Year

2015

Degree Name

Doctor of Philosophy

Department

School of Mechanical, Materials and Mechatronic

Abstract

The current research focuses on two problems: 1) How to improve brittle fracture propagation control for small diameter gas pipelines by investigating the difficulties or dilemmas encountered with DWTT; 2) How to improve the arrest toughness prediction for ductile fracture control of small diameter gas pipelines by investigating the Charpy specimen thickness effect on absorbed energy. Both experimental and numerical works are carried out to solve the current dilemma. Based on the investigation outcomes, recommendations on the improvement of current pipeline fracture control approaches are made to ensure a safe operation of the small diameter gas pipelines.

The findings demonstrate that the Charpy test is no longer suitable for transition temperature prediction, especially in small-diameter, thin-walled pipes, where various sub-size Charpy specimens could create more uncertainties. DWTT is essential for predicting the transition temperatures of small-diameter line pipes. Flattened DWTT specimens with reinforcement plates successfully minimise buckling and deliver more accurate transition temperature predictions compared to the results of full-scale tests. A new method to determine the FPTT by starting the DWTT from lower shelf is also proposed which needs to be further validated. As for ductile propagation control, the linear CVN absorbed energy/thickness relationship is replaced by an exponential relationship to improve the BTCM predictions for hightoughness line pipe steels.

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