Impression creep testing across a heat affected zone

Impression creep testing was applied for studying the creep strain rates in the heat affected zone of a P22 weld in order to support an FE analysis of a piping system. The specimen size recommendations for impression creep were violated in the sense that instead of a standard 10*10*2.5 mm specimen an oversize 10*10*10 mm specimen was machined such that the heat affected zone was in the middle of the specimen. By grinding the specimen after each test cycle, the material combination from the base material through the HAZ to the weld metal was “scanned” as the specimen got thinner. The validity of the measured strain rates is supported by FE analysis, which showed that the creep deformation is very strongly concentrated in the immediate vicinity of the indenter while the underlying material remains unaffected. The effect of the previous loading was removed by grinding off the top layer. The strain rate distribution and primary strain component distribution vs. distance from the fusion line were determined. These results were applied in the FE analysis of full size piping components.