[MW:9419] MW: 9389] MW: 9372] AC welding for P5A & P5C

    Hi Bhavesh,

 

I was in discussion with my good  friend Amitava on this issue. We're good friends in Canada,and even though he's in India, we're still  in touch. Attached are the data sheets from Amitava's company's products, with his due consent.

• UV 421 TT-Predominantly a  fluoride basic flux for DC power source.Basicity 3.3.Major constituents:-

 

• UV 420 TTR/420TTRW-Predominantly a  fluoride basic flux for DC/AC power source.Basicity 3.4.Major constituents:-

• UV 430 TTR-W- Predominantly a  fluoride basic flux for AC power source.Basicity 4.1.Major constituents:-

The basic fluxes fill much the same role in submerged arc welding as basic coatings do in manual metal arc welding. They have a low silica content and are composed of varying amounts of calcium carbonate and/or fluoride, alumina, calcium, manganese and magnesium oxides and rutile(see above).This combination of compounds gives a clean, low sulphur, low oxygen weld metal with good to excellent notch toughness. The basicity of a flux has a major effect on the weld metal properties, most importantly the notch toughness. As a general rule, the higher the basicity, the higher the toughness. The transfer of silicon and manganese into the weld metal is also limited when basicity goes up.

That's why AC flux with higher degree of basicity and with all the above the features(especially more Cao+Mgo and Less of Alumina+ MnO) will ensure more notch toughness in welds  than with DC fluxes. At the same time AC flux may be recommended for lower current also.

If you read the article from Kobelco, it explains nicely the "different Oxygen level" in an AC vs. DC weld .

I hope this would clear your doubt.

Thanks.

 

Pradip Goswami,P.Eng.IWE

Welding & Metallurgical Specialist & Consultant

Ontario, Canada.

Email-pgoswami@sympatico.ca,

pgoswami@quickclic.net

 

 

Thanks Amitabha,

 

As I know by AC welding oxygen pick up (Generally 160~200 ppm) during welding is quite less than DC welding (Generally 250~300 ppm) which gives you a better toughness property.

 

But, how the Oxygen pick up is less in AC welding?

 

Kindly explain mechanism of the same.

 

Regards,

Bhavesh Patel

 

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From: pgoswami [mailto:pgoswami@quickclic.net]
Sent: Saturday, January 22, 2011 12:04 AM
To: 'materials-welding@googlegroups.com'
Subject: RE: 9389] RE: 9372] AC welding for P5A & P5C

Hi Bhavesh,

Is your SAW wire flux combinations based on the Japanese Supplier(Kobelco)? Traditionally  Alternating Current power sources had been very popular with Japanese, I would say the concept originated with them. I'm talking about mid 1980's since when I started working.The advantages of AC being:-

• Cheaper power sources , AC. power sources would not require the rectification to convert to DC.
• Accordingly fluxes were formulated to suit AC.
• Moderate/Controlled  penetration as compared to DC.The penetration characteristics are DC(+ve) most, DC(-ve) least, AC in between.This(penetration) controls base metal dilution and heat input and accordingly notch toughness may be better. However notch toughness  property is not controlled by the power source type alone e.g A.C or D.C, because welding wire flux also have big role to play here.
• If  the welding process is Tandem Sub Arc, then the trail arc is usually AC, to prevent Arc Blow.
• AC/AC tandem arc is also quite common with Japanese fabricators

The materials you mentioned are used a lot in the refining industry.For hydro processing applications there're strict control on residuals and impurities. Some consumable manufacturers formulate  wire flux combinations only  for  AC power sources, while others  could meet such requirements with DC also.

 

The end result is that both DC and AC are feasible options for welding of those steels. The choice of AC over DC could be influenced by the welding consumable manufacturers' recommendations also.

 

Thanks.

Pradip Goswami,P.Eng.
Welding & Metallurgical Specialist & Consultant
Email-pgoswami@sympatico.ca,
pgoswami@quickclic.net

-----Original Message-----
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of amitabha.bhattacharya
Sent: Friday, January 21, 2011 7:04 AM
To: materials-welding@googlegroups.com
Subject: [MW:9389] RE: 9372] AC welding for P5A & P5C

Hi Bhavesh,
You may expect higher toughness values with AC welding for CrMo-steels.
Thanks
Amitabha

-----Original Message-----
From: materials-welding@googlegroups.com
[mailto:materials-welding@googlegroups.com] On Behalf Of JIGO
Sent: Friday, January 21, 2011 2:55 PM
To: Materials & Welding
Subject: [MW:9372] AC welding for P5A & P5C

Dear All,


Why we are using AC current for SAW welding in low alloy steel (Mainly for P5A & P5C) ?

Kindly share your valuable input.


Regards,
Bhavesh Patel
ISGEC, Dahej

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