Dear Pat,

My hunch is that the constant spring hangers had been wrongly selected at the start, as just in six years in a power plant for P22 piping to creep so much at 540 deg C is unusual. With the fix of additional support ( must be constant or soft variable spring type) if it is working fine, you can just revise the piping stress calc with this as-built condition & revise turbine stability calc/load comliance & document the change for future reference.
regards,

sam