Realistically simulating the creep response of welded components can help quantify the risk associated with operating inservice, high-temperature equipment and can validate new component designs in the power generation and petrochemical industries. Detailed finite element analysis (FEA) is employed in this study and is coupled with generalized, non-linear creep simulation techniques to investigate the elevated temperature response of welds. Depending on original heat treatment, creep damage progression is known to be accelerated by the mismatch in properties of the base metal, weld deposit, and heat affected zone (HAZ). This mismatch results in stress intensification that can accelerate creep damage near a weldment (typically in or adjacent to the HAZ). In this paper, the effect of implementing an elastic damage parameter that adjusts the stiffness of the material as a function of creep damage is examined. This type of damage mechanics model has a significant impact on the predicted damage evolution near weld deposits and can realistically mimic observed in-service failures. Additionally, commentary on different creep damage failure criteria is provided. The simulations presented utilize the Materials Properties Council (MPC) Omega creep methodology, with particular emphasis on the behavior of high-temperature, low chrome (1-1/4 Cr 1/2 Mo) piping with longitudinal weld seam peaking.
Application of these techniques to high-temperature, low chrome piping is relevant as there have been numerous related catastrophic failures in the power generation and petrochemical industries attributed to weld seam peaking. Commonly, weld peaking occurs during fabrication due to angular misalignment of rolled plate. Furthermore, for many fusion-welded piping fabrication standards, no tolerance for peaking is specified. Local peaking can induce significant local bending stresses, and for components that operate in the creep regime, the presence of peaking can lead to an increased risk for creep crack initiation, propagation, and eventual rupture. An overview of some well-known historical low chrome piping failures is provided in this paper, and a literature review on existing creep analysis and peaking measurement methodologies is offered. Additionally, the remaining life of low chrome piping systems is estimated and the sensitivity in results to variations in key parameters is highlighted; these parameters include operating temperature, magnitude of peaking, and the effect of heat treatment. The simulation techniques discussed in this paper are not only valuable in estimating remaining life of in-service components, but detailed analysis can help establish recommended weld seam peaking fabrication tolerances, appropriate manufacturing practices, and practical inspection intervals for high-temperature piping systems.