The safety relief valve handbook : design and use of process safety valves to ASME and international codes and standards

Contents PREFACE ................................................................................................... xi ACKNOWLEDGEMENTS ......................................................................... xv CHAPTER 1 History ................................................................................. 1 1.1 Acronyms, Abbreviations .................................................... 5 CHAPTER 2 Overpressure Protection .................................................... 6 2.1 General Defi nition of an SRV ................................................ 6 2.2 Where do SRVs Fit in the Process? ...................................... 6 2.3 Where do SRVs Act Within the Process? ............................ 7 2.4 Causes of Overpressure ........................................................ 8 2.4.1 Blocked discharge ..................................................... 8 2.4.2 Fire case ..................................................................... 9 2.4.3 Thermal expansion .................................................. 17 2.4.4 Runaway reaction .................................................... 18 2.4.5 Tube rupture in heat exchangers .......................... 18 2.5 Determine Overpressure Protection Requirements ......... 19 2.6 Overpressure Relief Devices .............................................. 21 2.7 Risk Assessment and Reduction ........................................ 24 CHAPTER 3 Terminology ...................................................................... 27 3.1 Testing ................................................................................. 27 3.2 Type of Devices ................................................................... 29 3.2.1 Reclosing pressure-relieving devices .................... 29 3.2.2 Non-reclosing pressure relief device ..................... 30 3.3 Dimensional Terms ............................................................. 31 3.4 Operational Terms .............................................................. 33 3.5 Component Terms ............................................................... 39 vi C ontents 3.6 Clarifi cation of the Terms: Set Pressure, Overpressure, Accumulation, MAWP and Design Pressure ..................... 42 3.6.1 PED versus ASME .................................................... 46 CHAPTER 4 Codes and Standards ....................................................... 53 4.1 Overview Operational Requirements ................................ 56 4.2 ASME and API Codes and Standards – Clarifi cations ..... 56 4.2.1 National Board approval .......................................... 57 4.2.2 Main paragraph excerpts from ASME VIII ............ 58 4.2.3 Main excerpts from American Petroleum Institute recommended practices related to safety relief valves ................................................... 64 4.3 NACE .................................................................................... 68 4.4 PED 97/23/EC (Pressure Equipment Directive) – CEN .... 71 4.5 ATEX .................................................................................... 75 4.5.1 European ATEX Guidelines .................................... 75 CHAPTER 5 Design Fundamentals ...................................................... 78 5.1 Construction Materials ....................................................... 79 5.2 Direct Spring-Operated SRVs ............................................. 79 5.2.1 Introduction .............................................................. 79 5.2.2 Functionality ............................................................ 80 5.2.3 General design ......................................................... 85 5.2.4 Design of main assemblies ..................................... 89 5.2.5 Design differences ................................................... 96 5.2.6 Types of spring-operated SRVs .............................. 99 5.3 Pilot-Operated Safety Relief Valves ................................. 110 5.3.1 Introduction ............................................................ 110 5.3.2 Functionality ..........................................................111 5.3.3 Types of POSRV ..................................................... 112 5.3.4 Summary ................................................................. 122 5.4 DIN Design ......................................................................... 123 5.5 Non-reclosing Pressure Relief Devices ............................ 124 5.5.1 Summary ................................................................ 128 CHAPTER 6 Installation ...................................................................... 129 6.1 Inlet and Outlet Piping ..................................................... 129 6.1.1 Calculating piping losses ...................................... 139 6.1.2 Calculating outlet piping ....................................... 144 Contents vii 6.2 Location of Installed SRVs .............................................. 147 6.3 Reaction Forces and Bracing .......................................... 147 6.4 Temperature Transmission ............................................ 151 6.5 Installation Guidelines .................................................... 151 CHAPTER 7 Sizing and Selection ....................................................... 158 7.1 Introduction ..................................................................... 158 7.2 Gas and Vapour Sizing .................................................... 162 7.3 Steam Sizing (Sonic Flow) .............................................. 165 7.4 Steam Sizing – Per ASME Section I ................................ 167 7.5 Liquid Sizing .................................................................... 169 7.5.1 Combination devices ........................................... 170 7.6 Two-Phase and Flashing Flow ....................................... 170 7.6.1 Some basics .......................................................... 172 7.6.2 Two-phase liquid/vapour fl ow ............................ 174 7.6.3 Two-phase system with fl ashing or non-condensable gas ........................................... 176 7.6.4 Subcooled liquid fl ashing .................................... 178 7.6.5 Two-phase system with fl ashing and non-condensable gas ........................................... 181 CHAPTER 8 Noise ................................................................................ 190 8.1 Risk of Damage to Hearing ............................................. 195 8.2 Planning an Accident ...................................................... 200 8.3 Noise from the SRV, Open Vent and Associated Pipe .. 200 8.4 Noise Calculations ........................................................... 201 8.5 Conclusions ...................................................................... 204 CHAPTER 9 Safety Relief Valve Selection ......................................... 207 9.1 Seat Tightness ................................................................. 207 9.2 Blowdown ........................................................................ 208 9.3 Service Temperature ....................................................... 208 9.4 Weight and/or Height ..................................................... 209 9.5 Backpressure ................................................................... 209 9.6 Orifi ce Size – Sizing ......................................................... 212 9.7 Two-Phase Flow .............................................................. 212 9.8 Type of Fluid .................................................................... 213 9.9 Reciprocating Compressors ............................................ 213 9.10 Liquid ............................................................................... 214 9.11 Materials .......................................................................... 215 viii C ontents CHAPTER 10 Maintenance and Testing ............................................ 217 10.1 Maintenance Frequency and Cost ............................... 217 10.1.1 Introduction ...................................................... 217 10.1.2 Maintenance cost ............................................. 218 10.1.3 Maintenance frequency ................................... 220 10.2 Transportation and Dirt ................................................ 224 10.2.1 Preinstallation handling and testing of pressure relief valves ....................................... 225 10.3 Troubleshooting SRVs ................................................... 226 10.3.1 Seat leakage ..................................................... 227 10.3.2 Chatter .............................................................. 229 10.3.3 Premature opening .......................................... 231 10.3.4 Valve will not open .......................................... 232 10.3.5 Valve opens above set pressure ..................... 232 10.3.6 Valve does not reclose ..................................... 232 10.3.7 Bellows failure .................................................. 232 10.3.8 Springs .............................................................. 235 10.4 Testing ........................................................................... 236 10.4.1 In situ testing of spring-operated SRVs ......... 238 10.4.2 In situ testing of pilot-operated SVs ............... 240 10.5 Maintenance Procedure ................................................ 241 CHAPTER 11 Cryogenic Applications ............................................... 249 11.1 Thermal Relief ............................................................... 251 11.2 Process ........................................................................... 251 11.2.1 Conventional spring-operated SRVs on cryogenic service ............................................. 252 11.2.2 Balanced bellows spring-loaded SRVs on cryogenic service ............................................. 252 11.2.3 POSRV on cryogenic service ........................... 254 11.3 Testing for Cryogenic Service ...................................... 256 11.3.1 The ‘ submerged test ’ ....................................... 256 11.3.2 The ‘ boil-off test ’ .............................................. 257 11.4 Conclusion ..................................................................... 258 CHAPTER 12 Specifying Safety Relief Valves ................................... 259 12.1 Summary of Overall Requirements .............................. 259 12.2 Materials ........................................................................ 260 12.3 Design ............................................................................ 261 12.4 Identifi cation .................................................................. 262 Contents ix 12.5 Inspection and Testing ................................................. 263 12.6 Preparation for Shipment ............................................. 263 CHAPTER 13 Non-conformance of Existing Pressure Relief Systems ......................................................................... 265 13.1 No Relief Device Present ............................................... 269 13.1.1 External fi re ...................................................... 269 13.1.2 Multiple scenarios ............................................ 270 13.1.3 Blocked outlet ................................................... 270 13.1.4 Thermal relief ................................................... 270 13.1.5 Tube rupture .................................................... 270 13.1.6 Others .............................................................. 271 13.1.7 Control valve failure ......................................... 271 13.2 Under/Oversized Safety Valves .................................... 271 13.2.1 External fi re ...................................................... 271 13.2.2 Blocked outlet ................................................... 272 13.2.3 Tube rupture ..................................................... 272 13.2.4 Multiple scenarios ............................................ 272 13.2.5 Control valve failure ......................................... 272 13.2.6 Others ............................................................... 272 13.2.7 Loss of condensing ......................................... 273 13.3 Improper Installation ..................................................... 273 13.3.1 Outlet pressure drop too high ......................... 273 13.3.2 Inlet pressure drop too high ............................ 274 13.3.3 Blocked relief pathway ................................... 275 13.3.4 Set pressure too high ...................................... 275 13.3.5 Others .............................................................. 275 13.4 What Can Go Wrong in the Process Scenarios ........... 276 APPENDIX SECTION: RELEVANT TABLES AND REFERENCES ...... 280 A Comparisons Between the Safety Valves Sizing Formulas ........................................................................ 280 B Backpressure Correction Factors ................................. 284 C Compressibility Factors ................................................ 286 D Ratio of Specifi c Heats k and Coeffi cient C ................. 287 E Capacity Correction Factor for Superheat, K sh ............ 288 F Capacity Correction Factor for High Pressure Steam, K n ........................................................................ 289 G Capacity Correction Factor for Viscosity, K V ............... 290 H Allowable Operating, Working, Relief, Set and Blowdown Pressures ..................................................... 292 x C ontents I Codes and Standards Organizations ............................. 293 J API 526 Data Sheet Recommendation .......................... 295 K Generic Sizing Program ................................................ 297 L Worldwide Codes and Standards (Most Common) ..... 298 M Properties of Common Gases ...................................... 299 N Relevant Conversion Factors ....................................... 301 FURTHER READING .............................................................................. 305 INDEX ...................................................................................................... 307