Fitness-for-Service Analysis Procedure – Determine Applied Stress at Location of Flaw
Applied stress at the location of the flaw should be resolved into membrane bending components. All forms of loading (i.e., internal pressure, discontinuity, and thermal) should be considered as follows:
1. Calculate maximum principal membrane stress at the operating pressure for cylindrical and spherical shapes using ASME Code design equations.
2. Calculate maximum principal membrane and bending stresses at nozzle opening using WRC Bulletins 107 and 297.
a. Consideration must be given to both internal pressure and significant external piping loads. Piping stress analysis may be necessary to determine piping loads.
3. Calculate principal membrane and bending stresses at internal or external attachments and vessel supports using WRC Bulletin 107.
4. Calculate discontinuity stresses at head-to-shell joints and transitions resulting from internal pressure using ASME Code, Section VIII, Division 2, Appendix 4, and combine with principal membrane and bending stresses.
5. Calculate thermal stresses at locations with significant temperature gradients, using ASME Code, Section VIII, Division 4, and combine with principal membrane and bending stresses.
6. Use finite element stress analysis to calculate all membrane and bending stresses when other methods will not provide satisfactory results.
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