United States Department of Transportation
i
Fundamental Mechanochemistry-Based Detection of Early Stage Corrosion Degradation of Pipeline Steels
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2020-05-11
[PDF-3.19 MB]
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Abstract:Corrosion of underground natural gas and liquid petroleum pipelines occurs by a variety of forms and requires specialized methods to detect and control. Stress corrosion cracking (SCC) is a form of corrosion that results in clusters or colonies of cracks on the surface of the affected pipelines. While the three conditions necessary for SCC (metal susceptibility, critical service stress and potent environment) are well understood, SCC remains as a leading operational safety concern. During SCC, the majority of the life of a pipe remains within the nucleation stage, wherein micro-damage is percolating very slowly, and below detection thresholds for commonly deployable nondestructive evaluation techniques. Utilizing our integrated understanding, from current CAAP project, for electrochemical transport current, stress, and morphology evolution during SCC early stage damage percolation in pipeline steel, the university plans to develop and characterize two complementary methods that are expected to provide quantitative measure of the damage level during the early stage of SCC, and thereby render a safe operational condition of the pipeline. This framework relies on a model based prediction of the onset and progression of SCC subsurface damage to enable the development of testing methodologies for accurate measurements of corrosion depth and extent of initial shallow cracks. The methodologies utilize: (i) electrochemical impedance spectroscopy (EIS). Intergranular corrosion penetration and stress corrosion crack length are manifested by particular features of the impedance spectra. Aided by the modeling framework, geometrical descriptors of corrosion can be determined directly from impedance spectra. And (ii) tailored 4-point probe (4PB) resistance/impedance measurements. We have observed extensive lattice damage in the near surface layer. The preliminary measurement of 4PB showed subtle changes in the measured electrical resistance. A tailored 4PB with optimized configuration and electronic circuit will be developed to measure the changes in electrical resistance of near surface layer as a function of the corrosion environment and history. Aided by geometric modeling of corroded cross section, geometrical descriptors of corrosion can be determined from the measured changes of electrical resistance. The complementary techniques would provide quantitative measure of the extent of subsurface damage, grain boundary grooving and early stage percolation of shallow cracks to enable further development of NDE corrosion detection techniques. The team spans several disciplines with diverse expertise in fracture and fatigue damage evolution (Bastawros), electrochemistry (Hebert) micro- and nano-measurements (Shrotriya), NDE for pipelines in-line inspection (Bond), and leverages the support and ongoing work with BP and others on pipe monitoring. This work leverages the provided sample set in a previous CAAP project by Kiefner and Associates. The model guided phenomenological understanding of the SCC mechanochemistry, and the quantifiable laboratory measurements of such degradation at different stages, will assist in the development of future deployable NDE methodology for the detection and monitoring of the early stage of SCC. These insights will enhance the operator ability to monitor changes in parameters germane to the corrosion prevention, while mitigating the corrosion impact on the pipeline sector.
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