Our services include Creep Analysis of reactors. Ideametrics can perform creep analysis of equipment as per Fitness-For-Service standard API-579-1/ASME-FFS-1 MPC omega method.
Methodology to determine a more accurate creep life prediction is to analyze the equipment with “real” operating condition with an explicit creep model using Finite Element Analysis (FEA). Ideametrics has used the explicit creep model with finite element method to solve several complex high temperature creep problems.
Below are the advantages and challenges of using Finite Element Analysis to solve creep problem
o Enables estimates of remaining creep life that are far more accurate than those obtained with linear-elastic analyses. Such estimates are of great importance in equipment strategy developments.
o Obtaining good understanding for where in the structure creep damage will first manifest itself, which can help prioritize inspection efforts.
o Ability to simulate actual historic operating condition (if data is logged!) and anticipated future conditions in any possible combination of normal operating, emergency loading (flooded cyclones), temperature upset conditions etc.
Challenges in using Finite Element Analysis for Creep Modeling:
o Material Properties for Creep Analysis
o Detailed FEA Model Required
o The creep protocol endorsed by Fitness-For-Service standard API-579-1/ASME-FFS-1 is the MPC Omega model. The uniaxial formulation of this model has shown good correlation to test data, but is not incorporated into commercial FEA codes.
Extensive user coding i.e. user defined dll’s of MPC omega method is required to successfully implement this model.
API-579-1/ASME-FFS-1 lists the acceptable creep damage as 80%, but does not offer guidance on allowances for localized effects.
As per ASME FFS creep damage to be at, or even less than 80%. This approach is particularly useful when coupled with a material softening model that reduces the stiffness of creep damaged material, which ensures stress redistribution away from the damaged regions is accounted for. This approach makes the analysis similar to limit-load analysis in that, if the FEA solver finds a converged solution, it is demonstrated that the parts of the structure that have less than 80% creep damage can adequately carry the load.
Ideametrics has experience in the detailed creep analyses described here and employs an implementation of the Omega protocol in the FEA code that has proven both robust and reliable.