In order to simulate ratcheting behaviour in SA 312 Type 304 LN stainless steel elbows, finite element studies were carried out under combined internal pressure and cyclic bending load. An elbow of 168 mm nominal outer diameter and average thickness 14.8 mm was studied under four different combinations of internal pressure and cyclic bending load. The internal pressure was varied in the range of 27.6 MPa to 39.2 MPa. The bending load was applied in the form of cyclic displacement which was varied in the range of ±41 mm to ±55 mm. Prior to ratcheting simulation, analytical studies were also carried out under internal pressure only and the strain values obtained at intrados, extrados and crown locations of the elbow. These values were compared with the values estimated using the expressions given in ASME codal provisions and those obtained during the experimental studies carried out earlier on four elbows. The elastic-plastic response of the elbow under combined internal pressure and cyclic bending load was simulated by using the Chaboche hardening parameters. Ratcheting strain values were obtained at different locations in the bent portion of the elbows and the results were compared with those obtained during the experimental studies. Details of the studies carried out and the results of the investigations are discussed in the paper.

Keywords: Ratcheting, SA 312 Type 304LN stainless steel, Elbow, Internal pressure, Cyclic bending, Finite element studies, Ratcheting strain