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

RISK-BASED INSPECTION METHODOLOGY, PART 5—SPECIAL EQUIPMENT 5-93
5
4.5
4
3.5
Actual Failure Data
Adjusted Curve
Failure Rate (%)
3
2.5
2
Failure rate is constant with overpressure
1.5
1
0.5
0
1 1.5 2 2.5 3 3.5 4
Overpressure Ratio (Pop Pressure/Set Pressure)
Figure 5.5—PRD Failure Rate as a Function of Overpressure
.6000
.5000
POFOD
.4000
.3000
Severe
Modified Severe
Effect of Environmental Modifier
Modified POFOD Curve
.2000
Default POFOD Curve
.1000
.0000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Years In Service
Figure 5.6—Effect of Environmental Factors on PRD Weibull Curves