2015 CSCE Annual Conference Regina - Building on our Growth Opportunities

2015 CSCE Annual Conference Regina - Building on our Growth Opportunities Conference


Title
The effect of circumferential flaws on the strain capacity of pressurized X52 pipelines


Author(s)
Ms. Diana Abdulhameed, University of Alberta (Presenter)
Mr. Celal Cakiroglu, University of Alberta
Mr. Millan Sen, Enbridge Pipelines
Dr. John Nychka, University of Alberta
Dr. Jung-June Roger Cheng, University of Alberta
Dr. Samer Adeeb, University of Alberta
Abstract

Tensile strain capacity (TSC) of pipelines with girth weld flaws have been traditionally measured experimentally using wide plate tests. However, Numerical analysis in recent studies showed that the TSC are affected by the level of internal pressure inside the pipeline, Y.Wang (2008). Most of the past studies focused on the effect of circumferential flaws on the TSC for pipelines of steel grade X65 or higher. The current Oil and Gas Pipeline System Code CSA Z662-11 provide equations to predict the critical TSC as a function of geometry and material properties of the pipelines. These equations were based on extensive studies on pipes having grades X65 or higher without considering the effect of internal pressure which makes it beneficial to be investigated. In this study, eight full-scale experimental tests of NPS 12" pipes with 6.91 mm wall thickness and grade X52 were conducted in order to investigate the effect of circumferential flaws close to a girth weld on the TSC for vintage pipelines subjected to eccentric tensile forces and internal pressure. A digital image correlation system and biaxial strain gauges were used to obtain the tensile strain along the pipe length during the test. Post-failure macro-fractography analysis was used to confirm the original size of the machined flaw and to identify areas of plastic deformation and brittle/ductile fracture surfaces. From the experimental and numerical results, the effect of internal pressure and flaw size on the TSC was investigated. The CMOD at failure for different pipes were compared.