A 30-inch subsea pipeline owned by a TWI industrial Member was dented by the anchor of a tanker in the North Sea. There was an urgent need to know if the dented pipe was fit for continued service until a full repair could be carried out. TWI was called in to help with the assessment.
Engineering Critical Assessments (ECA's) were carried with respect to fracture, plastic collapse and fatigue. Stresses in the dented region were estimated from finite element analyses and provided along with material data to TWI for the ECA. The analyses were based on postulated flaw sizes and the reported geometry of the pipe dent.
TWI analyses showed that the pipe was fit-for-service despite the elevation of stresses due to the dent. The fatigue analyses also confirmed that there was a significant time window for continued safe operation before a repair was needed. For operational reasons, the project had to be completed urgently over the Christmas and New Year holiday. The work was successfully carried out and enabled the client to take appropriate maintenance decisions.
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