The WRC 297 module in CodeCalc does a nice job of determining membrane + bending SIs but I don't see an easy way of determining membrane only SIs. Is this possible or must I work it out by hand ignoring the bending components?

Craig,

At this time, you would have to ignore the bending components and sum up the stresses and then compute the membrane stress intensity (Pl + Pm). It would be nice to implement the stress summation in WRC-297 module, similar to that in the WRC-107 module.

The loads that you enter should also be sustained (such as from weight or internal pressure). The stresses generated due to thermal expansion loads are categorized as Q and should be summed up to Pl + Pm + Q (membrane + bending).

In WRC modules, the Pm stress intensity is just the stress due to internal pressure. For a cylinder the maximum value is the hoop stress.