Back purging
Back purging
(OP)
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?
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





RE: Back purging
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TG-X series, on page 29
RE: Back purging
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.
RE: Back purging
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
RE: Back purging
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.
RE: Back purging
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
RE: Back purging
Here is the TGX pamhlet link. I think it should answer your question.
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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.
RE: Back purging
Thanks a lot for the clarifications and explanations.
Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN