Sulphide stress cracking and preferential weld corrosion performance of welds between modified A707 and C-Mn SCR pipe
Status: Completed
Date Announced: June, 2006
Project reference: 17797
Background
Tapered Stress Joints (TSJs) of steel catenary risers (SCRs), jumpers etc are often specified in modified grades of ASTM A707 material, which contain appreciable levels of Ni. During service it is known that over time wells can become sour and there is currently a large programme of work in progress within the industry addressing the performance of SCRs under mildly sour corrosion fatigue conditions (eg TWI project 14135). There are no sulphide stress cracking (SSC) or preferential weldment corrosion (PWC) data relating to the SCR/TSJ weldment, particularly with respect to the modified A707 materials. Currently there is a limitation on the nickel content of steels of 1% maximum stipulated in ISO15156-2:2003/MR0175-2003 for sour conditions, but no guidance is given for less severe conditions. Hence, there is uncertainty with respect to the suitability for mildly sour service of such joints. In addition, the dissimilar materials in the welded joint raise concern that preferential weldment corrosion could occur in service. The following describes work that addresses these issues by carrying out SSC testing in a mild sour condition and PWC tests in a sweet condition on A707 Grades 1 and 3 welded to C-Mn steel specimens.
Objective
The SSC and PWC behavior of specimens manufactured from modified ASTM A707 grade steels welded to C-Mn SCR pipe material in simulated Gulf of Mexico conditions is determined.
Participants
BHP Billiton Petroleum (Americas) Inc
Chevron Energy Technology Company
RTI Energy Systems
Shell International Exploration & Production Inc