Finite element simulation of welding residual stresses in martensitic steel pipes

Abstract

Finite element (FE) simulations of the welding of two high grade steel pipes are described. The first is a P91 steel pipe welded with a similar P91 weld consumable, and the second is a P92 steel pipe welded with dissimilar nickel–chromium based weld consumables. Both welds are multipass circumferential butt welds, having 73 weld beads in the P91 pipe and 36 beads in the P92 pipe. Since the pipes and welds are symmetric around their axes, the FE simulations are axisymmetric, allowing high FE mesh refinement and residual stress prediction accuracy. The FE simulations of the welding of the P91 and P92 pipes comprise thermal and sequentially coupled structural analyses. The thermal analyses model the heat evolution produced by the welding arc, determining the temperature history throughout the FE models. Structural analyses use the computed temperature history as input data to predict the residual stress fields throughout the models. Post-weld heat treatment (PWHT) of both pipes has also been numerically simulated by assuming that the FE models obey the Norton creep law during the hold time period at 760°C. The residual stresses presented here have all been validated by corresponding experimental measurements. Before PWHT, it has been found that, at certain locations in the weld region and heat affected zone (HAZ) in the pipes, tensile hoop and axial residual stresses approach the tensile strength of the material, presenting a high risk of failure. It has also been found that PWHT substantially reduces the magnitude of residual stresses by varying degrees depending on the material.

Keywords:

• Finite element simulation
• Fusion welding
• Martensitic steel pipes
• Residual stress
• Dissimilar Inconel Consumable
• P91
• P92
• IN625
• IN82

We would like to acknowledge the support of The Energy Programme, which is a Research Councils UK cross-council initiative led by EPSRC and contributed to by ESRC, NERC, BBSRC and STFC, and specifically the Supergen initiative (grant nos. GR/S86334/01 and EP/F029748) and the following companies: Alstom Power Ltd, Doosan Babcock, E.ON, National Physical Laboratory, Praxair Surface Technologies Ltd, QinetiQ, Rolls-Royce plc, RWE npower, Siemens Industrial Turbomachinery Ltd and Tata Steel, for their valuable contributions to the project. This paper is based on a contribution to the 9th International Conference on Creep and Fatigue at Elevated Temperatures/4th International Conference of Integrity of High Temperature Welds, organised by the High Temperature Committee of IOM3 in London, UK, on 25–27 September 2012.

Notes

This paper is part of a special issue on Energy Materials