You should design to ensure the loading complies with the nozzle loads for all design conditions. Unless you can obtain a waver for the loads from the pump supplier. Solving for thermal conditions is the first step, then solving for occasional loads will come next. Look at you pipe supports, guide systems and step by step resolve the high loads and/or moments acting on your pump nozzle.
Let me know if you have more questions.
Conor
http://www.bellowsmfg.com