Experimental Evaluation of Residual Stresses in Pipes Manufactured by UOE and ERW Processes

Pipes are basic elements used in the construction of pipelines for the long-distance transportation of oil and gas and their derivatives. They can be manufactured by cold forming processes such as UOE and ERW, both widely used in the oil and gas industry. These processes produce high levels of non-uniform plastic deformation, which introduce a new state of residual stress into the material. In some cases, these stresses combine with mechanical stresses generated by external loads leading to service failures, interrupting the transmission line and increasing the risk of accidents. Therefore, determining in advance the residual stress distribution in pipes is an important task which involves the evaluation of the structural integrity. Six pipe samples obtained by the UOE and ERW processes were measured and evaluated using a portable optical device that combines radial in-plane digital speckle pattern interferometer (DSPI) with the incremental hole-drilling technique to measure residual stresses. The experimental results indicate a distinct residual stress distribution for each manufacturing process, while the measured residual stress distributions in the longitudinal and circumferential directions were similar at all measurement locations along an individual pipe.