I am attempting to model structural steel elements attached to a piping model in an attempt to get more accurate results (as opposed to rigid restraints or displacements directly on pipe nodes).

The structure in question is attached to a boiler shell in real life. In order to model the thermal growth of the boiler I want to add displacements to the structural model instead of rigid FIXs. I want to do this because another part of the piping is truly fixed and I want to know what resulting restraint forces are.

Is it possible to assign rigid displacements to structural steel nodes instead of FIX?

Yes. Select a pipe element and add displacement, and just specify the structural steel node number in the displacement definition.

Easy as pie! Thank you Faizal. Is it true in general with all piping input properties with reference nodes that they are independent of the element on which they are specified?

probably best answered by Intergraph people. But as far as I know, as long as you can specify the node number, you can specify it at any element, except for SIF. For instance, you can specify restraint, displacement, nozzle flex, hangers or nozzle limit check at node 30 while elements 10 to 20 is selected, but you have to select the element containing node 30 to specify the sif there. however, to me it's a good practice to specify as much as you can at or near the "right" element. otherwise it's hard to follow your work.