Thursday, July 12, 2012

RE: [MW:14853] Heating/cooling rate requirement for PWHT

Hi!
Even though there is a restriction on cooling rate below  56 C  Some time  it is been accepted , provided you have to convince client . e.g. In case of Heat exchnagers , when it is being heatreated in one piece  along with tubes, It is very essential to heat treat with verylow heating rate Some time  you require  to keep 10C/hr This is to avoid distortion of tubes and damage to T/tsht weld . This is being accepted by Client.Howver you should have  qualified PQR for such low heating rate( If the weld requires Impact testing)
Therefore it depends upon the configuartion ,thickness variation of job ,require to be PWHT where we have to take the precaution to avoid any damage to the job
 
Regards
Hegde p.B.

--- On Thu, 12/7/12, kundan.ahirao@gmail.com <kundan.ahirao@gmail.com> wrote:

From: kundan.ahirao@gmail.com <kundan.ahirao@gmail.com>
Subject: RE: [MW:14848] Heating/cooling rate requirement for PWHT
To: materials-welding@googlegroups.com
Date: Thursday, 12 July, 2012, 11:57 AM

Yes it is not mandatory,it is very clearly stated that need not to less than 56 c/hr without any structural damages

-original message-
Subject: [MW:14846] Heating/cooling rate requirement for PWHT
From: Devin <yanfeixiu@gmail.com>
Date: 12-07-2012 8:39 am



Dear All,

As per ASME section Ⅲ NX-4623,Above 800°F(425℃) the rate of heating and
cooling in any hourly interval shall not exceed 400°F(222℃)divided by the
maximum thickness in inches of the material being heat treated,but shall
not exceed 400°F(222℃)and *need not to be less than 100**°F(56**℃)in an
hourly interval.*



Now the actual heating and cooling rate in our production we made is 50℃/hour
which is less than 56℃/hour required above. Our custom insist that this is
unacceptable and should be reheated. But my understanding is that the *56**℃is not a mandatory requirement
*and only the upper limitation is required. Do I understand this correctly?
PLZ guide me! Appreciate it!

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