Hi Leo.
I'm really not noticing this when I give loads to Structural Group unless they raise a concern on sizing the support. So far, nobody raise a concern from our structural group regarding this in my experience.
Let me guess it, Friction as we know is resisting any load that tends to have a horizontal component (e.g., thermal expansion load). In hydrotest case, thermal load is not present, what I can guess, is that maybe there is an imbalance in the support system that's trying to cause a horizontal component of load (weight), say an unsupported elbow that is hanging and trying to pull the pipe down and causing it to have a horizontal component of weight which might trigger friction to activate.
Just my guess. Please correct my interpretation of the friction loads.
Those that develop the algorithm for non-linear friction in stress analysis software can explain best since he knows deeply how the software is programmed.
Cheers!!!
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Borzki