Safety in oil and gas pipeline operations is achieved when the flaws present in pipeline members do not propagate beyond their critical size. The knowledge of pipeline flaws behaviour in the process of pipeline testing and operation is very important for well-grounded flaw acceptance regulations, selection of testing parameters and pipeline diagnostics rules. This paper offers an analysis of pipeline failure formation caused various flaws in the process of pipeline testing and operation at different loading rates. Some data are given about the influence of individual pipeline testing parameters such as the pressure value, the period of loading, the loading cycle) upon the flaw propagation kinetics.
Oil and gas pipeline failures are of different nature. They are explained by a number of causes and have various consequences. As a rule, in spite of all these differences, the breakdown starts from the failure of some individual pipeline member: the pipe, some structural components or a weld joint. The analysis of the causes and mechanizms of pipeline member failures shows that the process of breakdown starts primarily from planar surface flaws and it is a process which develops in time [Chaburkin. 1990]. One can detect three stages of breakdown: the growth of the crack from the flaw to a througth-1thickness growth; the growth of the through-thickness crack up to a critical-size flaw; and a supercritical propagation of the flaw. The formation of a through-thickness crack violates the leak-proofness of the pipeline and causes transported product. particularly feasible a leakage However, in many of the it is not cases to immediately stop the pipeline and repair it. Depending on the nature of the transported product and the danger of its escape, the leakage can be prevented by using a water-tight seal, while the pipeline is actually operating for some time with a through-thickness crack.
