Full Scale Fatigue Testing of Fatigue Enhanced Girth Welds in Clad Pipe for SCRs Installed by Reeling

Abstract

H2S is reported to degrade the fatigue properties of C-Mn steels with a factor of 10–20 in life, while clad pipes are reported to have a performance close to or as good as in air. Clad pipes could therefore be used in highly fatigue loaded parts of the riser to facilitate design of steel catenary risers (SCRs) that are connected to floaters in deep waters. A literature survey of high quality girth welds intended for SCR is included in this paper and compared with fatigue test data obtained in this project. The first nine full scale 15" clad pipe girth welds out of a program of 24 specimens are fatigue tested in a high frequency resonance test rig and reported. The pipes were tested as welded, hammer-peened and reeled. The 15" OD steel pipes with 316 cladding tested in this work were surplus pipes from the Norne pipeline project. The fatigue test pipes were fabricated using the same welding procedure and welding facilities at Technip’s spool base in Orkanger, Norway, as the Norne pipeline project. The Norne pipeline is the world’s first reeled clad pipeline. The objective of this work was to test premium quality girth welds with best possible fatigue performance in actual pipes under realistic conditions was. The effect of hammer-peening of the OD was therefore investigated. Post failure examination was performed to determine the type and size of defects at the fatigue crack initiation site.