When a flanged or valve is modeled after an elbow in AutoPIPE, does it affect the stiffness of the elbow in the analysis? If so, how?
Yes, the stiffness of an elbow is affected if the program detects a flange or valve component within a certain distance after and elbow. In AutoPIPE, please see the following help section for details on this distance:
Help > Contents> Contents Tab> Command Reference>Tools & Utility Commands>Model Options > Model Edit Options> Distance L/D from flange/valve to bend.
The effect of this setting on the flexibility factor can be seen in the Tools> Model Input Listing> Elbow Report. AutoPIPE's official training class covers this modeling approach and model option setting.
Again, Flanges or valves will increase the stiffness of the bend and flexibility and SIF factors are reduced due to preventing ovalling of the bend.