Mr Thakkar,
I would like add a few more notes on this chain of responses. To start with your query is not to the point. Which GMAW technique you have in mind ?. GMAW although accepted as a very good welding processes, have it's own limitations.
Traditionally GMAW have the following variations:- - Short circuiting (GMAW-S).
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Globular (GMAW-G);
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Pulsed (GMAW-P),
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The first 2 techniques(GMAW-S and GMAW-G) are really NO-GO for BPV fabrication, reasons :
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Short Circuiting Arc-Good for thin sections, frequent chances of lack of fusion, excessive spatter depending on the materials being welded.
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Globular-Higher spatter levels result in costly cleanup Prone to cold lap or cold shut incomplete fusion defects
On the other hand:
Spray- Reliable technique, but difficult to control with straight GMAW process, works well with Pulsed Mode
GMAW-P- Accepted by the industry widely. Some additional notes in API-582 areas follows:-
GMAW-P-may be used for any material thickness In any position. Welding shall be performed with the same make and model of welding equipment using the same program settings as those used in the procedure qualification.
The latest state of art techniques for GMAW is based on waveform technology, such as Lincoln STT or MilerRMD.. ASME Sec-IX,2010 has added quite a bit of description on this technique. Look in Appendix-H . Although non mandatory this appendix explains the pros and cons of waveform technology both from procedure and performance qualifications angle.
GMAW-P or Non- Pulsed based on waveform technology is considered to be most reliable and consistent. However for single sided full penetration joint there could be always ifs and buts, and possible additional NDE requirements from the clients. This technique had been used extensively and with success for high pressure piping in power plant and oil refineries to perform single sided full penetration welding but for pressure vessels still there are skeptisms.
ASME BPV design is traditionally based on CAT,A,B.C, D joints. For thick-walled vessels SAW is the prime welding technique for all fabricators.For CAT-A,B joints no-one would risk any lack of fusion defects in the root passes. If the WPS is established with GMAW at the root pass followed by SAW, every welding QA plan would call for a sound welmetal at the root If the sound root could be established with or without back-chipping (for GMAW) with 100% consistency, then you may apply the same at the discretion of the project specifications.
If the vessel thicknesses are less than 1" wall I would say thickness (typically 3/4") and smaller diameter typically less than 1 meter dia, use of GMAW-P , Lincoln STT or Miller RMD would be a good quality oriented welding process, provided good welder/operators training is done. However to get the consistently good production weld quality levels additional NDE( UT) should be mandated.
Thanks.
Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist & Consultant
Ontario,Canada.
I am from an industry manufacturing hydraulic excavators. We use GTAW extensively for welding high pressure line pipes with end flanges . Pressure upto 350 bar. The joints are but joints without back up strip
--- On Thu, 30/6/11, praveen alavandar <praveenakds@yahoo.com> wrote:
From: praveen alavandar <praveenakds@yahoo.com>
Subject: Re: [MW:11548] GMAW application restriction
To: materials-welding@googlegroups.com
Date: Thursday, 30 June, 2011, 6:02 PM
| Hi, If you application invloves welding of pipes (Where back chipping is not possible), there are two options for welding the root pass. 1. Use electrodes E 6010 or E 7010 (cellulosic Electrodes) or E 7016-1 for non critical lines (e.g., lines other than compressor suction / inlet lines). 2. Use STT (Surface Tension Transfer) Process for root pass, it is similar to GMAW short circuit transfer mode of metal transfer. You'll need to properly set the welding parameters to avoid any LOF, but once your welders are well trained, you can really see the productivity. Please note that some clients still have a restriction on using this process. If you application involves fabrication of pressure vessels, where you have enough access for back chipping the root pass, and you wish not to do so, then SAW is a good option. The joint preparation shall be such that the root face or the land should be long enough to prevent any burn though when welding the root pass, in addition to that you'll have to have tight butt joint (i.e.,) no root gap at all. After completion of one side, weld the other side (without back chipping) with SAW process, you parameters should be such that you have good cross penetration (engulfing the lan or root face) thus giving you a full penetration butt joint without the need for back chipping. Hope this helps. Regards, Praveen Alavandar
--- On Thu, 6/30/11, rajeev arora <rajeevarora007@gmail.com> wrote:
From: rajeev arora <rajeevarora007@gmail.com>
Subject: Re: [MW:11538] GMAW application restriction
To: materials-welding@googlegroups.com
Date: Thursday, June 30, 2011, 4:14 PM
there is electrode , which is having good penetration power i.e. E7010 , get check with the manufacture On 30 June 2011 17:39, Maulik Thakkar <mlkthakkar2@gmail.com> wrote: Dear,, With out chip back. I want the process which can replace slower GTAW for single sided full penetration joint with out any chip back
On Thu, Jun 30, 2011 at 3:55 PM, rajeev arora <rajeevarora007@gmail.com> wrote: SMAW On 30 June 2011 17:05, Maulik Thakkar <mlkthakkar2@gmail.com> wrote: Is there any option of GTAW for root run to be carried out in pressure vessel welding? On Thu, Jun 30, 2011 at 2:20 PM, AVA <ava.ssg@gmail.com> wrote: There is no limitation for GMAW in ASME code. But pay attention that some of gas cavities made in weld metal that are acceptable according to codes, but it’s make may risk for hydrogen induce. Then this process is commonly used for structural equipment’s, not in pressure parts. Regards A.V. From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Dinesh Somwanshi
Sent: Thursday, June 30, 2011 1:06 PM
To: materials-welding@googlegroups.com
Subject: Re: [MW:11528] GMAW application restriction generally GMAW is used for the filling & capping only.generally the amout of heat produced in this process also there will be chances of lack of fusion at the edges ( fusion boundaries ) the torch cup also makes sometimes for welding in the joint.But this process limited to only low pressure . You can follow with the s maw root & hot ,followed by remaining g maw .
regards
dinesh Why GMAW is not widely used for single sided full penetration joints (with out chip back) for pressure vessel industrial applications? Is there any problem regarding to penetraiton or lack of fusion? I am confusing. Request you to give technical answer. --
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--
Regards, Maulik H. Thakkar Larsen & Toubro, Hazira
--
Regards,
Rajeev Arora 0066-854490697 0066-818706419 --
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Regards, Maulik H. Thakkar Larsen & Toubro, Hazira
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Regards,
Rajeev Arora
0066-854490697
0066-818706419
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