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

Authors

  • Mohsin Sattar , Dr. A.R. Othman , Dr. M.F. Othman , M. Fazwan Musa

Abstract

—The complexity of the applied thermo-mechanical boundary conditions makes it critically
important in a creep failure analysis. Over the years, numerous creep laws were developed for prediction of
the deformation, damage evolution, and rupture of the materials subjected to creep phenomena. One of the
most widely used creep material models for numerical analysis is Omega model, developed by American
Petroleum Institute and Material Properties Council, to describe fitness for service engineering assessment of
mechanical equipment to ensure safe and reliable service life. However, the Omega model is not readily
available and directly integrated into Abaqus software codes, and the creep data is scarce for a complete
analysis. Therefore, the extrapolation of creep behaviour has been performed by fitting different forms of
creep models with a small number of creep data and then simulating beyond the available data points. In this
study, a creep analysis has been conducted on a steel cylinder vessel, to predict time-dependent plastic
deformation as well as creep behavior at elevated temperatures under constant stresses. A curve fitting
technique 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 obtained
from the Omega model (MPC project Omega). In addition, as the strain rates increased exponentially with the
stresses, regression analysis was used for predicting creep parameters to fit into Norton-Bailey model. The
uncertainties in extrapolations and material constants has highlighted to necessitate conservative safety factors
for design requirement. The results indicated that the inner walls of the cylinder vessel exhibit uniform
secondary creep deformation, under constantly applied pressure. The analysis formed the basis for the design
of thick- walled cylinder when exposed to internal pressure for long time. The study proved the significance
of FEA in predicting creep deformation and damage evolution of steel components

Published

2020-01-31

Issue

Section

Articles