Dear Vasu,
ASTM A 335 Gr.P11 is not dangerous compared to P22. We welded plenty of P11 and P22 heavy walled pipes in our work shop with GTAW+SAW>AW+SMAW .If your welder cannot complete the joint in a single stretch, fill 3 passes or 1/3 of the groove thickness whichever is greater before leaving the job (Recommended). Cover the entire circumference of the weld after 1/3 of the groove filled to avoid sudden cooling of the weld metal (recommended). Preheat the joint again as per the approved WPS before starting the welding again. Carryout MPT, if client insists (recommended).
Note: There was no post heat done by us during the fabrication of ASTM A 335 P11 thick walled pipes for medium pressure steam lines during interruption. But we covered the entire joint with thick insulation blanket. Even without MPT we have welded P11 joints nearly up to 63 mm thickness. No cracks observed in RT&UT and the hardness was with in the limit.Electric resistance heating we utilised only for P22 and for P11 we utilised propane gas torch.Client insisted us to do electric resistance heating for P11 material.But we got concession from our client by showing our past experience on this material and they approved our proposal for torch heating. This is my experience and the plant is still running without any problem.
Regards,
Limesh
On Mon, Dec 13, 2010 at 2:54 PM, Prasad Joshi <surpras@gmail.com> wrote:
Dear all,P11 is not a very crack-prone material. It all depends on the WPS and the profile of the joint. In my opinion, following points will govern in fairly deciding the requirement of any corrective actions:a) If the WPS specifiies the Post-heating, the same is mandatory and needs to be carried out w/o any delay before cooling to the RT.b) If the WPS is silent on this, then, it all depends on the rigidity of the weld-joint.
- If the joint is very thick and large diameter, the joint is prone to cracking due to restraints and lower strength of the joint during heating/cooling. In this view, it is very dangerous to discontinue welding immediately after root pass.
- The post-heating followed by slow cooling (wraping insulating cover over the heated part) will reduce the hydrogen cracking.
- In my opinion, the welding of joint can be resumed after carrying out MPT of the filler pass
I hope this clarifies,Regards,Prasad JoshiLinde Engineering India Ltd.On Mon, Dec 13, 2010 at 12:50 PM, manpreet <manpreetsin88@rediffmail.com> wrote:
Hi,
If welding is stopped for some time (less than a hour), the weld shall be covered to insure slow colling and 100% MT shall be done before presuming welding,
if for linger periods, Preheat would be required.
Regards
Manpreet Singh
Welding Engineer
On Sat, 11 Dec 2010 09:58:28 +0530 Prakash Hegde wrote
>Hi!Post heating is to be carried for weld which is dicontinued /interupted for long time where the preheated temeperature of the weld and surrounding area(Base)is not reducedYou can post heat discontinued weld and later on even next day you can continue the unfinished weldHowever it is always advisible to complete the critical metallurgy weld in one go only (Better not to interrupt) In case of power failure you can keep the weld under preheating temperature range till the power is restoredRegardsHegde P.B.
>
>
From: srinivas rao <ksrvasu@gmail.com>
>To: materials-welding@googlegroups.com
>Sent: Fri, 10 December, 2010 8:54:28 PM
>Subject: [MW:8670] Alloy Steel
>> Dear All,
>
>While welding of ASTM A335 Gr P11, what to do if welding was stopped after Root Pass ,Hot Pass and One Fill-Up done without completing the job? Can we do immediately Post Heating for the un-finished job and continue welding next day? or Should we cut and re-weld the joint?
>
>I have one more doubt... In the above situation what if welding and Pre-heating(coil heating) was stopped due to power failure for 2 to 3 hrs and the joint has to come to room temp. Should the joint be cut and re-welded?
>
>Regards,
>
>Vasu
>
>
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To post to this group, send email to materials-welding@googlegroups.com
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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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