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

2-28 API RECOMMENDED PRACTICE 581
P
is the pressure (operating, design, PRD overpressure, etc.), MPa (psi)
Po is the posterior probability for damage state 1
Thin
p1
Po is the posterior probability for damage state 2
Thin
p2
Po is the posterior probability for damage state 3
Thin
p3
Pr is the prior probability of corrosion rate data confidence for damage state 1
Thin
p1
Pr is the prior probability of corrosion rate data confidence for damage state 2
Thin
p2
Pr is the prior probability of corrosion rate data confidence for damage state 3
Thin
p3
S
is the allowable stress, MPa (psi)
Thin
SRP
is the strength ratio parameter defined as the ratio of hoop stress to flow stress
t
t bm
t c
t cm
t min
t rdi
TS
YS
α
is the furnished thickness of the component calculated as the sum of the base material and
cladding/weld overlay thickness, as applicable, mm (inch)
is the furnished or remaining base materials thickness of the component, mm (inch)
is the minimum structural thickness of the component base material, mm (inch)
is the furnished or remaining cladding/weld overlay material thickness of the component, mm
(inch)
is the minimum required thickness based on the applicable construction code, mm (inch)
the furnished thickness, t, or measured thickness reading from previous inspection
is the tensile strength at design temperature, MPa (psi)
is the yield strength at design temperature, MPa (psi)
is the component geometry shape factor
β 1 Thin is the β reliability indices for damage state 1
β 2 Thin is the β reliability indices for damage state 2
β 3 Thin is the β reliability indices for damage state 3
Φ
is the standard normal cumulative distribution function