Stainless Steel and Copper Nickel Corrosion

[TugboatEng]

I have a 90/10 CuNi keel cooler on a boat in salt water that is corroding in the immediate vicinity of it's stainless steel attaching bolts. The bolts are isolated from the exchanger and not the steel hull. Any surface that faces the fastener within about 6 inches has a significant reduction in wall thickness. There is also pitting of the stainless hardware. I believe 18-8 hardware was used. Perhaps using something more stable like 316 would reduce the rate of corrosion?

 

[weldstan]

The 316 won't be much an improvement. I suggest aluminum bronze fasteners. Is the wall thickness loss in the 90/10 or the carbon steel?

 

[TugboatEng]

The steel is protected by paint, there are no issues there. The manufacturer of the cooler recommends silicon bronze fasteners for attaching the anodes to the cooler but then stainless fasteners to the hull. I have no issues giving an aluminum bronze fastener a run. They are much closer in galvanic series. They will be protected by hull zincs so wastage shouldn't be too much of an issue.