Recent Developments on Welding, NDT and ECA of Clad and Lined Offshore Pipelines

Abstract

Abstract Due to the level of contaminants of Brazilian pre-salt fields, alloy 625, e.g. UNS N06625, clad or lined steel linepipes have been chosen in order to resist such environmental conditions. Recent advances on welding, non-destructive testing (NDT) and Engineering Critical Assessment (ECA) approaches for bimetallic materials have significantly changed since discussed in OMAE-2012. Regarding welding of alloy 625 clad and lined pipes, maximum welding interpass temperature, back purge gas control, root discoloration, visual inspection, root profile for fatigue performance and other issues are discussed herein. The Fatigue Crack Growth Rate (FCGR) to be adopted for alloy 625 is still one of the issues, since curves for alloy 625 in specific environment are normally not available. New appendix C of DNVGL-RP-F108 gives orientations regarding how to conduct tests in sour environment. DNVGL JIP on clad and lined material has made an extensive approaching of the undermatching condition of alloy 625 weld metal under different design strain levels. Regarding NDT, developments and improvements in Automated Ultrasonic Testing (AUT) methods have been obtained for inspection of Corrosion Resistant Alloy (CRA) girth welds and weld overlay. Film and digital radiography are still used for the inspection of the pipe end of the mechanically lined pipe, but ultrasonic solutions are under development. Welding and NDT challenges of alloy 625 reported in 2012 have been overcame by state-of-art technologies used in offshore rigid risers construction and installation. Alternative CRA materials are under research and development, but alloy 625 still is the most reliable option.