Assessment and detection of stress corrosion cracking by advanced eddy current array nondestructive testing and material characterization

Abstract

Oil and natural gas pipelines are under a combination of loading (stresses) due to their pressurized content and some kind of corrosive environmental operational condition including the content materials as well as soil side which is called Stress Corrosion Cracking (SCC). Since the SCC occurs at stresses within the range of typical design stresses, it can cause catastrophic failures without a significant indication in pipeline integrity beforehand. Efficient Nondestructive Inspection (NDI) during the operational life of the structures can prevent such failures by providing accurate information regarding size and characteristics of the SCC flaws. Since majority of SCC defects occur in surface and near surface regions of metallic pipeline, electromagnetic NDI (Eddy Current) is proved to be a promising inspection technique. In this study, Eddy Current Array (ECA) methodology, as a recent advancement and developed version of traditional Eddy Current (EC) NDI technique, was used for assessment of SCC generated in steel samples representing steel pipeline's material in a laboratory setup. ECA as an advanced eddy current NDI uses an array of eddy current coils to provide the scanning image of the inspection area. Prefabricated notches and SCC after a period of load-corrosion application to the samples were detected and characterized. Accuracy and repeatability of the results showed the efficiency of ECA for SCC characterization.