Evaluation of Cracks in Thin-Walled Pipe Using J Q

Abstract

Abstract Fracture toughness measurements on small samples are often considered valid (size independent) for a limited range of toughness and sample dimensions. In the present work, it is demonstrated that standard toughness tests are transferrable to thin-walled pipe provided the specimen width and pipe wall thickness are the same. Fracture toughness and tensile tests were undertaken on 508 mm (20 in.) diameter Grade API-5L X52 line pipe with a wall thickness of 5.7 mm. J tests were conducted on samples containing surface flaws to evaluate the fracture toughness of the thin-walled line pipe steel using the ASTM E1820 procedure. Owing to geometry limitations, JQ was determined from the resistance curves (J versus crack extension). The average measured JQ was 197 kJ/m2 for 5.3 mm wide samples. A series of full-scale rupture tests with crack and crack-in-corrosion flaws were conducted and the failure pressures were predicted using API 579 and the JQ results. The average difference between the predicted and experimental failure pressures was 21.4 % for the cracks and 11.0 % for the crack-in-corrosion flaws, demonstrating that the FAD method can be used with toughness characterized using specimens of similar thickness to the pipe, although the toughness results are not geometry independent.