An experimental investigation was performed to evaluate the J-integral resistance curve behavior of 10-cm (4-in.) nominal pipe size Schedule 80 welded Type 304 stainless steel pipe. Tests were performed in four-point bending at 288°C (550°F) on 1219-mm (48-in.)-long pipe specimens with machined flaws contained in circumferential welds. Two flaw geometries were investigated. The first was a through-wall crack growing circumferentially (simple) and the second was a 360-deg part-through radial crack superimposed on a through-wall circumferential crack (complex). During the tests load, load line displacement, crack mouth opening displacement, and electrical potential drop across the crack mouth were monitored. Elastic compliance and direct current potential-drop (DCPD) techniques were used simultaneously to estimate crack extension during the tests. Pipes containing simple cracks had an average J-initiation of 1120 kJ/m² (6400 in. · lb/in.²). The presence of the complex crack reduced the J-initiation level by approximately a factor of four and also reduced the apparent tearing modulus significantly as compared to pipes containing simple cracks.

A second part of this investigation concerned the use of laboratory-sized specimens of the same thickness as the wall of the pipe to model the J-R curve behavior of the simple through-wall cracked pipe. Large plan compact specimens were cut from a welded plate and tested at 288°C (550°F) using both elastic compliance and DCPD crack length estimation techniques. J-initiation values from the two types of specimens appear comparable, but the small amount of crack extension from the compact specimens limited comparison of the far-field J-R curve.