API Std 520-1 (2014) PSV Sizing & Selection

Description

Cover Special Notes Foreword Contents 1 Scope 2 Normative References 3 Terms and Definitions 4 Pressure-relief Devices 4.1 General 4.2 Pressure-relief Valves (PRVs) 4.3 Rupture Disk Devices 4.4 Pin-actuated Devices 4.5 Open Flow Paths or Vents 4.6 Other Types of Devices 5 Procedures for Sizing 5.1 Determination of Relief Requirements 5.2 API Effective Area and Effective Coefficient of Discharge 5.3 Backpressure 5.4 Relieving Pressure 5.5 Development of Sizing Equations 5.6 Sizing for Gas or Vapor Relief 5.7 Sizing for Steam Relief 5.8 Sizing for Liquid Relief: PRVs Requiring Capacity Certification 5.9 Sizing for Liquid Relief: PRVs Not Requiring Capacity Certification 5.10 Sizing for Two-phase Liquid/Vapor Relief 5.11 Sizing for Rupture Disk Devices 5.12 Sizing for Open Flow Paths or Vents Annex A (informative) Rupture Disk Device Specification Sheet Annex B (informative) Review of Flow Equations Used in Sizing Pressure-relief Devices Annex C (informative) Sizing for Two-phase Liquid/Vapor Relief Annex D (informative) Pressure-relief Valve Specification Sheets Annex E (informative) Capacity Evaluation of Rupture Disk and Piping System 100 % VaporFlow and Constant Pipe Diameter Bibliography Figures Figure 1—Conventional PRV with a Single Adjusting Ring for Blowdown Control Figure 2—Balanced-bellows PRV Figure 3—Balanced-bellows PRV with an Auxiliary Balanced Piston Figure 4—Conventional PRV with Threaded Connections Figure 5—PRV Operation—Vapor/Gas Service Figure 6—Typical Relationship Between Lift of Disk in a PRV and Vessel Pressure Figure 7—PRV Operation—Liquid Service Figure 8—Typical Effects of Superimposed Backpressure on the Opening Pressureof Conventional PRVs Figure 9—Typical Effects of Backpressure on the Set Pressure of Balanced PRVs Figure 10—Pop-action Pilot-operated Valve (Flowing Type) Figure 11—Pop-action Pilot-operated Valve (Nonflowing Type) Figure 12—Modulating Pilot-operated Valve (Flowing Type) Figure 13—Pilot-operated Relief Valve with a Nonflowing Modulating Pilot Valve Figure 14—Low-pressure Pilot-operated Valve (Diaphragm Type) Figure 15—Pressure Level Relationships for PRVs Figure 16—Typical Relationship Between Lift of Disk or Piston and Vessel Pressure in aPop-action Pilot-operated PRV Figure 17—Typical Relationship Between Lift of Disk or Piston and Vessel Pressure in aModulating-action Pilot-operated PRV Figure 18—Pressure Level Relationships for Rupture Disk Devices Figure 19—Rupture Disk Device in Combination with a PRV Figure 20—Forward-acting Solid Metal Rupture Disk Figure 21—Forward-acting Scored Rupture Disk Figure 22—Forward-acting Composite Rupture Disk Figure 23—Reverse-acting Rupture Disk with Knife Blades Figure 24—Reverse-acting Scored Rupture Disk Figure 25—Graphite Rupture Disk Figure 26—Rupture Disk Application Parameters Assuming No Superimposed Backpressure Figure 27—Common Types of Manufacturing Ranges and Corresponding Burst Pressure Marking Figure 28—Rupture Disk Application Parameters with Superimposed Backpressure Figure 29—Buckling Pin Valve Figure 30—Backpressure Correction Factor, Kb, for Balance Spring-loaded PRV(Vapors and Gases) Figure 31—Capacity Correction Factor, Kw, Due to Backpressure on Balanced Spring-loadedPRVs in Liquid Service Figure 32—Curve for Evaluating Coefficient C in the Flow Equation from the Specific Heat Ratio,Assuming Ideal Gas Behavior (USC Units) Figure 33—Curve for Evaluating Coefficient C in the Flow Equation from the Specific Heat Ratio,Assuming Ideal Gas Behavior (SI Units) Figure 34—Sample of Completed PRV Specification Sheet Figure 35—Values for F2 for Subcritical Flow Figure 36—Constant Backpressure Correction Factor, Kb, for Conventional PRVs(Vapors and Gases Only) Figure 37—Capacity Correction Factor, Kv, Due to Viscosity Figure 38—Capacity Correction Factors Due to Overpressure for Noncertified PRVs in Liquid Service Figure A.1—Rupture Disk Device Specification Sheet Figure C.1—Correlation for Nozzle Critical Flow of Flashing and Nonflashing Systems Figure C.2—Correlation for Nozzle Critical Flow of Inlet Subcooled Liquid Figure C.3—Backpressure Correction Factor, Kb, for Balanced-bellows PRVs (Liquids) Figure D.1—Spring-loaded PRV Specification Sheet Figure D.2—Pilot-operated PRV Specification Sheet Figure E.1—Pressure-relief System for Example Problem Figure E.2—Curve Fit for Cp/Cv = 1.4 (Crane 410, Chart A-22) Tables Table 1—Set Pressure and Accumulation Limits for Pressure-relief Devices Table 2—Example Determination of Relieving Pressure for Operating Contingencies for a Single Relief Device Installation Table 3—Example Determination of Relieving Pressure for Operating Contingencies for a Multiple Relief Device Installation Table 4—Example Determination of Relieving Pressure for Fire Contingencies for a Single Relief Device Installation Table 5—Example Determination of Relieving Pressure for Fire Contingencies for a Multiple Relief Device Installation Table 6—Example Determination of Relieving Pressure for Fire Contingencies for a Supplemental Valve Installation Table 7—Properties of Gases #65,0,-3 Table 8—Values of Coefficient C Table 9—Superheat Correction Factors, KSH Table A.1—Rupture Disk Device Specification Sheet Instructions Table B.1—Results for Supercritical Fluid Example Problem B.1.3 Table B.2—Results for Subcooled Liquid Example Problem B.2.2 Table B.3—Results for Gas Example Problem B.3.3 Table C.1—Two-phase Liquid/Vapor Relief Scenarios for PRVs Table C.2—Results for Direct Integration Example C.2.1.2 Table D.1—Instructions for Spring-loaded PRV Specification Sheet Table D.2—Instructions for Pilot-operated PRV Specification Sheet Table E.1—Determination of Overall Piping Resistance Factor, K