Hi! If you refer the ASME Sec VIII Div 1 code About rate of heating / cooling which is mentioned in UCS56 as below " The rates of heating and cooling need not be less than 56C/hr However in all cases consideration of closed chambers and complex structures may indicate reduced rate of heating and cooling to avoid structural damage due to excessive thermal gradient" Where we can interprit ---- My explaination as below ."Restriction of Cooling rate below 56C/Hr is not manadtory ( It says "need not be less than 56C/Hr and not a" SHALL BE" hence cooling rate restriction below 56c/hr is not mandatory ("Code says "need not Be " and not "shall be" therefore it is not mandatory) Therefore you can convince the client on following basis i) Your PQR is qualified on the consideration of lower cooling rate which is of more stringent /severe condition ii) Cooling / heating rate is not essential variable for PQR qualification when it is to be qualified for Impact (only Time and Temp of PWHT is essential variable req to be satisfied) iii) In your case you have a PQR with cooling rate below 56C/hr which is more stringent / severe which satisfied the UTS,Impact value Hence no need of qualifying the separate PQR You can put up the proposal by giving above explaination iv) some time if the job is critical with varience in thikness , configuration and combination of metallrgy , you require to be very cautious during PWHT to avoid steep difference in temperature (Temperature gradient) , Distortion , Therefore you need tocool /heat very slowly to avoid higher temp difference between contact thermocouples attached (To quote some of the spec/ client/consultants ask/ restrict the heating / cooling rate below 40C/hr with difference between the two thrmocouples temp of as close as 15-20C during Heating and cooling whenever the Job is critical My experience with client is --- Some of the clients are apprehencive that , some time UTS deteoriates with very slower cooling rate which we require to convince by showing data on PQR /results With warm Regards Hegde P.B.
--- On Thu, 12/7/12, Devin <yanfeixiu@gmail.com> wrote:
From: Devin <yanfeixiu@gmail.com>
Subject: Re: [MW:14856] Heating/cooling rate requirement for PWHT
To: materials-welding@googlegroups.com
Date: Thursday, 12 July, 2012, 8:42 PM
Dear Hegde, PWHT is performed to the butt weld with production steel thickness of 89mm requiring impact requirement, And the applicable PQR is made with the PWHT in the minimum cooling rate above 56℃/hour..So,Does that means that I need to requalify a new PQR with a more slow cooling rate as you mentioned?, I feel a little bit confused because the heating and cooling rate is not essential variable.
Regards, Devin 在 2012年7月12日星期四UTC+8下午6时11分45秒，Prakash Hegde写道： | 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
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！ -- To post to this group, send email to materials-welding@ googlegroups.comTo unsubscribe from this group, send email to materials-welding+ unsubscribe@ googlegroups.comFor more options, visit this group's bolg at http://materials-welding. blogspot.com/The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents. -- To post to this group, send email to materials-welding@ googlegroups.comTo unsubscribe from this group, send email to materials-welding+ unsubscribe@ googlegroups.comFor more options, visit this group's bolg at http://materials-welding. blogspot.com/The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
| -- To post to this group, send email to materials-welding@googlegroups.com To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com For more options, visit this group's bolg at http://materials-welding.blogspot.com/The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
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