Heat Treating Parameter 1

[SMF1964]

If I recall correctly, the the Larson-Miller parameter for creep, defined as
P = T(20+log t), where T is abs. Temp & t is hours,
can be used for time/Temperature substitution for heat treating of steels. I have a boiler tube (centerwall, max design metal temp 850 F) that may have experienced temperatures in excess of 1000 F for 3 years. I also have a piece of the same tube batch that never went into service. My question is this: would a piece of this tube placed in a furnace at 1200 F for 24 be expected to experience the same degree of microstructural degradation as the tubes in service at 1000 F for 25,500 hours? The LMP indicates yes, but it would be nice to get some other opinions.

 

[Carburize]

Generally speaking the Holloman-Jaffe (Larson-Miller) approach works well provided the microstructural process causing the property change is substantially the same at the test temperature as for the service temperature.In your example I would expect the 1200F test sample to be a good representation of the suspected 1000F service exposure.
For some experimental justification of the approach I would recommend "The Influence of Stress Relief on the Properties of C and C-Mn Pressure Vessel Steel Plates" by Gulvin, Scott, Haddrill and Glen. published in Journal of the West of Scotland Iron and Steel Institute Vol 80, 1972-1973

 

[metengr]

EPRI had published a report on "Boiler Tube Failure Metallurgical Guide" Volumes 1 and 2. This is a comprehensive evaluation of boiler tube failures, fabrication and microstructural degradation of your workhorse tube materials.

To simulate microstructural degradation, EPRI had used elevated temperature exposure and selected stress levels to evaluate spheroidization damage, which was ultimately tied to remaining creep life using LMP.

I would recommend you purchase this especially if you routinely conduct boiler tube failures. The report number is TR-102433 V-1 and V-2

 

[SMF1964]

Thanks, metengr - I have a copy. DNFrench's book is also useful, but did not have the EPRI work in it.