Seawater induced pitting of SS316L 1

[serendepidy]

I have a filter constructed from SS316L. It has experienced severe pitting around the sealing faces above and below the gasket.

How can I alleviate the situation to reduce the rate of pitting ? Should coatings be used or cathodic protection ?

What is the best way to rebuild the face of the seal so that we can return the filter to service ? Epoxy, machining or other ?

Any ideas wouold be greatly appreciated.

 

[mshimko]

Without any details, I offer the following:
1. Pitting of stainles steel under a gasket or o-ring is almost textbook-common.
2. If your filter has enough bulk to it and you can afford it, probably the best solution is to grind out the area under ther sealing surfaces (on both flange faces, say 1/8th inch deep, and 1/4 inch wider than the gasket), weld-cald a more noble material (inconel, for example), machine back to a smooth surface, and re-install. This is a great, albeit expensive fix.

 

[EdStainless]

The real problem is that someone put the wrong alloy into serivce. Sealing surfaces need to be a better alloy. Either weld overlay like mshimko suggested, or weld the unit to a new ring/flange.
The 6%Mo stainlesses will etch in seawater with tight crevices, but they are usually good enough. If you want something perfect go to a "C" type Ni-Cr-Mo alloy.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[serendepidy]

Does anyone think the rate of this corrosion mechanism could be exacerbated by MIC. This is a seawater system.

We have decided to use fibreglass filter to replace the SS316L from service. This seems the cheapest options. Any other cheap options ?

 

[unclesyd]

Bugs of all persuasions play a prominent roll in corrosion of SS in salt water.

What are you trying to filter?

 

[EdStainless]

No, MIC isn't an issue. Wrong alloy selection is the issue. You will get crevice corrosion quickly in 316L in sterile (synthetic) sea water at room temp.
If your temp and pressure allow, composites are a good choice.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm