Assessment of Pipeline Integrity after Trawling Impact by Investigating Dent with Gouge

Abstract

Mechanical damage from trawling gear interference amongst others cause a significant amount of damage to pipelines. The present study has done a review of current standards and recommended practise for assessment methods for unconstrained plain dent with gouge. A test method was developed to investigate stress concentration factor and fatigue life of the combined damage with plain dent and gouge. Three different indenter shapes was created and indented four dents on two welded round precision tubes (E235+CR1) with a diameter/thickness ratio of 51. Three of them also contained a gouge. After dent- ing, strain gauges was applied. The pipe samples was then pressurized to evaluate stress concentration factor (SCF).

A numerical model was created according to the experiment. The numerical model was consistent with the indention process, showing good results when comparing numerical and experimental results. The 3D acquisition tool Autodesk 123D Catch proved to be a good and efficient method to scan the pipe samples in order to create a three dimensional (3D) model. Numerical model predicted rerounding and dent depth at a satisfactory man- ner. Furthermore when comparing the strain gauges with numerical work with regards to SCF the model did not produce valid results. The strain gauges was located were the high- est values for strain was expected to be, however it was shown that there might be locations with higher strains and the initially assumptions was mistaken. Therefore the numerical model needs improvement when investigating SCF and fatigue life.