New regulations for gas transmission pipelines in the United States allow for the use of nondestructive evaluation (NDE) techniques to directly measure material properties in lieu of conservative default values when records are not traceable, verifiable, and complete (TVC).  Advanced NDE technologies and processes can be used to collect material property data opportunistically when the pipeline is exposed for inspection or repairs, significantly reducing costs compared to traditional cut-outs and laboratory testing. This paper describes recently developed and validated NDE methods based on Hardness, Strength and Ductility (HSD) testing and Nondestructive Toughness Testing (NDTT) to predict conventional laboratory measurements of the mechanical strength, toughness, and quality of pipeline steel and longitudinal welded seams. Both methods are implementations of frictional sliding where a hard stylus deforms a softer substrate and then slides along the sample surface, allowing for hundreds of measurements of the material response to be collected during a single experiment. HSD testing uses multiple spherical styluses of varying size to measure the material hardness at different magnitudes of plastic strain so that a representative stress-strain curve can be constructed, whereas the NDTT uses a wedge-shaped stylus with an internal stretch passage that propagates a shallow tensile crack along the surface. This paper will describe the fundamental basis and test procedures for these methodologies, as well as validation data collected on vintage pipeline materials. Successful case studies describing the application of these techniques within ongoing integrity management programs to perform material verification of steel grade and determination of low frequency or high frequency electric-resistance-welded (ERW) seams are presented for both gas and liquid transmission pipelines. Future possibilities include expanding the use of these techniques to reduce conservatism in dent assessment using a critical strain-based approach, and combining in-situ measurements of metal plasticity and fracture properties to develop more accurate predictive models for fitness for service assessments.


Advancements in Nondestructive Methods Using Frictional Sliding for Direct Assessment of Steel Pipelines and Welded Seams

Division / Sponsors: 
Pipeline Systems Division

Paper Proceedings: https://asmedigitalcollection.asme.org/IPC/IPC2020/volume/84447

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