Re: [MW:19702] Duplex UNS 31803 - FCAW Shielding Gas

 

Can you share any data for preheat methods for SS, duplex and other high alloys to be allowed in oil gas , refineries. Because we are using LPG to remove moisture in heavy thk. for duplex header boxes in korea.
Regards
Saravanan
Korea.

On Dec 16, 2013 1:31 PM, "c sridhar" <sridhar305@yahoo.com> wrote:

Welding duplex material UNS 31803

TIG 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.

 

 

Mr. Saravanan,

1. SS : Preheat is not required for most 300 austenitic grade stainless steels. The base metal should be brought to  room temperature, 60 to 75 degrees. Preheat is necessary when welding ferritic or martensitic grades. It is  also needed when joining metals that are thick or contain a high percentage of carbon.

2. DSS: Heat input significantly affects the cooling rate that results in the final microstructure. Too low a heat input will often result in a weld that is predominantly ferritic and will not have the same characteristics as the base metal. Often a moderately low preheat (below 75°C ) to remove the moisture on the surface combined with low heat input can achieve optimum phase balance without the formation of excessive ferrite.

Conversely, high a heat input results in slow cooling rates that increase the risk of the formation of inter metallic compounds or precipitates in the weld and HAZ. Choose a heat input with an appropriate intermediate cooling rate that favors austenite re-formation at high temperatures and retards sigma formation at lower temperature1.

For DSS, a relatively low heat input, in the range of 0.5- 2.5 kJ/mm and for SDSS, 0.2-1.5 KJ/mm is better.

Use of propane or induction heating is better compared to LPG  and to void carbon pick up.

 

3. AS: Preheat and inter pass temperature are very important. A range of 200 to 300°C is recommended to all alloy steel and also depends up on CE level .

 

Sridhar.

-------------------------------------------------------

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

 

 

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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

Dear Welding Experts ,

Could you please share quite urgently that,

which shielding gas is best applicable for FCAW-GS for welding Duplex material grade UNS 31803 ( P No. 10H ) and why ?

Also, share the best Preheat method for high alloy steels to remove moisture and for high thk joint applications .

Awaiting for your reply.

Thanks and Regards,

Saravanan,

Korea.

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