Ratcheting Strain Assessment in Pressurised Stainless Steel Elbows Subjected to In-plane Bending

Abstract

Abstract Ratcheting studies were carried out on Type 304LN stainless steel elbows, by applying steady internal pressure and cyclic bending. The elbows were of 168 mm nominal outer diameter and the average thickness varied from 14.7 mm to 15.1 mm. The elbows filled with water were pressurized between 27.6 MPa and 39.2 MPa. Cyclic bending load, under the opening and closing moments, was applied on the elbows at ambient temperature. During the ratcheting experiments, strains were measured at different locations in the curved and straight portions of the elbows using post-yield rosette strain gauges. Ratcheting strain and its rate of change were estimated at different locations of the elbows with increase in number of cycles. In the curved portion of the elbow, ratcheting strain was observed in the hoop direction at the intrados, crown and at a few other locations other than the extrados. No significant ratcheting was observed in both the axial and circumferential directions at the extrados location for all the specimens. The specimens failed by the occurrence of through-wall axial crack in the curved portion, at one of the crown locations, accompanied by simultaneous bulging.