Best alloy for brazing SS-316/copper?

[Enginerd]

Hello,

I need to braze copper tubing to an HX that is made of 316 stainless steel. Can anyone recommend an alloy based on experience?

I prefer not to use a flux since the half of the HX is carrying r410a, but I'll do whatever I need to make a strong leak-free joint.

Thanks!

[Electrocoolman]

I would reckon one that had a high 30 - 40% of silver. Still reckon that you will need flux.

Have you tried contacting the manufacturers of brazing rods over there in states. Normally they are very helpful.

[monkey spanners]

I think you need a special rod and a special flux for this. Also seem to remember something about any chlorine in the area of the joint causing corrosion along the joint face.
Will try and find my Johnson Mathey catalogue.

Like Electrocoolman says have a word with your local brazing rod manufacturer.

Jon

[monkey spanners]

Have a look here

http://www.jm-metaljoining.com/applications-pages2.asp?pageid=4&id=116

Jon:)

[US Iceman]

The silver solder I have used in the past for something like this was I believe 50%, but you also had to use the paste flux to keep the materials clean until the solder filled the joint.

[Enginerd]

Thank you for your input!

As recommended I checked with Harris, a "local" manufacturer. They suggested I use SafetySilv® 56. It flows readily, designed for SS, and is an alloy of the following metals:

Ag 56%
Cu 22%
Zn 17%
Sn 5%

Mfg. quote =>

High silver content alloy; makes premium-quality brazes. Free-flowing with unsurpassed capillary attraction and deep penetration. Ductility is high, and corrosion-resistance is suitable for all but strong chemical applications. Offers highest elongation of silver brazing alloys. Suitable for use in the food processing industry. Silver color is excellent match for stainless steel and silverware applications. NSF Certified to NSF C2.Use with STAY-SILV White brazing flux on applications requiring normal heat. Use STAY-SILV Black flux on heavy parts, where localized overheating may occur, and where parts are heated over a prolonged period. Stay-Silv black flux is also suggested when brazing stainless steel.


Thanks again!

Ray

[Enginerd]

Thanks for the tip on crevice corrosion. I didn't think of that!

[Miles Brennan]

As mentioned watch out for crevice corrosion - Johnson Matthey Argo-braze 56 is one of the alloys to go for, but it is extremely expensive and not the easiest to use.
I would suggest something like IPM 50N alloy which is fairly fluid, but has nickel which prevents the chance of nickel depletion at the joint interface and so helps to avoid crevice/interfacial corrosion.
If you need any further advice etc - contact me on miles.brennan@blueyonder.co.uk

Regards

Miles