ChemProCal • Piping & Hardware • Pipeline Corrosion & Metal Loss Remaining Strength Analyzer (ASME B31G)

PIPING & HARDWARE

Pipeline Corrosion & Metal Loss Remaining Strength Analyzer (ASME B31G)

Evaluates external/internal metal loss defects using Original ASME B31G, Modified B31G (0.85dL), and RSTRENG Folias bulging factors; calculates safe operating pressure (P_safe) and ERF.

Pipeline Line Pipe Specifications & Operating Pressure

Pipe Outside Diameter ($D$)

mm OD (24" NPS)

Nominal Wall Thickness ($t$)

mm (0.500")

Specified Min. Yield Strength ($\text{SMYS}$)

MPa (API 5L X65)

Maximum Allowable Operating Pressure (MAOP)

barg

Hoop Stress Design Factor ($F$)

Class 1 (0.72)

In-Line Inspection (ILI) Metal Loss Defect Geometry

Maximum Defect Depth ($d$)

mm (35.4% $t$)

Longitudinal Defect Length ($L$)

mm along pipe axis

Corrosion Growth Rate ($\text{CGR}$)

mm/year

ASME B31G Modified B31G (0.85dL) API 579 FFS

Pipeline Defect Fitness-for-Service Criteria

Smart pigging tools (magnetic flux leakage / ultrasonic ILI) frequently detect external corrosion and internal pitting:

80% Depth Limit: If defect depth exceeds $80\%$ of nominal wall thickness ($d/t > 0.80$), ASME codes strictly prohibit continued operation regardless of length. Immediate repair is mandatory.
Folias Bulging Factor ($M$): Internal pressure bulges the thinned metal outward, concentrating stresses. The Folias factor accounts for pipe curvature reinforcement.
Original vs. Modified B31G: Original B31G assumes a parabolic defect profile ($A = \frac{2}{3}dL$). Modified B31G adopts a more realistic $0.85dL$ effective area and increases flow stress by $10\ \text{ksi}$ ($\text{SMYS} + 68.95\ \text{MPa}$), eliminating unnecessary conservatism.

Pipeline Integrity Status

Corrosion Remaining Strength & FFS Evaluation

FIT FOR SERVICE AT FULL MAOP

Modified B31G Safe Pressure ($P_{\text{safe}}'$)

-- barg

Design MAOP: -- barg

Burst Failure Pressure ($P_{f,\text{mod}}$)

-- barg

Original B31G: -- barg

Remaining Strength Factor ($RSF$)

Original RSF: -- (Threshold: 0.90)

Years to 80% Wall Loss

-- years

Remaining Wall: -- mm

Original vs. Modified ASME B31G Comparison

Parameter	Original B31G	Modified B31G (0.85dL)
Flow Stress ($\bar{\sigma}$)	-- MPa	-- MPa
Folias Bulging Factor ($M$)	--	--
Burst Failure Pressure ($P_f$)	-- barg	-- barg
Safe Pressure ($P_{\text{safe}}'$)	-- barg	-- barg

Repair Action Recommendation

Classification: --

Defect Depth Ratio ($d/t$): --%

Dimensionless $z = L^2/(Dt)$: --

Per ASME B31G / B31.8, defects fit for service at full MAOP should be monitored on subsequent ILI smart pigging runs.

ASME B31G Pipeline Remaining Strength Theory

The assessment of corroded oil and gas transmission pipelines is governed by ASME B31G ("Manual for Determining the Remaining Strength of Corroded Pipelines") and API 579-1 / ASME FFS-1 (Fitness-For-Service).

1. Original ASME B31G (1984) Parabolic Formulation

The original standard assumes the corroded metal loss profile is parabolic with area $A = \frac{2}{3} d L$. Burst failure pressure is calculated using flow stress $\bar{\sigma} = 1.1 \times \text{SMYS}$ and the Folias bulging factor $M$:

$$P_f = \frac{2 t \bar{\sigma}}{D} \left[ \frac{1 - \frac{2}{3}\frac{d}{t}}{1 - \frac{2}{3}\frac{d}{t}\frac{1}{M}} \right] \quad \text{where} \quad M = \sqrt{1 + 0.8 \frac{L^2}{D t}}$$

2. Modified ASME B31G (0.85dL Method - 1991)

Full-scale burst test programs conducted by PRCI (Pipeline Research Council International) demonstrated that original B31G was excessively conservative, resulting in unnecessary cut-outs of serviceable pipe. Modified B31G incorporates an effective area factor of $0.85$, adjusts flow stress to $\bar{\sigma} = \text{SMYS} + 68.95\ \text{MPa}$ ($10\ \text{ksi}$), and utilizes an improved three-term Folias polynomial:

$$M = \sqrt{1 + 0.6275 \left(\frac{L^2}{Dt}\right) - 0.003375 \left(\frac{L^2}{Dt}\right)^2} \quad \text{for} \quad \frac{L^2}{Dt} \le 50$$

Tool Units

Input / Output Units

Configure global unit system preset or individual parameter dimensions.