When it is required to provide heat treatment to the dish end(PFHT) after forming..??

As far as know,

1. Percentage Fibre elongation (as per UCS-79) exceeds 5%

2 Required by client job specifications.

If none of the above mentioned case exists,then is it required to provide PFHT to the dish end..??

If YES,then what is that case...and what is the heat treatment required(Normalizing..??)..????
And alos,why it is required..??..(ie. to refine the grain structure or for any other reason..???)

Please advise.

Thanks in advance.

Thanking You.

The required heat treatment will be the stress relieving as in UCS-56.

when PFHT is not required by the user and exempt by the Code, there is no need to do it, right?

DK

Dear Dr. DK
I'm just new for this forum, so I apologize for my interference - especially that long after this post was subjected.

Maybe there is a reason to apply PFHT even though it hasn't been required by the user or by code…
I would perform PFHT when material is subjected to environment that contains SCC agents.
Let's say for instance: C.S. tank for ammonia (especially with presence of air…)

shmulik

The case you are refering is beyond the scope of Section VIII Division 1

You may or may not perform PFHT, it is up to you.

_________________
Thanks & Regards,
Nasir
Welding Engineer
DESCON Engineering Limited.
Lahore, Pakistan.
Mobile # 0092-336-4145402

Hello Nasir,

I agree. It is not a case of code requirement.
I consider it as a professional liability. I believe that as a designer I fully obliged to my client and I shall cover all professional aspects – not only those that covered by the code. I should take into account entire client's needs in order to supply a safe product of reasonable life-time. Client shouldn't be aware of all the professional aspects. That's why he trusts me to do the job for him.

Best regards!

PWHT is usually required to prevent "Stress Corrosion Cracking" (SCC) and usually for designing a vessel for lower tempertures, like Cryogenic vessels good to minus 320 degrees. Some jurisdiction here is the US require it for amonia tanks because filling a empty tank in the sun can drop the temperture of the metal quite quickly and start this cracking. Usually on the top of the tank in the weld heat effected area under a joggle joint like the one in UW-13(k) There may other application that PWHT is required or recommended in Section I and III construction.

ireuel
Requirement of PWHT / PFHT for this case has nothing to do with temperature drop. I would suggest you go over the following article. You may clearly see that heat treatment for anhydrous ammonia service is only a measure of SCC control.

http://www.nationalboard.org/Index.aspx?pageID=182

"Filling of empty tank" when tank is opened / not under pressure with any volatile (low boiling point) liquid leads to temperature drop towards liquid's saturation temp. whether it is "in sun" or not.
In that situation you shall follow code requirements and restrictions (UW-2 ; UCS-66 ; UCS-68 etc.)

SCC attack of Heat Affected Zone at a top of ammonia tanks caused due to air contamination, as ammonia tanks max. permitted filling is 54%-57% (DOT specifications).

There are some other situations that PWHT is recommended due to operating conditions of dynamic loads / temp. cycles, when residual stress is problematic even though it's not prohibited by a code requirement. For example:

http://www.nationalboard.org/Index.aspx?pageID=180

As I agree water and oxygen should be controled and is the major cause of this. !5 years ago in my first code shop I was assigned, built these tanks and all the cracking started on the head under the crimp made in the shell on the top of the vessel. The tanks were in the middle a field on a farm ususally in the hot sun and filling of the tanks were not being done IAW instructions, IE to quickly. The fill pressure was more than the venting capacity and the tanks were being filled more than the percent allowed by DOT. Just because they have a regulation doesn't mean everyone will follow the rules. All the conditions I discuss increased the cracking from it usual rate. I am sorry I left the water/O2 thing out, this was not intended. But the large temperture drop did increase the rate of the cracking. We visited many sites to find out why some tanks were cracking faster than others. The ones not filled properly were the one that were returning to the shop for repairs years before the ones filled properly. That was a field study I was part of and the one suppier change his procedure and the tanks lasted longer. Action and results.