No its not. Adequate hydrogen control will prevent any cracking issues. We have welded a lot of this material without any hydrogen bakeout and have never experienced any HAC. Problems with this alloy are oversold – with good up front preparation and reasonable care during fabrication and this alloy behaves itself.
John A. Henning
Welding & Materials
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of kannayeram gnanapandithan
Sent: Tuesday, July 23, 2013 11:26 PM
To: materials-welding
Subject: Re: [MW:18257] PHWT for P91
Hydrogen bake out always require for P91 welding with flux containing welding process irrespective of climatic condition.
Pandithan
Welding Consultant
On Wed, Jul 24, 2013 at 9:16 AM, Shomenath Bagchi <snbagchi@ymail.com> wrote:
Hydrogen bake is specially important in monsoon due to high humidity. It can initiate microscopic
hydrogen cracks if not baked in time, so very important in wet climate. These minute cracks can
be revealed by electron microscope.
From: kannayeram gnanapandithan <kgpandithan@gmail.com>
To: materials-welding <materials-welding@googlegroups.com>
Sent: Tuesday, July 23, 2013 10:13 AM
Subject: Re: [MW:18253] PHWT for P91
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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