By David Diehl, P.E., Executive Technical Director of Training, Intergraph CADWorx & Analysis Solutions
From a piping code perspective, if all your stresses are below the allowed limits, do you have any additional responsibilities for system design?
Yes. Referencing B31.3 - systems subject to severe cyclic conditions have additional design constraints in the piping specification, allowed fittings, joining methods and examination. Also, systems deemed under severe cyclic service are essentially excluded from category M (toxic) fluid service and there is no provision for this condition in nonmetallic piping systems. But these severe cyclic conditions are not clearly defined by the Code.
B31.3 Appendix F (Guidance and Precautionary Considerations) states that severe cyclic conditions are related to high stress range and a high number of cycles – a stress range approaching its limit and a cyclic factor (f) is less than its maximum value (e.g., N>7000). But there is no set criteria. So what is “high stress”? >90%? Here is another situation where early communication between owner and designer may reduce the impact from bad assumptions.
Simply eliminating red load case names from your CAESAR II output menu doesn’t necessarily mean your stress work is done.