Re: [MW:18279] PHWT for P91

PWHT is also for the re-precipetate the carbide uniformly with in the
structure to enhance the CREEP PROPERTY.

On 7/23/13, kannayeram gnanapandithan <kgpandithan@gmail.com> wrote:
> These has been discussed by experts in earlier forum. Aim of pwht is not
> only to reduce residual stress but to bring down the Hardness also.
> After completion of welding, put it on Hydrogen bake out( time according
> thickness) at temp more than preheat+100deg Celsius for 3 to 4 hrs.
> After completion of Hydrogen bake out, cover with glass wool to make it
> slow cooling till 70 degree Celsius and take it for PWHT
>
> Pandithan
> welding consultant
>
>
> On Mon, Jul 22, 2013 at 6:25 PM, rishikesh shahi
> <rishikeshshahi@gmail.com>wrote:
>
>> Dear Binoy,
>>
>> after completion of welding allow to cool the weld metal at 90 deg.
>> centigrade for the formation of complete martensite. in actual the 90
>> deg.
>> centigrade temp. is called Mf Temp. (Mf = Martensite finished temp.).
>> after
>> this we have to do the Post Weld Hydrogen Baking of Welded joint for 04
>> Hrs. at the Temp. of 350-400 deg. centigrade for diffusion of hydrogen
>> from the weld metal.
>>
>> After this you have to allow to cool the weld metal minimum 90 deg.
>> centigrade till completion of PWHT. but the cooling rate should not be
>> more
>> than 100 deg. centigrade.
>>
>> you have to maintain this temp. (90 deg. centigrade) before PWHT.
>>
>> as per code it is only telling about the minimum soaking time that is
>> 30Min., means understood that you are not restricted to maximum.
>>
>>
>> Regards.
>> Rishikesh Shahi
>> Welding Engineer
>> Doosan Power System India Pvt. Ltd.
>>
>>
>>
>>
>> On Tue, May 7, 2013 at 11:38 AM, Binoy Soman
>> <binoy.spp@daelim.co.kr>wrote:
>>
>>> ** **
>>>
>>> Dear experts,****
>>>
>>> ** **
>>>
>>> Kindly explain following queries****
>>>
>>> (a) PWHT holding time for P91 mentioned in B 31.1 is 1 hr/25 mm;
>>> minimum 30 minutes. Does it mean that if the thickness is 6/10/12.5 mm
>>> the
>>> holding time is 30 minutes & for 15 ,20,30,40 mm the holding time is 36
>>> 48,72,96 minutes respectively.****
>>>
>>> (b) I got some special heating curves for P 91 from our group. But
>>> Kindly explain about the reference /standard used for preparation of
>>> this
>>> heat curve ( eg- why the preheat maintenance is 4 hours & again free
>>> cooling). ****
>>>
>>> I raised these doubts earlier in [MW:17585], but I didn't receive any
>>> response. Please give your comments.****
>>>
>>> ** **
>>>
>>> ** **
>>>
>>> *S.Binoy*
>>>
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>
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