Toppling integrity: the domino effect of inaccurate material verification

Accurate verification of pipeline material properties is essential for ensuring the integrity of North America’s oil and gas transmission pipelines. Its importance is underscored by United States Pipeline and Hazardous Materials Safety Administration’s (PHMSA) recent Mega Rule legislation, which mandates testing of undocumented pipelines for reconfirmation of maximum allowable operating pressure (MAOP). Given that MAOP is dependent upon the grade of metal used, which can often be determined from accurate determination of yield stress (among other characteristics), material verification has become an increasingly important component in the integrity management programmes of pipeline owners and operators.

The importance of data accuracy

Accurate grade determination is no trivial matter. Mechanical properties, including yield stress and tensile strength, alongside other datasets such as chemical composition, microstructural features, and historical operating conditions, can help provide a good, but not necessarily perfect, determination of a pipe’s grade. Uncertainty can arise from a multitude of angles, including overlapping material properties for various pipe grades, operational error at the point of data collection, or system inaccuracies. This is why operators are mandated by legislation, such as the Mega Rule, to proceed with caution when determining pipe grade. This more conservative approach may lead to a reduced operating pressure and a reduced volume flowrate, but prioritises asset integrity. That, of course, should be the position, since the consequences of misidentifying pipeline grade can be far-reaching and devastating.

The risks of compromising pipeline safety are multifaceted, encompassing economic, environmental and safety concerns. For operators, a pipeline failure can result in substantial financial losses, not only due to the high cost of repairs and product loss, but also because of government fines, legal liabilities, and the long-term reputational damage a company may suffer. These incidents can lead to a loss of investor confidence, causing stock prices to plummet and plunging companies into financial freefall. Pipeline failures can also have consequences for both the environment and human populations that live near affected areas. Oil or gas spills may severely pollute bodies of water and the surrounding soil, disrupting natural ecosystems and causing long-term harm to wildlife. Pipeline explosions or leaks pose significant risks to nearby communities, leading to injuries or, in the most severe cases, even death. The release of hazardous substances can also cause long-term health problems for those exposed either directly or indirectly due to water and soil contamination. Cleanup efforts are often expensive and time-intensive and may not be able to reverse all of these consequences. For operators and inspection companies, these risks underscore the critical importance of accurate material verification and grade determination.

For these reasons, regulations that enhance pipeline safety should be supported. Frameworks like the Mega Rule legislation, which covers material verification, place the onus on owners and operators to ensure that the tools used for yield stress determination are technically defensible. These tools must undergo rigorous review, testing, and validation by subject-matter experts to ensure they meet the industry standard for accuracy and reliability. Such validation programmes are essential for ensuring technical defensibility and for comparing the accuracy of competing tools, upholding the industry standard for accurate data to support grade identification. Despite this, findings still show that some material verification testing technologies can misjudge pipe strength by more than 25%, which could severely skew grade determination calculations and have a significant impact on pipeline integrity efforts. Sub-standard accuracy should not be tolerated when the safety and integrity of critical national infrastructure is at risk. This is something that owners, operators, and the providers of material verification services ought to be aligned on.

Material verification and grade identification

One key component of the Mega Rule legislation is MAOP reconfirmation – or calculation of the maximum allowable operating pressure. The calculation is straightforward, requiring a few simple input parameters, including a specified minimum yield stress (SMYS). The value of SMYS that is used in these calculations is fixed and is dependent on the grade of the pipe, with common grades including X42 (SMYS = 42 ksi), X52 (SMYS = 52 ksi), and X70 (SMYS = 70 ksi), among others. However, it’s important to note that the actual yield stress of a pipe rarely matches the nominal SMYS value exactly. For example, while X42 pipe is associated with a SMYS of 42 ksi, the actual yield stress may vary due to manufacturing inconsistencies.

As an example, if a tool inaccurately measures a yield stress of 66 ksi, it would be reasonable to assume that the pipe grade is X65, when in fact an accurate measurement would show a yield stress to be 53 ksi, which would support an X52 call on grade, leading to this number being used in the MAOP calculation. If X65 was wrongly assumed, the resulting MAOP calculation could be dangerously overestimated, leading to the potentially devastating consequences discussed above. This is a key reason why accurate material verification is essential to grade identification and, by extension, pipeline safety.

Tools for pipeline material verification

Several approaches are available for in-situ material verification of metal pipelines, each with a distinct method for determining material properties. These methods include estimating yield and tensile strength from load-displacement data; analysing a material’s response to plastic deformation caused by creating grooves across the pipe surface; and combining hardness testing with chemical analysis and microstructural examination. The most recent advancement in this field, known as Profilometry-based Indentation Plastometry (PIP), involves measuring the full profile of an indent, rather than just its depth. This method leverages sophisticated software that compares the full shape of the indent with the outcome of a finite element simulation of the indentation test.

Assessing the accuracy levels of competing tools

Given the critical importance of accuracy in material verification, stakeholders in the midstream oil and gas industry have been evaluating the accuracy of material verification tools through head-to-head round-robin studies. These studies are an excellent mechanism for ensuring that the tools are technically defensible, as required by the Mega Rule legislation.

Read the article online at: https://www.worldpipelines.com/special-reports/27112024/toppling-integrity-the-domino-effect-of-inaccurate-material-verification/