API RP 581 - 3rd Ed.2016 - Add.2-2020 - Risk-Based Inspection Methodology

PRD Interdependence with Fixed Equipment ..................................................................... 45
Failure Modes ......................................................................................................................... 45
Use of Weibull Curves ........................................................................................................... 46
PRD Testing, Inspection, and Repair ................................................................................... 47
PRD Overhaul or Replacement Start Date .......................................................................... 47
Risk Ranking of PRDs ........................................................................................................... 47
Link to Fixed or Protected Equipment ................................................................................. 47
PRD POF (FAIL) ............................................................................................................................. 48
Definition ................................................................................................................................ 48
Calculation of POF to Open .................................................................................................. 48
PRD Demand Rate ................................................................................................................. 48
PRD POF on Demand ............................................................................................................ 50
Protected Equipment Failure Frequency as a Result of Overpressure ........................... 58
Calculation Procedure ........................................................................................................... 59
Probability of Leakage (POL) ....................................................................................................... 60
Overview ................................................................................................................................. 60
Probability of Leakage Calculation Procedure ................................................................... 60
Calculation Procedure—POL at Specified Inspection Interval ......................................... 62
Consequence of PRD Failure to Open ......................................................................................... 63
General .................................................................................................................................... 63
Damage State of the Protected Equipment ......................................................................... 64
Overpressure Potential for Overpressure Demand Cases ................................................ 64
Multiple Relief Device Installations ...................................................................................... 65
Calculation of COF to Open .................................................................................................. 65
Calculation Procedure ........................................................................................................... 66
Consequence of Leakage ............................................................................................................. 66
General .................................................................................................................................... 66
Estimation of PRD Leakage Rate ......................................................................................... 67
Estimation of Leakage Duration ........................................................................................... 67
Credit for Recovery of Leaking Fluid ................................................................................... 67
Cost of Lost Inventory ........................................................................................................... 68
Environmental Costs ............................................................................................................. 68
Costs of Shutdown to Repair PRD ....................................................................................... 68
Cost of Lost Production ........................................................................................................ 68
Calculation of Leakage Consequence ................................................................................. 68
Calculation Procedure ........................................................................................................... 69
Risk Analysis ................................................................................................................................. 70
Risk from Failure to Open ..................................................................................................... 70
Risk from Leakage ................................................................................................................. 70
Total Risk ................................................................................................................................ 70
Calculation Procedure ........................................................................................................... 70
Inspection Planning Based on Risk Analysis ............................................................................. 71
RBI Intervals ........................................................................................................................... 71
Effect of PRD Inspection, Testing, and Overhaul on Risk Curve ..................................... 71
Effect of PRD Testing Without Overhaul on Risk Curve .................................................... 71
Nomenclature ................................................................................................................................. 72
Tables.............................................................................................................................................. 76
Figures ............................................................................................................................................ 91