Stress Relief Heat Treatment

Date 02-07-2006 20:21

All,
I am wondering about the heating and cooling rate numbers that are given in AWS D1.5-2002 Section 4.4.
More specifically, 4.4.2.2 gives the max heating rate as 5600 / thickness in mm OR as 400*F / thickness in inches. This seems straight forward until the results are converted from Celsius to Fahrenheit, or vice versa. Then you will note that there is approximately 30*F difference in the results.
The cooling rates suffer the same error in the conversions, 7000 / t(mm) and 500 / t (inches).
The latter portion of 4.4.2.3 shows 85*C as equal to 150*F but my calculation shows 185*F. (The 1995 D1.5 shows 80*C as equal to 150* in the same paragraph; a little closer but still off at 176*F).
It seems the only accurate numbers are 315*C/ 600*F.

Has errata been issued on this that I obviously don't have?

Am I that far off in my numbers? (My calculator shows 100*C as being 212*F and 32*F as 0*C but I could be HUA.)

Will 30*F make any practical difference in the maximum heating and cooling rates?
I'm leaning to the conservative side and plan on using the metric numbers but it would be nice to know the story.

Thanks in advance,
Chet Guilford

By billvanderhoof (****)

Date 02-08-2006 06:19

Fahrenheit = celsius times 9/5 plus 32. Your calculations are correct. They probably forgot to add the 32 and then rounded to an even ten.
Bill

By HgTX

Date 02-08-2006 22:14

You only add the 32 degrees if you're talking about a temperature reading like you'd see on a thermometer. When you're talking about differences from one temperature to another, it's just the 9/5 multiplier. The rate of heating has to do with how many degrees the temperature needs to rise in one hour.

So you put the material in the furnace at no more than 315C/600F, and in one hour for a 1" (25mm) plate your temperature can be no more than
a) 315C + 5600/25 = 539C
b) 600F + 400/1 = 1000F

(1000F - 32) * 5/9 = 537C

It works out.

Hg

By CHGuilford (****)

Date 02-08-2006 22:48

Hg,
yours is the second response saying the same thing. The first time I heard that today it didn't make sense; just like the first time (and second) I read your response.

What I was missing is that adding the 32 degrees in the formula is simply to correlate the two scales to get the equivalent values. I overlooked that it doesn't matter where to start the scale from (other than starting point must be no more than 315C); that it's the rate of increase that is being measured.

Thank you for clarifying that.
Chet