302 SS spring rusting?

[tlee123]

We have a 302 SS compression spring that rides inside a borosilicate glass (Pyrex) tube. The wire dia is about .025 and the spring force is nominally 1 lb.

After about 250,000 cycles of the spring, it appears the spring is rusting on the OD where it rubs on the glass. The environment is room temp, 4 psia air, in an "office-like" setting. There are many rust colored particles nearby.

The spring was not passivated after coiling.

Any ideas on how this could be happening? Could the rubbing remove the protective layer on the SS?

Nearby there is a steel part that is not protected from corrosion and there is no rust on that part.

Thanks,

Tom

 

[Metalguy]

Sounds like the glass is rubbing thru the protective Cr oxide which is what makes stainless "stainless". So why isn't the CS also rusting? Because the 302 now has a large "relatively" cathodic area and a small rubbed anodic one.

Add the moisture in the air and a few conductive ions, and you have what you don't want-a miniature battery.

 

[israelkk]

If it is possible you can change the spring into a slightly tapered compression spring which will be more stable and will not rub on the glass wall.

 

[EdStainless]

The rubbing may also be wearing very small particles off of the SS. These have such a high surface area, and no passive film, that they will quickly rust.
You need to eliminate the rubbing contact.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[tlee123]

Thanks for the quick reponses.

We already have a design change put in place where both ends of the spring are centered in one coil depth counterbores. Previously it was centered on one end only, allowing the contact.

I posted so I could understand the mechanism behind the corrosion. I'll need it to explain to our customer.

We're also just about ready to run a test comparing springs that rub and ones that don't.

Thanks again,

Tom