“Stella” is Autodesk’s 3D modelling software application built specifically for the design of process plant facilities. The product is intended for use by plant designers at EPCs and Owner–Operators in process industries.
All I can say at this point is that it sure looks promising.
See In the Pipes for details how to get access to it.
In it you can see how to create specs, place equipment, model basic structures, route pipe, and all sorts of other groovy piping stuff (though not isometrics - it's coming - promise!).