Metal finishing Q&As since 1989

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Best treatment for corroding glavanized steel in marine environment?

2003

I am in charge of maintaining the lifesaving equipment onboard a large cruise ship. The biggest part of the job is taking care of the lifeboats which have numerous GALVANIZED STEEL PARTS that are starting to corrode.

The parts are less than 1 year old and I feel this should not be happening since they were designed to survive in a marine environment with low maintenance. For now, we have been treating it as regular steel, applying primer and paint. The problem is that most of the parts are moving parts with edges where regular coatings don't stay too great.

But I'm still looking for someone to confirm to me that this is the most efficient way to go?

Simon Lebrun
- Miami, Florida, USA

Many years ago the Navy had a problem with landing gear parts in their planes. These parts are VERY critical and have to be plated with Cadmium, baked in an oven, then painted at the factory. Objects and/or sand sometimes abrades or scratches the paint and Cad exposing the bare steel to corrosion, but it's not feasible to carry plating tanks on board. They now use brush plating technology which allows to replate by contact without a tank. It could be the answer to your problem.

Guillermo Marrufo
Monterrey, NL, Mexico
2003

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2003

The problem here may be two-fold. One, what type of corrosion are you seeing--penetration of the galvanized coating to allow red rust, or the normal white-gray corrosion of the zinc coating itself?

If bare steel is exposed, the original galvanized coating was probably too thin for this use--the protection of the base steel is directly related to the coating weight of zinc. The zinc itself will normally corrode in marine environments, and with moving parts abrasion of the zinc is going to increase the corrosion rate by removing the passivating zinc carbonate that forms.

To repair this, I would suggest at least investigating use of zinc-rich primers, esp. inorganic types which form zinc silicate. While surface preparation for these is more stringent than many other paints, the zinc silicate is one of the hardest and most durable surfaces around.

Robert M. Woods
- Cleveland, Ohio