Deformasjon av trykksatte rørledninger

Abstract

Offshore pipelines may be subjected to impact by anchor and trawl gear. An anchor impact will drag the pipeline out of its position, before it is released and the pipe straightens, due to the rebound and large axialforces. Damage and fracture may occur due to the highly complex stress and strain history in the pipe.This thesis is a continuation of work carried out in previous master theses on the subject and a part of an ongoing research program at SIMLab (NTNU) and Statoil ASA.Three pipes were deformed quasi-statically with different horizontal loads applied in the stretch bending rig at SIMLab. A deformation rate of 25 mm/min was applied. A visual inspection after bending could not reveal any cracks.An isotropic hardening material model was used as input for the numerical simulations in Abaqus/Explicit by the use of the SIMLab Material Model. A very good fit in the global response could be seen when comparing the numerical simulations with the corresponding experiments. When checking the strain evolution for the critical elements, a plastic hinge could be seen. It could also be seen that the largest strains were smaller in pipes with horizontal load compared to pipes without horizontal load.Digital Image Correlation was utilized to validate the numerical simulations, by comparing strains close to the indentation zone. This gave a reasonably well compliance.