Stress analysis and stress intensity factor computation of DNV X65 pipes subjected to four point bending

• Main Author: Lee, Shaun Raphael Kwok Yuen
• Other Authors: Pang Hock Lye, John
• Format: Final Year Project
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering::Aeronautical engineering
• Online Access: http://hdl.handle.net/10356/72091
• Institution: Nanyang Technological University

With improving modern day technology and profit driven oil and gas industries, the oil and gas pipeline network are on rapid expansion, and it is likely to see a continuing trend in the coming years. The upside of these high-pressure pipelines that are buried deep underground is the volume that it carries yearly and the design for safety in transportation compared to rail and road tanks. In spite of the high standards and regulations in place to ensure safe and secure pipelines, oil pipeline spills still amount to about a gallon per million barrel-miles, a figure drawn from the USA Association of Oil pipelines. Failures have occurred for the many reasons ranging from intrinsic defects in the materials, inadequacies in design and lack of structural maintenance [1], often resulting in catastrophic aftermaths - disruptive costs in cleaning and environmental pollution. This calls for concern in finding the quantitative relations between the crack length and the tendency of failure, which leads to the study of fracture mechanics, a vital specialization within the field of solid mechanics. The primary objective of fracture mechanics is to characterize local deformation around a crack tip of a material. In this current work, finite-element based on a parametric study of four-point bending is used to assess the stress intensities of deep surface cracks, while considering local limit load the remaining load bearing ligament. As current advice from empirical expressions derived from British Standards BS7910 and R6/FITNET may prove to be overly conservative, they will be regarded as basis for comparison for limit load solutions defined by finite element analysis. The ambiguity of limit load solutions and reference stresses from current standards will be addressed in this report as well. Proposed solution by Baik-Yamada for the shifting in neutral axis as a result of changing area of remaining load bearing ligament is also compared with finite element results. Finally, the failure assessment diagram of the specimens are computed using limit load solutions derived from finite-element work.