Search

Pipelines are commonly used in process industry for transport of fluids, as well as granular solids, due to their numerous advantages in comparison to other transportation means. Pipe integrity is essential for a reliable work of the entire plant, as well as for safety assurance. Also, serious ecological consequences may follow the pipeline failure in some cases, i.e. due to the leak of toxic, flammable or otherwise dangerous fluids in a chemical or some other plant. Therefore, it is very important to examine the fracture behaviour of pipelines, which is done here by testing the recently proposed ring-shaped specimens exposed to bending. The specimens were fabricated from a seam pipe for pressure applications (allowed for usage on temperatures up to 300 degrees C). Initial defects, very narrow notches, were machined either in the base metal and weld metal (seam) or in the base metal only. Regardless of the defect position, ductile fracture mechanism is observed in all specimens. The results show that the ring-shaped specimen can be successfully used for fracture characterisation of pipeline material, especially for thin-walled pipes which are not suitable for production of standard fracture mechanics specimens due to the insufficient wall thickness.

Integrity of cylindrical structures, such as pipes and small-scale pressure vessels, is typically assessed by testing fracture mechanics specimens, like compact tensile CT or single-edge notched bending, SENB. However, their fabrication is mainly not possible for thin-walled pressurised elements, commonly used in structures of process and energetic facilities, such as hydrogen and hydrogen carriers storage and delivery systems. Recently proposed nonstandard ring-shaped specimen is used to test the fracture resistance of pressurised cylinders with defects (cracks or notches) in the most critical direction - axial. Some of the advantages of the pipe-ring notch bend specimen, PRNB, are simple fabrication and same material history as actual exploited structure. A combined experimental-numerical procedure is applied for prediction of fracture behaviour of specimens (applicable to ductile metals, mainly steels and Al alloys), with the aim to further validate the new specimen. The results obtained so far lead to conclusion that PRNB specimen can be applied in integrity assessment of cylindrical structures.

Integrity of pipes is typically assessed by testing fracture mechanics specimens, such as compact tensile (CT) or single-edge notched bending (SENB). However, for some pipe dimensions it is not easy or possible to fabricate a specimen conforming to the requirements of standard procedures. A new type of specimen is proposed recently, which can be advantageous for relatively small pipe diameters and axial defects - the pipe ring notch bend specimen - PRNB. In this work, criteria for failure by ductile fracture of PRNB specimens are determined experimentally and by application of micromechanical analysis. The influence of size of the specimen, as well as size and shape of the stress concentrator, is analysed. The results of this study, along with previous authors' results, lead to the conclusion that the pipe ring specimens can be applied in integrity assessment of pipes with defects. Also, the benefits of their application include much simpler fabrication and the same material history as the pipe itself.