Snd,

My question was relevant, but seems to have given you the hump. If, for example you are dealing with a drain from a reciprocating pump, then imposed vibration when the pipe is not in service may be a primary consideration.

By 'the real world' I meant just that. 'Eh' (if it makes any difference) is actually the correct stiffness controlling parameter to apply to a dynamic run representative of the operating mode. In most cases I think 'Ec' would be acceptable, given the many other inaccuracies attandant to a stress calculation.

Incidentally, the application of 'Ec' to static analysis in accordance with B31.3 has been covered in previous posts, and in various other places.