For B31.1 / B31.3 and similar codes, the piping system is evaluated, from a
stress point of view by considering failure modes. This leads to the following load cases for evaluation:
- Sustained - for primary, force based loads
- Expansion - for secondary, displacement based self limiting loads
- Occasional - for primary extreme (wind, seismic) loads
For each of these conditions, the piping codes provide equations to determine both the
code stress and the
allowable stress. From a
pipe stress point of view, the system passes the code requirements if all of the
code stresses are less than the corresponding
allowable stresses.
The B31.1 / B31.3 codes do not consider the Operating Condition to be a
stress case, therefore, there are no equations provided to compute a
code stress or an
allowable stress.
CAESAR II computes an operating stress using a basic strength of materials equation,
but the allowable is set to zero since there is nothing to compare this stress to.
The Operating case is important and it must be evaulated for:
- The determination of maximum displacments.
- The determination of equipment and support loads.
- The computation of the "Expansion Stress Range".
There are other piping codes (B31.4 / B31.8) that do consider the Operating stress condition as a
code case. For these codes there is an allowable stress computed and compared to the actual stress in the pipe.
Take a look at the
CAESAR II Quick Reference Guide, for a list of the piping codes supported, the load cases addressed, and the equations for the
code stress and the
allowable stress. Note, these are the load cases that must be run for
stress evaluation. There may be other load cases necessary for structural or operational reasons.