Hi Ankur,
Controlling distortion while L-Seams welding in site conditions for a large dia vessels like coke drum could be quite challenging. This could be more daunting if there is little provision for re-rolling such large diameter. The best choices would be to follow balanced welding condition ( with equal edge prep or unequal vee, e.g. 2/3 prep outside and 1/3rd vee inside). See Fig-3 of the attached document.
The welding sequences could as such:-
1. Weld 50% of O.S bevel, measure the distortion level with profile gauge or other appropriate tools.
2. Chip back ,clear NDE, proceed to weld 50% of inside bevel, check the profile as above.
3. Continue to weld the rest by putting 2 welders in tandem (O/S and I/S). Check the distortion profile as and when required.
4. If L/Seam distortion is under control then proceed for clad restoration
In addition cross stiffeners and shape correction fixtures would be essential. Hydraulic devices could be useful for shape correction. Fixture designs would be best known to the production crews or the site welding engineers executing this welding. Controlling distortion would definitely involving some special skills not exactly as per book. Practical experiences of good fabricators are an asset. I am sure you have the same at site.
The attached article describes some claimed design and coke drum life improvement through elimination of many C-Seams. I am not sure if the same fabrication techniques being followed at your end.
However I think you would find this article as of interest.
Thanks
Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
Email-pgoswami@sympatico.ca,
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Ankur Mande
Sent: Saturday, July 10, 2010 9:04 AM
To: materials-welding@googlegroups.com
Subject: Re: [MW:5932] Distortion in Coke drums
Hi Pradeep,
Please find the point wise reply in blue.
Regards,
Ankur.
On 7/10/10, pgoswami@sympatico.ca <pgoswami@sympatico.ca> wrote:
Hi Ankur,
Is this a new drum for fabrication ?
- No, These are the regular equipments used in refineries.
What's the material thickness?
- The thickness varies from 22 mm at top to 50 mm bottom. The size of the equipment is 9.8 meters ID x 45 m Length. One long seam is roughly 3 meters in length.
What's the welding process to be adopted-SMAW+ SAW or GMAW+SAW or SMAW only.
-The welding process used is SMAW with vertical uphill progression.
Do you have any standards for weld edge prep?
- Yes, the standard are fixed.
What're the consumables recommended in the fabrication drawings/ design Specifications.
- The base material & consumable is of LAS.
Appreciate if you could provide those info.
Thanks
Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
> Date: Fri, 9 Jul 2010 22:49:19 +0530
> Subject: [MW:5919] Distortion in Coke drums
> From: prince.ankur@gmail.com
>
>
>
> Dear members,
>
> What welding sequence should be followed to control the bow type distortion
> during long seam welding in coke drums?? If any one has established any
> procedure please let me know:
> 1. The type of weld edge preparation
> 2. The diameter of electrode to be used
> 3. Any stiffeners to be welded during setup
>
> Regards,
> Ankur
>
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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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