Introduction

When a pipeline is laid on the seabed and heated, it will tend to expand. The expansion is resisted by the friction generated by the seabed. When the pipeline is cooled, it contracts but the effects of seabed friction mean that the pipeline ends cannot contract to the original position. On subsequent heatup and shutdown cycles, the pipeline ends cycle between the fully heated position and the cool-down position; this behavior is addressed in the traditional approach to pipeline expansion design.

However, in some cases thermal cycling can be accompanied by global axial movement of the pipeline; this global translation of the whole pipeline is termed pipeline walking. Over a number of start-up and shutdown cycles walking can lead to significant global displacement of the pipeline. Walking itself is not a limit state, but without careful consideration can lead to:

Walking is a phenomenon that can occur in short, high temperature pipelines. The term 'short'relates to pipelines that do not reach full constraint in the middle, but instead expand about a virtual anchor point located at the middle of the pipeline. Walking involves a global axial movement which occurs on cyclic load and does not reduce with the number of cycles.

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KW Ltd
Pipeline Walking
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Related Subjects

Pipeline Expansion

Cyclic Assessment

 

Pipeline Walking

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