Copper in the Galvanizing Kettle
Can galvanizing copper-containing steels damage my kettle?
For some time there has been a belief amongst galvanizers that any copper introduced into the kettle can quickly cause kettle damage. This belief is not entirely true. Copper is an impurity introduced into the kettle by three main sources:
- Prime Western zinc (can contain up to 0.02% copper)
- Some grades of brightener bar
- Copper-containing steel galvanized in the kettle (such as weathering steel)
The presence of copper in the kettle is a concern because it can cause the breakdown of the gamma intermetallic layer (and thereby the entire intermetallic formation) and also increase intermetallic layer formation. The increase in intermetallic layer formation can cause excessively thick galvanized coatings on steel, which tend to be more brittle than normal galvanized coatings. The breakdown and subsequent reformation of intermetallic layers caused by copper in the kettle have some major implications for galvanizers. The protective layer of intermetallics that form on the kettle wall, and protect it from erosion, can be broken down. The breakdown and then reformation of intermetallics consumes some of the iron in the kettle walls thereby reducing its thickness. If this cycle continues, holes can develop in the kettle. It is important to note the problems described above begin only when the copper level in the bath is around 0.23%. This means approximately 0.23% of your bath would have to be copper. This is a significant amount of copper for most kettles and is not likely to be seen during normal galvanizing practices.
The exceptions are when massive quantities of copper are introduced into the kettle by adding brightener bar with excessive levels of copper or when very large quantities of copper-containing steels are galvanized continuously in the kettle. So to answer your question, in most cases galvanizing copper-containing steels will not damage your kettle. The galvanized coating that develops on these types of steels could be thicker than normal and might also be matte gray since it might have little to no eta layer.
© 2020 American Galvanizers Association. The material provided herein has been developed to provide accurate and authoritative information about after-fabrication hot-dip galvanized steel. This material provides general information only and is not intended as a substitute for competent professional examination and verification as to suitability and applicability. The information provided herein is not intended as a representation or warranty on the part of the AGA. Anyone making use of this information assumes all liability arising from such use.