Stainless welding

[SBK]

Is the process of welding stainless without filler an acceptable weld?

I did these pieces of 1mm with 35amps and they seem strong enough.

Should I weld the inside also? its for a exhaust can so no extreme temps.

 

[backpurge]

The weld should penetrate right through to the inside, you wil have to purge the inside though

 

[SBK]

Do you need a separate bottle or can you buy a y adapter ?

 

[backpurge]

You can get a y adapter, you will need to put a flowmeter on to control the purge flow

 

[SBK]

OK Thanks.
What Lp/m should I set it at ?

 

[backpurge]

Once you've got all the air/oxygen out you only need a couple of litres per minute to keep the atmosphere inert

 

[SBK]

Right oh Thanks.

 

[ross27]

Is back purging really nesscesary for an simple car exhaust?

 

[backpurge]

If you want to ensure the weld fully fuses through the full thickness of the material, also reduces the chances of internal corrosion

 

[Jim_gsxr1000]

It's good practise, more important with exotic metals and really thin metals, F1 exhausts are 0.6mm inconell, it is welded in a purge tent to keep it protected!

 

[Angusdog]

Titanium Ariel Atom chassis in one such tent: (I love this image)

 

[Georgie]

Sorry if this is stupid, but what do you guys mean by "purg/back purg" the pipe?

 

[matt1978]

It means to create an Inert atmosphere in the section of tube that is being welded.

Sounds more complex than it is but basically you bung up both ends of the pipe, then have a gas supply (usually Argon) fed in at the lowest point and a exhaust hole in the highest point. Once the air has been expelled to a suitable level the remaining Argon will protect the underside of the root from Oxidation

 

[ross27]

Sorry if this is stupid, but what do you guys mean by "purg/back purg" the pipe?

Basically, it means forcing the air out of the inside of the pipe and filling it with argon. Have a look on Youtube for examples

 

[Rrunnach]

For example, process SS dairy pipe, it tube internal is not purged, root cokes up, milk flowing through, particle caught in coked up area, which in turn, will evenutally create bacteria. Food chain, folks get ill, possibly die!!

http://www.millerwelds.com/resource...rosion-resistance-and-increasing-productivity

 

[madkayaker]

I remember reading an actical on mountain bike welding shop where the welders wear BA kit as the room is full of argon!

 

[hotrodder]

I've got a vague recollection that might have been to do with clunk'n'fail?... they also had adverts/artwork showing their TIG welders in action welding aluminium complete with showers of sparks coming off the weld

 

[Georgie]

i cut a 4" flange off an old pipe and welded it to a reducer. all 316 stainless but i used 315 filler 3/32 with 1/16 thoriated tungsten, 6 cup . cleaned the surfaces then acetone and my welds were dark grey...almost looked like the had flux covering them...

will get pics tomorrow guarantee

any ideas?

 

[backpurge]

It not only ensures the weld is "clean" on the inside but allows the weld to penetrate the full thickness of the parent material.

If you don't purge, the metallic oxides that form on the surface of stainless steel prevent full fusion of the joint, you also get serious corrosion issues

 

[backpurge]

i cut a 4" flange off an old pipe and welded it to a reducer. all 316 stainless but i used 315 filler 3/32 with 1/16 thoriated tungsten, 6 cup . cleaned the surfaces then acetone and my welds were dark grey...almost looked like the had flux covering them...

will get pics tomorrow guarantee

any ideas?

Are you talking about the surface of the weld or the penetration bead, if it's the weld surface have you tried cleaning it with a stainless wire brush or using pickling solution, sounds like it could be oxide formation but can't tell without photos