Stress intensity factor analysis for offshore pipelines with interacting surface cracks

• Main Author: Mok, Darren Wei Xun
• Other Authors: Xiao Zhongmin
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/149795
• Institution: Nanyang Technological University

Offshore Pipelines are commonly used to transport extracted oil and gas resources back to land from the sea. Carbon Steels are one of the most widely used material to make the pipes and these pipes can be as long as hundreds of kilometers and can be located in depths of oceans around 2000m. These pipes are constructed manually by welding together many similar shorter pipes and then being laid underwater using various laying techniques. During the construction and laying process, defects such as cracks, voids, porosity etc. are bound to occur due to the presence of high thermal and bending stresses. The presence of such defects will lead to a shortened lifespan of the pipes and threatens the structural integrity of the pipe. This may eventually lead to the fracture of the pipe. However, some defects like cracks may eventually propagate faster than expected as these cracks are able to interact with other cracks and start to coalesce. This is particularly dangerous as the effects of interacting cracks do shorten the lifespan of the pipe more significantly as when compared to cracks who do not interact and coalesce together. The purpose of this report is to investigate the impact of interacting surface cracks on the lifespan of a Carbon Steel offshore pipe. Computational simulations have been carried out using a Finite Element Software Package, ANSYS Workbench 19.2 on a pipeline containing interacting cracks. This study concentrates on how the distance between the two interacting cracks will eventually lead to a higher stress intensity factor and reduce the lifespan of a pipe.