Battelle has been involved with safety and integrity of transmission pipelines since the 1950s. Consequently, major pipeline companies have come to rely on Battelle’s assistance in assessing pipeline integrity. As an example, Battelle was recently contacted by PEMEX regarding the continued operation of a pipeline transporting sour condensate. In-line inspection (ILI) in the fall of 1998 using a high-resolution “metal-loss detection” tool based on magnetic-flux-leakage (MFL) technology indicated a significant population of internal corrosion defects despite the application of inhibitor treatments.

The background image is representative of contour field generated by in-line inspection involving metal loss. Concentrations of color represent different depths.

PEMEX was particularly concerned since the ILI demonstrated widespread pitting corrosion and many large corrosion defects—the size of which led PEMEX to close the line shortly after the inspection. Battelle was charged with assessing the safe maximum operating pressure for the line and determining the extent, timing, and nature of repairs.

As a first step, Battelle established mechanical and fracture properties of the pipeline steel and then assessed leak and rupture failure scenarios as a function of operating conditions and defect geometry. Battelle also evaluated the accuracy of the ILI results by comparing reported defect sizes to actual defects removed from the line at conveniently accessible sites. Finally, Battelle assessed the overall integrity of the line and considered the likelihood and consequences of spills referenced to the results of the ILI.

In the assessment, Battelle considered usual measures of integrity, such as the very conservative industry criterion that led PEMEX to close the line. Next, recognizing that the actual fracture properties were high enough so that the industry criterion was grossly conservative, Battelle also evaluated alternative criteria that better reflected the true pressure capacity of the pipeline. This evaluation pointed to the need to repair defects located at just six sites, after which continued operation was possible.

Battelle developed a prioritized remediation plan and a hydrostatic testing protocol designed to prove the viability of its analysis and ensure the safety of the line. Since Battelle’s involvement, the pipeline has successfully passed the hydro re-test and was returned to limited service.

For more information on Battelle’s Pipeline Technology Center capabilities, contact Brian Leis at (614) 424-4421, leis@battelle.org.