PSI - Issue 22

Yaorong Feng et al. / Procedia Structural Integrity 22 (2019) 219–228 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Keywords: fracture control; crack initiation; crack arrest toughness; full-scale burst test; X80 steel pipe; gas pipeline

1. Introduction With the large number of oil and gas pipeline laying and long-term operation, pipeline accidents occur from time to time, resulting in huge losses and effects (Jiahua Pan, 1989; Starostin V., 1990; Ba Yang et al., 1995; Xuemei Lin., 1998). The fracture control of pipeline is an important measure to ensure the safety of pipeline operation. Because of the steel pipe manufacturing and construction and other reasons, as well as the pipeline in the long-term service condition may produce defects and damage, greatly increase the possibility of crack initiation. In the oil and gas pipeline, especially in the gas pipeline, when crack initiation, the crack enters the base material at a higher speed, this rapidly propagating crack may cause catastrophic damage, so it not only requires the pipe to have good crack initiation resistance, but also requires that the natural gas pipeline base material must have sufficient ability to prevent the rapid propagation of the crack. Charpy impact toughness is a traditional test method for evaluating material toughness. Although it can not correspond strictly to fracture mechanics parameters, it has been widely used in the evaluation of preventing brittle failure or ductile crack growth of structures due to its simplicity and ease of operation and large amount of data accumulation. In the research of natural gas pipeline fracture, people have been trying to find a suitable value to make the pipeline have enough ability to prevent crack initiation or crack propagation. Since the 1970s, a great deal of research has been done on crack arrest of ductile fracture of pipelines in the world (AGA, 1971; Maxey, et al., 1971; Eiber, et al., 1974; Bonomo, et al., 1980; Hansen, 1981; Holmes, et al., 1983; Vogt, et al., 1984; Jones, et al., 1984; Koch, 1986; John,1997; Sugie, et al., 1982). Through theoretical analysis, laboratory tests and full-scale burst tests, the prediction formulas of crack arrest toughness of steel pipes (such as Battelle formula) have been put forward. The typical formulas are as follows: C V =a σ H b R c t d . It can be seen that the toughness required for crack arrest C V is related to the hoop stress σ H , radius R , wall thickness t and other factors (a, b, c, d are constant). These formulas have been widely used in predicting crack arrest toughness of pipelines. The results show that the hyperbolic method and the prediction model and formula of crack arrest toughness proposed by Battelle in the early stage are no longer applicable to high toughness pipes (>94J). Kanninen et al., (1992), Leis and Eiber (1998), Wilkowski (1998), Rothwell (2000), Pussegoda et al., (2000) have done valuable work, aiming at the unsafe prediction of fracture toughness value of high-pressure natural gas pipelines by existing empirical formulas, which provides an important reference for fracture control of high-pressure gas pipelines. The 2 nd WEGP is the first major pipeline project in China to introduce natural gas from abroad, and it is the longest and largest natural gas pipeline in the world. The main gas source is imported natural gas from Central Asia, and the regulated gas source is domestic natural gas from Tarim Basin and Ordos Basin. The main target market of the project is South China, which was not covered by the 1 nd WEGP, and the market of North China and East China is taken into account through branch lines. The project includes one trunk line and eight branches. The pipeline starts at the first station of Horgos, Xinjiang, and passes through 15 provinces and municipalities throughout the country, ending in Hong Kong. The total length of the project is about 9000 kilometers. Among them, the length of the main line from Horgos to Guangzhou is about 4900 kilometers. The gas transmission capacity of the project is 30 billion cubic meters per year. The 2 nd WEGP started in February 2008 and was completed and put into operation in December 2012, has been safely operated until now. The 2 nd WEGP in China diameter is large (maximum pipe diameter 1219mm), high pressure (the highest design pressure 12MPa), the main line of a large number of X80-class steel pipe, gas source and pipeline along the geological situation is complex. In order to ensure the safe and reliable operation of pipeline in the long term, on the basis of analyzing and studying the results of international gas pipeline fracture control, the fracture control scheme and fracture toughness requirement of pipeline was put forward through systematic theory analysis and experimental research and full-scale gas burst test.