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Soldering/welding copper to stainless steel

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Dennis Rogers

Sat Jun 27 2009, 02:51PM

Registered Member #1837 Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65

Does anyone know the best way to accomplish this? I need to securely fasten 1/2" copper pipe to polished 18/10 stainless steel for my next project. Any tips appreciated. I don't want to screw up the polished stainless with failed attempts. Thanks.
Dennis

Proud Mary

Sat Jun 27 2009, 03:12PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Hello Dennis,

copper and stainless steel are best welded using an inert gas technique such as TIG (tungsten inert gas), or MIG (metal inert gas) but MIG is not so suitable where the sections to be welded are thin.

Most common stainless steels, like the 300 series, are prone to embrittlement if they are overheated - no doubt about it, this is a skill that has to be learned over time, so don't try TIGging costly parts until you feel you have sufficient experience with scrap pieces.

the_anomaly

Sat Jun 27 2009, 03:14PM

Registered Member #19 Joined: Thu Feb 02 2006, 03:19PM
Location: Jacksonville, FL
Posts: 168

You can attach them but it will not be structurally sound. The main problem is you need to heat the steel until it is molten and keep the copper from melting at the same time. I tried welding some copper to stainless steel using #3 tip with 4psi acetylene and about 5psi oxygen and mild steel filler rod. I just did a little tack weld to see if it held and I had to use pliers to get it off so perhaps a weld all around will suit your needs. I would use a #0 tip and maybe 2psi both oxy and actyl. I think that soldering and braising will not hold at this point and your best bet would be welding. I donâ€™t think you will damage the steel pipe (Although you will tarnish it) but you will likely melt too much copper in the process. Does it need to be conductive or just attached? Perhaps a clamp will better suit your needs.

Dennis Rogers

Sat Jun 27 2009, 03:19PM

Registered Member #1837 Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65

It does not need to be conductive, just attached. I think I might just take it to an experienced welder because it is thin stainless. I don't mind a little tarnish but wanted it to be minimal. Through-bolting will be a last resort but I didn't want to go that route because i need a water tight joint and don't want to deal with gaskets and such. Thanks for the quick input guys, I'll let you know what happens. I should have a project thread soon.

Dennis

Proud Mary

Sat Jun 27 2009, 04:45PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Flanges with gaskets might be suitable, from what you say

MinorityCarrier

Sat Jun 27 2009, 04:58PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

Try researching silver soldering. There are a variety of alloy/flux combos, one of which may work well for what you want to do.

Herr Zapp

Sat Jun 27 2009, 05:03PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Dennis -

Brazing or silver soldering will allow very strong, low-resistance joints to be made between copper and stainless steel, using a copper-based (brass) or silver-based filler metals. Brazing will require an oxy-acetylene torch, but silver-soldering can be done with a propane or MAPP gas torch, if the parts are not too large a heat sink. Brazing and silver soldering are done with the workpiece near dull red heat, so there is no actual melting of the workpieces. Silver soldering using a solder containing 35-45% silver yields very strong, good looking joints, and "standard" brazing or silver soldering flux allows the solder to "wet" both copper and stainless steel alloys simultaneously.

I don't think TIG welding (a process that melts the metal of the workpiece) is ever used to join copper alloys directly to stainless steel.

Regards,
Herr Zapp

Proud Mary

Sat Jun 27 2009, 06:19PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Herr Zapp wrote ...

I don't think TIG welding.... is ever used to join copper alloys directly to stainless steel.
Regards,
Herr Zapp

See: Practical Welding Letter, No. 27, November 2005

See also: Joining of Steel and Brass/Copper

"Stainless steel is routinely welded, but it must be done under an inert gas atmosphere. The most reliable method for welding stainless is the Tungsten Inert Gas (TIG) process, aka. GTAW and Helio-Arc. TIG welding has the advantage of a small weld head, lower heat input is required and filler metal is optional. The other common welding methods for stainless steel, Metal Inert Gas (MIG) and Shielded Metal Arc Welding (SMAW), are not as well suited for welding thin sections like beer keg walls. MIG is commonly used for all types of stainless welding but the weld gun must be held close to the work and this decreases its effectiveness in tight areas. MIG equipment will be more available to a do-it-yourselfer and should provide a satisfactory joint. SMAW
is commonly used for welding thicker pipe and tanks. It has the disadvantage of obscuring of the weld joint during the pass and the slag must be removed between passes. Equipment and electrode filler rods are readily available, however this welding process is not recommended for this application. The welder does not have the control necessary to insure a good weld."

John Palmer is a metallurgical and welding engineer for McDonnell Douglas Aerospace in Huntington Beach, California.

Herr Zapp

Sun Jun 28 2009, 02:02AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Harry -

Not to be argumentative, but I think you misinterpreted your citations.

The quoted text addresses welding of stainless steel only (that is, welding stainless steel to stainless steel). For this application TIG and MIG processes are absolutely ideal. TIG and MIG are the most widely used processes for welding stainless steel.

However, neither the quoted text or the paper by John Palmer mention anything at all about "welding" copper alloys to stainless steel alloys. The Palmer paper does say: "Brazing is useful for making high strength bonds between dissimilar metals".

I'd love to see anything that addresses directly welding stainless steel to copper alloys WITHOUT the use of a lower-melting-point "filler" metal (like brazing alloy or silver solder).

Regards,
Herr Zapp

Proud Mary

Sun Jun 28 2009, 05:59AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

See: PWL #027-Weldability for Weld Repair, Copper to Stainless, Filler for Beryllium Copper November 01, 2005...

Q: Can Copper be welded to Austenitic Stainless Steel?

A: Copper is readily welded to austenitic stainless steels with the Gas Tungsten Arc Welding (GTAW) by using suitable filler metals like ERCuAl-A2 or ERCu-Ni3. Welding is usually limited to thin sections, less than 3mm (0.13 in).

The use of alloy fillers wasn't excluded in the original conversation, nor was the term "welding" defined in such a way as to exclude filled joints.

According to Harris Products Group, their Aluminium Bronze A2 welding wire is suitable for TIG and MIG welding of copper to stainless steel - but in another place Harris describe this operation as 'difficult.'

Laser spot welding of stainless steel to copper/copper alloys is also a developing field.

Anyway that's my lot! I went on a 12-week welding course donkey's years ago, and what I remember now could be written on the back of a postage stamp.

In the future, we shall all be at the mercy of the graduates of quick training courses.

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