Accurate Determination of the Maximum Allowable Operating Pressure (MAOP) of Oil and Gas Pipelines

This technical brief addresses one of the most practically important calculations in pipeline operations: the maximum allowable operating pressure (MAOP). The MAOP calculation — MAOP = (Factors of Safety × SMYS × t) / OD — requires accurate knowledge of the specified minimum yield strength (SMYS), which is unavailable for thousands of miles of undocumented in-service pipelines.

The brief explains that while wall thickness (t) can be measured with an ultrasonic thickness gauge and outer diameter (OD) with a pipe caliper, SMYS must come from verified grade certification. When documentation is missing, operators must either measure the actual mechanical properties or assume a conservative yield strength of 24 ksi — which dramatically limits the pipeline's allowable operating pressure and transmission throughput.

Haggag explains why two commonly used field techniques — Positive Material Identification (PMI) and portable hardness testing — are inadequate for MAOP determination. PMI measures chemical composition but Equation 1 for MAOP does not require chemical composition; PMI was never intended to determine steel grade. Portable hardness testing can only estimate UTS, not yield strength, and PHMSA does not accept hardness results as replacements for tensile properties.

The ABI® test provides direct measurements of yield strength, ultimate tensile strength, the YS/UTS ratio, and fracture toughness from each single in-situ test on live pipelines. This capability satisfies the nondestructive testing requirements of 49 CFR Parts 192 and 195 for MAOP verification and has been used by pipeline operators in multiple states.