Erha and Erha North Development: Automatic Ultrasonic Inspection of Corrosion-Resistant Alloy Clad Steel Catenary Risers

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Erha and Erha North Project utilizes a steel catenary riser (SCR) system to connect the floating production, storage, and offloading vessel (FPSO) to the subsea infrastructure. The system is a hybrid, composed of both steel and clad corrosionresistant alloy (CRA) pipe, with the CRA clad pipes located in the touch-down and hang-off areas of the SCRs. The CRA clad pipe sections are required to obtain satisfactory fatigue life due to the presence of CO 2 and potential H 2 S in the production stream. In total, four production and two test lines were required, with a total of 1,120 m of CRA clad pipe installed.Ultrasonic inspection of the welds joining the CRA clad pipes proved to be technically challenging due to the bimetallic features of the weldment and the small flaw size allowable for this fatigue-dominant application. Further complicating this effort was the need for reliable flaw detection on a real-time basis to maintain the pipelay rate. To meet these challenges, Shaw Pipeline Services (SPS) was enlisted to develop an automatic ultrasonic testing (AUT) system capable of reliable inspection of the weldments. This paper discusses the AUT system qualification program, product implementation, and lessons learned. Included in these discussions are technological challenges and respective approaches for metallurgically bonded and weld overlaid clad girth weld ultrasonic inspection, as well as detailed sizing accuracy data on seeded (i.e., intentionally planted) defects during the qualification stage and sizing accuracy data on production welds with naturally occurring flaws.