Page 258 - Pipelines and Risers

Remaining Strength of Corroded Pipes 23 1

14.2.2 B31G Criterion
The B31G criterion (ASME 1993) is widely used to assess corroded pipelines for fitness for
purpose evaluation. The main equations in the ASME B31G criteria (1993) can be
summarized as follows.

Maximum Allowable Design Pressure, P
The maximum allowable design pressure in B31G criterion is expressed as:
(14.4)

where:
P is the maximum allowable design pressure
SMYS is the Specified Minimum Yield Strength
F is the design factor, which is normally 0.72.

Maximum Allowable Defect Length and Depth
In the B31G (ASME 1993), a criterion for the acceptable corroded length is given as below
for a corroded area having a maximum depth 'd' in the range of 0.1 c d/t c 0.8 where t is the
nominal wall thickness
La1low = 1.12BG (14.5)

where:
LllOw is the maximum allowable axial extent of the defect

B=./- l.ld It - 0.15 (14.6)

The Maximum Allowable Operating Pressure (MAOP) is defined to be less or equal to the
maximum allowable design pressure P given by Equation (14.4).
P
MAOP I (14.7)
Equating the Safe Maximum Pressure Level P' to the Maximum Allowable Operating
Pressure (MAOP), the maximum allowable defect depth dallow is:
a) For A54
MAOP
I--
31
d allow = 3 MAOP (14.8)
11p
1-
1. P a
b) For A>4