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Corrosion on SS316 threaded bar that was cut with a chop saw

August 30, 2011

Recently I was involved in a renovation project of a hotel that is located in the Caribbean. The faculties are close to shore an get sea blast. Part of the structure consist of woodwork that was joined using SS316 threaded bars that were cut to suit and then hold together with SS316 nuts on both sides. After a year in service all the threaded bar ends show significant corrosion. The ends were subjected to cutting using a chop saw (no coolant was used). Only the ends show corrosion, not the body of the threaded bars.
What could be causing this problem? Is it possible to solve the problem by grinding off the rust from the ends and then passivating the surface with nitric acid solution before re-installation?
Thanks for any help you can provide.

James Norton
Buyer - Tunapuna, Trinidad & Tobago

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Hi, James.

Yes, I think you have correctly identified contact with the steel blade of the chop saw as the cause of the rust, and passivation as the solution.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 31, 2011

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September 2, 2011

My guess is that they used an abrasive blade chop saw as it is portable, quick and relatively cheap.
The problem is that it quite literally burns the end off rather than truely cutting it off. This changes the metal considerably and provides many sites for the corrosion to start and propagate. Remember, it is stainless and not rust proof. The oxide coating goes a long way for rustproof, but as soon as any rust starts, it will spread.

Grinding the ugly off and then sending it out for passivation or electropolish will help a great deal.

James Watts
- Navarre, Florida