api rp 553 (1998)refinery control valves

Refinery Control Valves

API RECOMMENDED PRACTICE 553FIRST EDITION, SEPTEMBER 1998

COPYRIGHT 2002; American Petroleum Institute

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Manufacturing, Distribution and Marketing Department

API RECOMMENDED PRACTICE 553FIRST EDITION, SEPTEMBER 1998



SPECIAL NOTES

API publications necessarily address problems of a general nature. With respect to partic-ular circumstances, local, state, and federal laws and regulations should be reviewed.

API is not undertaking to meet the duties of employers, manufacturers, or suppliers towarn and properly train and equip their employees, and others exposed, concerning healthand safety risks and precautions, nor undertaking their obligations under local, state, or fed-eral laws.

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Generally, API standards are reviewed and revised, reafÞrmed, or withdrawn at least everyÞve years. Sometimes a one-time extension of up to two years will be added to this reviewcycle. This publication will no longer be in effect Þve years after its publication date as anoperative API standard or, where an extension has been granted, upon republication. Statusof the publication can be ascertained from the API Manufacturing, Distribution and Market-ing Department [telephone (202) 682-8000]. A catalog of API publications and materials ispublished annually and updated quarterly by API, 1220 L Street, N.W., Washington, D.C.20005.

This document was produced under API standardization procedures that ensure appropri-ate notiÞcation and participation in the developmental process and is designated as an APIstandard. Questions concerning the interpretation of the content of this standard or com-ments and questions concerning the procedures under which this standard was developedshould be directed in writing to the director of the Manufacturing, Distribution and Market-ing Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C.20005. Requests for permission to reproduce or translate all or any part of the material pub-lished herein should also be addressed to the director.

API standards are published to facilitate the broad availability of proven, sound engineer-ing and operating practices. These standards are not intended to obviate the need for apply-ing sound engineering judgment regarding when and where these standards should beutilized. The formulation and publication of API standards is not intended in any way toinhibit anyone from using any other practices.

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Copyright © 1998 American Petroleum Institute



FOREWORD

API publications may be used by anyone desiring to do so. Every effort has been made bythe Institute to assure the accuracy and reliability of the data contained in them; however, theInstitute makes no representation, warranty, or guarantee in connection with this publicationand hereby expressly disclaims any liability or responsibility for loss or damage resultingfrom its use or for the violation of any federal, state, or municipal regulation with which thispublication may conßict.

Suggested revisions are invited and should be submitted to the Director of the Manufac-turing, Distribution and Marketing Department, American Petroleum Institute, 1220 LStreet, N.W., Washington, D.C. 20005.

iii



CONTENTS

Page

1 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

3 CONTROL VALVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.1 Valve Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2 Valve Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.3 Valve Positioner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.4 Handwheels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.5 Switches And Solenoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.6 Transducers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.7 Booster Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4 SPECIFIC CRITERIA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114.1 Globe-style Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114.2 Rotary Style Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5 INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.1 Accessibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.2 Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145.3 Control Valve Manifolds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6 REFINERY APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.4 Boiler Feedwater Recirculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.5 Feedwater to Waste Heat Boiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156.6 Sulfur Recovery Unit Acid Gas Block Valve . . . . . . . . . . . . . . . . . . . . . . . . . 156.7 Sulfur Vapor to Eductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156.8 Liquid Sulfur to Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156.9 Hydroßuoric Acid Service. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166.10 Cat Cracker Bottoms Slurry Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166.11 Feed to Hydrocracker Fractionator (Flashing) . . . . . . . . . . . . . . . . . . . . . . . . 166.12 Reformer Hot Gas Block/Bypass (Three-Way Butterßy). . . . . . . . . . . . . . . . 166.13 Reactor Letdown with Erosive Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176.14 KO Drum Vent to Hydrotreater Flare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176.15 Antisurge Control Valves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176.16 High Volume, Low Pressure Air Blower Anti-Surge Valve . . . . . . . . . . . . . . 186.17 Crude Oil Processing Unit Throttling /Steam to Pre-Heat Exchanger . . . . . . 186.18 Pump Recirculation Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186.19 Crude Oil Processing Unit Heavy Bottoms (High Temperature Tar). . . . . . . 186.20 Crude Oil Processing UnitÑThrottling/Wash Oil . . . . . . . . . . . . . . . . . . . . . 196.21 Crude Processing UnitÑThrottling/Hot Oil . . . . . . . . . . . . . . . . . . . . . . . . . . 196.22 Spray Water to Desuperheater (Utilities) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196.23 Exchanger HGO BypassÑFCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206.24 Gas Oil RecirculationÑCaustic Hydrotreater (CHD) . . . . . . . . . . . . . . . . . . 206.25 Hot Separator Liquid to Hot Flash Drum (Power Recovery

Turbine Bypass)ÑHydrocracker. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206.26 Cold Separator Sour WaterÑHydrocracker . . . . . . . . . . . . . . . . . . . . . . . . . . 21

7 EMERGENCY BLOCK VALVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

v



1 Valve Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217.2 DeÞnitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217.3 Types of EVBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217.4 EBV General Instillation Guidelines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227.5 Actuator Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227.6 FireprooÞng . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

8 VAPOR DEPRESSURING VALVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238.2 Depressuring Valves and Actuator Requirements . . . . . . . . . . . . . . . . . . . . . . 23

9 HYDRAULIC SLIDE VALVE ACTUATORS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 9.2 Hydraulic Power Unit (HPU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 9.3 Slide Valve Positioner Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 9.4 Instrumentation Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249.5 Performance Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 9.6 Electrical Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259.7 Testing and Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259.8 Slide Valve Actuator Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figures1 Control Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 Live Loaded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Resilient Seat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4 Inherent Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5A Sliding and Rotary Stem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5B Sliding and Rotary Stem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6 Pressure Drop Through a Restriction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7 Cavitation Damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8 Typical Plug Damage from Flashing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 9 Multistaged Trim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 10 Diaphragm Actuator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 11 Double-Acting Spring Return Piston Actuator . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 12 Electrohydraulic Actuator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 13A Handwheels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 13B Handwheels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 14 Limit Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 15 Butterßy Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 16 Lug Style Butterßy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

vi



1


1 Scope

1.1

This Recommended Practice addresses the specialneeds of control valve applications in reÞnery services. Theknowledge and experience of the industry has been capturedto provide proven solutions to well-known problems.

1.2

This document provides recommended criteria for theselection, speciÞcation, and application of piston and dia-phragm-actuated control valves. It also outlines control valvedesign considerations, and discusses control valve sizing,noise, and fugitive emissions as well as deÞning types of com-monly used control valves and their actuators.

1.3

Recommendations for emergency block and ventvalves, on/off valves intended for emergency isolation orventing, and special design valves for reÞnery services, suchas FCCU slide valves and vapor depressuring systems, arealso included in this Recommended Practice.

2 References

All references shall be the latest edition.

API Publ 2218

FireprooÞng Practices in Petroleum andPetrochemical Processing Plants

RP 521

Guide for Pressure-Relieving and Depres-suring Systems

Std 556

Manual on Installation of Instruments andControl Systems for Fire Heaters andSteam Generators

Std 589

Fire Test for Evaluation of Stem Packing

Spec 6FA

SpeciÞcation for Fire Test for Valves

Std 607

Fire Test for Soft-Seated Quarter-TurnValves

Std 609

Butterßy Valves: Double Flanged, Lug-andWafer-Type

ASME

1

Boiler and Pressure Vessel Code, SectionVIII, Div. 1, International Society for Mea-surement and Control Standard S75 Seriesof Control Valve Standard

s B16.34

ValvesÑFlanges, Threaded, and WeldedEnd

FCI

2

70-2

Quality Control Standard for Control ValveSeat Leakage

NACE

3

Std MR0175-90

SulÞde Stress Cracking Resistant Metal-lic Materials for OilÞeld Equipment

OSHA

4

1910.95

Occupational Noise Exposure

U.S. EPA

5

40

CFR

Pt. 60 Appendix A, Attachment 1:

ReferenceMethod 21.

Determination of VolatileOrganic Compound Leaks

3 Control Valves

A control valve, as shown in Figure 1, consists of twomajor subassemblies: a valve body and an actuator. The valvebody is the portion that actually contains the process ßuid. Itconsists of a body, internal trim, bonnet, and sometimes a bot-tom ßange and/or bonnet ßange. This subassembly must meetall of the applicable pressure, temperature, and corrosionrequirements of the connecting piping.

The actuator assembly moves the control valve in responseto an actuating signal from an automatic or manual device. Itmust develop adequate thrust to overcome the forces withinthe body subassembly and at the same time be responsiveenough to position the valve plug accurately during changingprocess demands.

3.1 VALVE BODY

3.1.1

Process design conditions dictate the ANSI pressureclassiÞcation and materials of construction for control valves,provided the standard offering meets or exceeds all pipingand process control requirements. The valve end connectionsand pressure rating should, as a minimum, conform to thepiping speciÞcation. The valve material shall be suitable forthe process conditions.

3.1.2

Nickel alloy or stainless steel valve metallurgy shouldbe speciÞed for temperatures below -20¡F. High pressuresteam, ßashing water applications, and boiler feedwater ser-vice where differential pressures exceed 200 psi may requireharder, chrome-molybdenum alloys. Sour service valve mate-rials must meet the requirements of NACE MR0175-90. Cor-rosive and erosive components even in trace quantities mayaffect the metallurgical choice of the valve.

3.1.3

Inner valve parts should be the manufacturerÕs stan-dard where acceptable. Hardened trim may be required for

1

American Society for Mechanical Engineers, 345 East 47th Street, NewYork, New York 10017.

2

Fluid Controls Institute, P.O. Box 9036, Morristown, New Jersey 07960.

3

NACE International, 1440 South Creek Drive, P.O. Box 218340, Houston,Texas 77218-8340.

4

Occupational Safety and Health Administration, U.S. Department of Labor,Washington, D.C. 20402.

5

U.S. Environmental Protection Agency, available from the U.S. GovernmentPrinting OfÞce, Washington, D.C. 20402.



2 R

EFINERY

C

ONTROL

V

ALVES

corrosive, erosive, cavitating, or ßashing service, and wherevalve differential pressure exceeds 200 psi.

3.1.4

Flanges are the preferred end connection for globe-style valves, with butt-weld end connections acceptable forANSI classes 900 and above. Threaded valves and valveswith welded end connections are not recommended forhydrocarbon service and should be speciÞed only with theownerÕs prior approval.

3.1.5

Flanged control valve bodies are available with eitherintegral ßanges (machined as part of the body casting or forg-ing, or ßanges welded to the body), or separable ßanges (indi-vidual removable ßanges that usually lock in place on thevalve body by means of a two-piece retaining ring).

3.1.6

Flangeless valves have no ßange connections aspart of the valve body and are simply bolted or clampedbetween the adjoining line ßanges. Long bolts used withßangeless valves can expand when exposed to Þre andcause leakage. A Þre deßection shield and/or insulation is

recommended. In addition, high-tensile strength bolting isrequired.

3.1.7

Flange Þnish describes the depth of the grooves in thesurface part of a ßange which is available for the sealing gas-ket. If a special Þnish is required for gaskets, it should bespeciÞed with the valve. The typical standard is 125Ð250RMS, which provides a good sealing surface for the gasket.

3.1.8

The installed face-to-face dimension of integralßange globe style valves should conform to ANSI/ISAS75.03. Face-to-face dimensions of ßangeless controlvalves should conform to ANSI/ISA S75.04. Face-to-facedimensions of separable ßanged globe style valves shouldconform to ISA S75.20 or ISA S75.03. Butterßy valves arecovered by API 609. Caution should be used to install ßan-geless valves so that they will not leak in hydrocarbon ser-vice under Þre conditions.

3.1.9

The valve body size should be no less then twopipe sizes smaller than the line size. Smaller valve sizes

Figure 1—Control Valve

S

O

Adjusting Screw (with Lifting Ring)

Spring

Piston Stem O-ring

Cylinder

Piston

Piston O-ring

Stem Clamp

Gland Flange

Upper Packing

Yoke Clamp

Packing Spacer

Bonnet

Bonnet Flange

Seat Retainer

Seat Ring

Seat Ring Gasket

Body

Half Ring

End Flange

Adjusting Screw Gasket

Spring Button

Piston Retaining Nut

Actuator Stem Spacer

Actuator Stem Bushing

Actuator Stem O-ring

Cylinder Retaining Ring

Actuator Stem

Stroke Plate

Stroke Bellows

Yoke

Upper Stem Guide

Upper Stem Guide Liner

Bonnet Flange Bolting

Bonnet Gasket

Lower Packing

Lower Stem Guide

Lower Stem Guide Liner

Plug



API R

ECOMMENDED

P

RACTICE

553 3

must be reviewed to make sure that line mechanical integ-rity is not violated.

3.1.10

Final valve sizing should be reviewed by the valvemanufacturer.

3.1.11

Threaded seat rings should be avoided where possi-ble because corrosion often makes removal difÞcult.

3.1.12 Bonnets

Bonnets should be bolted. Bolting material should complywith ASTM A193/194/320 and should be compatible with thevalve body and bonnet.

Note: For the temperature range between -50¼F and 1000¼F, bolts and studsshould meet ASTM A193, Grade B7 speciÞcations. For temperaturesbetween 1000¼F and 1100¼F, bolts should be ASTM A193, Grade B16. Forlow temperature applications from -50¼F to -150¼F, bolts should be ASTMA320, Grade B7. Nuts should be ASTM A194, Grade 2H for the above appli-cations. Stainless steel bodies require stainless steel bolting. Higher gradevalve metallurgy requires 316 SST as the minimum bolting material.

Extended bonnets should be considered for process tem-peratures below 32¡F or above the temperature limits of thepacking materials shown below in section 3.1.13.

Bonnet gaskets should be fully retained 316 SST spiralwound, with polytetraßoroethelene or graphite Þller. Flat gas-kets made from PTFE sheet stock are acceptable where con-ditions permit. Insert reinforcements should be 316 SST orother appropriate alloy, as required.

3.1.13 Packing

a. Packing boxes should be easily accessible for periodicadjustment. The packing material should (1) be elastic andeasily deformable, (2) be chemically inert, (3) be able to with-stand applicable process conditions, (4) provide a degree ofÞre resistance, (5) minimize friction, and (6) reduce fugitiveemissions to meet regulatory requirements. Valve manufac-turerÕs packing temperature limits refer to the temperature atthe packing box.b. PTFE has excellent inertness, good lubricating properties,and is one of the most popular valve packing materials. Itmay be used in solid molded, braided, or turned form (V-rings) or as a lubricant for asbestos-free packing. Its tempera-ture limit with standard packing box construction is 450¡F. Ifused to meet fugitive emissions, virgin PTFE should be alter-nated with carbon-Þlled PTFE or similar minimal cold-ßowing material and live loaded. c. Graphite laminated or preformed ring packing is chemi-cally inert except when strong oxidizers are handled. This typeof packing can be used for temperature applications approach-ing 2000¼F. The biggest difÞculty caused by this type ofpacking is very high packing friction, which often requires anoversized actuator. Performance is often compromised,because of signiÞcant increases in hysteresis and deadband. d. Asbestos should not be used.

3.1.14 Fugitive Emissions

The Clean Air Act of 1990 or local requirements haveestablished strict limits on emission to the atmosphere of cer-tain hazardous substances. These substances are volatile haz-ardous pollutants listed in the National Emission Standard forHazardous Air Pollutants (NESHAP).

Increased emphasis on limiting packing leaks has resultedin the development of new packing materials and methods.Individual manufacturers are offering increasingly effectivedesigns, and vendors should be consulted for speciÞc applica-tions. See Figure 2.

Kalrez¨ also has excellent inertness and good lubricatingproperties. It does not cold ßow and therefore does not needlive loading. It is available in V-rings. The temperature limitwith standard packing box construction is 700¼F.

3.1.15 Seat Leakage

a. See ANSI/FCI 70-2 standard for deÞnitions of leakageclasses. Note that these deÞnitions change the way that leak-age is deÞned and tested between Classes V and VI. Controlvalves should have no less than a Class II leakage rating. Formost services, a Class IV rating is adequate. Class VI ratingsshould be considered only for applications requiring mini-mum possible leakage, and then only with owner approval.

b. Double-ported valves provide a Class II shutoff.

c. Single-seated globe valves with metal-to-metal seatingsurfaces meet Class IV. Class V shutoff can be achieved byproviding improved plug to seat ring concentricity or lappingseating surfaces and/or increasing actuator thrust. Resilientseats on single seated valves can provide Class VI shutoff.

d. However, before an insert material is selected, it should bedetermined that the insert is compatible with the process ßuid,pressure, and temperature. In addition to normal process

Figure 2—Live Loaded

Live-loading(not compressed)

Carbon-filledPTFE backups

Virgin PTFEV-rings

Wiper Rings

(compressed)



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condtions, shutdown conditions should be considered inselecting resilient seats. Steaming through a valve can damageor ruin a resilient seat. (See Figure 3.)

3.1.16 Control Valve Characteristics

a. Control valve ßow characteristics are determined princi-pally by the design of the valve trim. The three inherentcharacteristics available are quick opening, linear, and equalpercentage, as shown in Figure 4. A modiÞed equal percent-age characteristics generally falling between linear and equalpercentage characteristics is sometimes available. b. Positioners may use mechanical cams or be programmedto provide other desired characteristics. c. Installed characteristics often differ signiÞcantly frominherent characteristics if the pressure drop across the controlvalve varies with ßow. As a result, equal percentage plugs aregenerally used for ßow control applications because most ofthe Òsystem pressure dropÓ is not across the control valve.Linear plugs are commonly used for applications where mostof the Òsystem pressure dropÓ occurs across the control valve.

3.1.17 Control Valve Types

TodayÕs control valves operate by one of two primarymotions: reciprocating (sliding stem) motion (see Figure 5A,)

or rotary motion (see Figures 5B and 16). The selection of avalve for a particular application is primarily a function of theprocess requirements for control performance, pressure drop,temperature, and rangeability.

3.1.18 Sizing

a. ISA S75.01,

Flow Equations for Sizing Control Valves

, isthe basic source used. Per ISA 75.02,

Control Valve CapacityTest

, the tolerance for control valve Cv testing is ±5% at fullopening; the tolerance for partial openings is not stated. Con-trol valve data is based on water testing with a limited set ofsizes. The calculations become less accurate for ßuids signiÞ-cantly different from water, for very large or very small sizes,and for conditions different from laboratory conditions.b. The primary factors that should be known for accurate siz-ing are:

1. The upstream and downstream pressures at the ßowrates being considered. 2. The temperature of the ßuid. 3. The ßuid phase (gas, liquid, slurry) and the density ofthe ßuid (speciÞc gravity, speciÞc weight, molecularweight). 4. The viscosity (liquids). 5. The vapor pressure and critical pressure (liquids). 6. SpeciÞc heat ratio (gas). 7. The compressibility factor (gas).

c. As part of valve selection, the overall system in which thevalve is to be installed should be considered. A typical system(in addition to the control valves) includes a pump or com-pressor, which provides energy, and other types of reÞneryequipment, such as piping, exchangers, furnaces, and handvalves, which offer resistance to ßow. Note that the differen-tial pressure between the pump head curve and the systempressure drop curve is the amount of pressure available forthe control valve. If no control valve were used, the ßowwould always be at the rate indicated by the intersection ofthe two curves.d. The presence of reducers upstream and/or downstream ofthe valve will usually result in a reduction in capacity becauseof the creation of an additional pressure drop in the system bythese enlargements or contractions in series with the valve.Piping systems where both the inlet and outlet piping arelarger than the valve will result in an increased valve Cvrequirement. Capacity correction factors that can be appliedto calculated Cv values are readily available from most manu-facturers for the various styles of valves.e. In any ßow restriction, a portion of the pressure head ofthe incoming ßuid is changed to velocity head, resulting in areduction in static pressure at the vena contracta. Refer to Fig-ure 6. As the ßuid leaves the ßow restriction and assumesdownstream velocity, some portion of velocity head is recov-ered as pressure head. This process is termed pressurerecovery. The degree of pressure recovery is dependent upon

Figure 3—Resilient Seat

Figure 4—Inherent Characteristics

Soft Seat Ring

Insert Retainer

Insert

100

90

80

70

60

50

40

30

20

10

010 20 30 40 50 60 70 90 10080

Qui

ck O

pen

Linear

Equal Percen

t

Valve Life, %

Flo

w, %



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the internal geometry of the ßow restriction. The pressureexcursion in liquid ßow results in a vena contracta pressurelower than the downstream pressure. The vena contracta pres-sure may drop below the vapor pressure of the ßuid. As thepressure recovers it may stay below the vapor pressure (ßash-ing) or it may recover above the vapor pressure (cavitation).Flashing and cavitation are indications of partial or fullchoked ßow, which may affect sizing.f. Choked volumetic ßow occurs in gas or vapor servicewhen the ßuid velocity reaches the speed of sound at the venacontracta. With a constant inlet pressure, increasing the pres-sure drop no longer increases the ßow. This will affect thevalve sizing by limiting the pressure drop available for sizing.Pressure recovery has the effect of achieving choked ßow at apressure drop that is less than would be predicted by the criti-cal pressure ratio. This can become a problem for valves withhigh-pressure recovery, such as rotary valves. This necessi-tates the use of a larger valve or different valve style.g. Cavitation

1. Cavitation is the generation of bubbles in the lowestpressure portion of the valve, and then the subsequent col-lapse of these bubbles. See Figure 6. The bubble collapse(implosion) releases an intense liquid jet which candestroy a control valve in a short time. See Figure 7. It iseasily recognized by a characteristic sound Òlike rocksßowing through the valve.Ó A single compound such aswater is one of the most damaging ßuids. Hydrocarbonmixtures can have various vapor pressures for differentcomponents in the mixture, making it very difÞcult to pre-dict the onset or the severity of cavitation. Specialcavitation control trims are offered by manufacturers.

These can reduce or prevent cavitation. Some of thesetrims are subject to plugging in dirty services and shouldbe reviewed for suitability in each service.2. Valves with low-pressure recovery should be used tominimize or prevent cavitation. In some cases it may benecessary to use special components, or stage the pres-sure reduction through the use of two or more valves,or specially design elements in series.

h. Flashing1. Flashing occurs where the downstream pressure isless than the vapor pressure. See Figures 6 and 8.

Figure 5A and 5B—Sliding and Rotary Stem

Figure 6—Pressure Drop Through a Restriction

P2 (Cavitating)

P2 (Flashing)

Flow

Vena Contracta

Restriction

P1

P1 P2

Pv

Pvc

Pre

ssur

e

Distance



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Flashing, like cavitation, can cause physical damageand decreased ßow capacity. Velocity is the major con-cern. The outlet ßow increases velocity due to the ßuidchanging from a liquid to a gaseous state. A larger con-trol valve body size with reduced trim and larger sizeoutlet piping is usually required to prevent choking andexcessive velocity problems. 2. Flashing damage is usually less severe than thedamage from cavitation. However, restricted pipingconÞgurations at the valve outlet can cause the ßashedvapor to cavitate and cause piping damage downstreamof the control valve. Manufacturers should be consultedfor recommendations. 3. Outgassing of dissolved gases that have beenabsorbed by contacting (such as amine) is similar toßashing, but the relative amount of gas released ismuch harder to predict. The process engineer should beconsulted to obtain the correct outlet liquid and gasßow rates.

i. Rangeability1. The rangeability of the control valve should be consid-ered during valve selection. Control valves are availablewith published Cv rangeability of 50 to 1 and even greater,at constant pressure drop, a condition that rarely exists inactual practice. Typically, valves are sized with 10 to 20%

excess capacity at the high end and 10 to 20% below theminimum required capacity at the low end.2. A high rangeability is of little signiÞcance if the ser-vice conditions for the valves in question do not require it.The requirement for rangeability is to cover the maximumand minimum ßow rates at the real ßowing conditions.

j. Manufacturers should analyze all valve speciÞcations forcavitation, noise, or other detrimental factors, using the dataon the data sheets as a basis. Undesirable operating situationsshould be brought to purchaserÕs attention, including noise orcavitation severity. Manufacturers should propose possiblesolutions to these problems within the design limits of thetype of valve covered by the speciÞcation or indicate that aspecial design is required.

3.1.19 Noise

a. The predicted sound pressure level radiated from a controlvalve is a complex determination, and the allowable noiselevel in the installed location cannot be stated as one simplenumber to be speciÞed in all circumstances. This is particu-larly true where there are other noise sources in closeproximity, since they have an additive effect. The actual leveldepends on a number of factors, such as atmospheric dis-charge, physical location, proximity of other noise sources andtheir magnitude, piping system conÞguration and wall thick-ness, insulation on piping, presence of reßective sources, etc.b. Prediction of noise generated by a control valve is an inex-act science. Prediction levels for a valve operation atconditions speciÞed on the speciÞcation sheet can varywidely using various manufacturersÕ methods. c. To provide a basis for allowable noise level analysis, con-trol valves calculated to generate excessive noise levels shouldhave alternate valves proposed that will not exceed 85 dBA atone meter downstream and one meter out from the pipe. Foratmospheric discharge vent control valves (or system), thenoise level should not exceed 90 dBA at a point four metersdown from the vent exhaust and at a downward angle of 45degrees. No allowance should be taken for insulation orincreased pipe wall thickness over that speciÞed in makingnoise calculation, or in the valve or the noise reduction system.d. The calculated continuous noise level should not exceed 85dBA, measured where personnel may be continuously work-ing. This may not be one meter downstream and one meter outfrom the pipe. The Occupational Safety and Health Adminis-tration decreases the allowable time of exposure as the soundlevel increases, and the user is referred to OSHA 1910.95 forspeciÞc guidelines. It is the userÕs responsibility to determineif the sound level will meet OSHA requirements. e. Noise levels above 85 dBA may be allowable where per-sonnel are not working continuously. f. The maximum intermittent sound level should normallybe limited to 110 dBA.

g. In no case should the calculated sound level exceed 115 dBA due to possible mechanical failure.

Figure 7—Cavitation Damage



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h. Documented procedures and computer programs to esti-mate control valve noise are available from leadingmanufacturers, and they should be used to determine whethernoise is a consideration. However, noise prediction and miti-gation is a specialized effort generally requiring themanufacturer recommendation for an effective design. i. Valves with noise abatement or cavitation control trim withsmall passages tend to plug with debris, particularly duringstartup, and should be protected with conical or T-type strain-ers. See Figure 9.

3.1.20 Body Integrity

Hydrostatic testing of pressure-containing components isrequired per ANSI B16.34. For special services, other non-destructive tests are sometimes speciÞed.

3.1.21 Valve Assembly

The valve, actuator, and associated accessories, regardless ofmanufacturer(s), should be assembled, piped, aligned, tested,and shipped as a unit by the valve manufacturer. Tests mayinclude hydrostatic, stroke test, leakage, or accessory calibration.

3.1.22 Nameplate

The valve should be supplied with a permanently attachedstainless steel tag, stamped with the manufacturerÕs standarddata, and the tag or item number.

3.2 VALVE ACTUATORS

3.2.1

Pneumatic valve actuators, using air or gas, are pre-ferred for most process control applications. Electric motor orelectrohydraulic operators may be considered for specialapplications, particularly when pneumatic power is not avail-able. Electrohydraulic actuators are used where very highthrust forces are required.

3.2.2

Actuators are classiÞed as direct acting (an increasein air loading extends the actuator stem) or reverse acting (anincrease in air loading retracts the actuator stem). Some actu-ators are Þeld reversible. They can be changed from direct toreverse acting with no additional parts. Most manufacturerspublish tables that allow selection of actuator size based onvalve size, ßow direction, air action, pressure drop, packingfriction, and available air pressure.

3.2.3 Diaphragm Actuators

a. A spring diaphragm actuator is a single-acting actuatorwhere pressure is applied against a spring or springs. Uponloss of air, the spring will move the valve to the desired fail-ure position. Construction of a typical spring diaphragmactuator is shown in Figure 10.

b. Traditionally, the spring diaphragm actuator stroked overan input range of 3Ð15 psi. The frequent use of positionersand the requirements for tight shutoff have led to widespreaduse of higher pressures, utilizing the available air supply.

3.2.4 Piston Actuators

a. Piston (or cylinder) pneumatic actuators are used forcontrol valves where high thrust is required. Single-actingpiston actuators apply air pressure to one side of the pistonagainst a spring or springs. Upon loss of air the spring willmove the valve to the desired failure position. Double-act-ing piston actuators are considerably stiffer than single-acting designs and can therefore be used to control higherpressure drops. Double-acting piston actuators apply air toboth sides of the cylinder. Double-acting piston actuatorswithout springs require an external volume tank and tripsystem to achieve the desired failure position. Springs canbe added to double-acting piston actuators to provide theair failure mode. See Figure 11.

Figure 8 — Typical Plug Damage from Flashing



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Figure 9—Multistaged Trim



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b. Linear type piston actuators are used for globe style con-trol valves. They are also used for rotary valves with adapterlinkage. Scotch yoke or rack-and-pinion type piston actuatorsare normally used for on/off control, but may be used for reg-ulatory control if control degradation is not critical.

3.2.5 Electrohydraulic Actuators

A variation of the piston actuator is the electrohydraulic,actuator which uses an electric motor to drive a pump andsupply hydraulic pressure for the piston. For multiple valveinstallations, electrohydraulic actuators may be supplied by acommon electric motor/pump skid. See Figure 12.

3.2.6 Actuator Selection

3.2.6.1

Actuator selection guidelines are based on theassumption that the control valve will be required to operateagainst the maximum differential pressure speciÞed. Gener-ally, the worst case is to use the maximum upstream pressurewith the downstream pressure vented to atmosphere. Utiliz-ing this condition for selection of the actuator ensures ade-quate power for maximum service conditions but candramatically affect operator size, particularly on larger valvesizes. Actuators should be sized for the minimum air supplypressure available.

3.2.6.2

Stroking speed requirements should be reviewedand speciÞed for critical applications, such as compressoranti-surge control, or where closing speed should be con-trolled to prevent hydraulic water hammer.

3.2.6.3

Valve failure position should be carefully analyzedin the event that supply pressure or instrument signal is lost.Generally, the valve should fail in the safe direction on loss ofpower or signal.

3.2.6.4

The most reliable fail-safe action is achieved withan enclosed spring. If capacity tanks are required to provide

Figure 10—Diaphragm Actuator

AirLifts

SpringPushesDown

Upper Travel Stop

Diaphragm Plate

Loading Pressure

O-Ring Seal

Diaphragm RodSpring

Spring Seat

Indicator ScaleValve Stem

Travel Indicator

Stem Connector

Spring Adjuster

O-Ring Seal

Diaphragm

Reverse Actuator

Figure 11—Double-Acting Spring ReturnPiston Actuator

O

S



10 REFINERY CONTROL VALVES

reserve operating power, they should be sized to stroke thevalve twice. Capacity tanks should be stamped and otherwiseconform to ASME Code guidelines (see Part U-1, SectionVIII, Division 1, ASME Boiler and Pressure Vessel Code).Capacity tanks should be designed with all necessary acces-sories to ensure the required valve action and failure position.

3.2.6.5 The actuator case should be rated for the maximumavailable pneumatic supply pressure. Filters or Þlter regula-tors, if required, shall be supplied at the actuator inlet or thepositioner inlet.

3.2.6.6 The actuator should be sized to meet all control,shutoff, and valve leakage requirements. Shutoff capabili-ties should be investigated at conditions of maximum dif-ferential pressure.

3.2.6.7 To improve control valve performance, the effectsof low frequency response and excessive deadband and hys-

teresis should be addressed. The valve, actuator, and posi-tioner should be evaluated as part of the entire loop todetermine loop performance.

3.2.6.8 In general, the actuator materials of constructionshould be the manufacturerÕs standard.

3.2.6.9 Sliding stem actuators should be supplied with anindicator showing valve stem position. Rotary valve actuatorsshould have a travel indicator attached at the actuator end ofthe shaft, graduated in percent or degrees open.

3.3 VALVE POSITIONER

3.3.1 Valve positioners should be speciÞed for all applica-tions except on/off service. The valve positioner compares thevalve stem position with the signal generated by the controller.If the valve stem is incorrectly positioned, the positioner eitherincreases or decreases the air pressure to the actuator until the

Figure 12— Electrohydraulic Actuator

5 Volt ACCycle

FeedbackCam

BypassValve

Drain OffConnection

Air Bleed

CylinderShutoffValvesFeedback

Spring

Force MotorCoilInputSignal

BiasSpring

50 psig (3.4 Bar)

500 psig (34.5 Bar)

500 psig (34.5 Bar)

3-Section Pumpwith Built-InRelief Valves

Suction Filter

1/3 H.P.ElectricMotor



API RECOMMENDED PRACTICE 553 11

correct valve stem position is obtained. Pneumatic or electrop-neumatic positioners are used to improve valve performance.

3.3.2 The following is a list of functions a positioner canaccomplish:

1. Provide for split range operation.2. Reverse the valve action without changing the Òfail-safeÓ action of the spring in the actuator. (Note that thismay also be done with a reversing type relay.)3. Increase the thrust in spring diaphragm actuators.4. Modify the control valve ßow characteristic.5. Improve the resolution or sensitivity of the actuatorwhere high precision valve control is required. Precisionis enhanced by the availability of positioners with adjust-able gain.6. Reduce hysteresis.

3.3.3 Positioners should be installed using mounting platesor bosses provided for that purpose. The positioner should bemounted by the vendor, completely piped and aligned. Thepositioner should be supplied with pressure gauges.

3.3.4 Positioner bypasses should only be speciÞed withpneumatic positioners having the same or greater input signaland stroking range. Bypasses are not applicable with elec-tropneumatic positioners or with piston actuators.

3.3.5 Fast loops may require special tuning for best results.

3.3.6 Digital positioners further enhance valve perfor-mance, provide diagnostic information, and facilitate predic-tive maintenance programs.

3.4 HANDWHEELS

3.4.1 Manual handwheel operators should be supplied onlyon speciÞc request by the owner, or where bypasses are notinstalled. Side-mounted, lockable, screw or gear drive manualoperators, continuously connected and operable through anintegral declutching mechanism, are preferred. See Figures13A and 13B.

3.4.2 Handwheels should be permanently marked to indi-cate valve open and closed directions

3.4.3 When a handwheel is used for piston actuator, a cyl-inder bypass valve must be included.

3.5 SWITCHES AND SOLENOIDS

3.5.1 Hermetically-sealed proximity switches are preferredwhen independent ÒopenÓ or ÒclosedÓ indication of stemposition is required. See Figure 14.

3.5.2 Solenoid valves should be rated for continuous dutywith Class H high temperature encapsulated coils and be sat-isfactory for both NEMA 4 and NEMA 7 installations. Thevalve vent port should be equipped with an insect screen ori-

ented downward. Three-way solenoid valves are used withspring return actuators and double-acting actuators with posi-tioners. Four-way solenoid valves are used with double-act-ing actuators with no spring and on/off double-acting springreturn valves. Solenoid valves should be speciÞed so that theydo not require a minimum differential pressure across thevalve to actuate.

3.5.3 Valve trip solenoids should be installed in the actua-tor inlet tubing. When exhaust rate is critical, the solenoidvalve Cv should be selected accordingly. A quick exhaustvalve, working in concert with a pilot solenoid valve, may berequired if the trip solenoid does not have sufÞcient ventingcapacity. Quick exhaust valves have relatively large ventcapacity, with a Cv value at least ten times that of the typical1/4" solenoid valve.

3.5.4 Control valves with solenoids and limit switchesshould be speciÞed with 18" connecting leadwires orprewired to junction boxes. Low voltage and 120-volt wiringshould not be used in the same junction box.

3.5.5 DC voltage solenoids should be installed with a tran-sient voltage suppressor or diode mounted in parallel with thesolenoid coil. AC voltage solenoids should have a metal oxidevaristor mounted with the solenoid coil.

3.6 TRANSDUCERS

3.6.1 Electropneumatic transducers convert the electricaloutput signals from electronic controllers into pneumatic sig-nals that may be used to operate diaphragm actuated controlvalves or provide signals to pneumatic positioners. The use oftransducers with control valves is a common practice. Vibra-tion resistant transducers are required when mounted on con-trol valves.

3.6.2 Electropneumatic positioners are available whichconvert electronic signals to pneumatic output without a sepa-rate transducer. Electropneumatic positioners are widelyaccepted in lieu of separate devices.

3.7 BOOSTER RELAYS

Booster relays may be used to increase the speed ofresponse of the control valve.

4 Specific Criteria

4.1 GLOBE-STYLE VALVES

4.1.1 Globe-style valves are preferred for high pressuredrop applications, low ßow applications, or where cavitation,ßashing, or noise are considerations. However, some rotaryvalve models having a characterized ball or eccentric rotaryplug are suitable for these applications.




4.1.2 A globe-style valve that has a cast ßanged body andthat can be serviced while in the line is preferred. Split bodyvalves are not recommended except in special service, such asHF acid.

4.1.3 Three-way and angle body valves may be consideredfor special applications. Three-way valves can be used for pro-portioning control of converging or diverging ßow. Angle body

valves should be considered for coking service, where solidsare carried in suspension, for severe ßashing service, and wherethe piping design can take advantage of the valve geometry.

4.1.4 The recommended minimum globe body size is oneinch when installed in lines one inch and larger. Valvesinstalled in lines smaller than one inch should be line sized.Valve sizes 11/4", 21/2", 31/2", and 5" are not recommended.

Figure 13A and 13B—Handwheels

Figure 14—Limit Switches




4.1.5 Either integral or separable ßange bodies are accept-able. Valves having integrally cast ßanges are generally used,but separable ßanged valves are available.

4.1.6 Control valve bodies shall have the ßow directionpermanently marked on the body.

4.1.7 Stem or post-guided, unbalanced trim is preferred fortight shutoff applications or for ßuids containing suspendedsolids. Balanced, cage-guided trim is acceptable for applica-tions in clean, nonslurry service.

4.2 ROTARY STYLE VALVES

4.2.1 Cost considerations and certain process conditionsmay favor the rotary style control valve. Eccentric diskvalves (see Figure 15) are recommended in applications

requiring tighter shutoff, and in high ßow, low pressuredrops services. Rotary-segmented ball valves should beconsidered for highly viscous services and where greaterßow turndown ratios are required.

4.2.2 Butterßy valves with lug bodies (see Figure 16) mayhave threaded or unthreaded bolt holes. Wafer (unßanged)valves should have centering holes to ensure proper valve andgasket alignment. Long pattern valves having longer stud boltswith greater exposure should be insulated for Þre protection.

4.2.3 Particular attention should be given to clearancerequirements of butterßy disks. Heavy-wall pipe or lined pipecan interfere with disk rotation.

4.2.4 The valve shaft should normally be oriented in thehorizontal plane. The valve disk or ball should be positivelyattached to the valve shaft.

4.2.5 The actuator end of the shaft should be splined tominimize lost motion.

4.2.6 The shaft bearing should be designed to prevent theguide bushing from rotating in the body.

4.2.7 Shaft material should be stainless steel for carbonsteel or stainless steel valves. Other trim parts should be stain-less steel or better. The bearing material should not causegalling of the bearing or the shaft.

4.2.8 A shaft retention device should be provided on thenondriving end.

5 Installation

5.1 ACCESSIBILITY

5.1.1 All control valves should be installed so that they arereadily accessible for maintenance purposes and for operation

Figure 15—Butterfly Valve

Packing Retainer

Packing

Shaft

Packing Box Nut

Gland Flange

Packing Box Stud

Packing Follower

Shaft Bearing

Thrust Washer

Body

Taper Pin

Disk Stop

ShaftBearing

Thrust Washer

Disk

Figure 16—Lug Style Butterfly




of a handwheel, if one is provided. They should generally belocated at grade unless pressure head or other design condi-tions make such an arrangement impractical. When locatedabove grade, control valves should be installed so that theyare readily accessible from a permanent platform or walkwaywith ample clearances for maintenance purposes. Thereshould be sufÞcient clearance between the control valve actu-ator and the bypass line to allow removal of the actuator, bon-net, and plug. Preferred mounting is vertical.

5.2 LOCATION

5.2.1 Where there is a choice of location, it is desirable tohave the control valve installed near the piece of operatingequipment that should be observed while on local manualcontrol. In these cases, it is also desirable to have indicationof the controlled variable readable from the control valvehandwheel or the bypass valve.

5.2.2 Control valves used in process lines or fuel lines toÞred heaters should be located on the sides of the heater awayfrom the burners or at a sufÞcient distance from the heater,with blocks and bleed valves, so that the line can be drainedand the control valves removed without danger of a ßashback.An alternate method is to pipe the drain or bleed connection asafe distance from the heater.

5.2.3 High temperatures can cause premature failure ofactuator or positioner soft goods and electrical or electroniccomponents. Control valves should not be located adjacent tohot lines or equipment, or where temperature may be exces-sive. Consult the manufacturerÕs literature for maximum per-missible ambient temperature.

5.2.4 Electrical devices should be approved for use underthe applicable electrical area classiÞcation.

5.3 CONTROL VALVE MANIFOLDS

5.3.1 General

The design of control valve manifolds varies widely. In appli-cations where a process shutdown for the servicing of controlvalves cannot be tolerated and the process can be safely oper-ated manually, block and bypass valves should be provided.

5.3.2 Block and Bypass Valves

a. Where the greatest ßexibility is to be provided for futureexpansion, the block valves upstream and downstream of thecontrol valve should be line size. In situations where the con-trol valve is two sizes smaller than line size, the block valvesmay be one size smaller than line size.

b. For controllability, the bypass valve capacity should not besigniÞcantly greater than the control valve capacity. It is notunusual to make bypass valves smaller than the line size insuch cases.

5.3.3 Manifold Piping Arrangements

a. The manifold piping should be arranged to provide ßexibil-ity for removing control valves, particularly where ring-typejoints are used. Flexibility of piping is also necessary to keepexcessive stresses from being induced in the body of the con-trol valve. Vents and drains should be provided as required toservice the control valve. b. The piping around control valves should be self-supportingor should be permanently supported so that when the controlvalve or block valve is removed the piping integrity remains. c. Severe services may require special valve manifolddesigns. Design should be reviewed by user and manufacturer.

5.3.4 Swages

a. Where a ßanged or ßangeless control valve smaller thanline size is used, swages are placed adjacent to the controlvalve except where additional piping is required to permitremoval of the through bolts. Some users swage outsidethe valve manifold to use smaller block valves, but thisreduces the ßexibility of being able to change to a largercontrol valve on-line.

6 Refinery Applications6.1 Following are some speciÞc reÞnery control valve ser-vices with application notes and recommendations. The valvesrecommended represent the most economical solution to thegiven problem. These solutions have been proven in service.

6.2 Materials and packing suggested in these examples maybe modiÞed, based on vendors, suggestions and speciÞcapplications. Special environmental packing may be usedwhere required.

6.3 The user is cautioned to understand the signiÞcance ofthe recommendations and the limitations. It is more likely thata given problem will resemble an example than actuallymatch it. Thus, the user must use caution.

6.4 BOILER FEEDWATER RECIRCULATION

6.4.1 Operating Conditions

6.4.2 Valve Specification

Special designs are required for this extremely severeservice.

6.4.3 Trim

Cavitation control design, hardened, reduced port. A down-stream oriÞce plate, to reduce differential and cavitation, has

MaximumFlow (#/Hr) 100,000P1(psig) 2250P2 (psig) 0T (¡F) 160Ð180Fluid Boiler Feedwater




been used for some installations. This will only help at highervalve openings. On/off valve control is sometimes used forthis reason. Soft seats are normally not acceptable. Class Vshutoff rating is required.

6.4.4 Sizing

Conventional, choked ßow.

6.4.5 Notes

Consult with knowledgeable manufacturer for provendesigns.

6.5 FEEDWATER TO WASTE HEAT BOILER



One-inch carbon steel angle body, special application forcavitating service, outlet expander with replaceable erosioninsert. Diaphragm actuator with positioner.

6.5.3 Trim

Hardened plug and seat.

6.5.4 Sizing

Conventional, choked.

6.5.5 Notes

Mount valve close to boiler with expanded outlet to pre-vent cavitation damage due to restricted piping.

6.6 SULFUR RECOVERY UNIT ACID GAS BLOCK VALVE



Ten-inch, line size, high performance butterßy valve, ClassV leakage or better. Carbon steel body, NACE MR01-75 cer-tiÞed materials, double TFE packing required. On/off service,fail closed on loss of air supply or electric power to solenoidpilot. Open and closed limit position switches with hermeti-

cally sealed contacts. Stainless steel tubing and Þttings. Nocopper or brass components allowed.

6.6.3 Trim

Stainless steel disk and shaft.

6.6.4 Sizing

Conventional.

6.6.5 Notes

This is a safety application and requires NACE materials(per speciÞcation) and high reliability components.

6.7 SULFUR VAPOR TO EDUCTOR



Three-inch, line size, block valve, tight shut-off butterßy orplug valve. Fail closed actuator with solenoid pilot, limitswitches at open and closed positions. Carbon steel body,steam jacketed on/off service. NACE speciÞcation materials.No copper or brass components allowed.

6.7.3 Trim

Tight shut-off required.

6.7.4 Sizing

Conventional.

6.7.5 Notes

Line and valve are steam jacketed with 50 psig steam toprevent sulfur buildup in valve.

6.8 LIQUID SULFUR TO STORAGE



Plug type valve with actuator and positioner. Carbon steelbody, restricted trim.

NormalFlow (#/Hr) 10000P1(psig) 600P2 (psig) 55T (¼F) 228Fluid Boiler Feedwater

Normal ShutoffFlow (SCFH) 120,000 0P1(psig) 12 14P2 (psig) 11.8 0T (¡F) 120 120Fluid Acid Gas, MW = 37.1

Normal ShutdownFlow (SCFH) 2000 0P1 (psig) -0.6 0P2 (psig) -0.65 -0.7T (¼F) 300 300Fluid Sweep Air from Sulfur Pit, SG = 1.0

NormalFlow (GPM) 5 P1(psig) 30P2 (psig) 20T (¼F) 280Fluid Liquid Sulfur




6.8.3 Trim

Special characterized plug, stainless steel plug and seat.

6.8.4 Sizing

Conventional.

6.8.5 Notes

Body and ßanges are steam jacketed, 50 psig steam.

6.9 HYDROFLUORIC ACID SERVICE


Various ßows, pressures and temperatures. Hydroßuoric acid (HF), toxic and corrosive.


Carbon steel body (WCB) for moderate temperature ser-vices. Initial corrosion of the surface creates a protective bar-rier to limit further corrosion. Abrasion or water can removethis barrier. Use Monel body for high temperature servicesabove 300¡F (hot acid). Use Monel trim. Monel develops aprotective coating in service. It is necessary to allow adequateclearances at critical metal interfaces at the plug to guides,and seat to body, to allow for this buildup.

6.9.3 Quality Control

Because of the toxic nature of HF, the quality of thefoundry and valve manufacturer is important. VeriÞcation ofmaterials is required. It is important to eliminate any waterfrom the valve; thus, pressure testing with kerosene is oftenspeciÞed. Kerosene is less viscous than water and will bemore sensitive in Þnding casting defects and seat leakage.Leak detecting paint may be speciÞed for ßanges; the orangepaint turns green on exposure to HF. Refer to process licens-ers for detailed valve requirements.

6.10 CAT CRACKER BOTTOMS SLURRY OIL

Hydrocarbon/oil slurry with 15% solids.



Carbon steel body, segmented or eccentric ball design withshaft upstream and ßow exiting the valve across the seating

area (i.e., backwards). Trim solid alloy 6 plug, seat ring andretainer, 440C or Alloy 6 bearings, Nitronic 50 shaft.

6.10.3 Sizing

Conventional sizing for liquids, allowing for volume of Þnes.

6.10.4 Notes

Catalyst Þnes entrained in the slurry pose a severe erosionproblem and reduced trim life. Consider the impingementangle of the particles on the trim. For added resistance to ero-sion, upgrade the body to 316 SS or chrome-moly materialand the ball to ceramic. It may be advisable to purge the bear-ings with clean oil.

6.11 FEED TO HYDROCRACKER FRACTIONATOR (FLASHING)



Angle style globe valve with ßow down over the plug.

6.11.3 Trim

Hardened trim. A hardened liner in the valve outlet can bereplaced when worn.

6.11.4 Sizing

Conventional, ßashing, choked ßow.

6.11.5 Notes

Downstream piping length and restrictions should be mini-mized. Note that anytime ßashing occurs, it is very possiblethat cavitation may occur at any ßow disruption point in thedownstream piping, such as valves, elbows, or thermowells.

6.12 REFORMER HOT GAS BLOCK/BYPASS (THREE-WAY BUTTERFLY)


NormalFlow (GPM) 2042P1(psig) 60P2 (psig) 15T (¡F) 560Line (inch) 6Fluid Oil slurry, 15% catalyst Þnes with

0.010Ðto 0.015-inch particle size.

NormalFlow (GPM) 1150P1(psig) 586P2 (psig) 245T (¼F) 110Pv (psia) 593Pc (psia) 480Line (inch) 3Fluid Hydrocarbon Liquid

Minimum MaximumFlow (MSCFH) 800 1600P1(psig) 285 (max) 285 (max)P2 (psig) 282 (block) 0 (bypass)T (¼F) 1560 1560Fluid High Temperature Hydrogen





Butterßy, combination 20" block, 10" bypass, on tee. 10"bypass valve has Inconel 800 liner with refractory lining. Pis-ton actuator with high performance positioner. 347 SS body.

6.12.3 Trim

Special two-piece bearing for high temperature service,with tap for steam purge.

6.12.4 Sizing

Conventional.

6.12.5 Notes

Very special application. Consult with vendor.

6.13 REACTOR LETDOWN WITH EROSIVE SOLIDS



ÒAnti-cokingÓ angle valve, 1500# ANSI, 347 SS, 4" x 6"sweep angle body, expanding venturi outlet, with extendedbonnet, plug/guide purging system, piston actuator with highperformance positioner and valve position switch or transmit-ter. Heat treatment is required for the valve body.

Quality ControlÑ100 percent radiography of body and bon-net; liquid dye penetrant inspection; mill test reports; hydro-static test report; Þnal visual inspection; and NACE materials.

6.13.3 Trim

11/2" port, modiÞed parabolic plug, massive plug guiding,outlet liner. Plug, seat ring, seat ring retainer are mixture ofInconel 718, TC Grade 701, Inconel 625 with cobalt chromehard facing.

6.13.4 Sizing

There is no analytical method for sizing under theseextreme conditions.

6.13.5 Notes

This valve satisfactorily replaced a globe-style valve withvery short trim life.

6.14 KO DRUM VENT TO HYDROTREATER FLARE



An eccentric butterßy valve with soft seating is the eco-nomical choice. Class VI shutoff is required; pressure dropis low, and required capacity is high. NACE materials withcarbon steel body stress relieved.

6.14.3 Trim

317 SS disk, PTFE seal, PTFE lined 316 SS bearings,Nitronic 50 shaft.

6.14.4 Sizing

Conventional.

6.14.5 Notes

Materials should conform to NACE requirements (perspeciÞcation), due to acid gas service.

6.15 ANTISURGE CONTROL VALVES

6.15.1 Centrifugal compressors and blowers may enter acondition called ÒsurgeÓ at low ßow rates if there is insufÞ-cient mass ßow to maintain a stable discharge pressure.Because surge causes sudden changes in the forces on mov-ing parts and bearings, it may damage or destroy the com-pressor. The most common anti-surge control system directlyor indirectly, measures, the ßow through the compressor andopens a valve as required to maintain sufÞcient ßow to avoidan unstable pressure/ßow region. The valve should be sized,usually for several ßow and pressure conditions, to be sure itcan serve the full range of needs. It must respond quickly andaccurately to prevent a damaging surge in the compressor.

6.15.2 These valves typically generate high noise levelswithout noise abatement treatment. It is a business decision toevaluate the frequency and duration that the valve will berequired to open, along with the predicted noise level, before

Minimum Normal Maximum Flow (Inlet) 595 GPM 1386 GPM 1642 GPM Flow (Outlet) (GPM/SCFM) 570/140 1305/290 1580/346P1(psig) 1635 1571 1571P2 (psig) 395 395 395T (¼F) 820 820 814Fluid Gas OilÑßuid characteristics outgassing,

ßashing, cavitation, low angle and high angle parti-cle impingement, low pH.

Viscosity 0.24 cpVapor Press 395 psigCrit Press 711 psig

Solids 3% consisting of clay, catalyst, silica, 90% < 10 microns

H2S 3000 ppm

NormalFlow (SCFH) 23,760P1(psig) 11.0P2 (psig) 10.5T (¼F) 115Fluid Acid Gas




specifying the degree of noise control required. An exampleapplication is shown below.

6.16 HIGH VOLUME, LOW PRESSURE AIR BLOWER ANTI-SURGE VALVE



Four-inch high performance butterßy, for tight shutoff andwide rangeability. Piston actuator and high performance posi-tioner; specify stroke time based on estimated time constantof blower with discharge piping. Complete with silencer andheavy wall pipe between valve and silencer. Vendor shouldestimate noise with and without silencer and recommendinstallation details. Carbon steel body PTFE packing.

6.16.3 Trim

Carbon steel disk, stainless steel shaft.

6.16.4 Sizing

Conventional, choked.

6.16.5 Notes

This form of anti-surge valve vents to the atmosphereinstead of recycling the discharge to compressor suction. Thebutterßy valve provides considerable cost savings over thelow-noise globe style valve. User should specify acceptablenoise level, usually 85 dBA. Stroking speed response is criti-cal for this application.

6.17 CRUDE OIL PROCESSING UNIT THROTTLING /STEAM TO PRE-HEAT EXCHANGER



Post-guided sliding stem control valve, 2" globe valve ßowup, ANSI Class 300# WCB carbon steel body with graphitepacking; actuator with positioner.

6.17.3 Trim

Unbalanced 1.875-inch port, 316 SST plug with CoCr-Aon the plug seat and guide. Post guiding, with 17-4PH stain-less steel bushing, 316 SST seat ring with CoCr-A seat, and17-4PH seat ring retainer. ANSI Class IV shutoff.

6.17.4 Sizing

Conventional. Check for excessive noise.

6.18 PUMP RECIRCULATION VALVE


6.18.2 Valve Specifications

Globe-style control valve with ANSI Class 300# 8 x 6 inchWCC carbon steel body, Teßon packing, actuator, and posi-tioner for throttling service.

6.18.3 Trim

Stem-guided 7-inch port, unbalanced construction, 416stainless steel valve plug, and 410 stainless steel seat ring areselections with high hardness to combat erosive ßow; precipi-tation hardened 17-4PH cage. ANSI Class IV shutoff.

6.18.4 Sizing

Standard liquid sizing is adequate here for an initial evalua-tion. However, special procedures may be required to accountfor solids present in ßowstream; beware of underestimatingßow coefÞcient with standard liquid sizing equations. Sizingshould consider the erosive nature of the solids present in theßow stream; the equal percentage characteristic is preferredto position the operating conditions at an intermediate travelto avoid the high velocity ßow of low travel conditions. Theequal percentage characteristic will also provide relativelyuniform control loop stability over the expected range ofoperating conditions, compensating for the installed gaineffects of the pump curve. The 8 x 6 globe valve has the outletarea required and pressure recovery characteristics that mayavoid choked conditions in a conventional ball valve whilemaintaining the ability to operate at higher travels.

6.19 CRUDE OIL PROCESSING UNIT HEAVY BOTTOMS (HIGH TEMPERATURE TAR)


Minimum Normal Maximum ShutoffFlow (SCFH)15000 80000 125000 0P1(psig) 16 13 12 16P2 (psig) 0 0 0 0T (¼F) 270 270 270 270Fluid Air

NormalQs lb/h 250P1 psig 130dP psid 125T Satur (¼F ) 356T (¼F) 450Fluid Steam

Minimum Normal MaximumQ gpm (US) 1000 3200 7000P1 (psig) 422 400 306dP (psid) 372 350 256Fluid Crude Oil with 10Ð12% solids.SG 0.8 0.87 0.87Pv (psia) 3.00 3.00 3.00Vis 3.00 3.00 3.00





Eccentric rotary valve, ANSI Class 300# 3-inch C5 body,graphite fugitive emission packing, actuator and positioner forthrottling service. C5 chrome-moly body provides enhancedhardness characteristics with higher ANSI pressure/tempera-ture ratings. Reverse ßow (ßow passes plug, then seal) ballvalve preferred to maximize valve body life and divert highvelocity erosive ßow downstream. ANSI Class IV shutoff.

6.19.3 Trim

Reverse ßow full port trim conÞguration consisting of 17-4PH stainless steel seat ring retainer, Alloy 6 (Stellite 6) seal,and Stellite 6 valve plug with equal percentage characteristic.Reverse ßow conÞgurations will minimize high velocity ßowacross the rotary plug, seal, and inner valve body surfaces,helping maintain shutoff speciÞed and optimal body life. 17-4PH shaft and Stellite 6 bearing will provide high tempera-ture strength, as well as desirable corrosion and galling resis-tance. The 17-4PH/Alloy 6 shaft/bearing combination willminimize valve friction which would be caused by excessiveßuid particle buildup in the bearing areas.

6.19.4 Sizing

Conventional.

6.20 CRUDE OIL PROCESSING UNIT—THROTTLING/WASH OIL



Sliding stem globe style control valve with ANSI Class300# 3-inch chrome-moly body, graphite packing. Flow-up

self ßushing valve with actuator and positioner for throttlingcontrol.

6.20.3 Trim

Full 3-inch port with unbalanced, post-guided, equal per-centage 316 stainless steel plug with CoCr-A plug seat andguide. 17-4PH stainless steel seat ring retainer and 17-4PHstainless steel guide bushing. ANSI Class IV shutoff.

6.20.4 Sizing

Conventional.

6.21 CRUDE PROCESSING UNIT—THROTTLING/HOT OIL



Sliding stem globe style control valve with ANSI Class300# 4-inch chrome-moly body, graphite packing, and exten-sion bonnet. Flow down restricted port cage-guided balancedtrim with actuator and positioner for throttling control.

6.21.3 Trim

Restricted port, balanced, cage-guided trim with 316stainless steel valve plug with CoCr-A plug seat and guide.17-4PH stainless steel equal percent cage with Alloy 6(Stellite 6) seat ring and 316 stainless steel strain-hardenedstem. ANSI Class II leakage.

6.21.4 Sizing

Conventional.

6.22 SPRAY WATER TO DESUPERHEATER (UTILITIES)


Normal MaximumQ gpm (US) 285 340P1 (psig) 250 250dP (psid) 20 25T(¡F) 800 800Fluid1000 (¡F)

Crude unit heavy bottoms; high temperature of approximately erosive ßow with ÒstickyÓ particu-lates.

SG 0.762 0.762Pv (psia) 0.500 0.500

Normal MaximumQ gpm (US) 285 340P1 (psig) 25 25dP (psid) 20 20T (¡F) 600 600Fluid Intermediate temperature wash oilSG 0.762 0.762Pv (psia) 0.500 0.500

Normal MaximumQ gpm (US) 314 350P1 (psig) 85 85dP (psid) 20 20T (¡F) 600 600Fluid Intermediate temperature hot oilSG 0.85 0.85Pv (psia) 3.00 3.00

Normal MaximumFlow:gpm 0.37 0.75P1(psig) 400 400dp (psid) 183 133Temperature (¡F) 200 200Fluid WaterSG 0.96 0.96





One-inch globe style top-guided single port unbalancedßow up design valve. Body construction WCB 300 RFwith actuator and positioner for throttling control.

6.22.3 Trim

Trim 316 SST seat and stem with 316 SST Alloy 6-plugtip.

6.22.4 Sizing

Conventional.

6.23 EXCHANGER HGO BYPASS—FCC



Eight-inch three-way globe valve with diverging ßowand throttling applications. Carbon steel body. Actuatorwith fail down option and pneumatic positioner.

6.23.3 Trim

Stainless steel seat ring, plug, and strain-hardened stem.

6.23.4 Sizing

Conventional.

6.24 GAS OIL RECIRCULATION—CAUSTIC HYDROTREATER (CHD)



Four-inch globe valve with ßow down and tight shut-off.Carbon steel body, double TFE packing. Actuator with fail

close action, pneumatic positioner, and electro-pneumatictransducer with small-volume and self-operated regulator.

6.24.3 Trim

17-4PH cage, 416 SST seat ring, 316 SST stem.

6.24.4 Sizing

Conventional.

6.25 HOT SEPARATOR LIQUID TO HOT FLASH DRUM (POWER RECOVERY TURBINE BYPASS)—HYDROCRACKER



3" x 4", 1500 RF, angle-style axial ßow multi-step valve. 21/4

percent Cr, 1 percent Mo body, NACE conformance body andtrim. Class V shutoff required.

6.25.3 Trim

Expanding labyrinth plug with top and bottom balancedpiston guide. Hardened trim.

6.25.4 Sizing

The calculated Cv for this ßashing service is determined byadding the calculated Cv for liquid and the vapor at the outletconditions of the valve. Process simulation is required to cal-culate the amount of vapor ßashed. The ISA sizing equationsare inaccurate for this ßashing application. ManufacturersÕcontrol valve sizing programs which calculate ßashing onlyon the basis of single compound streams cannot be used forthis sizing calculation.

6.25.5 Notes

Inlet piping must be sized to minimize potential of ßashingat the valve inlet. Outlet piping shall be sized to avoid poten-tial for cavitation occurring downstream of valve. Valveinstallation with the body and actuator in the horizontal plane

Normal MaximumQ (barrel/day) 20,000 20,000P1 (psig) 140 140dP (psid) 5.00 1.00T (¼F) 650 650Fluid Heavy Gas OilSG 0.73 0.73Pv (psia) 3.00 3.00

Minimum Normal MaximumQ (bpd) 25,000 45,000 70,000P1 (psig) 1050 1050 1050dP (psid) 1000 1000 1000T (¡F) 400 400 400Fluid Gas OilPv (psia) 3.00 3.00 3.00SG 0.85 0.85 0.85

NormalFlow-Inlet (gpm) 2008Flow-Outlet (gpm) 1645Flow-Outlet (scfm) 6250P1 (psig) 2435P2 (psig) 360T-Inlet (¡F) 550T-Outlet (¡F) 545Pv (psia) 2449.7Pc (psia)-(pseudo) 286.0SG (liquid Inlet) 0.538SG (liquid Outlet) 0.627Mol Wt (Vapor) 23.580Fluid Hydrogen Liquid with trace H2S




simpliÞes piping and equipment layout. Trim style must betrash tolerant.

6.26 COLD SEPARATOR SOUR WATER—HYDROCRACKER



11/2", 1500 RF, angle-style high resistance multi-step axialßow valve. Carbon steel body, NACE conformance body andtrim. Class V shutoff required.

6.26.3 Trim

Series of equal capacity stages with last stage expansion.Relatively large ßow passages and trim shearing action allowlong service life and reduced potential for clogging which canoccur with other multistage trim styles. Hardened trim.

6.26.4 Sizing

The calculated Cv for this ßashing service is determined byadding the calculated Cv for liquid and the vapor at the outletconditions of the valve. Process simulation is required to cal-culate the amount of H2S ßashed. ManufacturersÕ controlvalve sizing programs which calculate ßashing only on thebasis of single compound streams cannot be used for this siz-ing calculation.

6.26.5 Notes

Outlet piping shall be sized to avoid potential for cavitationoccurring downstream of valve. Valve installation with thebody and actuator in the horizontal plane simpliÞes pipingand equipment layout. Trim style must be trash tolerant.

7 Emergency Block ValvesAn emergency block valve (EBV) is used as a means of

isolating ßammable or toxic substances in the event of a leakor Þre.

7.1 VALVE TYPE

Valve type is dependent upon the distance from the leaksource. Any valve in the Þre zone should be Þre-safe. A gatevalve, metal-seated ball valve, or high-performance butterßyvalve is considered to be Þre-safe. The valve selected shouldhave been tested to API Spec 6FA, Fire Test for Valves, or anequivalent standard test.

7.2 DEFINITIONS

7.2.1 Emergency Block Valves

Emergency block valves are designed to control a hazard-ous incident. These are valves for emergency isolation andare designed to stop the uncontrolled release of ßammable ortoxic materials. These valves should be Þre-safe rated valvesif they are within the Þre zone. The valves may be referred toas Types A, B, C, and D.

7.2.2 Determination of Fire Zone

This is the area which is unsafe to enter during an emer-gency situation. Distances are included as example onlyrefer to plant standards for actual distances. The area isconsidered to be within a 25-foot radius minimum sur-rounding the leak source.

7.3 TYPES OF EVBs

7.3.1 Type A Valve

A manually operated Þre-safe block valve installed at theequipment. This type of valve is installed when, in the eventof a leak, ignition is not expected

7.3.2 Type B Valve

This Þre-safe block valve should be installed at a minimumof 25 feet from the leak source when ignition is expected. TheType B valve is manually operated and is limited to sizes upto and including 8 inches, and pressure classes through 300#.For reasons of access, the valve should be accessible via aplatform with stairways or not be installed higher than 15 feetabove grade.

7.3.3 Type C Valve

The Type C valve is a power-operated Type B valve. Thevalve must be power-operated if larger than 8 inches orbecause a pressure class higher than 300# is required. Thevalve should be installed a minimum of 25 feet (outside of thepower zone) from the leak source and no higher than 15 feetabove grade. The controls should be at the valve in an acces-sible location.

NormalFlow-Inlet (gpm) 86.0Flow-Outlet (gpm) 81.5Flow-Outlet (scfm) 320 P1 (psig) 2404P2 (psig) 354T-Inlet (¡F) 122T-Outlet(¡F) 115Pv (psia) 512Pc (psia)-(pseudo) 1300SG (liquid Inlet) 0.960SG (liquid Outlet) 0.973Mol Wt (Vapor) 34.020

FluidWater with 2.36 mole % H2S and trace hydrocarbon




7.3.4 Type D Valve

This is an EBV with remote controls. There is no restric-tion as to where the valve may be located, but the controlsshould be a minimum of 40 feet from the leak source andshould be out of the Þre zone. An EBV installed at an eleva-tion greater than 15 feet above grade will also come underthis category. Both the actuator and that portion of the controlcable and tubing which is in the Þre zone should be Þre-proofed or designed to operate without failure during Þreconditions. Specify that the conduit/tubing/cable supports arerequired to be Þreproofed.

7.4 EBV GENERAL INSTILLATION GUIDELINES

7.4.1 Compressors

7.4.1.1 EBVs are typically required for all compressors200 HP or larger handling ßammable or toxic materials.

7.4.1.2 An EBV is required in all suction and dischargelines.

7.4.1.3 An EBV is required between stages and interstageequipment if the interstage equipment holds greater than1000 gallons of liquid.

7.4.2 Pumps

7.4.2.1 An EBV is typically required for pumps havingseals where the upstream vessel contains greater than 2000gallons of light ends or hydrocarbons above the auto ignitionpoint or above 600¡F.

7.4.2.2 An EBV is required where the upstream vesselcontains greater than 4000 gallons of liquid hydrocarbons.

7.4.3 Vessels

7.4.3.1 An EBV is required for vessels containing lightends or toxic material.

7.4.3.2 An EBV is required for vessels containing liquidsheavier than light ends, but above the ßash point.

7.4.4 Heaters

7.4.4.1 An EBV is required for each fuel gas or oil line toÞred heaters and boilers. A double block and bleed arrange-ment with a single or multiple valves is often used. Reopen-ing after a trip requires a manual reset which permitsrelatching only after all safety interlock parameters have beensatisÞed. Refer to API RP 556, Manual on Installation ofInstruments and Control Systems for Fired Heaters andSteam Generators.

7.4.4.2 An EBV is required for each feed line to a Þredheater that contains ßammable ßuid. The EBV should belocated outside the Þrewall or Þrezone, which contains theheater.

7.5 ACTUATOR SELECTION

7.5.1 Electric Motor Actuator

7.5.1.1 This is the Þrst choice for a gate valve. Because theelectric motor will fail stationary upon power loss, any valve ofthis type which is in the Þre zone must have its actuator Þre-proofed. Also, that portion of the control cable which is in theÞre zone should be Þreproofed. Fire/rated cable is an option.

7.5.1.2 For EBV service, it is more important to close thevalve than to protect the actuator motor. Therefore, the fol-lowing wiring precautions should be observed:

a. The closing torque switch should be bypassed and thevalve should close to make closed position limit switch.b. The control circuit fuse should be bypassed.c. The thermal overloads should be bypassed.d. Any thermistor in the motor windings should be bypassed.

7.5.1.3 For motor actuated valves, the actuator-to-valveadapter should be able to withstand the stall torque of themotor operator.

7.5.2 Pneumatic Actuator

7.5.2.1 This is the Þrst choice for quarter-turn valves.Fail-safe here refers to fail closed in the event of instru-ment air failure.

7.5.2.2 Fail-to-Safety in a Fire

This valve is remotely operable under normal circum-stances, but the actuator is sacriÞced in the event of a Þre. Aspring-return piston actuator on top of a metal-seated ballvalve is recommended. The pneumatic tubing connected tothe open port of the actuator should be sunlight-resistantpolyethylene tubing and be wrapped around the actuator.Alternately, a fusable plug can be used. When the valve isinvolved in a Þre, the tubing will melt and the valve willclose. The valve will remain closed despite involvment in theÞre. No ÞreprooÞng is necessary.

7.5.2.3 Operable During a Fire

This actuator should be hard-piped (no soft tubing) andshould be Þreproofed. A spring-closed actuator or a double-acting piston actuator with a fail-safe trip valve with twocheck valves in series and air bottle may be used.

7.5.2.4 Actuator to Valve Adaptation

For pneumatic actuated valves, the adapter should be ableto withstand the maximum torque generated by the actuatorwith the maximum design air pressure applied to the piston.The adapter must also be made of materials that will with-stand a Þre until the valve can be closed.




7.6 FIREPROOFING

7.6.1 FireprooÞng must withstand a 2000¼F petroleum Þrewhile keeping all internal electrical controls and wiring below2000¼F for a period of at least twenty minutes. The Þreproof-ing should be able to withstand a sustained water stream froma Þre hose. The ÞreprooÞng should be weatherproof and sun-light resistant. Refer to API Publication 2218, FireprooÞngPractices in Petroleum and Petrochemical Processing Plants.

8 Vapor Depressuring Valves8.1 GENERAL

8.1.1 Vapor depressuring systems are often installed onlarge volume hydrocarbon systems, especially those operat-ing at higher pressures. They are used to prevent upset condi-tions from actuating safety relief valves or to automaticallydepressure the equipment in emergency conditions, espe-cially in case of Þre. If there is a Þre around a vessel contain-ing both liquid and vapor, the unwetted portion of the vesselwill probably reach a temperature at which the strength of thematerial will be reduced. In this case, the relief valve wouldnot protect against vessel rupture, whereas a vapor depressur-ing system could reduce the pressure to a safe level. A vapordepressuring system should be provided for process equip-ment within a designated Þre area where, as a result of Þreexposure, the internal pressure would exceed 100 psig or 50%of design pressure, whichever is lower.

8.1.2 Emergency vapor depressuring facilities should con-sist of locally and remotely operated, manually and/or auto-matically controlled depressuring valves discharging into aclosed system.

8.1.3 Depressuring valves should be sized in accordancewith API RP 521 for conditions of Þre exposure, densitychange, and liquid ßash, assuming that depressuring starts atthe normal operating pressure or at the set point of the auto-matic pressure controller. The valves should be sized todepressure the system within 15 minutes to 100 psig or 50%of design pressure, whichever is lower, unless this depressur-ing rate would subject equipment to unacceptably low tem-peratures. Low temperature materials may be required for thedepressuring valve and its outlet piping.

8.2 DEPRESSURING VALVES AND ACTUATOR REQUIREMENTS

8.2.1 Control valves may be used for depressuring service.Some users specify two-position on/off valves only, whileothers may use throttling valves with pressure control pilotsand positioners.

8.2.2 Depressuring valves should be equipped with pneu-matic actuators with a spring for positive action on air failure.Actuator should be designed to open the valve with any pro-

cess pressure from 0.0 psig to 110 percent of the relief valveset pressure, and must hold the valve closed at 110 percent ofthe relief valve set pressure. Quick exhaust valves for rapiddepressuring of the actuator may be speciÞed for on/off valves.

8.2.3 For mechanical integrity, the minimum body sizeand rating should be 2-inch 300# ANSI ßanged, withreduced trim as required.

8.2.4 Valve plug should be a single seated metal seat withquick opening or linear trim characteristic, with process pres-sure tending to open the valve. Top or cage-guiding is accept-able. Soft-seated trim should not be used.

8.2.5 The depressuring valve and actuator combinationshould achieve a Class V shutoff.

9 Hydraulic Slide Valve Actuators

9.1 GENERAL

9.1.1 This section details requirements for hydraulic typeslide valve actuators with a dedicated hydraulic unit for eachvalve where the hydraulic unit is separate from the valve actu-ator. Central hydraulic units that are used to power multiplevalves are sometimes used. Some newer designs have an inte-gral hydraulic unit, which is mounted right on each slidevalve actuator. Other large continuous duty valves may usethese actuators.

9.1.2 Each slide valve can have a totally independenthydraulic and control system. The following minimum com-ponents should be included at or near each valve:

a. A slide valve actuator consisting of high pressure hydrau-lic cylinders, manual operator, adapter plates to mount theactuator to the valve bonnets, a position feedback sensor, andany locally required manifolding, tubing, or valving.b. A hydraulics skid containing all required hydraulic supplysystem components and positioning controls. This includesthe hydraulic oil reservoir, hydraulic pumps and drivers, Þl-ters, manifolding, valving and interconnecting tubing, servovalves, high pressure accumulators, pump controls, positionerelectronics, pressure gauges and miscellaneous otherinstrumentation.

9.2 HYDRAULIC POWER UNIT (HPU)

9.2.1 The hydraulic ßuid should be a nonßammable syn-thetic or natural type hydraulic oil suitable for use in highpressure, high performance hydraulic systems and ambienttemperature range.

9.2.2 The entire hydraulic system should be constructed of300 series stainless steel. The reservoir should be equippedwith vent and vacuum breaker valves set at no more than 2psig positive and 0.3 psig negative pressure, or as required bythe reservoir design. The reservoir should be provided with




additional inlets and outlets as required for Þlling and ventingoperations. Vents should be provided with Þlters to prevent oilcontamination. Some users blanket the reservoir with nitro-gen or provide a desiccant type drier on the vent to preventmoisture and dirt contamination of the hydraulic oil.

9.2.3 Each hydraulic power unit should be equipped withdual pumps and drivers. Pumps should be variable stroke pos-itive displacement types and be equipped with internal reliefvalves. Each pump on each HPU should be of identical con-struction. One pump should be driven by a constant speedelectric motor. The second pump is usually speciÞed to bedriven by an air motor, or can be powered by an isolated elec-trical feeder. Drivers should be sized to provide designhydraulic oil ßow at the hydraulic oil relief pressure. Themotor starter for the electric motor driven pump is usuallysupplied as part of the hydraulic unit.

9.2.4 The hydraulic power unit must include a pump con-trol system which will automatically start the spare pump,designated by a switch on the HPU front panel, if the hydrau-lic supply pressure drops below a pre-set pressure. Alarmcontacts indicating that the spare pump is running arerequired.

9.2.5 If coolers are required, dual coolers with a dual 3-way switching valve should be provided. Coolers should beinstalled on the hydraulic oil return stream. If air coolers areused, they should not require any type of forced air cooling.

9.2.6 The HPU should include high pressure oil accumula-tors with sufÞcient capacity to provide for two complete valvestrokes (full open to full closed, or vice versa, is one stroke).Accumulators shall be designed such that they can berecharged and maintained/removed online without shutdown.

9.2.7 The HPU should include all required interconnectingmanifolding, tubing, valving, etc. Dual high pressure hydrau-lic oil Þlters with valving necessary to allow switching of Þl-ters and change-out of Þlter elements should be provided. Alltubing Þttings should be O-ring seal SAE hydraulic type Þt-tings. Compression Þttings are not recommended.

9.3 SLIDE VALVE POSITIONER SYSTEMS

9.3.1 Each slide valve actuator should be provided with apositioning system complete with a local Þeld panel.

9.3.2 Each system should have dual inlet Þlters for hydrau-lic ßuid. These Þlters should be switchable so that Þlter ele-ments may be changed while on-stream.

9.3.3 For manual operation of the slide valves, eachactuator system should include a mechanical handwheeland the capability to readily bypass the hydraulic system.The design must permit removal of the hydraulic cylinderwhile the valve remains on handwheel control. A localhydraulic manual ÒOpen-Stop-CloseÓ control is also

required. In addition, a local manual hydraulic hand pumpor standby hydraulic accumulator backup hydraulic systemis required. Any manual operation should actuate dry con-tacts for remote alarm indication.

9.3.4 All systems should be self-contained. Single blockmanifolds with a minimum of interconnecting tubing are pre-ferred. Connections to the valve actuator cylinders should beßexible braided hose.

9.3.5 The positioner system must lock the slide valve inplace and activate an alarm contact upon any of the followingconditions:

a. Loss of feedback.b. Loss of control signal.c. Loss of power.d. Electronics failure.e. Excessive servo position deviation error.

9.3.6 The positioner should be electronic type and accept a4Ð20 ma DC control signal. The slide valve will be closed at 4ma and open at 20 ma. All wiring should be run with appro-priate high temperature wiring, or routed to avoid high tem-perature areas.

9.3.7 Electronic valve stem position feedback should beprovided to the positioner. Magneto-restrictive or LVDT tech-nology is preferred over slidewire or potentiometer tech-niques. The positioner system should also transmit a 4Ð20 masignal proportional to the valve stem position to the reÞnerycontrol system.

9.3.8 It is desirable to be able to calibrate the position feed-back system without stroking the slide valve.

9.3.9 The hydraulic supply and positioner systems mustinclude outputs for remote indication of diagnostic alarms(see 9.4.13 for complete list).

9.4 INSTRUMENTATION REQUIRED

9.4.1 Pump discharge pressure gauge on HPU gauge board.

9.4.2 Pump discharge pressure switch with circuit to auto-matically start the standby pump.

9.4.3 Pump suction pressure gauge on the HPU gaugeboard.

9.4.4 Vacuum breaker on oil reservoir.

9.4.5 Rotameter for nitrogen purge to oil reservoir.

9.4.6 Oil reservoir instruments:

a. Level sight gauge.b. Temperature indicator.c. High temperature switch.d. Low level switch.e. Low-low level switch to stop pumps.




9.4.7 Pressure gauge on HPU gauge board for Þltered highpressure hydraulic ßuid for distribution.

9.4.8 Accumulator(s) pressure gauge.

9.4.9 Temperature indicator on cooling water return fromhydraulic ßuid heat exchangers.

9.4.10 Accumulator low pressure switch.

9.4.11 Purge instruments (rotameter and pressure switch)for electrical boxes as required.

9.4.12 Selector switch for determining primary hydraulicpump. The no-selected pump automatically becomes theÒstand-by.Ó

9.4.13 Alarms

9.4.13.1 The package must include all required processswitches and an alarm indication system to advise the opera-tor of abnormal conditions. Alarms may be indicated at thepositioner Þeld panels and hydraulic unit (if these are sepa-rated) using LEDs, pilot lights, or alarm annunciators. Alarmsshould be included for each slide valve actuator for:

a. Low reservoir level*.b. High reservoir temperature*.c. Spare pump running*.d. Low-low reservoir level*.e. Low-low hydraulic pressure*.f. Low accumulator pressure.g. Positioner in local mode.h. Loss of control signal.i. Loss of feedback signal.j. Excessive servo error.k. Loss of power.l. Electronics purge failure (if used).

* Only one set of alarms required if a common HPU isused. Locate at HPU skid.

9.4.13.2 Provide dry Form C contacts to indicate posi-tioner common trouble and positioner failure alarms to thereÞnery control system.

9.4.13.3 The following alarm groups should be providedfor each slide valve:

a. Positioner Common Trouble Alarm.1. Low reservoir level*.2. High reservoir temperature*.

3. Spare hydraulic pump running*.4. Low accumulator pressure*.5. Positioner purge failure (if used).

b. Positioner Common Failure Alarm.1. Positioner in local mode.2. Loss of control signal.3. Loss of feedback signal.4. Loss of power.5. Excessive servo error.6. Loss of positioner power.7. Low-low reservoir level*.8. Low-low hydraulic supply pressure*.

* Only one set of alarms if a common HPU is used. If ded-icated HPUs are used, alarms are required for each HPU.

9.5 PERFORMANCE CHARACTERISTICS

9.5.1 Linearity of stroke and the transmitted position signalversus the input control signal should be within ± 0.25 per-cent full stroke.

9.5.2 Tracking error (setpoint deviation) should be ± 2 per-cent maximum.

9.5.3 Adjustable stroking speeds should be provided.

9.5.4 Stability of movement at constant position controlsignal input should not exceed 0.1 percent of full stroke(cyclical, peak to peak).

9.6 ELECTRICAL REQUIREMENTS

9.6.1 Area ClassiÞcation: Minimum Class 1, Division 2,Group D. The electrical equipment must be suitable for thearea electrical classiÞcation.

9.7 TESTING AND INSPECTION

9.7.1 A factory functional acceptance test, demonstrating thatthe entire system performs properly, is highly recommended.

9.8 SLIDE VALVE ACTUATOR SERVICE

9.8.1 Following is an example of a typical slide valve/actu-ator data sheet:




Location: RegeneratorValve Size: 36"Stroke Including Overlap: 23"Controlling Stroke: 191/8"Welded or Flanged: Welded Hot or Cold Wall Valve: HotJacking Conn. on Body: YesLip Seals Provided: YesPurges: Bonnet OriÞce Opening: 292 sq inches OriÞce Shape: BonnetActuator Type: HydraulicOperating Modes: Auto/ManualInput Control Signal: 4Ð20 ma.Local Control: YesCylinder ID: 14" Stroke Travel Time: 30 seconds Handwheel: YesAir Motor: No Positioner Type: Electronic Position Indicator: YesLimit Switches: No

Hydraulic System Pressure:250 psig or 2000 psig in high pressure service

Hydraulic Fluid: Hydraulic SyntheticsMultiple or Local System: Multiple Filter Location: Hydraulic Skid Filter Elements: Supply: 3 micron, high beta

Return: 50 micron Accumulator Capacity:Backup # of Strokes:



9/98—5C



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api rp 553 (1998)refinery control valves

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