Non-Linear Analysis Design Rules; Part 1: Code Comparison

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In September 2014, the CORDEL MCSTF Pilot Project was launched a project to investigate divergences and to promote international convergence of code requirements for non-linear analysis methods.

Major design rules in pressure vessel and piping codes, nuclear and non-nuclear, are based on the linear elastic method associated with the classification of stresses into primary stress (for load control), secondary stress (for strain control) and peak stress on the surface. This approach is only easy to develop for simple cases, such as cylindrical shell under axisymmetric quasi-static loads. For more complex geometries and load combinations, the stress classification methodologies available are complicated to implement, highly conservative and dependent on the user’s approach. Such difficulties are regularly encountered when designing and assessing nuclear power plant components, such as a vessel nozzle under complex piping loads or piping systems.

Consequently, non-linear analysis at design level is an efficient alternative to the basic linear elastic approach, using real material behavior and more accurate deformation criteria. One of the major benefits is to remove the issue of the classification into primary versus secondary stress associated with elastic analysis.

The first output of the project, the “Non-Linear Analysis Design Rules; Part 1: Code Comparison report”, reviews and compares the current code requirements in non-linear analysis for different failure modes and some degradation mechanisms in the major nuclear and non-nuclear design codes.

The CORDEL MCSTF is currently working on two further reports will be published as part of this project, the “Non-Linear Analysis Design Rules; Part 2: Good Practices”, which will presents recommendations for good industrial practices when performing non-linear analyses and the “Non-Linear Analysis Design Rules; Part 3: Benchmarks” which will present a set of benchmarks designed to provide input to support the set of good practices presented in part 2. 


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