omc paper ravena1 on fpso rbi

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A COST EFFECTIVE APPROACH TO RISK BASED INSPECTION FOR FLOATINGPRODUCTION STORAGE AND OFFLOADING (FPSO) UNITS AND GAS PROJECTS.

A COST EFFECTIVE APPROACH TO RISK BASED INSPECTION FORFLOATING PRODUCTION STORAGE AND OFFLOADING (FPSO) UNITSAND GAS PROJECTS.

D. A. Constantinis, EM&I (Maritime) Limited, D. M. Mortlock, EM&I (UK)Limited, T. Lyons EM&I (Maritime) Limited

This paper was presented at the 10 th Offshore Mediterranean Conference and Exhibition in Ravenna, Italy, March 23-25,2011. It was selected for presentation by OMC 2011 Programme Committee following review of information contained inthe abstract submitted by the author(s). The Paper as presented at OMC 2011 has not been reviewed by the ProgrammeCommittee.

AbstractThe Asset Integrity Policies of many Oil Majors require a comprehensivecriticality based Risk Based Inspection (RBI) approach to the integrity assuranceof pressure systems.

Development of the RBI system and implementation in terms of baselines andongoing operational inspections can be costly and can create additional risk toplant integrity.

An improved approach to RBI has been developed and implemented on FloatingProduction Storage and Offloading units and Gas projects world-wide.

The methodology adopted significantly reduces the time taken to develop the RBIsystem and integrate it into various industry standard databases. The methodalso considers innovative methodology for the gathering of baseline data andongoing inspections.

For example, creating inspection ports in insulated lines or pressure vessels canbe avoided thus saving cost and risk of Corrosion Under Insulation (CUI).

The presentation discusses latest developments for on-line inspection usingRadiographic Backscatter Computed Tomography which enables through-wallinspections of insulated vessels without damaging insulation and the practicalapplication of digital radiography and pulsed eddy current to improve in serviceasset integrity assurance.



IntroductionThis paper discusses the reasons why Risk Based Inspection (RBI) has becomean important element of Asset Integrity Management and how it has be applied ina cost effective manner on FPSO and Gas projects around the world.

The authors draw on practical experience form a number of case histories tohighlight how the RBI Plans can be practically implemented through baselinesand ongoing inspections using non-destructive testing methods applied withminimum operational disruption.

The RBI requirement and how it fits into an effective Asset IntegritySystem.There have been a number of mechanisms adopted to assure the integrity ofpressure systems over the years.

The driver for asset integrity assurance has often been the catastrophic failure of

critical pressurized plant and this has resulted in various codes of practice thataimed to ensure that critical plant was designed, constructed, operated andmaintained so that it remained safe over its intended life.

Regulatory and certifying organizations set prescriptive rules and codes toregulate and provide guidance on the design, construction, operation andmonitoring of pressurized systems. Part of these regulations and codes includedthe prescriptive monitoring of plant condition using inspection and non-destructive testing methods applied at various stages of the pressure systems ’ life.

The prescriptive approach included a requirement to examine both the externaland internal condition of piping and pressure vessels. However, inspectionmethods in the early days did not enable a reliable assessment of internalcondition of many types of pressure vessel and thus the requirement for shuttingdown the pressure vessel for an internal visual inspection was the adoptedapproach. Piping inspection was considered less important and was largelyrestricted to external visual inspections with the occasional opportunistic internalvisual.

While this methodology certainly allowed a careful look at internal condition, itwas costly, reduced productivity and created its own safety and environmentalrisks. Furthermore, the results of the inspections often showed that there was no(or very little) internal deterioration and the pressure vessel would be duly re-instated and put back into operation.

Unfortunately, this approach did not stop catastrophic failures.

This might have been because of a number of factors, for example:



The assumption that the rates of deterioration were constant even thoughoperating conditions were changing

The application of the same level of inspection, irrespective of risk orconsequence of failure

The commercial and/or operational pressures that may have led to poorquality or deferred inspections

The belief that, as long as the prescriptive rules were observed, the plant wassafe

Although the frequency of catastrophic failures was low, the consequences insafety, environmental and business terms were so severe that industry workedhard to develop a better way to avoid catastrophic plant failures and thus assure

Asset Integrity.

It became clear that Asset Integrity assurance is a combination of many factorsof which Risk Based Inspection (RBI) is one important component.

It would probably at this point be useful to define what we mean by ‘AssetIntegrity’ and ‘Risk Based Inspection’

‘ Asset Integrity Management are those actions required to ensure that criticalequipment is designed, constructed and operated so that it remains safe and fit-for- purpose throughout its life’.

‘ Risk Based Inspection is the optimized application of appropriate inspectionmethodology to equipment based on the risk and consequence of their failure insuch a manner as to provide reliable information on condition and deteriorationrates ’ .

It is thus clear that Asset Integrity is the result of optimizing a combination ofmany factors such as an understanding of plant criticality, degradationmechanisms, appropriate design, construction, plant operation and maintenance.

Inspection merely helps in understanding the current condition and rate ofdegradation, provided that the baseline data, design philosophy, operatingconditions, maintenance regimes and other such data are also known and linkedin to the condition assessments and prediction. For example, it would be possibleto design and build a plant that would never need maintenance or inspection butthe cost would be prohibitive in most instances.

To summarize, RBI is an evolution from prescriptive regulations and is a methodfor optimizing the inspection process – it supports good Asset IntegrityManagement but relies on knowledge of other factors in order to design the RBIprogramme, to interpret the results and to predict future condition.



Case History - Designing an RBI system for an FPSOThe FPSO in question was a conversion which had been redeployed, on lease,for an Oil Major and was operating on a deepwater field offshore Brazil.

The project started with a kick-off meeting to define the key stakeholderobjectives and to agree on key project issues such as data availability, baselines,database selection and database inputs and outputs.

An effective RBI system depends on complete and accurate data both at the setup stage and throughout the asset life.

This data includes:

Line / Vessel Lists

Material of construction Operating temperatures and pressures Design temperatures and pressures (if operating values not available) Insulation / lining / cladding details System criticality information Basic fluid composition P&IDs PFDs Heat and Material Balance Process System Description RAM study Materials selection basis Fabrication drawings, Datasheets etc

Process stream data is required to assess the possible damage mechanismsand their relative effects on the material of construction.

Heat and Material Balances contain information on the fluid flowing betweenmajor equipment items in a process. Typically, the operatingtemperature/pressure, volume flow rates and compositional data such as CO 2,H2S, water and amine content are modeled. They are the best source ofinformation for an RBI study before start-up or early on in the life of the asset.

After a reasonable period of operation, process monitoring data for exampleand production chemistry should be used where possible.

Each line and/or vessel was assigned a representative process stream. Wheredata conflicted with other sources such as the line list, the compositional datafrom the Heat & Mass Balance only was used. Process streams which have verysimilar corrosivity were grouped together. Corrosivity only was considered as theconsequences of failure due to release of the fluid will be captured elsewhere.



The data required was found through a review of various documentation fromvarious sources such as the P&IDs, PFDs, Heat and Material Balance, etc.

Where data was not available assumptions were made and the rationale behind

the assumptions was noted. In all cases the assumptions erred towards aconservative, worst case corrosion scenario until proven otherwise.

The data was input to an EM&I-RBI master spreadsheet specifically designed forthe asset in question and the selected database. This allowed the data to bemanipulated more easily, rather than inputting the data line by line into thedatabase as is usually the case.

A risk screening was carried out to identify items which had negligible likelihoodof failure (LoF) or consequence of failure (CoF). The decision was then madeby the RBI facilitator on whether to include low risk items in the detailed

assessment. In the case of a quantitative detailed assessment where data isreadily available it may be no added effort to include all items.

Figure 1 – Typical Risk Screening Matrix

Screening can be performed at any level such as a complete facility or processunit, down to multiple or individual pieces of equipment. It is recommended to doa good quality risk screening where data is readily available such as a complete



process line list/vessel list. If data is less readily available a risk screening bysystem may be more appropriate.

The EM&I-RBI Master Spreadsheet has been developed to assist with the RiskScreening process, production of Corrosion Circuits, and selection of Damage

Mechanisms. Data gathered was input into this spreadsheet.Reference tables as shown in the tabs in the Master Spreadsheet are requiredwhich are specific to the Client / asset. These tables are used to convert projectspecific codes into generic groups. For example, a table of piping materialclasses is required to divide them into ‘carbon steel’ and ‘stainless steel’ and atable of Stream Numbers may be used to group similar streams into one.

Figure 2 – EM&I-RBI Master Spreadsheet showing data required to Assess LoF and CoF

The following Damage Mechanisms common to oil & gas processing facilitieswere chosen by as applicable to the Risk Screening process. Recommendedpractices API 571, 581 & DNV RP G101 were referenced to establish susceptiblelines based on material of construction, operating conditions and service. Thenumber of Damage Mechanisms which are included in the risk screeningspreadsheet depends upon the amount of data available, and is expected to varybetween projects.

Chloride Induced Stress Corrosion Cracking Wet H 2S Cracking Amine Stress Corrosion Cracking Atmospheric Corrosion Carbon Dioxide (carbonic acid) Corrosion Corrosion Under Insulation Dissimilar Metal (galvanic) Corrosion Local Corrosion and Uniform Corrosion (Seawater & freshwater effects) Microbiological (sulphate reducing bacteria induced) Corrosion Erosion Corrosion Amine Corrosion Liquid Metal Embrittlement (LME)



The formulae in the EM&I-RBI Master Spreadsheet reflected the DamageMechanism criteria and identified items which may be susceptible to one ormore of these. Some of the criteria are difficult to assess with a calculationand, in some cases, the RBI facilitator needed to use engineering judgement

based on all available information.

Figure 3 – Typical Damage Mechanisms Assessed inEM&I-RBI Master Spreadsheet

The other component in the risk screening is the consequence of failure. Thecriteria for consequence of failure were assessed based on the properties of theitem in question, such as a line or vessel.

Formulae in the spreadsheet are used to reflect these criteria and to identifyany items which may be critical to health, safety, environment or business. Theparameters need to be agreed with the Client and compared against anycorporate.

Services selected as being hazardous to health were fuel gas, process gas, ventgas, acid gas, high pressure flare, low pressure flare, nitrogen, condensate andwell stream.

Safety critical elements were assessed in terms of the propensity of a fluid toignite and whether it is contained at a dangerous pressure, thus increasing thechance of catastrophic failure.

Environmentally critical elements were assessed as those the release of whichto the atmosphere or overboard would result in an environmentally highconsequence and included liquid hydrocarbons, condensate and well stream.Closed drains were also included depending on volume.

Business critical elements included the loss of production associated withreduced operability, and was assessed by system. The cost ofrepair/replacement can also be assessed at this stage if information is readily



available. Gas compression, inlet separation and deluge systems are examplesof common business critical systems however guidance from the Client shouldbe sought as it is after all their business.

Figure 4 – Consequences of Failure in the EM&I-RBI Master Spreadsheet

Baseline Surveys A separate but crucial issue is how to measure deterioration trends on criticalcomponents so that the condition can be predicted with reasonable accuracy.This requires a strategy for defining the baseline condition of the criticalcomponents at an agreed point in time, preferably before start up.

A baseline strategy developed and implemented during construction andcommissioning stages, will be a worthwhile investment and, whilst there may bedifficulties in persuading the project team to allow this to take place (for fear ofdisruption to the project schedule), experience has shown that not only can thisbe achieved without disruption, but that benefits such as cost reductions andbetter quality will be achieved.

Experience has also shown that using pipe schedule thickness with tolerances ofsay +/- 12.5% does not give the level of accuracy required. For example, atypical carbon steel corrosion rate might be 0.1mm / year whereas pipeschedules can have a manufacturing tolerance of many times that figure. Thiscan lead to misleading results when operational inspection thickness data isgathered, and could mask serious corrosion issues. Furthermore, the normalquality control processes are unlikely to detect other issues such as incorrectschedules and materials.

Previous projects have shown that baseline surveys carried out in the fabricationyard detected around 14% of out of specification piping, errors that at would havebeen much more expensive to rectify during operations and could have led tounexpected failures.



Baseline surveys are best carried out during the construction phase, beforeinsulation is applied, when it is less costly to carry out the inspections andremedial action for out of specification components can be implemented morereadily.

A further objection is that the baseline survey will interfere with the projectconstruction progress. Experience has shown that this need not be the case andin fact, if the baseline survey is properly planned, the baseline work can evenassist the project by avoiding delays and costs in rectifying quality issues later inthe construction process.

Typical baseline teams comprised 1 or 2 technicians at each construction site,equipped with ultrasonic thickness gauges, hardness testers, positive materialidentification kit, digital cameras, coating thickness gauges, etc

A further choice that had to be made was to decide whether to apply baseline

inspections to critical components only. This option would have reduced costsprovided that criticality assessments had already been carried out. However, theoperators were not sure which non critical components may have become so infuture. The decision was therefore taken to extend the baselines to includecertain non-critical items.

Once the baseline survey was completed and the data has been input to thedatabase it was crucial that a system was put in place to capture any changes tothe way the plant was operated so that the RBI remained current.

Baseline data spreadsheets were created and utilised to upload the inspectiondata rather than entering the data one location at a time as is normal practice.

Data was reviewed by a competent engineering authority prior to upload to thedatabase to avoid the difficulty of locating and correcting errors after upload.(Such errors may result in serious consequences when used to decide likelydamage mechanisms and inspection methodologies and periodicities).

Inspection MethodologyThe database provided guidance on the location and frequency of ongoinginspections as well as information on the expected failure mechanisms and thusthe type of inspections to be performed.

Wherever possible, non-intrusive inspection methods were chosen.

The RBI procedures included guidance on how best to take advantage ofopportunistic inspections, for example when plant is opened up for maintenanceor unplanned shutdowns.



There are numerous NDT methods available, ranging from basic techniquessuch as ultrasonic thickness gauging and crack detection, through to Digital(Computed) Radiography, Pulsed Eddy Current, Backscatter ComputedTomography, SLOFEC, CHIME to name but a few.

Careful selection of the optimum NDT techniques (with validations if required fornew applications) can provide effective means of monitoring the condition ofcritical pressure systems without the risks and production disruption associatedwith internal inspections.

Digital Radiography provides an opportunity for reducing costs and minimizingrisk of CUI. This is achieved by taking radiographs with a precise calibrationmethod which takes account of penumbral unsharpness and thus allows moreaccu rate measurement of wall thickness of piping up to 6” OD without having toaccess the pipe surface through inspection ports. This methodology offers thefollowing benefits:

Reduced cost of creating inspection ports on insulated lines Reduced risk of water ingress to the pipes outer surface through the

inspection ports and thus reduced risk of CUI Capability of inspecting for internal, external and under-clamp corrosion,

water ingress, weld root erosion, heat trace condition etc with onetechnique

Flexibility when choosing inspection locations Increased inspection coverage compared to single point readings

Figure 5 – Digital Radiography Image



Pulsed Eddy Current (PEC) is a method that has been applied to insulatedcomponents with diameters larger than 6 ” OD. The technique measure s totalmaterial loss rather than actual wall thickness and thus is generally used asscreening tool.

Figure 6 – Pulsed Eddy Current InspectionImage courtesy of PNDT

Other techniques such as Saturation Low Frequency Eddy Current (SLOFEC TM)have been successfully applied and offer the opportunity for rapid scanning andthrough wall screening of piping and vessels.

Figure 7 – SLOFEC Image of Pipe Defects



Backscatter Computed Tomography (BCT) in particular shows a lot of promise inbeing able to carry-out ‘one-sided radiography ’ through multiple layers on a widerange of materials and components. Recent trials on gas plants for an Oil Majorin Canada successfully demonstrated the ability of the technique to inspect thethrough wall condition of insulated or PFP coated pressure vessels and piping.

This ability for single sided inspection of multiple layer structures has led tofurther planned trials on flexible risers and LNG containment.

Figure 8 – Back Scatter Tomography Equipment and ImageShowing Internal Corrosion (12” OD Insulated Pipe)

Part-intrusive inspections are sometime applied which enable internalexamination of specific areas such as the ‘furniture ‘within a pressure vessel butwithout the risk, cost and production disruption of a full internal inspection.Various CCTV and boroscope methods are used for this purpose.



Figure 9 – CCTV Image – Part Intrusive Inspection

Thermal imaging is also a technique used to inspect for various conditionsincluding build-up of solids and damaged / wet insulation.

Figure 10 – Thermographic Image of Pressure VesselShowing Fluid Levels and Solids Build-up

So far we have focused on RBI inspections of pressure systems. There arefurther benefits to be gained by applying similar methodologies to structuralcomponents, for example, Under Water Inspections in Lieu of Dry-docking(UWILD).

Under Water Inspections in Lieu of Dry-docking (UWILD) has evolved to meetClass requirements for assets that wish to defer a dry-dock survey. Theseinspections are conventionally carried out by divers and ROVs and were



originally intended to be carried out in sheltered waters. When applied to FPSOsthe waters are often not sheltered leading to high risk and high cost surveys.

New methods show that by applying an RBI approach many of the inspectionsthat would be carried out by divers or ROVs can be carried out from within the

hull as part of the normal periodic internal tanks structural surveys. This canreduce both costs and risks and provide more accurate condition data on thestructural condition of critical components.

CONCLUSIONSThe application of RBI combined with appropriate Inspection/NDT methods cansupport the Asset Integrity Management process and reduce cost and risk.

Case history experience has shown that developing an RBI system using themethods discussed is less costly and time consuming than previous methods.

However, in order for the process to be effective long-term it is necessary toimplement baseline surveys (preferably during the construction phase) and usean appropriate database to manage the data.

Integration with the maintenance and production teams introduces furtherbenefits through opportunistic inspections and ensuring that changes in operatingconditions are monitored to continually update the relevance of the RBI activity.

New inspection methodology optimizes the ability to carry out the inspectionsnon-intrusively and on line leading to reduced inspection downtime and betterknowledge of asset condition.

Finally, whereas RBI has generally been applied to process pressure systems,significant benefits can be generated by using similar methods on other criticalelements such as structures, hazardous area equipment (HAE) etc.

omc paper ravena1 on fpso rbi

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