Inspection of Pressure-relieving Devices

Downstream Segment

API RECOMMENDED PRACTICE 576 THIRD EDITION, NOVEMBER 2009

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Copyright © 2009 American Petroleum Institute

Foreword

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iii

Contents

Page

1. Scope 1

2. Normative References 1

3. Terms and Definitions 2

   1. General 2

   2. Dimensional Characteristics of Pressure-relief Valves 3

   3. Operational Characteristics—System Pressures 3

   4. Operational Characteristics—Device Pressures 4

4. Pressure-relieving Devices 5

   1. General 5

   2. Pressure-relief Valve 6

   3. Safety Valve 6

   4. Relief Valve 7

   5. Safety-relief Valve 10

   6. Conventional Safety-relief Valve 10

   7. Balanced Safety-relief Valve 11

   8. Pilot-operated Pressure-relief Valve 13

   9. Pressure- and/or Vacuum-vent Valve 15

   10. Rupture Disk Device 18

5. Causes of Improper Performance 25

   1. Corrosion 25

   2. Damaged Seating Surfaces 25

   3. Failed Springs 27

   4. Improper Setting and Adjustment 30

   5. Plugging and Sticking 31

   6. Misapplication of Materials 32

   7. Improper Location, History, or Identification 32

   8. Rough Handling 33

   9. Improper Differential Between Operating and Set Pressures 35

   10. Improper Discharge Piping Test Procedures 35

   11. Improper Handling, Installation, and Selection of Rupture Disks 35

6. Inspection and Testing 36

   1. Reasons for Inspection and Testing 36

   2. Shop Inspection/Overhaul 36

   3. Visual On-stream Inspection 49

   4. Inspection Frequency 50

   5. Time of Inspection 52

7. Records and Reports 53

   1. Objective 53

   2. The Need to Keep Records 53

   3. Responsibilities 53

   4. Sample Record and Report System 54

Annex A (informative) Pressure-relief Valve Testing 55

Annex B (informative) Sample Record and Report Forms 58

Figures

Page

1. Full-nozzled, Top-guided Safety Valve 7

2. Relief Valve 8

3. Safety-relief Valve with O-ring Seal 9

4. Conventional Safety-relief Valve 11

5. Balanced Bellows Safety-relief Valve 12

6. Balanced Bellows Safety-relief Valve with Auxiliary Balancing Piston 12

7. Low-pressure Diaphragm-type Pilot-operated Valve 14

8. High-pressure Pilot-operated Valve 15

9. High-pressure Pilot-operated Valve with Optional Dual Outlets 16

10. Weight-loaded Pallet Vent Valve 17

11. Spring and Weight-loaded Vent Valve 17

12. Rupture Disk Device—Rupture Disk in a Typical Holder 19

13. Conventional Domed Rupture Disk 19

14. Scored Tension-loaded Rupture Disk 20

15. Reverse-acting Scored Rupture Disk 21

16. Reverse-acting Scored Rupture Disk with Knife Blades 22

17. Graphite Rupture Disk 23

18. Combination of Reverse-buckling Disk Assembly and Safety-relief Valve 24

19. Acid Corrosion in Carbon Steel Bonnet Caused by Leaking Seating Surfaces 26

20. Acid Corrosion on 18Cr-8Ni Steel Inlet Nozzle 26

21. Chloride Corrosion on 18Cr-8Ni Steel Nozzle (with Machined Seating Surface) 27

22. Sulfide Corrosion on Carbon Steel Disk from Crude Oil Distillation Unit 27

23. Chloride Attack on 18Cr-8Ni Steel Disk 28

24. Pit-type Corrosion on 18Cr-8Ni Steel (Type 316) Bellows 28

25. Monel Rupture Disks Corroded in Sour Gas Service 28

26. Body and Bonnet Coated with Epoxy for Corrosion Protection 29

27. Seating Surface of Disk Deformed by Chattering 29

28. Seat and Disk Damaged by Frequent Operation of Valve Too Close to Operating Pressure 29

29. Spring Failure Due to Corrosion 29

30. Spring Failure Due to Stress Corrosion 30

31. Inlet Nozzle Plugged with Coke and Catalyst After Nine Months in Reactor Vapor Line 32

32. Outlet Valve Plugged with Deposits from Other Valves in Common Discharge Header 32

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

34. Spring Failure Due to Stress Corrosion 33

35. Disk Frozen in Guide Because of Buildup of Products of Corrosion in Sour Oil Vapor Service 34

36. Rough Handling of Valves Should be Avoided 35

37. Identification Tag for Pressure-relieving Device 38

38. Block Valves on Safety-relief Valve Inlet and Outlet Sealed Open and Bleeders Installed

    to Depressure Inlet and Outlet 39

39. Sulfur Deposits in Body of Valve 40

40. Safety Valve and Relief Valve Leak Detector 45

A.1 Typical Safety Valve and Relief Valve Test Block Using Air as a Test Medium 57

1. Sample Form for Recording Pressure-relieving Device Specifications 59

2. Sample Historical Record 60

3. Sample Inspection and Repair Work Order Form 61

4. Sample Testing Report 62

5. Sample Condition, Repair, and Setting Record 63

6. Sample Setting Record and Repair Order 64

7. Sample In-service Report 65

Inspection of Pressure-relieving Devices

1. Scope

   This recommended practice (RP) describes the inspection and repair practices for automatic pressure-relieving devices commonly 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 RP 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 control system and specifies that the repair organization maintain and document a training program ensuring that personnel are qualified.

   
   

2. Normative References

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

API 510, Pressure Vessel Inspection Code: In-service Inspection, Rating, Repair, and Alteration

API Standard 520 (All Parts), Sizing, Selection, and Installation of Pressure-relieving Devices in Refineries

API Standard 521, Pressure-relieving and Depressuring Systems

API Standard 526, Flanged Steel Pressure-relief Valves

API Standard 527, Seat Tightness of Pressure Relief Valves

API Recommended Practice 580, Risk-Based Inspection

API Recommended Practice 581, Risk-Based Inspection Technology

API Standard 620, Design and Construction of Large, Welded, Low-pressure Storage Tanks

API Standard 2000, Venting Atmospheric and Low-pressure Storage Tanks (Nonrefrigerated and Refrigerated)

ASME PTC 25 1, Pressure Relief Devices

ASME Boiler and Pressure Vessel Code (BPVC), Section I: Power Boilers

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

   1

2. API RECOMMENDED PRACTICE 576

ASME Boiler and Pressure Vessel Code (BPVC), Section IV: Heating Boilers

ASME Boiler and Pressure Vessel Code (BPVC), Section VI: Recommended Rules for the Care and Operation of Heating Boilers

ASME Boiler and Pressure Vessel Code (BPVC), Section VII: Recommended Guidelines for the Care of Power Boilers

ASME Boiler and Pressure Vessel Code (BPVC), Section VIII: Pressure Vessels; Division 1, Division 2 and Division 3

ISO 4126-6 2, Safety devices for protection against excessive pressure—Part 6: Application, selection and installation of bursting disc safety devices

NACE MR 0175 3, Petroleum and Natural Gas Industries—Materials for Use in H2S-Containing Environments in Oil and Gas Production

NACE MR 0103, Materials Resistant to Sulfide Stress Cracking in Corrosive Petroleum Refining Environments

NB-18 4, Pressure-relief Device Certifications

NB-23:2004, National Board Inspection Code

3 Terms and Definitions

3.1 General

For the purposes of this document, the following terms and definitions apply.

3.1.1

car seal

A locking seal that when placed in position and closed, locks and must be cut or physically broken to be removed.

3.1.2

galling

A condition whereby excessive friction between high spots results in localized welding with subsequent splitting and a further roughening of rubbing surfaces of one or both of two mating parts.

3.1.3

non-reclosing pressure-relief device

A pressure-relief device, which remains open after operation. A manual resetting means may be provided.

3.1.4

pin-actuated device

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

1. International Organization for Standardization, 1, ch. de la Voie-Cruese, Case postale 56, CH-1211, Geneva, Switzerland, www.iso.org.

2. NACE International, (formerly the National Association of Corrosion Engineers), 1440 South Creek Drive, Houston, Texas 77218-8340, www.nace.org.

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