plating, anodizing, & finishing Q&As since 1989
Can stainless be re-passivated?
My boats submerged (in salt water)outdrive 300 series stainless steel parts/prop shaft have been exposed to a heavy dose of swimming pool chlorine for about three weeks, the stainless taking on a black mottled sponge like appearance, though still smooth to the touch. The source of the chlorine has been removed, the boat is still moored in salt water. Will the stainless become "passivated" again, or is a very expensive overhaul/replacement of parts required? I recognize that this is out of your usual scope, but cannot find anyone in the local boat/marine community that has an answer.
- San Diego, California, USA
You apparently already know of the problems caused on stainless by chlorine from swimming pools. This is obviously an unusual situation where you have the combination of swimming pool water and salt water in the ocean.
If the steel has any pit corrosion microscopically, you will continue to have ongoing problems. The stainless will not repassivate under these conditions. The stainless SHOULD be pulled out and repassivated to be safe. Realizing that you may not want to do this, you should be VERY careful to watch the parts to make sure that you do not have ongoing corrosion and even structural damage later.
Stellar Solutions, Inc.