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topic 59791

How do spotwelds affect steel's resistance to rust?



February 17, 2015

Q. Hi,

We have a common spotweld assembly of 2 small plates, one a common steel and the other is oncology 825. We had to rework some units with this spotweld assembly. To test another part of the total assembly, we had to put them in water for 3 hours. Nothing but water is in this container. Then several units have big rust leaks around the spotweld area.

I think it's from the spotweld itself but I would like to know how the spotweld affected the steel to have rust after only 3 hours in the water. I guess there's crevice rust involved in there.

thank you,

Mario

Mario Lepire
- Canada


February 2015

Hi Mario. I'm thinking that your spell-check program substituted oncology for Incoloy?

I am not a corrosion theoretician and can't tell you whether crevice corrosion vs. galvanic corrosion or other corrosion modes are involved. Capillary action will draw water up into the crevice, and it will leak out and stain. But we should not see the corrosion of bare steel in 3 hours as a quirky phenomena. Rather, we must realize that bare steel has essentially NO corrosion resistance and requires some sort of rust preventative if it is not to be plated or painted immediately. Good luck.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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