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topic 60495

SS304 Nuts are corroding, but not Bolts or washers or anything else

August 21, 2017

Q. I request your kind attention to give me tip or ideas on following matter -- SS 304 Nuts fast & rapid corrosion (60 day) leaving SS304 Bolts and washer, Column pipes, Pump Healthy

I am facing following problem:
We use SS304 Bolts and Nuts fasteners on Deep Submersible pump, facing rapid corrosion on nuts only , changed nuts 3 times but all the time NUT corrodes, leaving bolts Washer healthy. Earlier on we used MS Galvanized Bolts & nuts and they lasted 6-10 months with little corrosion attack. Why same material bolts, nuts, washer, only nuts are corroding so fast within 60-50 days, whereas water quality has been same? Brackish, over 4 years, and the SS304 pumps are doing OK all this time. We have changed nuts from different sources with same results kindly enlighten me.

Kamran Choudhri
Drilling Water wells, Submersible Pumps Installation, Water Works lines - Karachi,SINDH,Pakistan


August 2017

A. Hi Kamran. I can quickly see four possibilities--

1. The first being that the nuts are not 304SS and everything else is. This seems unlikely because you have tried several suppliers.
2. The second possibility is that the nuts were not passivated. You can have a few specially passivated to be sure.
3. The third possibility is that the nuts are highly stressed because of their tightness, in such a way as to create a galvanic hotspot.
4. The fourth possibility is that a thread sealant or other material unique to the nuts is hastening the corrosion.

If you could just lightly spin an extra nut onto one of the bolts you could confirm or refute possibilities 3 & 4. Good luck.

I have heard anecdotally that nyloc type processes reduce the corrosion resistance of stainless steel; I have no reason to either believe or disbelieve it, just to suggest it as a topic for your study if it's applicable.

Regards,

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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
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