Regression Analysis Of Omega Model To NortonBailey Law For Creep Prediction In Fitness For Service Assessment Of Steel Material

—The complexity of the applied thermo-mechanical boundary conditions makes it criticallyimportant in a creep failure analysis. Over the years, numerous creep laws were developed for prediction ofthe deformation, damage evolution, and rupture of the materials subjected to creep phenomena. One of themost widely used creep material models for numerical analysis is Omega model, developed by AmericanPetroleum Institute and Material Properties Council, to describe fitness for service engineering assessment ofmechanical equipment to ensure safe and reliable service life. However, the Omega model is not readilyavailable and directly integrated into Abaqus software codes, and the creep data is scarce for a completeanalysis. Therefore, the extrapolation of creep behaviour has been performed by fitting different forms ofcreep models with a small number of creep data and then simulating beyond the available data points. In thisstudy, a creep analysis has been conducted on a steel cylinder vessel, to predict time-dependent plasticdeformation as well as creep behavior at elevated temperatures under constant stresses. A curve fittingtechnique called regression analysis has been used in combination with Norton-Bailey model, based on API579 standard values. Different creep strain rates on material, stress and temperature- dependent were obtainedfrom the Omega model (MPC project Omega). In addition, as the strain rates increased exponentially with thestresses, regression analysis was used for predicting creep parameters to fit into Norton-Bailey model. Theuncertainties in extrapolations and material constants has highlighted to necessitate conservative safety factorsfor design requirement. The results indicated that the inner walls of the cylinder vessel exhibit uniformsecondary creep deformation, under constantly applied pressure. The analysis formed the basis for the designof thick- walled cylinder when exposed to internal pressure for long time. The study proved the significanceof FEA in predicting creep deformation and damage evolution of steel components