Purging/Backing gas in inco alloy welding

Date 05-19-2020 13:17

You might get away with backing with flux. 3 mm sounds pretty thin if you are trying to minimize melt-through and burn through. You have to protect the root side from oxidation if you expect to achieve a quality weld.

Al

By Atuuel

Date 05-20-2020 10:01

But how to protect root side in SAW welding? Argon backing?

By 803056

Date 05-20-2020 12:33

Most people use flux. the same flux you are using to weld. You fabricate a bar with a shallow groove in which you place the flux. Then use an air bladder that can be inflated to press the bar and flux up against the underside of the groove.

Al

By Atuuel

Date 06-04-2020 16:59

Thanks
This thing is also possible.
But is there not any easy way.
Like to skip these backing gas/flux option.

Any such joint design configuration.

By Jim Hughes (***)

Date 05-20-2020 21:23

Atuuel,
Quickest answer is yes, it is required. A couple of questions. 1. What is the diameter? 2. what is the configuration? i.e. double jointed pipe, or is it pipe to fitting? 2. Are you required to back gouge or back grind to sound metal? I'm going to give a response but need more info. Since it's pipe it should be fairly easy to place high heat purge balloons in the pipe, (depending on the answer to question 1 is) build a dam in the pipe with rice paper, or just purge the pipe during welding. Last option could be ceramic tape to be used as backing. Gulco makes a very good product.

By Atuuel

Date 06-04-2020 16:57

Thanks for suggestions,

Previously while manufacturing ss pipes with gtaw we used argon gas backing supported on a long boom.
Same can be used while saw welding.

But while reviewing one pqr from a pipe manufacturing company we noticed, saw welding was done without backing gas for Incoloy pipe.

As backing flux or gases are extra consumptions i am thinking if we can weld first pass with little heat input so that oxidation on other side should be so small that it will have no effect on joint properties. And (double v configuration for saw) while welding other side groove with saw welding we can melt that small oxidation part in the weld metal.
Now question is if there is any limit on acceptable oxidation that will not affect joint properties.

By Jim Hughes (***)

Date 06-05-2020 17:46

Not sure what COC your welding to, diameter and thicknesses your welding. Didn't see it the original post but the oxidation is going to be pretty heavy with no protection. Oxidation increases and weldability decreases has been my exp. If you could grind prior to back welding would fix your problem also. But on the other hand, sound like you have a PQR that shows it was welded without backing gas then the process has been proven out. If you have to qualify a Procedure then follow the one you have from the other pipe company and see what the tests prove.