Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries

Part II—Installation

API RECOMMENDED PRACTICE 520 FIFTH EDITION, AUGUST 2003

REAFFIRMED, FEBRUARY 2011

Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries

Part II—Installation

Downstream Segment

API RECOMMENDED PRACTICE 520 FIFTH EDITION, AUGUST 2003

REAFFIRMED, FEBRUARY 2011

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Copyright ? 2003 American Petroleum Institute

FOREWORD

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iii

CONTENTS

Page

1. SCOPE 1

2. REFERENCES 1

3. DEFINITION OF TERMS 1

4. INLET PIPING TO PRESSURE-RELIEF DEVICES 1

   1. General Requirements 1

   2. Pressure-Drop Limitations and Piping Con?gurations 1

   3. Inlet Stresses that Originate from Static Loads in the Discharge Piping 4

   4. Inlet Stresses that Originate from Discharge Reaction Forces 5

   5. Isolation Valves in Inlet Piping 8

   6. Rupture Disk Devices in Combination with Pressure-Relief Valves 9

   7. Process Laterals Connected to Inlet Piping of Pressure-Relief Valves 9

   8. Turbulence in Pressure-Relief Device Inlets 9

5. DISCHARGE PIPING FROM PRESSURE-RELIEF DEVICES 9

   1. General Requirements 9

   2. Safe Disposal of Relieving Fluids 9

   3. Back Pressure Limitations and Sizing of Pipe 9

   4. Considerations for Pilot-Operated Pressure-Relief Valves 9

   5. Stresses in Discharge Piping During Release 11

   6. Isolation Valves in the Discharge Piping 11

   7. Rupture Disks Installed at Outlet of Pressure-Relief Valves. 11

6. ISOLATION (STOP) VALVES IN PRESSURE-RELIEF PIPING 13

   1. General 13

   2. Application 13

   3. Isolation Valve Requirements 13

   4. Examples of Isolation Valve Installations 18

   5. Administrative Controls Related to Isolation Valves 18

7. BONNET OR PILOT VENT PIPING 18

   1. General 18

   2. Conventional Valves 18

   3. Balanced Bellows Valves 18

   4. Balanced Piston Valves 18

   5. Pilot-Operated Valves 20

8. DRAIN PIPING 20

   1. Installation Conditions that Require Drain Piping 20

   2. Safe Practice for Installation of Drain Piping 21

9. PRESSURE-RELIEF DEVICE LOCATION AND POSITION 22

   1. Inspection and Maintenance 22

   2. Proximity to Pressure Source 22

   3. Proximity to Other Equipment 22

   4. Mounting Position 22

   5. Test or Lifting Levers 22

      Page

   6. Heat Tracing and Insulation 22

10. BOLTING AND GASKETING 23

    1. Care in Installation 23

    2. Proper Gasketing and Bolting for Service Requirements 23

11. MULTIPLE PRESSURE-RELIEF VALVES WITH STAGGERED SETTINGS. . . 23

12. PRE-INSTALLATION HANDLING AND INSPECTION 23

    1. General 23

    2. Storage and Handling of Pressure-Relief Devices 23

    3. Inspection and Testing of Pressure-Relief Valves 23

    4. Inspection of Rupture Disk Devices 23

    5. Inspection and Maintenance of Pin-Actuated Devices 24

    6. Inspection and Cleaning of Systems Before Installation 24

APPENDIX A RUPTURE DISK INSTALLATION GUIDELINES 25

APPENDIX B INSTALLATION AND MAINTENANCE OF PIN-ACTUATED

NON-RECLOSING PRESSURE-RELIEF DEVICES 27

APPENDIX C TECHNICAL INQUIRIES 29

Figures

1. Typical Pressure-Relief Valve Installation: Atmospheric (Open) Discharge 2

2. Typical Pressure-Relief Valve Installation: Closed System Discharge 3

3. Typical Rupture Disk Device Installation: Atmospheric (Open) Discharge 4

4. Typical Pressure-Relief Valve Mounted on Process Line. 5

5. Typical Pressure-Relief Valve Mounted on Long Inlet Pipe 6

6. Typical Pilot-Operated Pressure-Relief Valve Installation 7

7. Typical Pressure-Relief Valve Installation with Vent Pipe 8

8. Typical Rupture Disk Device in Combination with Relief Valve:

   Inlet Side Installation 10

9. Avoiding Process Laterals Connected to Pressure-Relief Valve Inlet Piping 11

10. Typical Pressure-Relief Device Installation with an Isolation Valve 12

11. Typical Pressure-Relief Device Installation for 100 Percent Spare

    Relieving Capacity 14

12. Alternate Pressure-Relief Device Arrangement for 100 Percent Spare

    Relieving Capacity 15

13. Alternate Pressure-Relief Device Installation Arrangement for

    100 Percent Spare Relieving Capacity 16

14. Three-Way Changeover Valve?Shuttle Type 17

15. Three-Way Changeover Valve?Rotor Type 17

16. Three-Way Changeover Valve?Ball Types 19

17. Typical Flare Header Block Valves 19

18. Typical Isolation Block Valves for Spare Compressor 20

19. Typical Installation Avoiding Unstable Flow Patterns at Pressure-Relief

Valve Inlet 21

Sizing, Selection, and Installation of Pressure-relieving Devices in Re?neries Part II?Installation

1. Scope

   This recommended practice covers methods of installation for pressure-relief devices for equipment that has a maximum allowable working pressure (MAWP) of 15 psig (1.03 bar g or 103 kPA) or greater. Pressure-relief valves or rupture disks may be used independently or in combination with each other to provide the required protection against excessive pressure accumulation. As used in this recommended practice, the term pressure-relief valve includes safety relief valves used in either compressible or incompressible ?uid service, and relief valves used in incompressible ?uid service. This recom- mended practice covers gas, vapor, steam, two-phase and incompressible ?uid service; it does not cover special appli- cations that require unusual installation considerations.

   
   

2. References

   The current editions of the following standards, codes, and speci?cations are cited in this recommended practice:

   API

   RP 520 Sizing, Selection, and Installation of Pressure- Relieving Devices in Refineries, Part I—Sizing and Selection

   RP 521 Guide for Pressure-Relieving and Depressuring Systems

   RP 576 Inspection of Pressure-Relieving Devices

   ASME1

   B31.3 Process Piping

   Boiler and Pressure Vessel Code, Section VIII, ?Pressure Vessels?

   
   

3. Definition of Terms

   The terminology for pressure-relief devices that is used in this recommended practice is in general agreement with the de?nitions given in API Recommended Practice 520 Part I.

   
   

4. Inlet Piping to Pressure-Relief Devices

   1. GENERAL REQUIREMENTS

      For general requirements for inlet piping, see Figures 1 through 3.

      
      

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

      
      

      1. Flow and Stress Considerations

         Inlet piping to the pressure-relief devices should provide for proper system performance. This requires design consid- eration of the ?ow-induced pressure drop in the inlet piping. Excessive pressure losses in the piping system between the protected vessel and a pressure-relief device will adversely affect the system-relieving capacity and can cause valve instability. In addition, the effect of stresses derived from both pressure-relief device operation and externally applied loads must be considered. For more complete piping design guide- lines, see ASME B31.3.

         
         

      2. Vibration Considerations

Most vibrations that occur in inlet piping systems are ran- dom and complex. These vibrations may cause leakage at the seat of a pressure-relief valve, premature opening, or prema- ture fatigue failure of certain valve parts, inlet and outlet pip- ing, or both. Vibration in inlet piping to a rupture disk may adversely affect the burst pressure and life of the rupture disk. Detrimental effects of vibrations on the pressure-relief device can be reduced by minimizing the cause of vibrations, by additional piping support, by use of either pilot-operated relief valves or soft-seated pressure-relief valves, or by pro- viding greater pressure differentials between the operating

pressure and the set pressure.

1. PRESSURE-DROP LIMITATIONS AND PIPING CONFIGURATIONS

   For pressure-drop limitations and piping con?gurations, see Figures 1, 2, 4, and 5.

   
   

   1. Pressure Loss at the Pressure-Relief Valve Inlet

      Excessive pressure loss at the inlet of a pressure-relief valve can cause rapid opening and closing of the valve, or chattering. Chattering will result in lowered capacity and damage to the seating surfaces. The pressure loss that affects valve performance is caused by non-recoverable entrance losses (turbulent dissipation) and by friction within the inlet piping to the pressure-relief valve.

      Chattering has sometimes occurred due to acceleration of liquids in long inlet lines.

      
      

   2. Size and Length of Inlet Piping to Pressure- Relief Valves

When a pressure-relief valve is installed on a line directly connected to a vessel, the total non-recoverable pressure loss

1