Despite being a method of choice for the detection of stress corrosion cracking (SCC) on carbon steel surfaces, eddy current array (ECA) technologies are still rarely being used for measuring the depth of these cracks. Phased array ultrasonic testing (PAUT) remains the technique of choice. While offering a high level of accuracy on crack depth, PAUT is still relatively slow and dependent of the operator carrying out the inspection. There is currently a strong need in the pipeline industry for a technology that would ally the speed and ease of use of ECA with the depth sizing capabilities of PAUT. This paper presents the most recent advances of eddy current array technologies for the depth sizing of SCC in carbon steel pipelines. Several field trials have been conducted to validate the performance and accuracy of tangential eddy current array (TECA) through comparisons with controlled grinding of the SCC indications. These results show that the main advantages of ECA over PAUT reside in the short amount of time required to locate and size the deepest crack within a colony of SCC, in addition to being more user-friendly and less operator dependent. Ultimately, the field results presented in this paper show how TECA could transform the work of technicians in the digs, and above all, ensure a more reliable management of SCC related threats in pipelines.
Stress corrosion cracking (SCC) is a failure mechanism that occurs in susceptible materials exposed to a corrosive environment and submitted to tensile stress above a certain threshold. In the presence of these combined factors, SCC can occur and potentially lead to the failure of an asset. This failure mechanism has been widely reported in several susceptible alloys of carbon steel, making SCC a considerable threat for pipelines in contact with corrosive soil. The cracking initially takes the form of localized clusters of fine and shallow cracks on the external surface of the pipe, with most of the surface left unaffected (Figure 1). These colonies of cracks are typically oriented with the axis of the pipe, perpendicular to the hoop stress. However, transverse SCC can also occur from transverse stresses caused by construction misalignment or various geotechnical factors such as dents or ground movement1,2. If not identified and repaired quickly, these cracks can expand and interlink with each other, eventually forming long and deep cracks that will force operators to lower the operating pressure of the pipeline. This will lead inevitably to a lower productivity of the asset and higher environmental risk.
