AbstractSubsea pipelines are subjected to external damage by fishing trawlers or dragged anchors which may result in a pipe defect such as a puncture, dent, gouge, crack or a combination of such defects (Allouti et al., 2014). Therefore, evaluation of these defects is very important in terms of assessment and for continued safe operation. The present study is a review of the current codes, standards and recommended practise for assessment methods for dent and crack defect. Cracks present coincidentally with dents, represents a new hybrid defect in pipelines that are not acceptable in the existing codes and standards. At present, there are different assessment methods for different types of defects in pipelines.In this work, the current defect assessment methods for predicting the fatigue life of pipe dents and dents with crack are reviewed. The aim of this study is to evaluate the effect of dent with crack defects on the fatigue life of natural gas transmission pipelines. In order to illustrate the effect of a crack on the dented pipe, this study is divided into two parts. The first part is to study on the effect of dents alone on the fatigue life of the material, while the second part is to study on the effect of dents and crack on the fatigue life. Therefore, a parametric study using finite element numerical models was conducted to study the effect of plain dent and dent with crack on the fatigue life of the pipeline.To understand the failure response of these defects, this paper presents finite element analysis on a parametric range of various defect parameters to assess the fatigue life of in a pipe grade API 5L Gr. X-65 having a diameter of 323.85 mm and 5.397 mm wall thickness. The study focuses on the effects of pipe geometry, dent geometry, presence of crack, crack depth crack orientation and pressure fluctuations on the of the fatigue life behaviour. a Bar shape indenter was used to simulate longitudinal dents. A pipe dent models with Various dent depths ranging from 2% to 12% of the pipe wall thickness were also simulated to investigate the effect of dent geometry. Moreover, models for dent and crack defects with three different crack depths ranging from 10% to 40% of wall thickness were analysed to investigate the effect of crack size and geometry. Pressure fluctuations were also investigated and were ranging from 0n to 80% SMYS to investigate the effect of pressure variation.This paper discusses the results obtained from the finite element numerical models and the parametric study with the conclusions drawn.Keywords: Pipeline, Dents, Dent-crack defect, Crack depth, Fatigue life, SCF

Fatigue Assessment of Pipelines With Dent and Crack Subjected to Cyclic Pressure Loading

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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