Letter 034

Can high pH corrode SST?

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I was given the task to aid in degreasing some flexible metal conduit that was supposed to be stainless steel. Upon immersing the conduit in LPS Precision Clean (4:1 dilution w/ water) for 1/2 hour, I noticed that the bright finish on the conduit had turned to a dull grey in many places. Since I do not know the actual material of the conduit (yet), can anybody tell me if pH 12 solutions have this sort of effect on stainless steel? FYI, LPS Precision Clean contains the following per the MSDS - Tetrapotassium Pyrophosphate, Sodium Metasilicate, and Dipropylene Glycol Methyl Ether along w/ some unspecified surfactants.

Jeff Albom
- El Granada, California

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High pH solutions are reported to dissolve the chromium in SST, and you'll find references to this in the plating handbooks; but on the other hand I have seen SST successfully used as the material of construction for heating coils and tanks for very high pH soak cleaning stations.

So, based on book knowledge, my head says, yes, a high pH solution can corrode stainless steel. But my gut says, based on the experience of years, nah, I don't think that conduit is series 300 SST--maybe aluminum or galvanized steel.

Sorry that I didn't really have any answers for you. But I'd love to hear them when you find them.


Ted Mooney, P.E. 
finishing.com
Brick, New Jersey

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