Corroded Pipeline Assessment
Class 1: 0.72 | Class 2: 0.60 | Class 3: 0.50 | Class 4: 0.40
Measured along pipe axis (longitudinal extent of corrosion)
Modified B31G: Less conservative, uses SMYS+10ksi flow stress. Preferred for modern assessments.
Original B31G: More conservative parabolic area, uses 1.1×SMYS. Legacy method.
Understand B31G assessment methodology, Folias factor, RSTRENG, and pipeline integrity management
ASME B31G is a standard used to determine whether a corroded section of pipeline can continue to operate safely at its maximum allowable operating pressure (MAOP). It calculates the safe remaining pressure capacity based on the defect dimensions, pipe geometry, and material properties.
Original B31G uses a parabolic (2/3 dL) metal loss approximation and flow stress of 1.1×SMYS. Modified B31G uses a rectangular 0.85dL approximation and flow stress of SMYS+10,000 psi. Modified B31G is less conservative and more commonly used for modern assessments because it better represents actual burst test data.
The Folias factor (M) accounts for the stress concentration caused by a through-wall flaw in pressurized pipe. It depends on the defect length relative to the pipe diameter and wall thickness (L²/Dt). Longer defects produce higher Folias factors, meaning greater stress concentration and lower safe pressure.