Where the
world gathers for metal finishing
Q&As since 1989


-----

RVS corrosion due to copper reaction?

We are working on a school project for the railway. On the track line side cabinets are standing in open air. These cabinets are made of stainless steel type 316L. We are being told that the cabinets can corrode because of a copper reaction. Were not sure if this is true, and if it's true we would like to know the exact details of this reaction.

With kind regards,

Sjoerd G
Student - Leeuwarden, Friesland, The Netherlands
2004

---

2003

Sjoerd, it sounds like you are asking us to clarify for you what your project is supposed to be about. I don't think we can do that. It is true that copper is a noble metal which "wants" to plate out onto other metals, driving them into solution, and there are other potential reactions as well. But where is the copper supposed to be coming from and in what form? Copper dust from wear on conductor bars? Root killer sprayed around the tracks? Electrical wiring directly connected to the enclosure? etc., etc.

Please ask your prof if necessary, then clarify what the project is, and maybe someone can help. Thanks.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

---

Mr. Mooney, the copper is coming from the overhead lines. The overhead lines provide the train of electrical energy (approximately 3 kV). When a train is passing by, the overhead line and train connection will produce sparks. These sparks produce the copper parts that (maybe, we have got to figure that out) can cause corrosion on RVS (316L). My question is: What kind of reaction can (is possible in open air under railway circumstances) take place due the corrosion of the RVS.

Sjoerd Greidanus
- Sneek, Friesland, The Netherlands
2004

---

First of two simultaneous responses -- 2004

That's better, thanks! Yes, I would expect copper particles landing and lying on the tops of the stainless steel enclosures to cause galvanic corrosion because copper is a more noble material than even passivated stainless steel. Dissimilar metals which are connected by both a metallic path (the copper touching the stainless) and an ionic path (rainwater or other sources of moisture) form a galvanic battery which produces electron flow through the metallic path and sacrifical cathodic protection of the noble metal by dissolution of the less noble metal.

Because of the small size of the copper particles, I would expect this to manifest itself as pitting and discoloration around each copper particle and a visual and tactile roughness. I have never really examined this actual situation, so I'm talking only of the possible chemistry of a hypothetical situation. It may be a widely known and serious problem or there might be reasons why such a situation is not a real problem.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

---

Second of two simultaneous responses --

Copper as copper chloride is frequently one of the additives in a stainless etchant. One thing to remember is there are no absolutes in plating or in corrosion. What might work very well in 99 settings may fail miserably in one setting. Most people can not come close to identifying all of the variables.

James Watts
- Navarre, Florida
2004

Thanks for your answers. They were very useful.

Greetings,

Sjoerd G
- Sneek, Friesland, The Netherlands
2004