Can Larson-Miller Be Applied To Stress Relief Situation?
Can Larson-Miller Be Applied To Stress Relief Situation?
(OP)
We were doing a routine local stress relief on a weld repair of a 4130 casting last night and our induction heater controls malfunctioned. Our normal stress relief for the repair in question would have been 1150 deg F for 2-hours. We could only get upto 1000 degrees out of the heaters as measured by thermocouples placed on the item near the repair area.
I ordered the operation to go ahead at 1000 degrees but increased time to 2 1/2 hours. This was a desperate "seat of the pants" call on my part. Later on I looked at the Larson-Miller equation to see how right or wrong my call may have been and discovered I was getting some absurd numbers, or else I just don't have a clue on what I am doing. Please comment on the following:
Larson-Miller: Thermal Effect = T(log t + 20)/1000
equation used:
T1[(log t1) + 20]/1000 = T2[(log t2) + 20]/1000
where T1 = 1150 deg F = 1609.7 deg R
t1 = 2 hours
T2 = 1000 deg F = 1459.7 deg R
t2 = to be determined
after plugging in above values, I get a t2 of ~245 hours.
So that means my stress relief at 1000 degrees for 245 hours provides the same effect as 1150 deg F at 2 hours. This seems absurd, so I conclude I am misapplying this equation. PLEASE ADVISE and thanks if you will help.
I ordered the operation to go ahead at 1000 degrees but increased time to 2 1/2 hours. This was a desperate "seat of the pants" call on my part. Later on I looked at the Larson-Miller equation to see how right or wrong my call may have been and discovered I was getting some absurd numbers, or else I just don't have a clue on what I am doing. Please comment on the following:
Larson-Miller: Thermal Effect = T(log t + 20)/1000
equation used:
T1[(log t1) + 20]/1000 = T2[(log t2) + 20]/1000
where T1 = 1150 deg F = 1609.7 deg R
t1 = 2 hours
T2 = 1000 deg F = 1459.7 deg R
t2 = to be determined
after plugging in above values, I get a t2 of ~245 hours.
So that means my stress relief at 1000 degrees for 245 hours provides the same effect as 1150 deg F at 2 hours. This seems absurd, so I conclude I am misapplying this equation. PLEASE ADVISE and thanks if you will help.





RE: Can Larson-Miller Be Applied To Stress Relief Situation?
With regard to your actual application, the 'ridiculous' times you were calculating are actually closer to reality. The ASME welding code does provide extended times for lower temperatures in certain circumstances and they are substantially longer than a boost of a half hour that you applied (even though I recognize your application may not be a code weld). I suspect your 2½ hour heat treatment did nothing significant.
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
If there is any doubt you can redo the thermal treatment at the recommended temperature to satisfy any question.
In your case stress relief and tempering are two distinct operations.
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
As correctly mentioned by unclesyd, the relief of residual tensile stresses can be very effective at small times and does not follow the tempering correlation for steels. One added benefit is that you will reduce stresses during tempering. So, the extended times you see in the ASME B&PV Code are correlations developed for tempering not only stress relief.
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
So Unclesyd, when you say, "A reduction of 150F would require an increase in holding times to five hours per inch of thickness. In a pure stress relief situation there is reduction of approximately 90% of the stresses in the first few minutes..." THIS IS KNOWLEDGE THAT I NEED MORE OF - CAN YOU ADVISE ON REFERENCES AND OTHER READING MATERIAL; web searches are not getting me any good results.
Thanks all.
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
I did come across some information recently that I was able to re-confirm its location at the web site below. I was involved the NBIC in revising the local PWHT discussion;
www.for
Battelle has been doing research work on local PWHT especially related to weld repairs in the field. If you can download this document, there was a parameter that was apparently developed by MPC/Battelle for evaluating stress relief, not tempering.
If you need more specific information, I would contact the forengineers web site.
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
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Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
But the remaining residual stresses are, as said before by some authors, practically only depending on the applied temperature. Time has only a small influence (at least for usual pressure vessel materials).
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
http://www.pyromaitre.com/
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
Thanks SJones and Ulyssess for mentioning the Holloman-Jaffe equation, this gave me some new directions to explore. There is another thread here on Eng-Tips that discusses this and has a good outline of the H-J equation:thread 794-92824. Although I am cautious of some of the information as no reference was cited and a Kelvin temperature conversion is applied to the holding temperature but not applied to heating or cooling rates.
I have also found Metengr reference by Sinha interesting, it uses a material coefficient of "18" instead of "20" as used by many other texts ,and seems to make a large difference in the computed times.
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
Apologies if it goes pear shaped through my lack of formatting skills:
H = T*(20 + log torr)/1000
torr = t + T/(2.31*K1*(20 - log K1)) + T/(2.31*K2*(20 - log K2))
t = holding time in hours
K1 = heating rate K/kour
K2 = cooling rate K/hour
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
Do I presume correctly the your K1, K2 and T are all in degrees Kelvin?
How about a reference for that form of the equation?
Thanks
RE: Can Larson-Miller Be Applied To Stress Relief Situation?
and
B Lee, TWI UK, "What Is The Holloman-Jaffe Parameter"
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/