An Operator’s Experience of Managing the Threat of Axial SCC

Abstract Stress Corrosion Cracking (SCC) is one of the three time-dependent integrity threats classified under ASME B31.8S for managing system integrity of Natural Gas (NG) transmission pipelines. The experience of Enbridge Inc. and its affiliates (for purposes of this paper, collectively, “Enbridge”) of managing axial SCC threat through the Electromagnetic Acoustic Transducer (EMAT) In-line Inspection (ILI) program is discussed in this paper. Enbridge has run more than 9000 miles of EMAT tool in its US and Canadian transmission pipelines, of which significant mileage is baseline runs and subsequently recent mileage for reinspection. Overall tool performance is discussed for both baseline and reruns from the perspective of initial EMAT callouts and subsequent in-the ditch validation of EMAT features. Both high pH and near neutral pH SCC, confirmed in the ditch, and subsequent metallurgical laboratory assessment, has been discussed for Enbridge’s US and Canadian assets. Tool performance has been discussed leveraging Enbridge’s vast mileage of EMAT data using API 1163 unity plot methodology comparing tool called features and in-the-ditch and laboratory validation data. Finally, Enbridge’s Bellhole inspection and repair protocol has been discussed specific to EMAT related digs for managing the Axial SCC threat.