Provided you have accurate dimensions and materials for the pump nozzles and they are uniform wall thickness, modeling those elements as piping should not be a problem.

However, modelling the pump casing as piping can get you into trouble. While it is not obligatory to make it perfectly rigid, the "best" way is to get the stiffness values from the manufacturer.

An alternative would be to model the casing in Nozzle Pro which will calculate stiffness values.