Microstructure, hardness and fracture resistance of P235TR1 seam steel pipes of different diameters

Steel pipelines in industrial plants consist of different elements, including seamless and/or welded (seam) pipes. Properties of welded pipes, including their fracture behaviour, depend on the characteristics of both, the base metal, and the weld metal. In this work, two seam pipes are considered having different diameters and manufactured of P235TR1 steel. Hardness and microstructure were examined on the samples which contained the seam zone, to capture the influence of heterogeneity. Fracture resistance of the pipeline material, i.e. of both base metals and both seams, was determined by experimental examination of the recently proposed Pipe ring notch bending specimens with sharp stress concentrators. Differences between the two tested pipes, including the influence of the heterogeneity caused by the welded joint, were determined by comparison of the crack growth resistance curves. Effects of the initial stress concentrator shape, sharp machined notch or fatigue pre-crack are discussed.