Failure prevention of seafloor composite pipelines using enhanced strain-based design

Abstract Steel pipes are widely used in offshore structures and buried seafloor pipelines. Buried single-wall pipelines or piles of fixed offshore platforms crossing the earthquake fault can experience very large displacement, which could cause considerable damages or failures to the pipes. The elevated strains induced in pipelines from welding connection between the pipes also can drastically reduce the pipe’s performance. Therefore, to prevent these types of damages and failures, this research used an enhanced strain-based design method along with finite element analysis, developed bonded and unbonded double-wall composite pipes, which were in replacement of the single-wall ones, and studied the effects of welding on the double-wall composite pipeline in terms of wrinkles, ovalization, stresses, and strain. Here, the double-wall annulus of the pipelines was grouted with polymer. Extensive experiments were performed with displacement loads being applied to the pipelines in clay and in air and the results were analyzed. It was found that using an enhanced strain-based design method, failures in the pipelines could be significantly reduced or possibly even eliminated. This work would also potentially lead to a new area of research in the oil and gas industries since the elevated strains induced in pipelines due to weld could lead to several modes of failure. In addition, this research found some significant impacts in terms of safety due to the bond between steel and polymer and weld imperfection in the pipelines.