Process engineers are the primary creators of pipe stress problems.
If you can, try to get a copy of the data sheets used to purchase the pumps. Those will typically tell you the truth of what the pump will be operating at.
As MoverZ astutely pointed out, "design" is often an inflated number (temperature and pressure) intended to insure the wall thickness calculations are conservative enough. While they typically have little to no impact on the selected wall thickness, their artificial nature can have a big impact on the stress analysis, particularly where strain sensitive equipment is concerned.
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Edward L. Klein
Pipe Stress Engineer
All the world is a Spring