L51694 Investigation of Techniques for Bulk Stress Measurement on Exposed Pipelines-Phases I and II

Differential movement of a buried pipeline resulting from terrain instabilities such as subsidence, fault slippage, frost heave, ice scouring, soil movement, and landslide can create localized areas of high stress in a pipeline. These areas may be susceptible to mechanical failure and therefore may compromise the structural integrity of the line. Nondestructive testing (NDT) methods that can detect high-stress regions and measure the magnitude of the stress in the pipeline are needed to determine if or when remedial action must be taken to prevent stress-related damage. The areas of high stress can compromise the integrity of the pipeline, despite the fact that the highly stressed areas may not be readily detectable.

 This report describes two phases of development for a nonintrusive technique to quantify the local, throughwall average axial stress in an exposed pipe. The technique selected for evaluation and development is a low-frequency, electromagnetic technique, called multiparameter magnetic measurement (MPMM). MPMM is a combination of existing magnetic techniques including magnetic hysteresis measurement, nonlinear harmonic analysis, and multiparameter correlation. The work included both a proof-of-principle demonstration of the technique using samples of grade X-42, X-46, and X-52 pipe (Phase I), and further determination of practical applicability of the MPMM technique (Phase II). Phase II focused on evaluating the variability of magnetic response to stress among five samples of grade X-42 pipe.