Stainless Steel Corrosion

[sewerratt]

What is causing this and is it a cause for concern? (See pic) We have 304 stainless pipe, bolts, nuts, & washers (per submittal) submerged in a storage tank holding treated, chlorinated drinking water. pH is 7.7. Chlorine residual is 1.7ppm. Pipe was installed about 6 months ago. Tank was brought off line and drained to inspect another item and this was found. Any thoughts?

thanks

 

[Unotec]

Did you use some sort of lock-tite? Judging from the photos, your problem is not the steel but something used in the nuts/bolts.

 

[sewerratt]

Good question. I'll follow up with the inspector and find out.

 

[bimr]

Looks like the piping installer put some sort of sealant around the bolts to seal the bolt holes.

It was probably not necessary. You should check to make sure that the sealant is certified for use in potable water.

Does not appear to be corrosion of stainless steel.

 

[CivEnvEng98]

The steel isn't even blushed.....that's not your problem.

Whatever the lubricant and/or sealant that was used on the bolts/flange holes is what has the rust appearance. Whatever it is, sure hope is was NSF approved.

 

[rconner]

While I guess it may be a popular perception that these are "stainless" materials (and this perception indeed may even influence the initial selection of materials), this is just one more incident that reveals that such materials are not immune to corrosion, nor stain-free. Like with any other materials, rustng or staining effects may or may not be a practical concern, depending on extent in investigation and application etc. The gaskets at least still look pretty well compressed!

 

[Artisi]

If it's not some form of jointing material - get it identified by analysis.

 

[rngrrix]

I think you have one of several issues. One is that 304 stainless and chlorine are not compatible.The higher the chlorine the more quickly the reaction. A few years back we had a level gage nearly corrode through on a bleach storage tank because it was stainless, this occured after two weeks of service. The tank was originally designed for caustic storage and the level column was insulated. You should get an analysis, if the goop appears to have metal oxides in it I would change the oxidizer from chlorine to another more compatible (approved) treatment program.

I think the gasket is over-compressed so you may be getting some gasket degradation as well. I always fix what I know is wrong first so go with new gasket material, like teflon, then re-inspect after a few months.

 

[bimr]

"AISI 304 Stainless steel (W.nr. 1.4301). 304 SS is used as the standard material of construction for potable water applications. It is generally applicable for applications in the mild to moderate corrosive grading category. It can also be used in the presence of chlorides up to 1000 ppm, provided water temperature is less than 50°F (10°C)."

http://www.us.grundfos.com/web/down...99BF3220BD644F38882570120070DC56?OpenDocument

 

[Pump2005]

It could be a lesser grade of Stainless Steel. Also, SS is coated with Chromium giving it extra resistance which can be removed when nuts and bolts are tightened.