A comparison of experimental results and computations for cracked tubes subjected to internal pressure

A cylindrical pipe that is used for gas transportation is mainly submitted to stresses originating from internal pressure. Other stresses are due to weight and the unexpected movements of supports and/or the ground. The first give rise to circumferential stresses, the second to longitudinal bending stresses. Here, we study the case of pipes that are joined by welding. This weld is an eventual source of defects, where cracks can originate. But there are other kinds of defects that can come from corrosion pits or accidental notches caused by diving machines, or in the case of work on the pipe. In this last case, the notch corresponds to a reduction of the section, which is enhanced by the stress-concentration factor. The objective of this work is to compare the prediction of finite-element computations with fracture experiments on such notched pipes. The results are given in terms of stress-concentration factors and show some discrepancy with the experimental results. As the mechanical properties have been measured on standard plane specimens, a transfer problem to curved structures is suspected to be at the origin of the difference, because with the dimensions of the pipe it is not possible to have standard and curved specimens in the same direction of rolling, and the mechanical properties of this pipe are different in the circumferential and transverse directions.