Hi Saravanan,
Mixed gases are always better options for FCAW of DSS than pure(100%) CO2 shielding. Please read through API-TR-938C, Clause 4.4 and other clauses for guidance. Also you may refer the attached link for guidance also. Some of the potential risks of 100% CO2 shielding are :-
- poor toughness
- higher hardness in the weld and HAZ
- meeting corrosion test requirements.
Usually DSS is always chosen for demanding applications. Hence the welding consumables and the shielding gases have to be of "quality product".Or else failure in welding test or in service are inevitable.
If 100% CO2 shielding meets all of your project requirements, PQR qualification, radiographic consistency, lower weld defect rates then it's worth trying. Otherwise saving a few "bucks" here and there" may mean bigger headaches at the end. Usually for offshore projects and especially with DSS, clients are very specific. The proposal have to be backed up by the quality results/reports.
The recommendations of the consumable manufacturers mentioned below is worth considering, as the product formulation, testing and qualification are all by them through rigorous process/es.
Thanks.
Pradip Goswami, P.Eng,IWE
Welding & Metallurgical Specialist
Ontario, Canada
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Saravanan Sornam
Sent: Monday, December 30, 2013 6:45 PM
To: materials-welding@googlegroups.com
Subject: Re: [MW:19732] Duplex UNS 31803 - FCAW Shielding Gas
Dear Welding and Metallurgy Experts,
-- With ref. to the below mail ,
in most of the welding consumable manufacturer's recommendation like SandVik, Metrode, FCAW duplex filler for the material UNS 31803, to be done with Argon 75 to 80 % and rest by Co2 shielding gas for optimum results.
Are there any potential risks , corrosion problems Or SCC arises during process in Oil Gas, refineries and other plants, when we use FCAW with 100% Co2 shielding gas ?
Because we are going to propose to our client with 100% Co2 shielding gas for FCAW ( Duplex S31803 material ) , for Production Coolers of GAS development Project.
The fluid inside the header boxes are Hydrocarbon and its condition is Vapor & Liquid mixed.
If you have such records, please do share with me.
Regards,
Saravanan
Korea
On Mon, Dec 16, 2013 at 2:15 AM, c sridhar <sridhar305@yahoo.com> wrote:
--Welding duplex material UNS 31803TIG welding is usually performed with pure argon as the shielding gas. Resistance to, in particular, pitting corrosion can be considerably raised by the addition of up to 2% nitrogen. However, because the risk of pores increases with increased nitrogen content, the latter should not exceed 2%. The addition of around 30% helium markedly increases arc energy and thus enables a considerable increase (20–30%) in welding speed. In the welding of duplex steels, the addition of hydrogen is not to be recommended. In combination with the high ferrite content (over 70%), this can lead to hydrogen embrittlement. Single-sided root beads must be welded with a backing gas. This is normally the same as the shielding gas. A backing gas should also be used for tack welding all the way up until weld thickness is at least 8 mm.FCAW is most suitably performed using argon with an addition of 16–25% carbon dioxide as the shielding gas. Welding with pure carbon dioxide is also possible, but arc stability and weld pool control are noticeably poorer. However, compared with a mixed gas, one advantage is that penetration is slightly better. Also compared with a mixed gas, the voltage should be increased by 2–3 volts when welding with pure carbon dioxide. This prevents the arc being too short.
Also enclosing filler wire details and hope it will of help to you.sridhar
From: Saravanan Sornam <saravanshyla@gmail.com>
To: materials-welding@googlegroups.com
Sent: Sunday, 15 December 2013 4:21 PM
Subject: [MW:19600] Duplex UNS 31803 - FCAW Shielding Gas
--Also, share the best Preheat method for high alloy steels to remove moisture and for high thk joint applications .which shielding gas is best applicable for FCAW-GS for welding Duplex material grade UNS 31803 ( P No. 10H ) and why ?Dear Welding Experts ,Could you please share quite urgently that,
Awaiting for your reply.Thanks and Regards,Saravanan,Korea.
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