Creep failure on a main or reheat line?
Well, it is more likely that it is a sort of stress/corrosion creep that occurs at corners and junctions where the stress intensity can be just a tad higher. You will see this form as radial cracks around opening for pressure sample points and such.. but if the crack is aligned with the run of the pipe then it can open up like a hot dog in time.
The steel used to make these high pressure lines has 2.5% Chrome and it is pretty creep resistant at temperatures around 1000 degrees which is the design temp for this sort of line. In the boiler itself, this material is run as high as 1150 but at a reduced life expectancy. To have a failure down near the Turbine would require some additional stress amplifier or stress/corrosion mechanism to get the ball rolling even at 40+ years. Unfortunately, this sort of thing is all too common.