Stainless corrosion

[blnorman]

I have a solid "stem" made from 316 stainless. The part has almost been eaten away from the inside (again, it's not hollow). It's used in commercial water application. What could attack the steel that badly? Elemental analysis does show a small % of sulphur (0.3 - 3.0 depending on the specific spot). I have not been told the time frame this was in service.

 

[unclesyd]

It sounds like you may have MIC, Microbiologically Induced Corrosion. This is where a bacteria will attack SS in an aqueous environment and as in you case literally destroying it.

Could you post a picture of the stem?

Could you post the conditions that the stem sees?

 

[blnorman]

Haven't been told the actual conditions other than commercial water. Here's what's left of the stem.

 

[metengr]

After reviewing the picture this looks like MIC attack. Normally, the damage starts at the surface where the bacteria attaches, colonizes and from there the damage moves subsurface and results in clusters of caves (corroded material). The end result looks like damage that started from the inside out.

I would suggest you Google MIC damage in stainless steel for more information and conditions that can cause this damage.

 

[unclesyd]

If this was done by bugs it's the worst case I've seen in many a year.
Another possibility if the water has high chlorides and the stem sat there under stagnant conditions it could literally dissolve, as in your case.

Try to get the properties of the water so a little analysis of your problem could be made and suggestions to mitigate same.

In the mean time I would not go back with SS under the same conditions as seen by this part.

 

[blnorman]

Did just that, and you're right it may be the cause.

There have only been 2 failures in 2 years like this though. I have no idea what the number in service are. Any idea why one may be more susceptible than another of the "same" composition?

 

[EdStainless]

What is this inside of? Tight fit? What material?

This is crevice corrosion, doesn't really matter if it was driven by microbes, simple Cl level (doubt it), or some funky water additive.
Water temperature, conductivity, oxygen content, tight crevices, lots of food for microbes.... this list could go on. A few small changes in the environment and I can change the corrosion rate by 1000x.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[blnorman]

Trying to get more specific details.

 

[blnorman]

Still haven't gotten specifics, but have another question. The stem has a 302 stainless blade attached to the bottom (pinned in a slot in the stem). The 302 appears to have been attacked under the stem. What would go after 316, but leave 302 alone?