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Offshore pipelines are occasionally subjected to accidental impact loads from trawl gear or anchors, which may damage the pipe. In this study, a series of indentation experiments carried out on offshore steel pipes covered by a multi-layer polymeric coating solution is presented. Polymeric coating solutions are often applied to pipelines to act as corrosion protection and thermal insulation. Despite not being designed for it, the polymeric coatings are experienced to have an energy absorbing capacity, which is the main topic of the investigation herein. In design codes and guidelines, coatings are traditionally not accounted for when determining the energy absorbed by a pipeline during impact. This makes estimates overly conservative. The main goal of this experimental work is thus to investigate the contribution a typical polymeric coating makes to the energy absorption in a pipeline during impact. To this end, a series of indentation experiments carried out on offshore steel pipes covered by a multi-layer polymeric coating solution is performed. The test program includes quasi-static and dynamic denting experiments on both coated and uncoated full-scale pipe cross-sections. All pipes tested have a length of approximately 1 m. The sharpest indenter from the relevant guidelines is used, as a sharp indenter is more likely to penetrate the coating compared with a blunter one. Based on the outcome of the tests, the polymeric coating is found to absorb a considerable amount of the kinetic energy delivered by an impacting object.

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Offshore pipelines subjected to accidental impact loads from trawl gear or anchors may experience large global deformations and large local strains, creating a complex stress and strain history. In this study experiments and numerical simulations have been carried out to investigate the impact of a pipeline which is subsequently hooked and released. Material and component tests have been performed to investigate the behaviour during impact, and to observe if/when fracture occurs. The pipes were first impacted in a pendulum accelerator at varying velocities before they were pulled straight in a tension machine. Fracture was found in the impacted area of all the pipes during straightening. Material tests were done to determine the characteristics of the X65 grade steel. Numerical simulations showed excellent compliance with the impact phase, while the load level in the stretching phase was a bit overestimated.

Offshore pipelines are frequently subjected to accidental impact loads, e.g. from anchors or trawl gear. A lot of parameters -including the pipe geometry, material properties, pipeline content, impact velocity, etc. -influence the course of such an impact. Some of these parameters have been studied quite extensively while others not so much. This study presents material and component tests on specimens taken from an X65 offshore pipeline.

Abstract. Anchors or trawl gear occasionally impact offshore pipelines, resulting in large local and global deformations. Impact velocities are typically less than 5 m/s, but local strain rates may be very high. In this study strain rate effects in an X65 offshore material was characterised by split Hopkinson bar tests, while the cross-section homogeneity and possible anisotropic behaviour were determined by quasi-static material tests. Further, dynamic impact tests at prescribed velocities were carried out on simply supported full scale X65 steel pipes. Next, deformation-controlled quasi-static tests with the same boundary conditions were conducted. The level of deformation in the quasi-static tests were set to be equal to what was attained in the dynamic tests. Finally, an assessment of the differences between the dynamically and quasi-statically loaded pipes was made in terms of force-displacement response, energy absorbed, and fracture. An optical light microscope and a scanning electron microscope were used to investigate fracture surfaces arising from the various tests.