Mixing Copper with SS

[navan4]

I would like to know if anyone has had personal experience about using products that mix copper and ss in their construction.
I always thought that both metals do not expand in the same way, I will post some links to make myself clearer.

https://www.aliexpress.com/item/3284424 ... 6e01d777ad

https://www.northstills.com/product/2-i ... re-boiler/

https://milehidistilling.com/product/8- ... rpose-kit/

I would think that these products would be subject to much higher stresses, since both materials do not expand in the same way, thus being prone to leakage and/or reduced durability., am I right or wrong in this assumption?

[Expat]

Plenty of experience around here on that topic, including my own; mixing stainless and copper is common.

There are no issues. If you use the proper soldering technique the result is a strong connection which will last forever.

[StillerBoy]

Plenty of experience around here on that topic, including my own; mixing stainless and copper is common.

Same here.. and never had an issue with mixing.. what you have read will apply if there is no provision for expansion, but since there are joints with ptfe gasket, the joints become flexible..

Mars

[pope]

The only issue with mixing is leaving copper out of an area where you might want it for its chemical reactivity (like in the boiler when doing a spirit run), this is easily overcome by putting copper pieces in the boiler.

[Swedish Pride]

got Cu soldered in to SS, no issues yet

[cayars]

Something to keep in mind is the temps the metals are exposed to.
We're only running stills in the 200F range.

[Saltbush Bill]

You are over thinking things..calm down and enjoy the hobby.

[navan4]

Something to keep in mind is the temps the metals are exposed to.
We're only running stills in the 200F range.

That sounds logical, only with temperatures a lot hoter would that have an impact I guess.

You are over thinking things..calm down and enjoy the hobby.

Thank you for those wise words.

[navan4]

Plenty of experience around here on that topic, including my own; mixing stainless and copper is common.

Same here.. and never had an issue with mixing.. what you have read will apply if there is no provision for expansion, but since there are joints with ptfe gasket, the joints become flexible..

Mars

Well it was more about the bond between the copper and ss not the gasket I was talking about, but cayars explained this already.

[Expat]

Plenty of experience around here on that topic, including my own; mixing stainless and copper is common.

Same here.. and never had an issue with mixing.. what you have read will apply if there is no provision for expansion, but since there are joints with ptfe gasket, the joints become flexible..

Mars

Well it was more about the bond between the copper and ss not the gasket I was talking about, but cayars explained this already.

That's exactly what I was talking about.

[DetroitDIY]

Coefficient of linear thermal expansion for Cu is about 16 to 16.7 x 10^-6, Stainless 304 is 17.3 x 10^-6, Stainless 316 is 16 x 10^-6.

So, if you have a 4 inch pipe joining copper to stainless, going from room temp to boiling water (68F - 212F), with the worst case coefficient differential, the difference you will tend to develop is a diameter difference of 0.000416 inches... 10 micrometers.

Your solder or weld joints are more than capable.

A different issue I've seen is the solder showing some corrosion. A bit of white, chalky substance at those unions. I haven't seen it a the Cu to Cu joints. I believe this is likely some galvanic corrosion caused by the different redox potentials between the copper and stainless constituents. But, I don't notice any real effect on my system.

A different take on this galvanic corrosion issue. I had some rum that I thought was bad... sulfur issues. I put it in moderately thin walled stainless pot, added a muslin bag full of copper tube cut-offs (letting it rest on the bottom of the pot) and let is sit for several weeks. It corroded two nearly invisible pin holes through the bottom of the pot.

Perhaps the greatest issue I find is not with mixing the two, but with attempting to solder SS to anything. Not being a welder, I'm left with soldering. With proper cylindrical unions, I can get it well enough (though it may take a few attempts to get tight). With butt / bulkhead joints, like where I soldered a SS ferrule onto a SS bowl for a super sized funnel... well, it worked well until it fell of the shelf a week ago in the cold and had a cohesive failure.

Trying to solder closed those pin holes in the SS pot I mentioned has also met with a lot of ugly, unsuccessful work.

Wish I had equipment and skills to weld...

[Swedish Pride]

if you are trying to solder bowls a high watt soldering iron is your friend.
For soldering ferrules to a bowl the torch is fine, but for joining the bowls together and Iron it the way to go.

Harris stay clean makes all the difference, it can be done with normal plumbing solder but I don't need the hassle so just use harris stay clean

[navan4]

Coefficient of linear thermal expansion for Cu is about 16 to 16.7 x 10^-6, Stainless 304 is 17.3 x 10^-6, Stainless 316 is 16 x 10^-6.

So, if you have a 4 inch pipe joining copper to stainless, going from room temp to boiling water (68F - 212F), with the worst case coefficient differential, the difference you will tend to develop is a diameter difference of 0.000416 inches... 10 micrometers.

Your solder or weld joints are more than capable.

A different issue I've seen is the solder showing some corrosion. A bit of white, chalky substance at those unions. I haven't seen it a the Cu to Cu joints. I believe this is likely some galvanic corrosion caused by the different redox potentials between the copper and stainless constituents. But, I don't notice any real effect on my system.

A different take on this galvanic corrosion issue. I had some rum that I thought was bad... sulfur issues. I put it in moderately thin walled stainless pot, added a muslin bag full of copper tube cut-offs (letting it rest on the bottom of the pot) and let is sit for several weeks. It corroded two nearly invisible pin holes through the bottom of the pot.

Perhaps the greatest issue I find is not with mixing the two, but with attempting to solder SS to anything. Not being a welder, I'm left with soldering. With proper cylindrical unions, I can get it well enough (though it may take a few attempts to get tight). With butt / bulkhead joints, like where I soldered a SS ferrule onto a SS bowl for a super sized funnel... well, it worked well until it fell of the shelf a week ago in the cold and had a cohesive failure.

Trying to solder closed those pin holes in the SS pot I mentioned has also met with a lot of ugly, unsuccessful work.

Wish I had equipment and skills to weld...

Thank you for this very informative post, I never thought of corrosion being an issue when combining them.