What is ASME B31G used for?

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.

What is the difference between Original B31G and Modified B31G?

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.

What is the Folias bulging factor?

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.

B31G Remaining Strength Calculator | Corroded Pipeline Assessment

Pipe Data

Outside Diameter

Nominal Wall Thickness

Pipe Grade

SMYS

psi

Operating Conditions

MAOP

psig

Design Factor (F)

Class 1: 0.72 | Class 2: 0.60 | Class 3: 0.50 | Class 4: 0.40

Defect Data

Maximum Defect Depth

Defect Axial Length

Measured along pipe axis (longitudinal extent of corrosion)

Assessment Method

B31G Method

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.

About ASME B31G

Assessment Levels:
Level 0: Simple depth check (<20% wall OK)
Level 1: B31G formula (this calculator)
Level 2: RSTRENG effective area (profile-based)

Key Parameters:
Defect depth (d), length (L), pipe diameter (D), wall thickness (t), SMYS, MAOP, design factor (F)

Regulatory Basis:
49 CFR 192.485 requires remedial action for defects that exceed the acceptance criteria. ASME B31G provides the engineering basis for determining whether a corroded segment can safely operate at MAOP.

📚 Learn the Theory

Understand B31G assessment methodology, Folias factor, RSTRENG, and pipeline integrity management

Read Engineering Guide →

Assessment Results

Safe Maximum Pressure

psig

Failure Pressure (burst) -

Safety Factor (P'/MAOP) -

Remaining Strength -

Defect Depth -

Folias Factor (M) -

Flow Stress -

Hoop Stress at MAOP -

Barlow Pressure -

Max Allowable Length -

Method -

Method Comparison (Safe Pressure)
Modified: - psig | Original: - psig

Formula

P' = (2tS/D) × [(1-Ad) / (1-Ad/M)]

P' = Safe maximum pressure (psig)

t = Wall thickness (in)

S = Flow stress (psi)

D = Outside diameter (in)

Ad = Area ratio (0.85×d/t or 2/3×d/t)

M = Folias bulging factor

Standards & References

ASME B31G-2012
Manual for Determining Remaining Strength of Corroded Pipelines
49 CFR 192.485
Remedial Measures: Corrosion
PRCI PR-3-805
RSTRENG Effective Area Method
API 579-1 / ASME FFS-1
Fitness-For-Service Assessment

Engineering Notes

d ≤ 10% t: Generally acceptable without further analysis (pit-type)
d ≤ 80% t: Evaluate using B31G formula
d > 80% t: Repair required regardless of length
Modified B31G is standard practice for ILI-based assessments
RSTRENG (Level 2) uses actual corrosion profile for less conservative results
Interacting defects: Adjacent anomalies within 3t spacing must be combined

Common Pipe Grades (SMYS)

Grade B: 35,000 psi
X42: 42,000 psi
X52: 52,000 psi
X60: 60,000 psi
X65: 65,000 psi
X70: 70,000 psi

B31G Remaining Strength Calculator