefacings should be in accordance with the relevant flangecode or manufacturer's proprietary requirements.

Flanges are marked to identify the size, pressurerating and flange material, as shown in Figure 2.4 onpage 7. The pipe schedule used with the flange should

BOLTED JOINT TECHNOLOGY AND PRACTICE

also be marked. Corresponding bolts and nuts also carrymaterial identification marking. These should conformto the relevant fastener specification.

2.3.2 Gaskets and seal rings

Correct gasket or seal ring selection and installation areimportant and only those specified in the piping materialspecification should be installed. The gasket creates theseal between the two flange faces and contains theinternal pressure of the joint.

As with flanges, gaskets and seals can be marked toidentify principal characteristics, as shown in Figure 2.5on Page 7.

There are three main types of gasket: non-metallic,semi-metallic and metallic. Application selection isdependent on service conditions.

2.3.2.1 Non-metallicThese are made from elastomers, cork, compressedfibres, plate minerals and PTFE. Usually the materialsheet is cut to the shape of the flange sealing face. Theyare generally used for low to moderate pressures andtemperatures and see wide chemical service includingacid and alkaline applications.

2.3.2.2. Semi-metallicThese combine a combination of non-metallic filler forcompressibility and metal for strength. They aretypically used for higher temperature and pressureapplications compared to the non-metallic types.Common types include:

— Spiral woundThese gaskets are constructed with spirally woundmetal and soft filler (see Figure 2.6 on page 7). Awide range of metals can be used for the windingstrip and support rings as well as various fillermaterials. On raised face flanges, the gaskets havean outer support ring which locates inside the boltPCD. They can also be supplied with an inner ringfor higher pressure system usage. The inner ring isalso used where high process flow rates or abrasivemedia are found; the inner ring reduces turbulenceat the pipe bore. On spigot or recess flanges asimple sealing element gasket is used with noadditional support rings.

— Metal jacketedThese clad gaskets have been traditionally used onheat exchangers. A variety of metals can be used toencase a soft filler material. It should be noted thatsome heat exchanger flanges have stress raising'nubbins' on one face and the non-seamed face of

the double jacketed gasket is intended to go againstthis face; this is an important assembly feature.

— KammprofileThis is a solid metal ring having a serrated toothform profile on both faces. A covering layer ofgraphite or PTFE is applied which compresses intothe serrated surface as the gasket is loaded. Theseare used increasingly for heat exchanger flanges(see Figure 2.5 on page 7).

2.3.2.3 MetallicThese are made from one or a combination of metals ina variety of shapes and sizes for high temperature andpressure usage. The metal ring fits into grooves thathave been machined into the flange faces. Due to thehigh application pressures, the seating stresses andcorresponding bolt tension are necessarily large to givesufficient deformation to overcome flange surfaceimperfections and distort against the groove surfaces soas to overcome high service pressures. Oval andoctagonal types (see Figure 2.7 on page 7) arecommonly used in oil and gas applications under ASMEB 16.20 and API 6A. RX rings are perceived to be self-energising whilst the BX type are designed to fit into arecess that allows metal to metal contact when theflanges are tightened.

2.3.2.4 Specific seal ringsThese will be found on proprietary equipmentmanufacturers' joints and should be assembled andtightened in accordance with the manufacturer'sspecification.

2.3.2.5 All gasketsGaskets and seal rings should be suitable for theirintended operating conditions and be capable ofproviding a seal under the varying loads imposed byfluctuations in pressure and temperature. Dependingupon the application, the main requirements are any orall of the following:

— Hardness and compressibility.— Flexibility.— Resistance to heat.— Resistance to pressure.— Resistance to corrosive action.

Under no circumstances should gasket compound orgrease be applied to the gasket or flange faces. Note thatfor some clamp connectors, the manufacturersrecommend that the seal ring be lubricated.

Gaskets and seal rings should be:— Stored in their original packing until required.


— Kept horizontal and flat.— Where applicable, left on their individual backing

boards until immediately prior to fitting.

Specific difficulties can arise with insulating gasket setsand appropriate precautions should be taken if these areto be used.

2.3.3 Bolting

Correct bolt selection, procurement and installation arecrucial and only the bolt type as specified in theequipment material specification should be installed.

On ASME B16.5 type flanges, for example, thebolts are designed to carry pressure end load at thegasket and also provide the load required to compressthe gasket into the flange face in order to effect a seal.

Bolt diameters and lengths are specified in therelevant flange code and should also be stated on thefabrication/erection detail drawing. Bolt lengths mayhave been increased to allow for bolt tensioningequipment, or spades, spacers, drip rings and wafervalves, and the associated extra gaskets. Although theamount of specified bolt protrusion may vary there mustbe sufficient protrusion for full thread engagement.Many specifications call for a protrusion length of threethread pitches through the nut. Where hydraulictensioners are used a minimum of one bolt diametermust protrude through the nut to enable safe andeffective tensioner operation.

The bolt and nut grades and manufacturer'sidentification should be stamped on both and should becorrectly identified before they are used (see Figure 2.8on page 7). They should both be in compliance with theequipment material specification. The selected fastenermaterial and diameter must provide sufficient elastic oryield strength capacity to safely sustain the design loadrequirement, service bolt loads and any compensatoryoverloads needed from the tightening method.

Coatings such as hot dipped galvanising and PTFEshould also comply with the appropriate coatingstandard. Bolts with different coatings should not beused on the same flange joint.

Bolts, nuts and washers used for joint make-upshould be clean, rust free and undamaged. Fasteners canbe considered for reuse after considering their servicehistory, operating environment and original riskassessment. Any service coating must be in goodcondition and still provide 100% fastener surfacecoverage. This is especially important forPTFE/Organic barrier coatings. Section 7 providesguidance on in-service inspection.

The number of reuses and subsequent life of thebolt should be based on the level of assurance providedby the tightening methodology selected. Greaterreusability and longest service life will be providedwhere the bolt tension requirement is assured by usinga load control measurement system with the selectedtightening tool. If the bolt is suspected of beingoverloaded or yielded during a previous installation, itshould never be reused.

2.4 PRINCIPLES OF JOINT ASSEMBLY ANDDISASSEMBLY

2.4.1 Identification of joint and selection ofcorrect components

Ensure the correct materials are available, matchingthose detailed in the piping specification, including:

— Flanges of correct size, type, material and rating.— Bolts of correct size, material, and length for

flange and tightening method.— Nuts of correct grade and size.— Correct thread lubricant.— Correct gasket is available.

2.4.2 Inspect the components and flange faces

Ensure that:

— Components and flange faces are clean andundamaged and of the correct surface finish.

— Nuts and bolts are clean and free running but notsloppy on threads.

— Gaskets are clean and free of damage.

2.4.3 Assemble the components

Components should be assembled in accordance withthe procedure relevant to the joint type andspecification, and the tightening method to be used.

Ensure that:

— Bolts are lubricated on threads.— Nuts to be tightened are lubricated on the spot

faces.— Bolts are set correctly in the flange to allow for the

correct thread protrusion and fitting of tools.— Gasket is centred correctly.


Figure 2.3: Example of flange face configuration

Figure 2.4: Flange identification markings

Figure 2.5: Kammprofile gasket withIdent and class marking

Figure 2.6: Schematic of typical spiralwound gasket

Figure 2.7: Type R octagonal ring type joint Figure 2.8: Stud point and nut showingidentification markings


2.4.4 Alignment

Flanges should align initially in the un-stressedcondition without any external forces applied unlessstipulated within the design (e.g. cold spring). ASMEPiping Code B31.3 (1999 Edition) 335.1.1(c) stipulatesthat flange faces shall be aligned within 1 mm in 200mm measured across any diameter, and flange boltholes should be aligned within 3 mm maximum offset(see Figure 2.9). However, this is considered to be amaximum and best practice is to use half this tolerance,thereby making the alignment tolerance 0,5 mm in 200mm. In general, because of the many variables involved,company standards should be set as to allowablemisalignment, but large forces should be avoided. It isrecognised that misalignment greater than that specifiedhere, particularly on pipework connected to non-load-sensitive equipment, may be acceptable.

However, pulling the flanges into position couldcause unacceptable loads and deflections in other partsof the system, and means that bolt load is being used topull the flanges together instead of to compress thegasket. If additional force greater than can be applied bya single person is required, where flange misalignmentor pulling together is excessive or outside the companystandards, or where considerable loads are required tocorrect the misalignment, then the appointed TechnicalAuthority should be consulted and the outcomerecorded.

2.4.5 Breakout

The following precautions should be taken whenbreaking a joint:

1. Ensure beyond all doubt that the line or piece ofequipment being worked upon has been correctlyisolated and vented to atmospheric pressure, andflushed and purged if appropriate.

2. Ensure that all safety precautions and work permitinstructions are in place and are strictly adhered to.

3. Take a position upwind of the flange wheneverpossible. Never stand in line radially with theflange face. Release the bolt furthest away,allowing any residual pressure of gas or liquid toblow away from you. Do not remove the nut andbolt at this stage.

4. Continue to release the remaining flange nuts, butdo not separate them from the bolts until the flangejoint has been fully broken.

Note: It could be the fifth or sixth bolt to be releasedbefore the seal is broken.

CAUTION: For pressure energised seals on compactflanges or hub connectors, care must be taken that thejoint is released before removing the bolts. Personnelshould also be aware of the risk of pipe spring or suddenmovement as bolt loads are released.

2.5 CONTROLLED TIGHTENINGOF JOINTS

Before tightening of the joint is considered, it isnecessary to consider breakout. It may be that the jointhas already been assembled and tightened before, forexample as part of a test programme duringconstruction, or the joint is being opened as part of amaintenance programme after a period in service.

The objective of any tightening is to achieve a correctand uniform clamping force in the joint. The operatorneeds to know the bolt load or bolt stress value requiredirrespective of what parameter he will be measuringduring the tightening cycle. He also needs to know thetightening methodology selected.

-1 mm

1 mm

Angular offset

3 mm

Centre-line offset

Figure 2.9: Alignment tolerances


The bolt load or stress will have been calculated tobe suitable for the joint and its service conditions. Thesedetails should be obtained from the record and datamanagement system for the site (see Section 5). Anychanges in the flange system such as its size, type andmaterial could change the bolt stress requirement andsubsequent selection fastener material/diameterselection. Similarly any gasket change could alsochange the design bolt load. Any such changes must bechecked with a Technical Authority.

Hot dip galvanised bolting could change the threaddimensions and this should be considered whenselecting the correct tensioner or torque tool.

On completion of tightening, the joint should betagged and details recorded in accordance with the site'srecords and data management system.

The following points are specific to the relevanttightening technique.

2.5.1 Torquing specific considerations

2.5.1.1 LubricantRegardless of the torque tool used, lubricant has asignificant effect on the achieved bolt load or stress fora given torque. A known good quality lubricant, suitablefor service and of proven coefficient of friction must beused. It is recommended that where possible sites adopta single lubricant policy; this avoids the opportunity forconfusion.

Extra care needs to be taken with high frictionsurface coatings.

Lubricant must be properly applied to 'working'surfaces only. This includes the bolt threads and thebearing faces of the nuts.

2.5.1.2 Tighten ingTorque tightening should be carried out sequentially, instages to 100% of specified full torque, using the cross-bolt tightening method. Typically three stages of 30%,60% and 100% are used. It is important that the flangeis brought together evenly to prevent overloading of thegasket at any point and this should be monitored at alltimes during the process. Once the first 100% level hasbeen achieved a check pass should then be carried outon all bolts using a clockwise pass to ensure all bolts areat the final torque level. If a bolt load assurance systemis used then the final tightening cycle or check ismeasured by bolt load. It is possible that the use of abolt load assurance method can reduce the number ofintermediate, pre-torque cycles.

The joint will continue to settle under load andthe number of passes at 100% will be influenced by thetype of joint and its gasket type. For example, cutgaskets and most ring type joints can be considered as'soft' joints whereas metallic gaskets such as spiralwound types can be considered as 'hard' joints. A softjoint may require more torque passes to reach therequired bolt load in all bolts.

Figure 2.10 shows cross bolt torque tighteningsequences from ASME PCC1.

Figure 2.10: Cross bolt torque tightening sequence

16 BoltFlange

8 BoltFlange

4 BoltFlange


Figure 2.11: Use of multiple torque tools

2.5.1.3 Use of multiple torque toolsMultiple torque tools can be used on a joint to helpflange faces keep parallel during the tightening process.As with hydraulic tensioners, the use of multiple toolscan also reduce the effects of elastic interaction causingvariation in the residual bolt load achieved. The use ofmultiple tools can also increase joint assembly speed.

In a typical application four torque tools areconnected to a hydraulic pump and arranged evenlyspaced around the joint as shown in Figure 2.11. Whenthese bolts are tightened, the tools are then moved to thebolts that lie equidistant between the previous toolpositions, should there be an odd number of boltsbetween the tools. When there is an even number ofbolts between the tools, the bolts that are nearest theequidistant location are tightened next. On the first pass,typically 30% of the final torque is applied to the bolts.This first cycle is important in pulling flange facesparallel and achieving satisfactory gasket seating.

The tightening procedures are dependent upon theindividual supplier of the equipment. An example of aprocedure is for 50% of the bolts to be tightened in thefirst pass followed by a second pass in which all thebolts are tightened to full torque. A third checking passis then made to ensure that the effects of elasticinteraction are minimised. However the methodologymay vary for differing vendors and therefore theprocedures must be checked with the supplier.

Where space permits and when there are sufficienttools and equipment available, it is possible for all boltsto be tightened simultaneously to their final torque valuethereby eliminating the need for intermediate steps.

2.5.2 Hydraulic tensioning specific considerations

2.5.2.1 Key requirementsHydraulic tensioning involves the use of a number oftensioners simultaneously to tighten a joint. The numberof tensioners and passes must be known to determineoperating pressures. When tensioning, it is important toensure that the correct bolt tensioning procedure is usedin order to obtain a secure and long-lasting leak-freejoint. Usually bolts are tensioned in alternate phasesusing specified hydraulic pressures, taking into accountthe load loss factor. In high risk joints where a loadcontrol system is used a more streamlined procedure ispossible.

Flanges should be checked for squareness aftereach tensioning phase. Confirm the bolt load with abreak loose/check pass. Where load control systems areused this basic check is not required.

Bolt lengths need to be increased by one boltdiameter distance to accommodate the hydraulic jack.

Hot dip galvanised bolting could change the threaddimensions and this should be considered whenselecting the correct tensioning tool. This should benotified to the tensioning company at an early stage.

2.5.2.2 Tensioning pattern or coverIdeally tensioning should be applied simultaneously toall studs in one operation. Where this is not possible,tensioning should be applied in phases using twodifferent pressures, followed by a break loose/checkpass, as shown in Figure 2.12. Where a load assurancesystem is used the break loose/check pass is notnecessary.

2.6 BOLTED JOINT RELIABILITY

2.6.1 Reliability factors

The reliability of a bolted joint is dependent on threekey factors:

— Joint/flange design and calculated bolt load.— Joint component quality.— Correctly assembled and installed design bolt load.

These three factors are critical to joint reliability.Measure and control these factors and bolted jointreliability is assured.

Once the bolt design load objective has beenestablished the operator needs to consider the criticalityof the joint in terms of operating pressures, processfluids and health and safety. This will determine thelevel of assurance required on installed bolt load, and

10


1s t Pass at Pressure 'A' 2nd Pass at Pressure 'B'

Figure 2.12: Tension tightening sequence

selection of tightening control methodology to achievethe design objective.

The design of the joint is outside the remit of thisdocument; however, it is intended to provide amanagement system that can gather the correctinformation from the design specification and applytechniques, procedures and systems, to manage the jointin line with design objectives. The following notes areprovided for information on that basis.

2.6.2 Bolt load calculations

It is crucial that the design bolt load required to seal thejoint has been calculated using an approved method andis known prior to joint installation. The value for eachjoint and the source of the value should be recorded inthe site's record and data management system. Thisfacilitates consistency and traceability and allowsconscious decisions to be made regarding bolt loadshould an issue arise with a joint.

The recognised codes generally provide a methodfor calculation based on operating conditions such aspressure and temperature. The most frequently usedcode is the ASME Boiler and Pressure Vessel Code. Itis relatively simplistic in predicting gasket performance.The latter is an important factor and it has beenrecognised that more realistic and definitive gasketperformance data are required. Both in USA and Europegasket testing is being conducted, the results of whichwill be incorporated into an updated ASME code in thefuture.

There are other service loads acting upon the jointwhich can be just as significant as the internal pressure.Transverse vibration, axial cyclic fatigue and structuralloading all come into play. The joint can also sufferrelaxation or increase in compression dependent oncomponent materials and temperature. The strength

capacity of all joint components - bolt, gasket andflange - is also an important assessment to avoidoverloading and damage from the tightening forces usedin achieving the residual design load and subsequentservice loads. Calculation methods based on VDI 2230(Systematic calculation of high duty bolted joints) takeinto account these different loading conditions. Onesuch design code, EN 1591 (Flanges and their joints.Design rules for gasketed circular flange connections.Calculation method), is specific to pressure-containingflanged joints but certain gasket performance data arerequired from the gasket manufacturers for thecalculation. Gasket manufacturers also provide designbolt loads for various standard flange ratings based onthe gasket performance data.

2.6.3 Bolt tightening

The purpose of tightening a bolt is to stretch the bolt(like a spring) within its elastic limit such that in tryingto return to its original size it imparts a clamping forceon the flange.

Bolted joints can be tightened by a number oftechniques. Torsional based methods range from thesimplest low cost spanners through to impact, manualand hydraulic wrenches. These apply a torsional forceto generate tensile loading in the bolt. Bolt tensionersare different in that the bolt is loaded by applying adirect axial tensile force with hydraulic jacks to stretchthe bolt. Some of this stretch is then captured by theturning down of the permanent nut. A mechanicalvariation on this method uses torque tightened smalldiameter screws going through the flange's load bearingnut and reacting against a jacking washer, therebytensioning the bolt.

None of these systems directly measures theachieved bolt load. However steps can be taken to

11

improve correlation between actual residual bolt loadachieved and the tightening system's power input oftorque or initial hydraulic pressure. Robust procedures,well maintained, calibrated tooling and the use ofcompetent operating personnel help improve thecorrelation.

Totally uncontrolled tightening with spanners is nota preferred option for tightening any size of bolt.However, where a risk assessment identifies asignificant risk and where a superior tightening methodis not possible, e.g. in a space too restricted for torqueor tensioning equipment, spanners can be used with aload control system.

2.6.3.1 Torque tighteningTorque control methods such as impact wrenches havefar less load control than hydraulic wrenches. For thesmaller bolts (< 1", M24) calibrated and maintainedhand torque wrenches will generally provide goodpractice for controlled torque tightening.

The variation in a torque reading and the resultantbolt load is dependent on many factors e.g:

— Friction in the fastener mating interfaces.— Fastener quality e.g. nicks, thread laps, general

damage etc.— Tolerances in bolt, nut and flange dimensions.— Tolerances in bolt, nut and flange material and

mechanical properties.— Operator competence.— Accuracy of the torque application device.— Bolt diameter.— Surface coatings and lubrication.

Great care has to be taken in evaluating the frictionalconditions and resultant friction factor used in thetorque tension equation to improve the reliability incorrelation between torque and bolt load. The choice oflubricant, surface coating and fastener quality canimprove the torque/ bolt load variation. One newhydraulic torque system uses a hardened washerintroduced under the load bearing nut such that itsdesign provides system reaction and reduces bendingstresses associated with traditional torque reactionagainst the adjacent bolt or joint structure. The washerhas a specially prepared bearing surface that is intendedto improve friction consistency, in the nut bearinginterface face, and bolt load variation.

2.6.3.2 Torquing processIt is vital to ensure that the correct bolt torque figuresare available prior to making up a flange joint. Theseshould be stored along with the source of the bolt loadcalculation in the site's record and data management

system. Torque values for particular bolt sizes can befound within specific operators' standards or, in the caseof proprietary manufacturers' connectors, from theircatalogue or from approved bolting service providers.When selecting values great care must be taken toensure that the same lubricant or anti-seize compoundis used as stated in the data sheet from the managementsystem. The actual lubricant friction factor must berecorded. Many sites find it advantageous to specify onelubricant for all bolt torquing operations. Elasticinteractions in the joint can significantly affect theresidual bolt load achieved through torque tightening.These effects can be reduced by simultaneouslytightening a number of bolts in the joint with multipletorque tools similar to hydraulic tensioningmethodology. This procedure is detailed in 2.5.1.3.

2.6.3.3 Hydraulic tensionersWhen joint conditions are favourable and all bolts in ajoint are tightened simultaneously, hydraulic tensionerscan provide a consistent bolt tension. Whilst the bolttension, or preload, is known through the hydraulicpressure applied, the residual bolt load at the end of thetightening cycle is subject to the amount of relaxationthat occurs on load transfer. The latter depends on anumber of factors, some joint related, some tool relatedand others 'fitter' related, e.g:

— Tolerances in bolt, nut, flange and gasket materialproperties.

— Tolerances in bolt, nut, flange and gasketdimensions.

— Operator skill and control of technique.— Load loss factors during the process.— Calibration of pressure gauges.— Correctly maintained tensioning system.

Two specific types of load loss factors to be consideredwhen calculating the required level of compensatoryhydraulic overload pressurisation are Tool Load LossFactor (TLLF) and Flange Load Loss Factor (FLLF).TLLF occurs in all tensioning cases, whereas FLLFdoes not occur in 100% tensioning.

— Tool Load Loss Factor

When the load is applied to the tensioner it stretches thebolt and lifts the permanent nut clear of the surface.Whilst the load is held by the tensioner the nut is thenturned back against the flange surface. When thetensioner pressure is released the load transfers from thetensioner to the threads of the nut. In taking up the loadthe threads deflect resulting in a loss of load. This factoris allowed for in the calculation of applied load.

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Note: This means that with hydraulic tensioning ahigher load than the residual design load should alwaysbe applied.

— Flange Load Loss Factor

Flange Load Loss Factor only occurs when less than100% tensioner coverage is used.

When using only 50% cover (e.g. eight tensionerson a 16 bolt flange) when the second pass is applied, thegasket undergoes further compression, effectivelyrelieving some of the load in the bolts tightened by thefirst pass. By tightening the first pass to a higher load,i.e. adding on FLLF, the need for more than one pass atthe second pass pressure can be avoided.

It should be noted that when two passes are usedthe combination of FLLF and TLLF may mean that theapplied bolt stress is greater than the yield stress of thebolt. An alternative technique such as multiple passes atthe second pass or pass B pressures may then berequired.

Careful use of load factor curves to predict theabove factors and realistic selection of the system forshort, medium and long grip length joints can improvethe correlation between compensatory overloadpressurisation and the residual design load target. Asindicated above, the number of jacks selected for thetightening can improve the load transfer relaxationsituation, particularly with respect to joint elasticityeffects.

2.6.3.4 Tensioning processThe hydraulic tensioning values needed to achieve theresidual design load derived from 2.6.2 should beobtained from the record and data management system.Tool pressures must be specific to the tool used. Thebolt tensioning operation must be carried out inaccordance with the tension equipment manufacturer'sspecified procedure and the load loss factors should berecorded. Ideally tensioning should be appliedsimultaneously to all studs in one operation. Where thisis not possible, tensioning should be applied in phasesusing two different pressures as described 2.5.2.2.

2.6.4 Equipment and tools

In order to improve flange integrity and safety inoperation, it is important that pneumatic and hydraulictorque/tensioning equipment meets the requiredspecification and is maintained and calibrated as aminimum on an annual basis or more often ifcircumstances warrant it. Gauges should be calibratedprior to extended use.

There should be clearly defined procedures statingwho is responsible for ensuring that tools are calibrated

and for ensuring that tools are used by personnelcompetent and trained in their use. Such proceduresshould be specific to the equipment employed.

2.6.5 Load control systems - Assured bolt load

The selection of control of installed bolt load throughtorque, hydraulic pressure or direct through a loadcontrol system, should be dependent on the riskassessment. Assured bolt load provides assured jointreliability assuming the design and component qualityand assembly are also assured.

Selection of an appropriate tightening methodologywith bolt load assurance will provide the minimum risk.Risk increases if bolt load assurance is not provided.

It is recommended that any load control system is100% load test calibrated to ensure all bolts tightened inthe joint are loaded correctly and to the system'sassured accuracy tolerance.

Several techniques are commercially available tocontrol and assure bolt load, as set out below.

2.6.5.1 Direct length measurementThis method uses mechanical extensometry to measurethe bolt extension. Accuracy is dependent on the levelof physical load test calibration carried out. A readilyavailable technique is the indicating rod bolt type. A rodis inserted into a drill hole in the bolt that runs thefastener's complete length. The rod is anchored at theopposite end to where the measurement takes place. Atthe measuring end a precise datum face is machinedleaving the rod end flush with the bolt face. Relativedisplacement of the rod compared to the bolt face ismeasured and calibrated against bolt load by physicalload test.

2.6.5.2 Ultrasonic direct length measurementThis method determines the stress by measuring thetime of flight of an acoustic pulse travelling from oneend of the stud or bolt to the other. The time will varydepending on the extension and the stress in the stud orbolt. The monitored time is proportional to the boltextension and stress and can be converted to provide anoutput as a bolt tension or stress as required. The pulseis generated by a hand-held processing unit and isindependent of the tightening method.

Accuracy is dependent on precise datum facesmachined at each end of the fastener, the level ofphysical bolt load/extension load testing carried out andoperator skill. It is recommended that only skilledoperatives are used to carry out this technique. 100%load test calibration can provide accuracy results similarto mechanical methods. Calibration by calculation onlyprovides the least degree of accuracy.

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2.6.5.3 Load monitoring sensorsThere are several load monitoring sensors commerciallyavailable. These include capacitance, fibre optic andstrain gauge techniques that take the form of sensorinserts placed into a converted bolt. Another type is thecompression load cell that fits like a washer under thenut or bolt head. One load cell monitors any change inthe nut face stress using an amorphous material. Othertypes use strain gauges in the cell structure.

Signals from all types of sensors can be read by ahand-held device or hard-wired logging systems; theyhave future potential for remote signal monitoring. Thesensors are particularly useful where there is a need tocontinuously monitor bolt load in service.

2.6.5.4 Mechanical load indicating boltsThese comprise standard bolts converted to monitor boltload. The bolt has a pin with a rotor attached, anchoredin an axial drill hole. The rotor air gap is set to rotatefreely until a specified bolt load is achieved. Theindicator is enclosed in a protective cap. Simple fingerfeel of this cap determines bolt load status. Tension isindicated at make-up and throughout the life of the joint.Variations of this technique include a dual indicatingmaximum/minimum load range system as well as avisual indication system.

2.7 INTEGRITY TESTING

The combination of the procedures and processesrecommended in this document together withappropriate testing prior to going on line and in-serviceinspection programmes described in Section 7 willprovide the highest level of assurance. Testing is not asubstitute for correct assembly and controlledtightening. It should be standard practice to assembleand control-tighten joints correctly the first time toeliminate rework and minimise downtime.

2.7.1 Levels of pressure testing

Once the joint has been tightened and certified, anddetails recorded in the record and data managementsystem, the joint should be subject to an integrity testprior to going into service. The level of testing isdetermined by the operator and will normally compriseone or more of the following:

— Standard pressure (strength) test.— Leak test.— Service test.— Functional test.

Pressure testing should be carried out to a documentedprocedure which complies with the HSE Guidance NoteGS4 'Safety in pressure testing'. Additional guidancecan be found in the OCA 'Guidance Notes of GoodContracting Practice - Pressure Testing'.

2.7.1.1 Standard pressure (strength) testOn newly constructed or installed pipework andpressure equipment, company standards will normallyconform to a relevant design code such as ASMEB31.3. The objective of a strength test is to prove thequality of materials and construction of the equipmentbefore it enters service or re-enters service followingsignificant repair. This test is carried out at a specifiedpressure above the design pressure - detailed within therelevant design code.

Pressures are typically 1,25 to 1,5 times the designpressure for hydrostatic tests or 1,1 times for pneumatictesting.

This is a strength test of the system and whilst itwill indicate some issues with joints it does not provideassurance of the integrity or in-service reliability of thebolted joint.

2.7.1.2 Leak testLeak testing may be carried out on equipment prior tostrength testing. In this case, testing should be limitedto a pressure not exceeding:— 10% of design pressure.

Leak testing is normally carried out on equipment inorder to prove the integrity of joints disturbed after astrength test has been successfully completed or duringsubsequent maintenance work. In this case, testingshould be limited to a pressure not exceeding:

— 110% of design pressure, or— 90% of relief valve set pressure if still in place and

un-gagged.

NB - on older equipment, the strength test is likely tohave been carried out several years earlier.

2.7.1.3 Service testA service test is one which is normally carried out on ajoint where it has not been possible or practicable tocarry out a leak test first. Service tests are carried outwith the pressure system in service, normally duringstart-up. The test is normally carried out (but notnecessarily always) at maximum normal operatingpressure using the process fluid as the test medium,supplemented by water or inert gas from an externalsource if necessary. The scope of service testing is todemonstrate joint integrity for any joints where leak

14


testing is not reasonably practicable, i.e. witness joints.

2.7.1.4 Functional testThis test is normally carried out at the working pressureusing a suitable test medium. Its objective is to ensurethat the equipment and its components function properlye.g. valve cycling.

2.7.1.5 Testing mediumsHydraulic test mediums (incompressible fluids) arecommonly treated water, glycol or diesel. These havelow stored energy; however, there can be materialcompatibility issues which require consideration e.g.chlorides on stainless steel.

Pneumatic test mediums (compressible fluids) arecommonly nitrogen with a helium trace, air or steam.

Safety NoteStrength testing is almost always carried out usingliquids (hydrostatic or hydraulic testing). Althoughpressure testing using a liquid is not without risk, it isby far the safer method and should be used whereverpracticable. Pressure testing using air, steam or gas(pneumatic testing) is more dangerous because of thehigher energy levels involved.

The energy released during a total failure ofequipment containing compressed air can be up to 200times the energy released by the same test if water wasused as the test medium. Pneumatic strength testingshould never be carried out using flammable gas.

Pneumatic leak testing to 10% of design pressurecan be used to find small but significant leaks inequipment which will contain flammable gases and/orliquids.

Caution should also be taken when carrying outhydrostatic testing at low ambient temperatures (<7ºC)to avoid the risk of brittle fracture.

Refer to the HSE Guidance Note GS4 'Safety inpressure testing' and the associated research report forfurther details.

2.7.1.6 Testing using process fluid or gasFor process hydrocarbons systems, although it is not thepreferred means of testing, under certain conditions itmay be considered appropriate to carry out testing withthe service fluid rather than with water, nitrogen orsome other medium. This should only be consideredwhere it can be clearly demonstrated that it isimpractical to carry out leak testing due to the

configuration of the system, and the hazards associatedwith the introduction of high pressure testing equipmentwould be greater than the hazards associated withservice testing.

Where this method is proposed it should only becarried out in accordance with a company procedure forservice testing and a written justification must berecorded and a risk assessment carried out.

2.7.2 Test recording

The type of test, specification and acceptable leakagerate criteria should be determined and documented bythe operator based on the criticality assessment alreadycarried out on the joint to determine the assembly andtightening assurance specification.

Results of tests should be recorded in the recordand data management system.

2.7.3 Witnessedtesting

joints and reverse integrity

Where joints have no means of isolation to allow leaktesting of the installed joint, such as the last connectionon an open flare line, or where a large number of jointsmakes it impracticable or unreliable to conduct a leaktest, the operator should regard this as a higher risk jointin his criticality assessment and therefore consider anumber of additional steps including:

— Witnessing assembly of the joint.— Witnessing controlled tightening of the joint.— Applying a load assurance system to assure the

required bolt tension has been achieved.— Using a reverse integrity test using a proprietary

gasket. This is based on the principle ofpressurising the annular space above and below theseal ring using a test gas, usually nitrogen.

Witnessed joints should be highlighted in the record anddata management system, including the results of anytests or witness inspections.

2.7.4 Joint failure during integrity testing

Where a joint fails an integrity test, then applying morebolt load alone is not the answer. Investigation andanalysis in accordance with the measures described inSection 6 should be carried out.

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CRITICALITY ASSESSMENT

3.1 INTRODUCTION

There is a variety of bolted joints involved inpressurised systems, ranging from low pressure jointscontaining water or compressed air to high pressurejoints containing steam, hydrocarbons or explosive orpoisonous gases. Although every joint should bedesigned and installed to safely contain the pressure andcontents specified, it is logical that joints at higherpressure or with hazardous contents will requireadditional vigilance due to the potential consequencesof failure.

The criticality of a joint may have an effect on anumber of areas addressed in the management systemincluding:

— Choice of tightening method.— Choice of personnel assembling and tightening the

joint.— Level of bolt load assurance.— Level of records and data stored against the joint.— Level of inspection and testing prior to entering

into service.— Level of testing and inspection in service.

3.2 ASSESSING THE RISKS WITHBOLTED JOINTS

The level of risk will primarily be based on the serviceconditions the bolted joint is exposed to, along with theimpact any release would have on the operational,

safety and environmental aspects of the local and distantenvironment.

For onshore, this will often be part of the Control ofMajor Accident Hazard (COMAH) assessment for thesite.

For offshore, Safety Case, PFEER and PipelineSafety Regulations will apply. The UK Health andSafety Executive OIR/12 database contains usefulinformation to enable offshore industry operators todevelop their risk assessment.

Risk may also occur with joints containingharmless fluids e.g. water, which would damagebuilding fabric or product, or risk interaction withelectrical installations if they leaked.

There are a number of areas which will affect thecriticality of the joint. These can be grouped as follows:

3.2.1 Leak potential

One method of determining the criticality of a joint is toconsider the potential for a leak. The potential for a leakwill increase with:

— Process and test pressures.— Cyclical load.— Vibration load.— Low temperature.— High process temperature.— Structural load.— Corrosive environment.— Aggressive environment.— Unknown conditions of any sort.

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The contents of the pressure system have a major effecton the criticality of the joint and should be consideredin determining the level of inspection, control andtesting applied to the joint. A joint's criticality willincrease if the contained service is:

— Hydrocarbon.— Corrosive.— Explosive.— Poisonous or noxious.— Radioactive.— High temperature.— Environmental contaminant.— Expensive.

Such joints would often be viewed as at least of mediumcriticality.

3.2.3 Loss potential

The criticality may also increase if loss of the servicewould render the plant inoperable. For example a fireservice line, although having safe contents, would causea plant shutdown if inoperable. Similarly a coolingwater system for a computer plant could be highlycritical.

The loss potential may also increase with pipe sizeand the area through which it runs.

Local factors must always be considered when assessinga joint's criticality. Table 3.1 describes some of thefactors which may occur at individual joint level.

3.2.5 Joint criticality rating

The criticality of the joint is shown in Table 3.2. Thecriticality level can be determined by considering all ofthe factors identified in 3.2.1 to 3.2.4. The operatorshould use the level of criticality to set standards andspecifications for:

— Joints which will be included in the managementsystem.

— The level of inspection and assurance at assemblystage.

— The level of personnel who will control tighten thejoints.

— The control tightening method.— The level and method of bolt load assurance.— The level of inspection during the controlled

tightening stage.— The type and level of integrity test prior to entering

into service.— The type and level of in-service inspection.

Table 3.1: Local factors

Factor

Vibration or slug flow

Cyclic temperature

Substitute materials to those inPiping Specification

Local joint history

Untested joints

Vendor package joints

Exception on joint

Problem

If severe may cause joint to loosen

If severe may cause joint to loosen

Compatibility not guaranteed

If this individual joint is misaligned or difficult to close, or if this type ofjoint is problematic on this site

Cannot be leak tested prior to start-up (e.g. tie-in points)

Often assembled and tightened to vendor's system, outside of assetsystem

Flange face marked, piping load, history of leakage with root causeunidentified

18

3.2.2 Service fluid


3.2.4 Local factors

CRITICALITY ASSESSMENT

Table 3.2: Joint criticality - Examples of criteria used and controls applied

Joint Criticality

Low

Medium

High

Controls

— Joint identified and recorded in database— Assembly not witnessed but carried out to a procedure by trained and competent

contractor— Bolt loads taken from database— Controlled tightening applied by use of hand torque wrench or torque wrench— Tightening carried out by competent personnel (see Section 4)— Integrity test by local arrangement— In-service testing includes visual inspection

— Joint identified and recorded in database— Assembly witnessed or a sample of joints witnessed and carried out to a procedure

by trained and competent personnel— Bolt loads taken from database— Controlled tightening applied by use of hand or hydraulic torque wrench or tensioner

by competent personnel— A sample of joints witnessed by specialist personnel— Integrity test may include nitrogen helium or similar— In-service testing in accordance with the techniques described in

Section 7— Consider use of load assurance

— Joints uniquely identified in database and identified as High criticality— Assembly by specialist contractor or witnessed by specialist contractor— Controlled tightening using hydraulic tensioner or hydraulic wrench with load

assurance system by specialist personnel— Integrity test using nitrogen helium or similar prior to entering into service— In-service inspection at higher level in accordance with the techniques described in

Section 7

3.2.6 Sample risk assessment selections

Assured design bolt load on installation by measuringwith a load control system provides assured jointreliability or minimum risk with any tighteningtechnique. Under the same joint conditions reliabilitywill be less assured and risk will increase by using onlythe tightening technique. Selection is down to theoperator's risk assessment, past history of the joint andassociated life cost of the techniques available to him.These examples are not intended to be prescriptive butshow possible methodology selection subject to anoperator's individual situation.

ANSI B.16.5 150 LB 5 INCH; HAZARDOUS FLUID.¾ in. bolt Torque tightening; torque control; known lowfriction lubricant for friction factor control.

The operator may decide this application does notwarrant the use of a load control system. The smallerdiameter means that torque tightening is a more cost

effective procedure than tensioning. The shorter griplength joint also makes the tensioner less reliable as acontrol system. By thoroughly researching the frictionfactor for the preferred lubricant and taking into accountthe surface coating and bolt quality, torque tensionvariations may be reduced.

ANSI B.16.5 600LB 10 INCH; HAZARDOUS FLUID.1,1/4 in. Hydraulic tensioner tightening

Whilst the 1.1/4 in dia bolt could be tightened using ahydraulic wrench, it may have insufficient control toprovide a reliable level of bolt load. The serviceconditions in terms of pressure, temperature andcontained fluid provided intermediate risk. The boltdiameter and grip length were such that the hydraulictensioner could provide sufficient bolt load for jointreliability under service conditions.

We could have this same 600 lb flange but servicetemperatures could be high (350°C plus) and/or cycling.This could present an increased risk such that assurance

19


is needed on installed bolt load. For this a load controlsystem is used with hydraulic tensioner tightening tominimise the risk of a leak.

ANSI B.16.5 900LB 16IN, HAZARDOUS FLUID.1,5/8 in. Hydraulic tensioner tightening; load controlsystem.

Some operators link tightening method selection to boltdiameter. For example, hydraulic tensioners are usuallyspecified for diameters 1,1/8 or 1,1/4 diameter andabove. The larger the diameter, the more effectivetensioners become compared to torque in terms ofproviding tightening power with variation in bolt load.The higher pressure, pipe diameter and process gas inthis situation results in the operator regarding risk as'high'. Therefore assurance on installed bolt load isnecessary and a load control system is required toensure design objectives are achieved on installation. Itwould be quite feasible however to select a hydraulictorque wrench with a load control system for thisapplication.

Tightening method selection based on boltdiameter; whilst satisfactory for general 'rule of thumb'on low and some intermediate risk standard ANSIflanges, the policy could be problematic for nonstandard joints especially those where the bolt diameterto clamp length ratio is relatively small (less than fourto one for example). Where one would normallynominate tensioning for a larger bolt diameter, the lattersituation could result in the target bolt load beingpractically unreachable due to joint elasticity. Thehigher compensatory hydraulic overload may be outsidethe elastic capacity of the bolt or even the capacity ofthe hydraulic jack itself.

3.2.7 Record the criticality assessment

The joint risk criticality should be recorded in therecords and data management system (see Section 5).

Before work on any joint (e.g. design, modificationor maintenance) the risk criticality should be identifiedand recorded. If the risk criticality has not already beenidentified and recorded, a criticality assessment shouldbe performed and recorded in the records and datamanagement system.

3.2.8 Risks to personnel

It is important to note that assembly of flangedconnections involving the use of high pressure hydraulictools and systems will present a level of inherent risk tothe operator which if not assessed, controlled and ifpossible mitigated, may result in a serious incident. Forall flange assembly operations the risks during assemblyshould be fully and formally assessed, the selection ofmethods and tooling reviewed, hazards identified andwhere possible, the risks mitigated on the basis of theALARP (As Low As Reasonably Practical) principle.All personnel involved should be made fully aware ofthe potential dangers of accidental leakage of highpressure hydraulic fluid from the tools and systemsdeployed.

During training of personnel, it should beemphasised that the risks from high pressure fluidsystems are constantly present during the tightening/loosening procedures. The need for constant observationand inspection of the equipment throughout the wholeoperation should also be stressed.

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TRAINING AND COMPETENCE

4.1 INTRODUCTION

All personnel carrying out work on bolted joints shouldbe trained and competent to a level appropriate to therequired technical skills and failure risks of the jointinvolved. Similarly, supervisory personnel and assessorsshould also be trained and competent to ensure they areaware of the issues involved in achieving a leak-freejoint.

4.2 COMPETENCE MANAGEMENT

Control of the competence of people working on boltedpipe joints is a critical factor in achieving joint integrity.Hydrocarbon release incident data for the UK offshoreoil and gas industry indicate that poor bolted pipe jointmake-up is a major cause of leaks, and a review ofhistorical causes confirms that the skills and practicesused have not given leak-free joints. Therefore animportant element of a management system is to ensurethat any person working on a given joint has beentrained and assessed as competent to perform the task.

Fundamental to the demonstration of personnelcompetence is the provision of a documentedcompetence management system that:

— Contains clear standards for recruitment, training,development and ongoing competence assessment.

— Is based upon, equivalent to or better than anationally or industry-recognised technicalstandard.

— Provides demonstrable capability for all staffpersonnel who might be expected to make, break or

maintain joints, or to supervise or assess suchwork.Includes a process to assure that third party vendorsand contractors can demonstrate that theirpersonnel are managed using equivalent systems toequivalent competence standards.

4.3 TRAINING

The skill levels that individual companies use willdepend on a number of variables. For example, acompany with a large number of personnel may decideon a number of skill levels appropriate to the type ofwork an individual may perform. Other companies maydecide to train all their personnel to a higher level as amatter of course. This approach is particularly relevantto remote sites where it is imperative to have personnelwith the necessary skills available at all times. As such,the training specifications for the following EngineeringConstruction Industry Training Board (ECITB)TECSkills units have become the benchmark standardsfor the UK offshore oil and gas industry:

PF010 Jointing Pipework using Flanged Joints (HandTorque Tightening).

PF015* Assembling and Tightening Bolted FlangedConnections.

PF018 Assembling and Tensioning BoltedConnections.

PF019 Assembling and Tightening BoltedConnections (Hydraulic Torque Tightening).

*superseded by PF018 and PF019

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Schemes operated by individual companies should bealigned with these or equivalent specifications. Suchschemes should also address those individuals usedduring turnarounds and periods of high activity whosecore function is not assembly and tightening of boltedjoints.

4.4 ONGOING COMPETENCE

Successful completion of an appropriate training courseis only the first step towards gaining and demonstratingcompetence. The course should be followed up by anagreed training and assessment plan between the coachand learner, which will establish whether the traininghas been effective and identify gaps in the learner'sskills and knowledge. Together with a logged record ofexperience and a site assessment, this can lead to arecognised qualification such as the ECITB's TECSkillsunits PF010, PF018 and PF019 (see 4.5). These units,with supporting material, may contribute as evidencetowards obtaining a vocational qualification unit (see4.6).

An example of the competence requirements forauthorised bolt tightening personnel is given in Table4.1.

To assist in demonstrating ongoing competence, arecord should be maintained of each individual'smechanical jointing performance. This should comprisedetails of the types of joints the individual has workedon (including evidence that a representative sample ofjoints have been made up in the presence of a competentassessor), whether the joints have performedsatisfactorily, and details of any further trainingrequired. It is the responsibility of the individual tomaintain this certified history and to have it formallyvalidated by an approved assessor. If there is no recordof successful past work within a 12-month period it isrecommended that an assessment is performed toidentify any re-training requirements.

An example of a mechanical jointing performancerecord is shown in Figure 4.1.

4.5 TRAINING IN ENGINEERINGCONSTRUCTION SKILLS (TECSKILLS)

The ECITB's Training in Engineering ConstructionSkills training programme (TECSkills) is an example ofa flexible training scheme for craft and other siteoperatives to cater for both initial and skill enhancement

training. It is rooted in the Engineering CompetenceStandards (ECS) based on national occupationalstandards for the engineering construction industry.Successful completion of TECSkills On-the-JobPerformance Units or equivalent units from otherIndependent Accreditation Organisations (IAOs) (see4.7) can contribute to the evidence requirements ofvocational qualifications. An occupationally competentcoach and IAO representative support the learner in theattainment of new skills and knowledge whenundertaking training or performing these units.

In response to the UK oil and gas industry, theECITB developed training and performance unitsPF010, PF018 and PF019 for assembling and tighteningbolted flanged connections. These units form part of theTECSkills training programme for training pipe andmechanical fitters, hence the PF title.

4.6 VOCATIONAL QUALIFICATIONS

A vocational qualification (e.g. National or ScottishVocational Qualification - N/SVQ) is effectively aportfolio-based validation process that will includeonsite assessment by an occupationally competentassessor. No training is necessarily required to take avocational qualification. The qualification is based onevidence of competence by a variety of techniques,including documentary evidence, questioning, siteobservation and testimonials. A competent assessor willeasily identify weak candidates.

The standard of candidate able to pass a vocationalqualification is controlled by the awarding body in linewith national guidelines.

4.7 INDEPENDENT ACCREDITATIONORGANISATIONS

Examples of bodies who can be contacted for advice aregiven below. There are many other agencies andindividual companies which are available to providetraining. However, it is essential to ensure that thetraining they provide is to a recognised standard.

ECITB (Engineering Construction Industry TrainingBoard)

SEMTA (Science, Engineering and ManufacturingTechnologies Alliance)

API (American Petroleum Institute)

22


Table 4.1: Competence requirements for authorised bolt tightening personnel

Key Requirement

Training provided should include knowledge of the specific joint types employed at the worksite. Operatorsshould ensure that any training carried out on their behalf meets with this requirement.

Knowledge BaseAwareness of:— Health and safety precautions— Pressure, temperature and hostile environmental factors (such as corrosion and vibration) on the

degradation of bolted assemblies— Factors which result in bolt load variation— Applied and residual loads— The effect of different lubricants on friction losses— The relative accuracy of different methods of tightening— The techniques for application of tensioned bolt loading— Joint assembly methods and tightening procedures— The need to check gaskets, nuts and stud bolts against specification— Safety precautions when handling and removing Compressed Asbestos Fibre (CAF) gaskets— The requirement to tag and complete records for assembled joints— The need to:

Check the compatibility of the selected torque tools and equipment capacity prior to useTop up oil levels in hydraulic pumpsClean and protect tools and equipment from corrosion

Understanding of:— The principles of joint component sealing action— The principles of bolt elongation and tensile stress— The function of gasket or seal types— The importance of correct bolt loading— The effect on bolt load and seal compression using different methods of tightening— The importance of using the correct lubricant— The importance of the correct selection of joint components to comply with the design specification— The correct sequence and number of tightening passes required for torque and tensioned bolts— The principles and techniques used for direct bolt length measurement— The need for and using reporting procedures when defects or faults in bolt tightening equipment or its

assembly are identified— The principles of preparing bolted joint connections for assembly— The need for seal face cleanliness and for nuts to be free-running— The effect of joint alignment and gap uniformity on residual bolt loading— The importance of gasket storage, handling, preparation and installation— Good installation practice for bolting, washers and nut orientation for tightening method and equipment

to be used— The need to report variances from design specifications and tightening procedures— The principles and requirements for the safe selection, calibration, installation and use of hydraulic

torque and bolt tensioning equipment— The principles of carrying out bolt de-tensioning and joint breakout safely and correctly— The importance of attending product-specific training and following the manufacturer's procedures for

proprietary joint types— Why mixing components from different equipment manufacturers is prohibited— The principles of inspection after tightening and the procedures and techniques to be used such as 'break

loose' tests (check passes) and bolt tightness 'tap-test'— The requirements for the storage, preparation, maintenance and calibration of torque tools and bolt

tensioning equipment for its safe use

23


Table 4.1: Competence requirements for authorised bolt tightening personnel (cont'd)

Ability to:— Recognise and rectify faults with torque or tensioning equipment— Interpret joint or flange manufacturer identifying marks— Identify defects, distortion and surface irregularities on flange sealing faces and threads

Demonstrated Application of KnowledgeDemonstrate ability in:— Preparation of all joint components— Correct selection and assembly of joint components— Diagnosis and rectification of problems with hydraulic equipment— Selection and correct installation of hydraulic torque or tensioning equipment— Correct application of the various tightening techniques— Carrying out specified tightening sequence and subsequent tightening passes to ensure axial alignment

and squareness of joint assembly— Carrying out joint breakout safely and correctly— Carrying out bolt 'break loose' tests (check passes) to check integrity of assembled tensioned assembly— Completion of a joint record sheet— Integrity and inspection checks of completed joint assembly— Maintaining a personal portfolio of joint assembly

Demonstrate awareness of:— The health and safety precautions at the worksite— Hot bolting and live plant procedures and risk assessments

24


JOINTING PERFORMANCE RECORD

Name ID No Installation Date

This is to certify that the Technician named above has produced satisfactory leak-free mechanical joints ofthe types indicated below within the past 12 months.

Joint Type

RTJ

Raised face

Insulating gasket

Compact

Clamp connector

Taper-Lok

Kidney

Other (installation-specific)

SatisfactoryPerformance Requires Training Date Signature Comments

Note:1. This record does not replace a recognised NVQ but certifies a Technician's ongoing competence in

making a specified mechanical joint.2. It is recognised that certain installations do not have all types of joints.

Supervisor(Position)

Name:

Signature:

Date:

Verified(Position)

Name:

Signature:

Date:

Figure 4.1: Example jointing performance record

25

RECORDS, DATA MANAGEMENT ANDTAGGING

The certainty of a successful joint being made upincreases if data are controlled and historical data existon the activities carried out in the past. Recordingtraceable data encourages best practice at the time of theactivity, and will provide useful planning data for thenext time the joint is disturbed.

Learning from incidents is important. Amanagement system should include the means forgathering relevant data, which should be collected byeveryone involved in bolted joints and periodicallyreviewed to establish trends, performance andimprovements. This can be achieved if records and dataare kept for each joint as part of a management controlprocess.

5.1 JOINT IDENTIFICATION

In order to record data and plan activities - each jointneeds to be clearly and uniquely identified.

This requires the joint to be physically tagged sothat its identity is clear and visible at the joint locationincluding a unique Joint ID number in order that it canbe recognised in a joint database or other record system.

All joints should be tagged, there are alsoadvantages to having both permanent and temporarytags assigned to joints.

5.1.1 Permanent tag

The purpose of a permanent tag is to uniquely identifya joint throughout its life cycle, enabling all activitiesand data on that joint to be recorded. Permanent tags

should be securely attached to the joint and may hold noother data than the unique tag number. In selecting apermanent tag, consideration needs to be given to theattachment method, the temperature of the flange andtag and security device material, the permanence of thetag markings, and avoidance of corrosion spots due todissimilar metals or water traps.

5.1.2 Temporary tags

The purpose of a temporary tag is to uniquely identifya joint during a work scope and to indicate the status ofthe joint during the work scope. The tag will normallyhold a unique ID number for the joint which istraceable; it may also hold a small amount ofinformation such as tightening method and date, personwho assembled the joint, person who tightened the jointand person who tested the joint. A common method isto use multipart tags where the status is indicated by thecolour of the portions remaining on the tag.

Common status conditions are:

— Joint to be broken out/Joint broken out.— Joint to be assembled/ Joint assembled.— Joint to be controlled tightened/Joint tightened.— Joint to be tested./Joint tested.

Joint tagging can bring a number of benefits:

— Control competence.— Assist in the preparation of work permits.— Provide cross-shift communication of job status.— Assist job completion confirmation.

27


— Aid leak and seep searches by identifying disturbeditems (which have a higher probability of leaking).

— Support a record and data management system.

5.1.3 Example tagging procedure

The following is an example tagging procedure.Individual operators' schemes will depend upon avariety of issues including the number of joints to betagged and the size of local organisation.

All joints that are to be made or disturbed duringconstruction or maintenance work should be identified,recorded and tagged. The tag should be fitted using asuitable tie and in a position adjacent to or on the joint.

The person who breaks the joint(s) should mark upthe tag identification numbers on a copy of the relevantIsometric or P&ID and its corresponding register. TheIsometric or P&ID and register should be controlled bythe relevant designated person. These recordscomplement the leak test certificate and provide anaudit trail.

At the completion of each stage of the job(inspection, assembly, tightening and testing) theresponsible person should record their name against thatstage. This could be done directly on the tag or therelevant task could be crossed off on the tag and thename recorded in the work pack.

Once testing has been satisfactorily completed, theremovable insert of the tag should be returned to the jobco-ordinator. The task completion should be recorded inthe work pack when all joint tag bodies are returned,indicating that all work has been completed. This can bechecked against the permissions required for restartingthe plant.

Plant start-up should be prevented until all the taginserts are signed off and returned to allow sign-off ofthe job.

After start-up and while the root of the tag remainsattached, search teams should patrol the disturbed areaand inspect tagged joints for leaks and seeps. Any leaksor seeps should be reported to a nominated supervisor.

The root of the tag should be left on the joint untilthe operation is satisfied that the joint is not likely toleak (normally 48 hours after start-up.) During thatperiod the tag makes leak searches more effective.

An example of a multipart tag is shown in Figure5.1.

Figure 5.1: Example of a multi part tag

5.2 RECORDS AND DATA MANAGEMENT

A successful record and data management system willaid and provide information during the work planningand execution process.

Once unique joint IDs have been established thenuseful and essential data can be recorded against them.As work is carried out and recorded the status of thedisturbed joints should be updated to reflect the status ofall joints including temporary blinds. This processshould be carefully controlled and reported as laid downby the management process.

The preparation and collection of data bycompetent personnel will assist in ensuring all joints areassembled, tightened during construction or reinstatedduring maintenance and ready for leak-free service.Additionally, as the status of all pipework has beencarefully monitored, it should not be possible tointroduce pressure into any joint before all joints havebeen reinstated.

28

RECORDS, DATA MANAGEMENT AND TAGGING

5.2.1 Recommended data

The following data are recommended as a minimum forbolted joints on critical services:

5.2.1.1 Joint details— Identity of joint.— Joint location.— Drawing references.— Size, type, class.— Flange and bolt material.— Gasket specification.— Approved bolt stress and source.— Approved tightening method and settings/tools to

achieve approved bolt stress.— Lubricant used.

5.2.1.2 Additional dataAdditional data can be recorded to make the systemmore user friendly and effective as a planning tool, suchas:

— Status of the joint.— Any exceptions or anomalies regarding the joint.— Location description of the joint.

5.2.1.3 Joint history— Starting at the construction stage: Records of

assembly, break out, reassembly, inspections andcontrolled tightening. Including personnelinvolved, equipment and procedures used. Resultsand measurements taken where appropriate.

— Records of inspection and testing of the joint.— Records of subsequent disassembly, inspection,

assembly, tightening and testing during operation

and maintenance of the asset.— Records of any modification, exceptions

deviation from standards with the joint.or

Whilst this data can be kept in hard copy format, adatabase system is recommended due to the highvolume of data required and the ease of searching andretrieving data that computerised systems offer.

5.2.1.4 Joints included in the databaseIt is recommended that the operator as a minimumkeeps records for all joints on critical services and thoseon other services which have a history of leakage, orpotential to leak, and that this is kept with any relevantprocedures for monitoring the specific joint. Tominimise the possibility of the problem resurfacing,methods for countering the leak should be includedwithin the individual joint records.

There are however benefits in maintaining a systemfor all joints, in terms of safety, efficiency andtraceability. Statistics show that using a system tocontrol joint integrity will reduce the effort required toachieve a successful integrity test.

5.3 REVIEW

The entire process and outcome should be reviewed bymanagers and members of the work team. Identifiedimprovements to the activities, work scopes andprocedures should be recorded and retained for whenthe work is next repeated.

Information of performance and good practiceshould be shared with industry.

29


30

6

MANAGEMENT OF LEAKS

6.1 INTRODUCTION

The objective of a correctly designed and installedbolted joint is to provide a long-term tight seal andprevent ingress or egress of fluids through the joint.However, leaks can occur and the Duty Holder oroperator has overall responsibility to manage thissituation. This section introduces some importantfeatures that may be required of the management systemfor pressurised systems after joint make-up. Theseinclude:

— Management of leaks and releases and theappropriate engineering risk assessments that mightbe required.

— Definition of leaks.— Integrity testing of joints as an assurance measure

of joint tightness.— Potential options for repair or replacement of

leaking joints.

6.2 ENGINEERING RISK ASSESSMENTOF LEAKS

The degree of review or assessment of leaks will dependupon the industry, the nature of the process fluid andpressure and temperature conditions; all factorsaffecting the criticality of the joint (see Section 3). Insome situations it may be acceptable for joints to leak.

However, there are a significant number of industrieswhere good business practice or regulatory requirementsmake it essential to formally assess loss of containmentevents and determine root cause and measures toprevent recurrence.

When a leak or incident occurs, a commonapproach to manage such situations is an engineeringrisk assessment which utilises the collective skillswithin the organisation to address three fundamentalquestions:

— Safety impact to ongoing operations - is it safe tocontinue to operate the plant?

— Environmental impact - what is the environmentalimpact of continued operations?

— Economic cost - what is the business cost?

An engineering risk assessment should be performed toestablish whether it is acceptable to continue operations.The assessment should also identify control or hazardmitigation measures required such as increasedsurveillance or plant de-rating. Alternatively theoutcome of the assessment might indicate that there issignificant hazard with continued operation and thatimmediate shutdown, repair or replacement is required.

It should be noted that most companies have someform of environmental policy which requires recordingemissions from process systems. In the UK statutoryrules require reporting of leaks and emissions dependingupon the fluid and the magnitude of the leak.

31


6.3 STAGES AT WHICH LEAKS OCCUR 6.4 CORRECTIVE ACTIONS

Leaks often occur when the joint is under test, asdescribed below. However, regardless of when a leakoccurs, it should always be investigated and recorded inthe records and data management system (see Section5). This will not only store useful data against the jointand assist in preventing the same issue arising on thesame joint in future, but will also enable trend analysisto prevent leakage on other joints. A leak decision andanalysis tree, such as the example illustrated in Figure6.1, can assist in determining an appropriate course ofaction and also provides input to the data managementsystem.

6.3.1 Standard pressure (strength) test

A leak occurring during a strength test is an indicationthat there is a major issue in the installation of thebolted joint. Although the joint is subject to a higherthan working pressure at this stage, it is not subject totemperature or cyclic loading and therefore leakageduring this activity suggests poor assembly or appliedbolt load. Identifying and correcting the cause isessential for reliable operation of the plant.

6.3.2 Leak test

A leak test is not a replacement for correct joint make-up and tightening; rather, it is merely part of theassurance process. Where a joint is just failing a leaktest it is tempting to increase bolt load. However if thebolt load was correctly applied in the first instance,increasing the bolt load could be hiding a problem, e.g.a nipped gasket or grit on the gasket, which willmanifest as a service leak later.

6.3.3 Service testing

Where the service test identifies a slight leak, there willbe a temptation to apply more bolt load to seal the leak.This may be successful, but if the load was correct inthe first place then consideration must be given toidentifying why the joint leaked (see also 6.3.2 above).

6.3.4 Leaks occurring during start-up oroperation

These leaks potentially have the greatest impact notonly for safety but also commercially as they will eitherdelay start-up or stop production.

Where a release is identified, a corrective action mustbe carried out to secure a tight joint. Some measuresinclude:

— Depressurise the system, and check load on bolts.— Identify root cause of the problem (and notify

appropriate authorities).— Depressurise and completely remake the joint after

component inspection.

Other measures such as hot bolting and tightening oflive joints are not recommended.

6.5 DEFINITION AND DETECTION OF LEAKS

The following definition of a leak is widely used in theupstream oil and gas industries:

A release of hydrocarbon or other hazardous fluidshould be recorded as a leak when the release rate isequal to or greater than:

— Liquid leaks:A release rate of one drop per 15 seconds (fourdrops per minute).

— Gas leaks:A release that will cause a hand-held gas detector10cm 'downwind' of the release source to indicate20% Lower Explosive Limit (LEL).

The most likely method of detecting a leaking boltedjoint is observation by operations and maintenancepersonnel or inspection personnel during routineoperation in the plant. There is no substitute for 'linewalking' as most leaks are of relatively smallmagnitude. The more significant leaks may also bedetected by plant safety systems such as gas detectorsor, in extreme cases, by the process control system.

All leaks should be tagged and entered in themaintenance system for repair and the record and datamanagement system as soon as is reasonably practical.It may also be reportable.

An emission from a joint with a lower release ratethan a leak is described as a seep. These too should betagged and periodically checked to ensure they have notworsened, and be entered into the maintenance systemfor repair at the next scheduled service for that item. Itshould also be recorded in the records and datamanagement system.

32

MANAGEMENT OF LEAKS

Joint failure leakagerate above the targetacceptance criteria

Is thisa single failure

or are there numerousfailures in the

system?

Is there acommon style of joint that

is failing?Technical reviewrequired

Is theleakage rate above

the maximum acceptancecriteria?

Is the technicalauthority willing to approve

the leakage result?

Is thetorque/tension

applied to the jointcorrect for this application?(Check procedure and all

assumptions made)

Update workpack withnew torque/tension

figures

Has thetorque/tension

been correctly appliedin the field?

Correctly applythe torque/tension

in the field

Break the joint andinvestigate failure mode.Apply rigorous checks.

Reassemble and retightenjoint to approved method.

Figure 6.1: Example leak decision and analysis process

33

PASS OR FAIL?PASS

START

SINGLE

FAIL

NUMEROUS

YES

NO YES

NO

YES

NO

YESNO

NO

YES

SUCCESS

TIME OUT


Leaks may pose special risks in confined spacessuch as pits, trenches, buildings and modules. Examplesinclude concentration of toxic or poisonous gases orheavier than air asphyxiates such as argon or carbondioxide gas.Fugitive emissions as described in the IPPC regulationsare beyond the scope of this section. It is assumed thatissues such as Best Available Techniques (BAT) forsealing have been addressed by the specifiers anddesigners of joint systems.

6.6 MANAGING LEAKS AND REPAIRS

An engineering risk assessment will provide a technicalbasis for reviewing repair options which can range fromshutdown and repair/replace to continued operation withno intervention. The choice of options may be furtherrestricted by Company policy depending upon the typeof facility. In many industries, unplanned shutdown forrepairs is normally avoided wherever possible.

Whatever the planned course of action, it should beformally documented before work begins and carriedout in a safe, managed and controlled manner. Nomatter what the circumstances, the temptation to tightenup the joint beyond design parameters should beresisted.

There are a number of candidate repair andreplacement strategies. These include:

— Continued service accepting the joint leakage:It may be acceptable to permit continued leakagefrom the joint based upon the engineering riskassessment and environmental impact until aplanned shutdown.

— Continued service operating with de-rating:It may be acceptable to permit continued jointservice by imposing a control measure such as de-rated duty point or downgrade condition. This maybe appropriate where the leak rate is pressure ortemperature activated.

— Isolate and repair the leaking joint (line isolation):There may be sufficient valves to isolate theleaking flange and allow maintenance to be carriedout. This may prove difficult in some plants wherethe valves do not provide tight shut-off or therequired level of isolation as required by thecompany's safety policy cannot be achieved.

— Shutdown unit, isolate and repair joint:In some instances, where safe isolation cannot be

achieved, the only option may be to shut down theplant to carry out the repair. An example of such asituation is given in Figure 6.2 which shows aflange with gasket seating face pitting. Corrosion atthe bottom of the pipe has caused metal loss of theentire gasket seating width and resulted in a leak. Inthis case a unit shutdown was undertaken to replacea pipe spool.

Carry out on-line repairOn-line repairs to live plant have been carried outusing techniques such as encasement clamps andvarious forms of glass and carbon fibre wraps.These are considered to be engineering repairs andneed appropriate technical skills and installationcompetences. Specialist service companies canprovide this type of product on a world-wide basis.Some high level guidelines on safety considerationsare presented in EEMUA publication 199.Guidelines on requirements and qualification ofrepairs to corroded or damaged piping usingcomposite wraps are presented in ISO documentISO/PDTS 24817. A typical clamp type repair isillustrated in Figure 6.3.

Detail design considerations include:- Definition of the expected design/operating

life of the repair.- Impact of fluid on bolting, e.g. exposure of

some bolting to fluids with H2S or chlorides.- Pressure end cap forces.- Site constraints such as insufficient space to

install a clamp.

6.7 LEARNING FROM LEAKS

In order to prevent future leaks lessons should be learntfrom past incidents. Operators should develop a processto capture data in a form that can be readily reviewedand analysed. The process should aim to:

— Improve the quality of information gathered onjoint leaks.

— Identify and better understand the causes offailure(s).

— Provide data for the hydrocarbon leaks database.— Provide data for long-term learning on leak

occurrence.— Ensure periodic review and learning.

These details should be recorded in a data managementsystem.

34

MANAGEMENT OF LEAKS

Figure 6.2: Flange with gasket seating face pitting

Figure 6.3: Encasement clamp repair on a 24 in. seawater line to stop leak on stub of composite flange

35


36

7

IN-SERVICE INSPECTION

7.1 INTRODUCTION

In-service inspection of bolted joints is an integralactivity to ensure the continued integrity of the jointsand as such should be built in to all relevant inspectionprogrammes. This section looks at the possible damagethat can occur, the inspection methods available fordetection of defects and the mitigation measures thatcan be put in place to minimise such degradation.

A summary of the key issues addressed in thissection is included in Table 7.1.

7.2 RISK ASSESSMENT

For high-risk joints it is recommended that methods areimplemented for monitoring bolt stress to ensure thatpre-load is maintained. Generally, a risk assessmentshould be carried out to determine the inspectionrequirements.

The following factors should be considered forspecific joints:

— High temperature pipework may cause bolts tocreep and cause leakage.

— Large numbers of temperature cycles can cause thebolts to loosen.

— Mechanical vibration or shock loading may causethe flange bolts to loosen.

— Areas of high external corrosion may cause thebolts to lose integrity. Susceptible locations includeinsulated pipework, bolts open to harshenvironments or those subject to deluge systemtests.

— Internal corrosion can cause flange faces to losematerial.

— Flange orientation, particularly blind flangesinstalled horizontally, allowing water to collect inthe holes. Stud bolts in blind flanges in firewatermains have suffered this form of damage.

7.3 DEGRADATION MECHANISMS

A number of degradation mechanisms can contribute tothe failure of a bolted joint, most of which are corrosionrelated. Figures 7.1 - 7.11 (see pages 39-41) illustratethe most common problems found.

7.4 INSPECTION TECHNIQUES

7.4.1 Non-destructive testing

The most common method of in-service non-destructiveinspection is visual inspection, normally carried out aspart of general visual inspections of pipework orstructures as opposed to specific bolt inspections. Thelimitations of this method are that only the externalparts of the joint are visible which will detect loosebolts and corrosion; however the extent of surfacedegradation on the strength of the joint is difficult tomeasure.

Where bolt threads or nuts show the effects ofsignificant corrosion then further investigation shouldbe undertaken to ensure that the joint is still fit forpurpose. Some Operators use a Performance Standardto quantify the extent of bolt degradation. An exampleof a PS for low alloy steel bolting material is shownbelow:

Bolts shall be visually examined for evidence ofcorrosion and other defects (mechanical damage or

37

Table 7.1: Summary of key issues

Damagetype

General corrosion

Galvanic corrosion

Localised boltcorrosion

Crevice corrosion

Fatigue

Creep

Stress corrosioncracking

Hydrogenembrittlement

Flange facecorrosion

Typicalconditions

Exposed areas

Dissimilar metals -flanges, bolts, gaskets

Dissimilar metals, exposedareas

Exposed areas

Joints subject to vibration,cyclic loading

High temperatureapplications

A combination of achloride-containingenvironment, susceptiblematerial and tensile stress

Hydrogen can form onsurface during manufactureor be caused by CathodicProtection

Pipework containing acorrosive medium,dissimilar materials

Inspectiontechnique

Visual, sample removal,Cylindrical Guided WaveTechnique

Visual

Sample removal, visual,Phased Array UT, CGWT

Visual, sample removal

Visual, Phased Array UT

Time-of-flight UT

Phased Array UT

Visual, highlighting anycorroded High StrengthFasteners for replacement

Intrusive visual, UT

Mitigationmeasures

Material selection, threadprotectors, coatings

Material selection, gaskets,bolt/flange insulating kits,weld overlay

Material selection

Material selection

Pipework design

Material selection, ASMESA-453

Material selection

Material selection - mostcommon in High StrengthSteels e.g. ASTMStandards A345 Gr BD,A490and A547 Threadprotectors and coatings

Material selection, gasketselection, weld overlay

cracking). Bolting showing signs of mechanical damageto plain shanks or threaded portions within the stressedportion or any cracking shall be replaced with newbolting.

Bolts, studs and screwed fasteners that havecorroded such that the diameter of the smooth shank orthe major thread diameter is less than 90% (i.e. 10%loss in diameter) of the nominal size, after removal ofthe corrosion product, shall be replaced with newbolting.

A number of more specialised techniques areavailable which can be used to check for specificconditions; these include:

— Phased Array Ultrasonics - detects thread wear andcracking from the bottom of the threads, asillustrated in Figure 7.11 (see page 41).

— Time of Flight (TOF) UT - measures boltelongation.

— Cylindrically Guided Wave Technique (CGWT) -detects corrosion wastage.

— Ultrasonic inspection of flange faces using shearwave transducers - detects flange face corrosionand erosion.

— Black light NDT of threads and body on bolts thatare to be re-used on high critical joints - detectsstress cracking.

7.4.2 Destructive testing

Where degradation is thought to have occurred andassessment is not possible through non-destructivetechniques, sample removal of bolts for destructivetesting can be carried out to estimate if joints are still fitfor purpose. Finite element analysis has also been usedto model the effects of progressive removal of layers ofbolt material.

7.5 DEFECT MITIGATION MEASURES

In-service inspection requirements can be greatlyreduced by designing the bolted joint to include

38


measures which will reduce the risk of degradation dueto mechanical damage and corrosion. The following aresome commonly used measures:

— Material selectionCorrosion-resistant alloys e.g. stainless steel,duplex and cupro-nickel alloys are used. However,they can suffer specific rapid failure mechanismssuch as stress corrosion cracking. In addition, thehigh costs of these materials restricts widespreaduse.

— Thread protectorsNeoprene, polyethene and aluminium are common.However, the potential for loss of threadengagement strength needs to be assessed.

CoatingsBolts can be supplied with a variety of lifeextending surface treatments such as hot dip spungalvanising, which research shows offers the bestlong term protection. Zinc, PFTE or electrolessnickel are also used.

Cathodic protectionUsed for underwater applications. However, thereis usually a need to apply coating to the pipeworkand flange joints to minimise the risk of hydrogenembrittlement.

Flange protectionGaskets (material selection is important to avoidgalvanic corrosion), flange protectors, coatings.

Figure 7.1: General corrosion(General corrosion of flanges and bolts.)

Figure 7.2: Galvanic corrosion (1)(Galvanic corrosion where dissimilar materialshave been used for the bolts and one flange.)

Figure 7.3: Galvanic corrosion (2)(Galvanic corrosion where dissimilarmaterials of bolts only has been used.)

Figure 7.4: Localised corrosion(Severe localised corrosion of bolt body.)

39


Figure 7.5: Crevice corrosion(Advanced crevice corrosion of a stainless steel bolt.)

Figure 7.6: Fatigue(Failed bolt displaying typicalfatigue failure characteristics.)

Crack Initiation Site

(6.7X)

Figure 7.7: Stress corrosion cracking(Failure surface of bolt which had been subject to thecombined influence of tensile stress and a corrosiveenvironment - a typical example would be austenitic

stainless steel in high chloride conditions.)

Crack Initiation Site

Figure 7.8: Hydrogen embrittlement(Fracture surface of a bolt that resultedfrom hydrogen embrittlement cracking.)

Figure 7.9: Flange face corrosion(Flange face corrosion in seawater pipework.)

Figure 7.10: Galvanic corrosion(Galvanic corrosion of clamped assembly seal ring.)

40


Figure 7.11: Phased array ultrasonics

41

42


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