Development of an Ultrasonic ILI Tool for the Assessment of Crack-Type Anomalies in Ammonia-Carrying Pipelines

Abstract The in-line inspection (ILI) of pipelines used to transport anhydrous ammonia is challenging since several components that make up a typical ILI tool used for the inspection of oil and gas pipelines are not compatible with the anhydrous ammonia. Magnetic Flux Leakage (MFL) and Deformation (DEF) tools have been developed in the past to assess anhydrous ammonia pipelines for corrosion and deformation anomalies. However, assessing for crack-type anomalies has never been possible as no ammonia-compatible ultrasonic ILI tool has been developed. Feasibility studies have in the past been undertaken to address this problem but so far none of these investigations has resulted in a successful ultrasonic ILI tool build for inspection of ammonia carrying lines. As a result, the operators of these pipelines have been conducting ultrasonic ILI inspections using water to navigate the tool through the line during a hydrotest. This process is not only expensive, but it also causes months of interruptions in flow due to repairs and other factors related to the procedure. The opportunity to be able to conduct ultrasonic (crack) ILI inspections during the normal operation of this ammonia pipeline system would result in a significant cost saving for the client. The paper will report on the findings of the project undertaken by NDT Global on behalf of NuStar Energy to investigate options for an ultrasonic ILI tool capable of detecting and sizing axial cracks, in particular fields of stress corrosion cracks (SCC), in ammonia-carrying pipelines. A description of the tool qualification and verification procedures will also be outlined.