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Peter_1
10-07-2013, 07:49 AM
Is it realy necessary using counterflow nitrogen flow (inside) when soldering (TIG welding) SS for nitrogen to prevent forming of oxydation inside the weld?
The main purpose is to TIG the tubes leaktight I suppose and what's inside isn't realy important?

Do you use a gap (to see better the gap) between 2 tubes when soldering or do you try to put the 2 ends as close as possible together? If you use a gap, how wide hen?

ICE/RUNNER
10-07-2013, 07:22 PM
When TIG welding stainless steel pipes that are going to be used to transfer gasses or liquids I would use the same shield gas the welder uses. You really need to purge the pipes as your welding to get clean welds. As for the gap between the pipes you need a slight gap so you can get full penetration of the weld, a general rule is to make the gap the same size as the filler rod you will be using, so a 1.5mm rod would be a 1.5mm gap. An important thing to remember with welding any pipes that are going to be under pressure is they will need to be tested, sometimes a normal nitrogen pressure test will do, other times you will need to get the welds NDT tested depeding on your application and specification.

I hope this helps.

Josip
10-07-2013, 09:21 PM
Hi, Peter_1 :)


Is it realy necessary using counterflow nitrogen flow (inside) when soldering (TIG welding) SS for nitrogen to prevent forming of oxydation inside the weld?
The main purpose is to TIG the tubes leaktight I suppose and what's inside isn't realy important?

Do you use a gap (to see better the gap) between 2 tubes when soldering or do you try to put the 2 ends as close as possible together? If you use a gap, how wide hen?

I'm not a welder, but according to my experience it is necessary .... without purging SS pipe weld does not of good quality ... question is to use nitrogen or you must use argon .... take a look

http://huntingdonfusion.com/en/news/white-papers/230-why-should-you-use-inert-gas-purging-when-welding-stainless-steel-titanium-and-nickel-alloys.html

http://www.tubenet.org.uk/technical/whypurge.html

Best regards, Josip :)

Grizzly
10-07-2013, 10:10 PM
Simply put.
The trace gas is used to prevent porosity in the weld not to stop impurities within the (brazed Joint)
One is a welded joint and the other is a soldered / brazed joint.
The standard required to meet the EU standard for Ammonia pipework is way higher than other *****s / refrigerants.
With exception of Co2 which is of a similar high standard.
The gap is small when soldering to use the capillary action to move the third party material.
IE braze fuze's between the 2 surfaces to be joined.

The gap for welding is much larger as you are creating a physical blend of the s/s and the filler rod.
With 2 passes of the welded joint.


A basic answer but hopefully it's understood.
Grizzly

Josip
10-07-2013, 10:27 PM
Hi, Grizzly :)


Simply put.
The trace gas is used to prevent porosity in the weld not to stop impurities within the (brazed Joint)
One is a welded joint and the other is a soldered / brazed joint.
The standard required to meet the EU standard for Ammonia pipework is way higher than other *****s / refrigerants.
With exception of Co2 which is of a similar high standard.
The gap is small when soldering to use the capillary action to move the third party material.
IE braze fuze's between the 2 surfaces to be joined.

The gap for welding is much larger as you are creating a physical blend of the s/s and the filler rod.
With 2 passes of the welded joint.


A basic answer but hopefully it's understood.
Grizzly

Good point ;).... but Peter was asking about soldering and then (TIG welding -Tungsten Inert Gas welding -nowadays GTAW)

for soldering is not necessary to use inert gas for sure .... for welding is necessary to use inert gas

... the strength of soldered joint is not as good as weld joint ...

Best regards, Josip :)

Peter_1
11-07-2013, 06:50 AM
Thanks, I meant indeed TIG welding. It's because we're busy with a small NH3 plant and the welders make a spacing between the 2 tubes with their filler rod. I thought it was better to place the 2 tubes very close against each other so that the welding goes faster because they don't need to fill wide gaps then. I thought the porosity inside the tube due to the absence of an inert gas wasn't such a problem, as long as the tubes withstand their strength- and/or pressure test and a leaktest.

chemi-cool
11-07-2013, 08:09 PM
Peter.
I do bits and pieces from SS for milk tanks, I always use gas flow inside the pipes while welding, not nitrogen but argon, never leave any gaps and build the weld on the outside.