ASME B31G

Covers — remaining-strength assessment of pipelines and piping with volumetric metal-loss (external corrosion): estimating failure pressure from corrosion geometry (length, depth) and pipe/material properties, and determining a safe operating pressure or acceptance.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Crack-like flaws, dents, and non-metal-loss damage → API 579-1 / ASME FFS-1.
• The pipeline design/operating code → ASME B31.4 / B31.8 / B31.12.
• The inspection/ILI program that finds the corrosion → the operator's integrity-management program.

B31G evaluates metal-loss corrosion only; other flaw types use FFS-1.

B31G provides assessment methods for corroded pipe:

• Corrosion Geometry — measured length and maximum depth of the metal-loss area.
• Failure-Pressure Estimate — computed from geometry, diameter, wall, and material (SMYS/flow stress).
• Method Selection — original B31G, modified B31G (0.85dL), or effective-area (RSTRENG), with differing conservatism.
• Safe Operating Pressure — a reduced MAOP or acceptance for continued operation.

ASME B31G is the pipeline industry's method for judging whether a corroded (metal-loss) pipe segment still has adequate pressure strength. After an in-line inspection or dig reveals external corrosion, B31G estimates the failure pressure from the corrosion length and depth and the pipe/material, yielding a safe operating pressure or an accept/repair decision.

It offers progressively less conservative methods — original B31G, modified B31G (0.85dL), and effective-area (RSTRENG) — so an anomaly that fails the simple method may still pass a more refined one. For non-metal-loss damage (cracks, dents), the broader API 579-1 is used.

Engineering Note: Match the B31G method to the data and consequence — the original method is quick but conservative and can force unnecessary repairs, while the effective-area (RSTRENG) method needs a detailed corrosion profile and is worth it only when the extra accuracy changes the decision.