Back purging

[Fizza453]

While making full penetration groove welds in SS with GTAW, we use back purging at root.
I came to know that there is such a wire exists that does not require back purging, is there such a wire? its name? its manufacturer?


Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[Duwe6]

It is made by Kobe / Kobelco. I have started investigating it, as a part-time 'hobby' project. I should be able to post something towards the end of this year.

http://www.kobelcowelding.com/20100119/Kobelco Flux Coated Wires 2009.pdf

TG-X series, on page 29

 

[muld0020]

We use it sometimes. It works well for what it does, but there are limitations. Its called flux cored tig rod. It works great for open root pipe welds.

It is SFA 5.22 and R308LT1-5, R309LT1-5, and R316LT1-5

You can only do a single stringer root pass with it. You can't do multiple passes on top of one another. Your root gap is very important during production. It's not good for repairs. It also takes more work to clean prior to the next pass.

 

[Fizza453]

What makes R308LT1-5, R309LT1-5, R316LT1-5 capeable of producing sound roots (free from burn through)?
I compare the composition R308LT1-5, R309LT1-5 and R316LT1-5 with E308LT1, E309LT1 and E316LT1 and found that carbon in former ones are reduced to 0.03 from 0.04 and silicon is increased to 1.2 from 1.0.

Is reduction in carbon from 0.04 to 0.03 and increase in silicon from 1.0 to 1.2 makes them capable of producing sound roots or somewhat else?

How reduced carbon and increased silicon produves sound roots withou using back purging?


Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[muld0020]

The GTAW "rod" is a Flux Cored TIG Rod the flux shields the root. This protects the root and eliminates the "heat tint/sugaring" of the back side of the weld that you would get if you used bare wire and no backing.

The carbon content has very little to do with the reason for back purge. The reason for it is a heavy oxide layer with a chrome delpleted layer under will form (heat tint/sugaring) when you do not protect the root (backing). This area would have less corrosion resistance. There are several ways to prevent this, double sided welding, open root with back purge, ceramic tiles, or these flux cored TIG rods.

 

[Fizza453]

Muld0020,

You mean oxygen (from the atmosphere) reacts with chrom (from the weld pool, so sugaring takes place.
Flux will eliminate the reaction between oxygen and chrome, as oxygen helps in burning.

Am I correct?

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[muld0020]

Here is the TGX pamhlet link. I think it should answer your question.

http://www.kobelcowelding.com/pamphlet(TGXseries).pdf

It does take a skilled welder to use it, and the slag removal can be an issue at times. Another product to look at is solarflux, it's a brushed on coating to the back side of the joint.

 

[Fizza453]

Muld0020,

Thanks a lot for the clarifications and explanations.

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN