Abstract
Corrosion-resistant alloy (CRA) mechanically lined pipes (MLPs) have long been known as a cost-reduction alternative compared to CRA-clad (metallurgically bonded) pipes. Additional advantages also exist, including improved fit-up and installability, a wider choice of CRA materials, pipe dimensions and a lower carbon footprint. MLPs provide at least the same corrosion resistance as the CRA-clad pipes; however, as the liner is not metallurgically bonded to the carbon steel outer pipe, there is an additional failure mechanism of liner buckling during installation or strain associated with lateral buckling. Despite this, MLPs have been successfully installed in the subsea by reeling on several projects and many are currently in service without concerns. For any submarine pipeline, fatigue damage may be accrued from the loads incurred by fabrication, transportation, installation, pipeline spanning, thermal cyclic loading, instability, and interference loads such as fishing. As such, fatigue cracking can occur at both the girth weld and the triple point. Currently, the triple point is not classified in the fatigue design of many standards and there is limited data in the literature regarding the fatigue performance of the triple point. In this paper, full-scale bending testing was conducted on a 273.1 mm outside diameter MLP before a full-scale fatigue resonance testing. The full-scale bending testing was undertaken to replicate the through-life stresses experienced by the triple point, whereas the full-scale fatigue resonance testing was undertaken to understand the fatigue performance of the triple point. A periodic inspection of the liner was also performed during the full-scale fatigue testing as there is always a concern that the liner might crack before the back steel.
