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Pitting in SS 316 bolts and flanges in sea water application

Wr operate a desalination plant and have 4 wells for the supply of saline water. We use SS316 bolts and flanges in its inner housing. Lately we are experiencing worst kind of pitting and corrosion in our flanges and specially bolts. Why?

Saad Ullah Khan
- Karachi, Pakistan
2002

You have to change your metal or protect it by cathodic action with special anodes and imposing a current. Once pitting begins it will proceed very fast and can produce catastrophic failure. The chloride concentration and the acidity (pH) inside pits is greater than in the rest of the surface and 316 is not resistant to this because it depends on nickel and chrome oxides to protect but these oxides dissolve in hi chloric solutions.

Guillermo Marrufo
Monterrey, NL, Mexico
2002