From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of limesh M
Sent: Monday, December 13, 2010 7:35 AM
To: materials-welding@googlegroups.com
Subject: Re: [MW:8718] Alloy Steel
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. -- The covering of the weld should be done after performing post-heating or hydrogen bakeout. API 934E- recomemndations for P11 &P12 steel is -"The DHT shall be performed at a minimum metal temperature of 570°F (300°C) for duration of one hour minimum"(typically for all thicknesses of hydrtreaters). If the fabrication it is a pipework the post-heating may be performed at the the typical interpass temperature (e.g 250deg C max for P11/P12 steel) but typically for 30 min max.
Carryout MPT, if client insists (recommended). --This is considered to be a good practices.Depending on the interruptions there could be occurrances of delayed cracking some time.
Note:- If welding is done consistently using H4 SMAW electrode and H5 SAW wire+fluxes, the above requirements may be minimized..
Relative Advantages and Disadvantages of Resistance Heating. The relative advantages of resistance heating are as follows:
(1) Standard heaters can accommodate a wide variety of part sizes and geometrical configurations.
(2) Continuous and even heat can be maintained throughout the welding operation (including during long breaks) from preheat/interpass heating through to postheating or PWHT.
(3) Temperature can be adjusted accurately and quickly.
(4) Welders can work in relative comfort and do not have to stop intermittently to raise preheat temperature.
(5) Non-uniform or gradient heat input can be obtained easily, such as may be required for the top and bottom halves of a pipe or where pipes are attached to heavier sections such as valves.
The relative disadvantages are as follows: -
(1) Elements may burn out during a heat treatment. The possibility of this occurring is greatly reduced if elements are inspected/maintained before each use.
(2) Inadequate work practices may create the possibility for a resistance element to short itself out to the pipe, producing arcing spots
Relative Advantages and Disadvantages of Flame Heating. The relative advantages of flame heating for local heating of welds are low cost and portability.
The relative disadvantages of flame heating are as follows:
(1) Minimal precision and repeatability.
(2) Minimal uniform temperature distribution.
(3) The great amount of operator skill it requires.
(4) Risk of damaging the material
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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