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I would like to solder a drain fitting onto my ultrasonic cleaner's tank. The fitting and the tank are both stainless steel. During its operation, the tank is filled with a cleaning solution and heat is applied to accelerate the process.

I'm concerned the silver solder joint and or the tank itself may become compromised overtime. Could there be a galvanic reaction between the solder and the tank, especially in the presence of mildly corrosive cleaning agents and heat?

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  • $\begingroup$ It depends on the composition of your inox. There are several sorts of inox. But usually the potential of usual inox alloys is not very different from the silver redox potential. So the corrosion looks improbable. $\endgroup$ – Maurice Mar 2 at 8:24
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The composition of Silver solders, themselves, as presented in this reference shows large differences in percentages of the anodic zinc and the cathode metal, with respect to possible galvanic based corrosion:

The compositions for the most commonly used jewelry grade silver solders are as follows, in descending order of melting point, from Knuth’s “Jewelers’ Resource”. Their compositions may vary with the different manufacturers, especially in the zinc content:

IT (extremely hard) 80Ag, 16Cu, 4Zn (sometimes no zn)

Hard 75Ag, 22Cu, 3Zn

Medium 70Ag, 20Cu, 10 Zn

Easy 65 Ag, 20Cu, 15 Zn

Extra Easy 56 Ag, 22 Cu, 17 Zn, 5 Sn

Easy Flo 45 Ag, 15 Cu, 16 Zn, 24 Cd

There is at least one study, to quote from Corrosion Issues in Solder Joint Design and Service:

Corrosion is an important consideration in the design of a solder joint. It must be addressed with respect to the service environment or, as in the case of soldered conduit, as the nature of the medium being transported within piping or tubing. Galvanic-assisted conosion is of particular concern, given the fact that solder joints are comprised of different metals or alloy compositions that are in contact with one-another.....

Functionally, however, it is the loss of material, be it the filler metal or the loss of nearby substrate-material, that most sibtificantly impacts solder joint performance and reliability. Material loss degrades the joint’s capacity to support a mechanical load, provide hermetically for a container structure, or sustain continuity in an electrical circuit.....

The predominance of one or more corrosion mechanisms, be it uniform, pitting, or crevice corrosion, as well as the rates of material loss, are very sensitive to the alloy properties (composition, phase distribution, oxide layer chemistry and thickness, etc.) and the service environment.

So, to answer your question, there is likely cause for your concern, but based on the last comment, a correct assessment likely requires the precise nature of the Silver solder employed and what chemicals, and associated mixes, that could act on the solder joint over time.

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