TIG - Sanitary SS

[TroyWood]

Hey guys,

I'm fairly new to the forums and I have been looking around for some information on thin wall sanitary SS TIG welding. Thin being in the 1/6" and under range, and my application is brewing equipment. I have done a fair amount of TIG welding, but have never really messed around with back purging. I get the general idea as far as purging goes and I will be performing a butt weld between a flange and a piece of tubing coming out of a brewing vessel. My question is this:

When I research back purging a lot of the talk is about joint preparation. For my application, should I follow the "0 landing" approach and slightly bevel my edges to a tight fit? Also, I know it is common practice for many to not use filler for such an application..but I'm not a fan of cracked welds. Any advice would be greatly appreciated.

-Troy

[Paul Seaman]

I have seen flux used inside instead of back purge, never personally done it. beveling the mating surfaces oposite to one another, one inward and one outward seems to have helped me with aluminum vessels. I again cannot speak for Stainless, in your application.

Peace,
Paul

[sailor]

If by thin wall you mean 1/16'' instead of 1/6'' then I go tight fitup with no bevel and use 035'' mig wire for filler. The stuff I do doesn't carry any pressure but has to be strong.

[TroyWood]

Opps,
I meant 1/16"...missed my typo. Thanks for the advice guys. This needs to be strong as well, but pressure is not an issue.

One last question for you sailor, I have read there is a few issues with assuring that you get a nice bead on the inside. Do you typically bump your heat up a little as compared to a typical "ascetically pleasing weld" for thin gauge to assure this? I have been doing some practice welds on a joint comparable to what I will be doing, I notice there is no sugar at all and the outside weld looks as I would like it..but the inside seem is not completely sealed. Any recommendations? Thanks again for your time.

-Troy

[wrenchnride247]

Just butt them together on that thin of a material no bevel, as sailor said. Back purging is the best way to weld sanitary tubing. You need to be able to cap both ends of the piece off. Several companies make purge kits for tubing, but aluminum foil will work. Insert a argon hose in one end through the foil, and leave a small hole in the other end to allow pressure to escape. You only need about 5cfh. running through the purge hose. Use a 1/16th tungsten and about 40-50 amps. You really shouldn't need filler on this if the fit is good, and when your done the iside should look like the outside. (you might want to practice this on something else first) Sanitary tubing comes in 316 grade SS. If you use filler it needs to be 316L. This alloy of SS has molybdenum in it which increases resistance to corrosive liquids. (like what most companies use during a CIP)

[TroyWood]

Great, sounds good. After posting I made a few more practice attempts and it looks good. Thanks for your input Wrench, I had the general concept in mind..but it never hurts to ask. Happy welding

[popspipes]

Just butt them together on that thin of a material no bevel, as sailor said. Back purging is the best way to weld sanitary tubing. You need to be able to cap both ends of the piece off. Several companies make purge kits for tubing, but aluminum foil will work. Insert a argon hose in one end through the foil, and leave a small hole in the other end to allow pressure to escape. You only need about 5cfh. running through the purge hose. Use a 1/16th tungsten and about 40-50 amps. You really shouldn't need filler on this if the fit is good, and when your done the iside should look like the outside. (you might want to practice this on something else first) Sanitary tubing comes in 316 grade SS. If you use filler it needs to be 316L. This alloy of SS has molybdenum in it which increases resistance to corrosive liquids. (like what most companies use during a CIP)

I agree with this.
I used to make purge plugs out of armaflex insulation, plastic foam packing etc, cut them with a homemade cookie cutter type tool, I also kept a roll of heavy aluminum foil in the gang box as well for the short fittings etc.

Cut the tube ends with a chopsaw, lathe, coldsaw etc, remove burrs, tack the joint together and weld it up after letting the purge flow long enough to remove the atmospheric air from the inside.
Then use a ss wire brush to clean the welds while the tube is still hot.
3M makes some good wheels to remove the tarnish as well, I use a 2S FN 8"x 1" x 1/2".
For buffing the inner weld like on a short ferrule etc I used a die grinder with cut up squares of 3M 7440 hand pads with a 1/4" bolt thru the center to fit the die grinder, it removes the tarnish but leaves the weld intact.
Be careful at the finish of the weld, I used to speed up before breaking the arc to keep from cratering as they will show up on the inside as well.
I have seen crater holes go all the way thru the tube.
I made adapters to use these wheels on a 4 1/2" angle grinder.
Sanitary welds very seldom require filler, except in a case of poor fitup etc.

[popspipes]

Sanitary tube comes in 304 304L 316 316L, and other grades I am not familiar with. When I was working we used almost exclusive 304, today they are using 316 as the 304 isnt quite the quality it was a few years ago. I even saw rust on some new 316 tanks, I think something has changed with the metalurgy maybe??
Sanitary Tig isnt hard to do but does require practice to become proficient in your sanitary welds.

[superflux]

Purge only!

NEVER use Solar Flux or any type of contaminate inside sanitary or other high purity systems. This would allow bacteria to collect and this is why you never use socket weld fittings in any food process systems. Infact, the inside pentration should be as smooth and flush as if it were not welded.

[paulrbrown]

Solar Flux is a mama to get off, even when you can get at it with a wire brush......good for big open areas which would be hard to back gas, but not pipe.....masking tape can be used to seal ends of tube, as l9ng as you are not too close...hope this helps, Paul