Simulation on the weld crack growth in the surface of oil/gas pipes by using a magnetic-structural coupling algorithm

Oil/gas pipes in petroleum industry are working in a complex environment. weld crack in the surface of pipes is one of the major causes for pipe failure. Quick crack growth under the pressure of the liquid in pipe has been reported as the root cause for many catastrophic accidents. It is therefore important to study key scientific issues associated with in-service detection of crack growth at pipe weld. By using virtual crack closure technique (VCCT), this dissertation discusses the impact of micro-crack growth at different welds, builds a magnetic-structural model for pipe welds with consideration of crack size and renewal of node coordinates (mesh reconstruction), makes repeated crack growth computation and magnetic field analysis and, thereby, proposes a magnetic-structural coupling algorithm. From the numerical analysis based on this algorithm, we are able to identify the position of a weld crack as well as to judge whether the crack will grow or not and growth process according to four eigenvalues (crack width, crack length and the peaks of horizontal and vertical components of the magnetic induction intensity) that are used to describe the crack growth, thus determine the damage degree of the pipeline weld. The algorithm offers a theoretical reference for the magnetic flux leakage (MFL) based detection and assessment of weld cracks of in-service pipes.