Creep life assessments and creep pips 2

[kclim]

Does anyone have much experience with the above topic? Specifically, has anyone run successful life assessment programs at their plants based on creep pip measurements on pipework? Concerned about the quality of the measurements, given how easily the tips may be damaged and how accurate the readings need to be.

Thanks

 

[metengr]

I would not put much emphasis on the measurement of in-situ creep deformation. Why? Because, as with boiler tube creep failures, for piping systems creep failure can occur in very localized regions containing either pre-existing defects, mismatch of creep deformation due to either alloy segregation or weld heat affected zones within the length of pipe material, different heats of pipe material used for an entire pipe run and local grain size differences due to fabrication or handling. All the above can result in locations of early creep failure.

Just too many variables both from a material and operating standpoint when you think of the linear feet of pipe and number of strain gages that would be required to really look for the onset of creep damage before the pipe fails at a location which had no monitoring.

I would consider acoustic emission monitoring for creep damage before creep pip measurements.