I can't answer your question regarding D1.5 directly, as I do not know this code. Just some comments regarding the terminology:
Post Weld Heat Treatment (PWHT) is a generic term that is used for any heat treatment following welding. This can be:
1) Stress relieve
2) Annealing (Different types.)
3) Normalizing
4) Tempering
5) etc.
Of these, stress relieve is probably the most common type of PWHT. The term "stress relieve" does not necessarily mean that it is performed as a PWHT. In some instances (e.g. following excessive bending or deformation of material) it may be required to perform a stress relieve, even if no welding has taken place. In this case the stress relieve is not a PWHT.
In your question, you also seem to equate stress relieve and annealing. While a sub-critical anneal cycle may resemble that of a stress relieve, annealing and stress relieve is not the same. The object of a stress relieve is to reduce residual stresses, while that of annealing is to "soften" the material. Generally annealing is done by heating the component to above the transformation temperature and cooling slowly.
In reply to your second question, the entire PQR test specimen would generally be subjected to the PWHT. Should you subject the test specimens to PWHT, they would "scale". This means that at the very least, you would have to clean this scale off. The specimens could also undergo minor dimensional changes. Do you have a reason why you would want to machine the specimens first, and then doing the PWHT?
Hope this helps
Regards
Niekie
Niekie
Thanks for your comments.
I equated annealing with stress relieving because the specs in this case state that annealing is defined as stress relieving in accordance with D1.5 section 4.4... at least for this job.
This all came about because PWHT is an essential variable for our PQR. Naturally, we would like to not have to run another set of tests if we don't need to. So in splitting hairs, it was pointed out to me that the code sections I listed treat PWHT and thermal stress relieving as different animals, so maybe we wouldn't have to run more tests. My feeling is that more tests need to be run 'cause if not the same thing, it is still heating enough for metallurgical changes to happen.
The second question came about because we were having a time finding someone with an oven that will fit a 1.5 inch, 250 lb test plate in it. Some that I talked to felt that only the machined specimens get PWHT not the entire plate. I do not agree with that but thought I'd throw it out there in case I am wrong.
Anyway, I was just looking for another opinion to either confirm or negate my own.
Thanks again,
CHGuilford
CHGuilford
Have you considered a local PWHT? There are contractors who will come and build a furnace on or around your part and perform a PWHT on site.
All it amounts to is tack welding thermal couples to the piece and covering it with heaters and insulation. Most are computer controled and produce a strip chart recording of where ever and how many TC's you install.
Ron
Yes, that's what we will be doing for the PQR plate. For the weldments themselves, a contractor will be setting up a gas fired furnace in our yard.
As I was explaining before, while researching all this, some people raised the question wondering if thermal stress relief could be considered as different than PWHT and they hoped PQR testing wouldn't be needed. And then I was asked if the machined specimens could be heat treated instead of the entire plate because we have a small oven that could do the job. The full plate won't fit inside but the specimens will.
Naturally, if an easier and cheaper way to do it can be found, it makes sense to do that, as long as all complies with the specs. In this case it ain't gonna work.
Thanks for your input.
CHGuilford
To be honest I can't think of any reason why it would make a difference, after all the object is to get uniform temperature through out the piece.
The test is of the weld and the HAZ not the base material, so why would it matter?
By -
Date 06-05-2001 18:39
If the object is to merely fit the test piece into the furnace, by cutting it into smaller sections, then I must agree with Ron that it should not be a problem.
Regards
Niekie
