MEASUREMENT OF THE RESISTANCE TO FRACTURE EMANATING FROM SCRATCHES IN GAS PIPES USING NON-STANDARD CURVED SPECIMENS

摘要

The experimental procedure for measurement of the notch fracture toughness of the API 5L X52 steel using a non-standard curved specimen with a notch simulating the expected scratch damage of gas pipelines has been developed. The concept of the notch stress intensity factor based on the volumetric method has been employed and the corresponding notch fracture toughness K_(p,c) was obtained. In this case, the notch fracture toughness was calculated using the critical load determined by acoustic emission and the results of finite element analysis of the elastic-plastic stress distribution ahead of the notch tip. The notch fracture toughness J_(p,c) in terms of te J-integral has been estimated by means of the load separation method which allows measuring the η -factor. In this case, the original representation of the J-integral as total energy release rate and the tests records have been used. The proposed procedure allows avoiding calculation of the stress intensity factor for non-standard specimens to determine the notch fracture toughness J_(p,c). Development of the present methodology encourages replacing the conservative crack-like defects approach. The results on the notch fracture toughness of the API 5L X52 steel can be used in the modified failure assessment diagram for structural integrity assessment of gas pipelines damaged by scratches.