After hydrogen bake out, it should not be more than 72 hrs without PWHT. Environment should be dry, no physical movement. It always better to do pwht as early as possible, such a heavy thick not advisable. Check all NDT before taking for PWHT
--Once our shop got a relax from client to keep it as long as one week if the storage was done with assurance that relative humidity would be low and not create risk of cracking due to water.
What we did during that time was using heater in storage shade and monitoring humidity.
Anyhow, no body is comfortable to see 15E welded joint stayed without PWHT too long. PT/MT and volumetric inspection after PWHT is highly recommended.
Regards,
C.Nopadon
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of pgoswami
Sent: Friday, February 26, 2016 11:59 AM
To: materials-welding@googlegroups.com
Subject: [MW:24374] RE: 24373] Time between Hydrogen Bake Out and PWHT
Hi Mac,
One week without PWHT on 3.5" think Grade -91 Steel is too long. In spite of hydrogen bake out one may get cracking. Did any one check the hardness of weld and HAZ by any means (just for curiosity??).
Also prior to the DHT the welds should be cooled to Mf temperature which is generally the ambient temperature. In absence of it full martens tic transformation won't happen causing poor creep strength in these steels. DHT may be adopted before the PWHT, however not advised to delay PWHT so long.
It's worth looking at.
Thanks.
Pradip Goswami, P.Eng,IWE
Independent Welding & Metallurgical Engineering Specialist & Consultant.
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com]
Sent: Thursday, February 25, 2016 3:47 PM
To: Materials & Welding
Subject: [MW:24373] Time between Hydrogen Bake Out and PWHT
Dear Sirs,
We welded a 15E Pipe material (16 inch - 87mm thickness).
Our procedure will be preheated with 205 deg centigrade then welding and will be
( hydrogen ) bakeout and perform PAUT, If accepted in PAUT, immediately followed
by PWHT and will perform MT.
Process is B31.1
The joint has been accepted by PAUT, my query is, how long should be acceptable if there is a delay in performing PWHT?
Right now it is almost 1 week that the welded joint is not yet PWHT.
Need your advice.--
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