Failure investigation and prevention for off-shore pipes with internal pressure

• Main Author: Ng, Peiqi.
• Other Authors: Xiao Zhongmin
• Format: Final Year Project
• Language: English
• Published: 2011
• Subjects: DRNTU::Engineering::Mechanical engineering::Mechanics and dynamics
• Online Access: http://hdl.handle.net/10356/45708
• Institution: Nanyang Technological University

Pipes are classified as one of the safest and convenient mode of transportation for flammable liquid and hazardous gases. Fatigue cracks are commonly identified in the welded region of the pipes, regardless of its application. Even with an insignificant crack, its presence may cause a huge reduction in the capability of the materials during application. With the rapid technological advancement in material assessment, more advanced non-destructive testing (NDT) and crack assessment protocols have been proposed for pipe inspection. However, some crack assessment protocols are proven to be too restrained and it should be given leeway to compromise on its minimum recommended fracture toughness. Overly restricted protocols may impose difficulties. The objective of the project is to perform comprehensive investigation on the fatigue crack within the welded region of the pipe. With the use of finite element software, ABAQUS, detailed solid finite element analysis are conducted to study the crack initiation and crack propagation. This project attempts to identify and analyse the simulated crack growth of both embedded and surface cracks for different crack depth are obtained. Crack tip opening displacement is employed and crack growth is accounted for. Relationship between the crack tip opening displacement, ratio of half crack height to half crack length b/a, and crack depth are also established and examined in the report. The effect of circumferential crack growth with biaxial loading and tensile loading are also presented in the report. The results of solid finite element analysis are compared with failure assessment diagram BS7910 for verification of the minimum recommended fracture toughness. A user-friendly approach of strain based failure assessment is proposed.