Damage progression effect in subsea pipelines under trawl gear impact

Davaripour, Farhad (2020) Damage progression effect in subsea pipelines under trawl gear impact. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The structural behaviour of pipelines is considerably dependent on the loading condition. The common industry practice for the assessment of a pipeline against an accidental event is to design the pipe against an interference load applied laterally and in the perpendicular direction. As such, the potential plastic damage is imposed at only one location and normal to the pipeline. However, there are accidental scenarios where the resulting damage could progress along the pipe. In this regard, recent studies showed a potential significant drop in the structural resistance of a plate when the interaction between the plate and the indenter translates the resulting plastic damage along the structure. As such, it is reasonable to investigate the potential similar considerable effect of damage progression for pipelines. Accordingly, a series of physical tests using a novel test apparatus was employed in the present thesis to identify, introduce, and investigate the damage progression effect in pipes. The investigation was conducted with the focus on the interference between the bottom trawl gear and subsea pipelines. The test results showed that the structural resistance of a pipe could drop significantly, where the plastic damage imposed on a pipe is translated and induced longitudinally along the pipe. Furthermore, using numerical simulations, the importance of the damage progression effect on the mechanical behaviour of subsea pipelines subject to diagonal trawl impact or subsequent trawl impact was demonstrated. In conclusion, the present thesis introduced and investigated a new mechanical behaviour in subsea pipelines, which should be considered in the assessment of failure limit states in pipes, against the bottom trawl impact or any accidental events where the progression of plastic damage along the pipe is likely.

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