1. Impellers are rotating parts. They are lifetime limited. Normally, shot peening during the repair is limited up to 4x. I heard from cases that more than 5 x shot peening over the lifetime destroyed the part during service. The coverage should not exceed no more than 1000% in total except special areas like holes which are peened under impingement angle of 45°.
2.The operating temperature up to 500°C.
During service the compressive strees will be reduced, but not to zero. The rest of it and the other effect of shot peening will be good enough.
