Inspection of

Pressure-Relieving Devices

API RECOMMENDED PRACTICE 576 SECOND EDITION, DECEMBER 2000

Inspection of

Pressure-Relieving Devices

Downstream Segment

API RECOMMENDED PRACTICE 576 SECOND EDITION, DECEMBER 2000

SPECIAL NOTES

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Copyright © 2000 American Petroleum Institute

FOREWORD

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

Suggested revisions are invited and should be submitted to the manager of the Standards Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005.

iii

1. Pressure Relief Valve 3

2. Safety Valve 3

3. Relief Valve 4

4. Safety Relief Valve 5

5. Conventional Safety Relief Valve 5

6. Balanced Safety Relief Valve. 5

7. Pilot-operated Pressure Relief Valve 5

8. Pressure and/or Vacuum Vent Valve 8

9. Rupture Disk Device 8

1. CAUSES OF IMPROPER PERFORMANCE 15

   1. Corrosion 15

   2. Damaged Seating Surfaces 15

   3. Failed Springs 15

   4. Improper Setting and Adjustment 17

   5. Plugging and Sticking 20

   6. Misapplication of Materials 22

   7. Improper Location, History, or Identification 23

   8. Rough Handling 23

   9. Improper Differential Between Operating and Set Pressures 24

   10. Improper Discharge Piping Test Procedures 25

2. INSPECTION AND TESTING 25

   1. Reasons for Inspection 25

   2. Shop Inspection/overhaul 25

   3. Visual On-stream Inspection 33

   4. Inspection Frequency 34

   5. Time of Inspection 35

3. RECORDS AND REPORTS 35

   1. Objective 35

   2. The Need to Keep Records 35

   3. Responsibilities 36

   4. Sample Record and Report System 36

Page

APPENDIX A SAMPLE RECORD AND REPORT FORMS 37

APPENDIX B PRESSURE RELIEF VALVE TESTING 45

Figures

1. Full-Nozzle, Top-Guided Safety Valve 4

2. Relief Valve 4

3. Safety Relief Valve with O-Ring Seal 6

4. Conventional Safety Relief Valve 7

5. Balanced Bellows Safety Relief Valve 7

6. Balanced Bellows Safety Relief Valve with Auxiliary

   Balancing Piston 8

7. Low-Pressure Diaphragm-Type Pilot-Operated Valve 9

8. High-Pressure Pilot-Operated Valve 10

9. High-Pressure Pilot-Operated Valve with Optional Dual Outlets 11

10. Weight-Loaded Pallet Vent Valve 12

11. Spring-and Weight-Loaded Vent Valve 12

12. Rupture Disk Device—Rupture Disk in a Typical Holder 13

13. Conventional Domed Rupture Disk 13

14. Scored Tension-Loaded Rupture Disk 14

15. Reverse-Acting Scored Rupture Disk 16

16. Reverse-Acting Rupture Disk with Knife Blades 17

17. Graphite Rupture Disk 18

18. Combination of Reverse-Buckling Disk Assembly and Safety Relief Valve 19

19. Acid Corrosion in Carbon-Steel Bonnet Caused by Leaking Seating Surfaces . . 19

20. Acid Corrosion on 18Cr-8Ni Steel Inlet Nozzle 19

21. Chloride Corrosion on 18Cr-8Ni Steel Nozzle

    (with Machined Seating Surface) 19

22. Sulfide Corrosion on Carbon-Steel Disk From Crude-Oil Distillation Unit 20

23. Chloride Attack on 18Cr-8Ni Steel Disk 20

24. Pit-Type Corrosion on 18Cr-8Ni Steel (Type 316) Bellows 20

25. Monel Rupture Disks Corroded in Sour-Gas Service 21

26. Body and Bonnet Coated With Epoxy for Corrosion Protection 21

27. Seating Surface of Disk Deformed by Chattering 21

28. Seat and Disk Damaged by Frequent Operation of Valve

    Set Too Close to Operating Pressure 21

29. Spring Failure Due to Corrosion 22

30. Spring Failure Due to Stress Corrosion 22

31. Inlet Nozzle Plugged with Coke and Catalyst After Nine

    Months in Reactor Vapor Line 22

32. Outlet Valve Plugged with Deposits From Other

    Valves in Common Discharge Header 23

33. Moving Parts of Valve Fouled with Iron Sulfide (FeS2) 23

34. Valve Stuck Because of Iron Sulfide (FeS2) Deposits 24

35. Disk Frozen in Guide Because of Buildup of Products of

    Corrosion in Sour-Oil Vapor Service 24

36. Rough Handling of Valves Should Be Avoided 24

37. Identification Tag for Pressure- Relieving Device 26

38. Block Valves on Safety-Relief-Valve Inlet and Outlet Sealed Open

    and Bleeders Installed to Depressure Inlet and Outlet 27

39. Sulfur Deposits in Body of Valve on Way to Repair Shop 28

40. Safety-Valve and Relief-Valve Leak Detector 31

B-1 Typical Safety-Valve and Relief-Valve Test Block Using Air as Test Medium. . . 46

Inspection of Pressure-Relieving Devices

1. Scope

   This recommended practice describes the inspection and repair practices for automatic pressure-relieving devices com- monly used in the oil and petrochemical industries. As a guide to the inspection and repair of these devices in the user's plant, it is intended to ensure their proper performance. This publication covers such automatic devices as pressure relief valves, pilot-operated pressure relief valves, rupture disks, and weight-loaded pressure vacuum vents.

   The scope of this recommended practice includes the inspection and repair of automatic pressure-relieving devices commonly used in the oil and petrochemical industry.

   The recommendations in this publication are not intended to supersede requirements established by regulatory bodies. This publication does not cover weak seams or sections in tanks, explosion doors, fusible plugs, control valves, and other devices that either depend on an external source of power for operation or are manually operated. Inspections and tests made at manufacturers' plants, which are usually covered by codes or purchase specifications, are not covered by this publication.

   This publication does not cover training requirements for mechanics involved in the inspection and repair of pressure- relieving devices. Those seeking these requirements should see API 510, which gives the requirements for a quality con- trol system and specifies that the repair organization maintain and document a training program ensuring that personnel are qualified.

   
   

2. References

   This following standards and specifications are cited in this recommended practice:

   510	Pressure Vessel Inspection Code: Inspec- tion, Rating, Repair, and Alteration
   RP 520	Sizing, Selection, and Installation of Pres- sure-Relieving Devices in Refineries, Part I, "Sizing and Selection," and Part II, "Installation"
   RP 521	Guide for Pressure-Relieving and Depres-

   API

   
   

   suring Systems

   Std 526 Flanged Steel Pressure Relief Valves

   Std 527 Seat Tightness of Pressure Relief Valves

   
   

   Bull 2521 Use of Pressure-Vacuum Vent Valves for Atmospheric Pressure Tanks to Reduce Evaporation Loss

   ASME1

   PTC 25 Pressure Relief Devices Boiler and Pressure Vessel Code, Section I “Power Boilers” Section IV “Heating Boilers”

   Section VI “Recommended Rules for Care and Opera- tion of Heating Boilers”

   Section VII “Recommended Guidelines for Care of Power Boilers”

   Section VIII “Pressure Vessels,” Division 1

   NACE2

   Std MR0175 Sulfide Stress Cracking Resistant-Metallic Materials for Oil Field Equipment

   NB3

   NB-18 Pressure Relief Device Certifications

   NB-23 National Board Inspection Code

   
   

3. Definitions

   
   

   1. GENERAL

      1. car seal: A self-locking seal that when placed in position and closed, locks and must be cut with wire cutters or physically broken to be removed. Local jurisdictional requirements may specify the acceptable method(s) of sealing or locking block valves.

      2. non-reclosing pressure relief device: A pres- sure relief device, which remains open after operation. A manual resetting means may be provided.

      3. pin-actuated device: A non-reclosing pressure relief device actuated by static pressure and designed to func- tion by buckling or breaking a pin which holds a piston or a plug in place. Upon buckling or breaking of the pin, the pis- ton or plug instantly moves to the full open position.

         
         

   2. DIMENSIONAL CHARACTERISTICS OF PRESSURE RELIEF VALVES

      1. effective discharge area: A nominal or computed area used with an effective discharge coefficient to calculate

Std 620 Design and Construction of Large, Welded,

Low-Pressure Storage Tanks

Std 650 Welded Steel Tanks for Oil Storage

Std 2000 Venting Atmospheric and Low-Pressure Storage Tanks (Nonrefrigerated and Refrigerated)

1

1. ASME International, Three Park Avenue New York, New York 10016-5990, www.asme.org.

2. NACE International, 440 South Creek Drive, Houston, Texas, 77084, www.nace.org.

3. National Board of Boiler and Pressure Vessel Inspectors, 1055 Crupper Avenue, Columbus, Ohio 43229, www.nationalboard.com.