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:
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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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