FRACTURE-TOUGHNESS PARAMETER IN A PIPELINE

This paper discusses the problem of determining the characteristic values in ductile fracture mechanics on the basis of the fracture toughness, K(Ic), for a double-sided spiral submerged arc weld pipeline material. Special interest was directed towards relatively thin ready-to-use pipes of the hot rolled steel API 5L-X52. For this purpose Charpy V-notch impact tests on subsized specimens were performed at temperatures ranging from - 80-degrees-C to 0-degrees-C. The specimens were taken from the weld zone and the parent material remote from the welds. The V-notches were so oriented as to reproduce the fracture path which would result through the pipe thickness. Using the estimated K(Ic) from the above measurements and the available design data for the pipeline, the maximum acceptable sizes of different defects were calculated. The variabilities of material properties and stresses about the assumed design values were also treated statistically to ensure that a standard for detection of a tolerable defect size at a required probability can be established.