Characterization of Tensile and Fracture Properties of X52 Steel Pipes and Their Girth Welds

• Author / Creator

  Lin, Meng

• Enbridge vintage Norman Wells Pipeline made of X52 steels has transported crude oil from Norman Wells, Northwest Territories (NWT) to Zama, Alberta since 1985. It is the first fully buried pipeline that traverses permafrost regions in Canada, and is often subjected to adverse geotechnical conditions. It is significant to investigate the resistance of the buried X52 steel pipeline in response to the imposed substantial stresses and strains caused by impacts and displacements from geotechnical instability.

  In this thesis, tensile and fracture properties of X52 steel pipes and their girth welds are determined by small scale material tests. An original girth weld which was manufactured in 1980s and a new girth weld which was manufactured in 2013 are both studied and their material properties compared to the corresponding heat-affected zones and the pipe base metal. Tension tests are conducted to obtain stress-strain curves and determine the tensile properties of X52 pipe. The strain-hardening region of the true stress-strain curve is characterized into the empirical mathematical expressions otherwise known as the Hollomon equation and the Ramberg-Osgood equation. The stress-strain curve of X52 steel pipe is compared to curves obtained from higher grades of steel pipes and the comparison between the ductility of X52 steel pipe and other grades is discussed. Charpy V-notch impact tests are conducted to measure the energy required to fracture a V-notched specimen and determine the fracture properties of the pipe material. The decrease of the test temperature reduces the impact toughness and increases the probability of brittle fracture. The empirical correlation between the test CVN energy and the fracture toughness of X52 pipe is emphasized. Based on the test results, the tensile strain capacity of X52 pipe is predicted according to the empirical equation provided by CSA Z662-11. While the tensile strain capacity equations were developed based on tests conducted on higher grades of steel, the results of this work allowed the use of these equations to predict the amount of reduction of tensile strain capacity due to the presence of girth weld defects.

• Subjects / Keywords

  • Charpy V-notch impact test
  • X52 Steel
  • Norman Wells pipeline
  • Stress-strain curve

• Graduation date

  Spring 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3X05XM68

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.