Corrosion of Stainless steel anchors

Koen is correct: 316 stainless will not corrode in seawater. But it's not ordinary NaCl (table salt) from seawater that's corroding the bolts. Limestone dissolves in rainwater which runs down the rock, also picking up NaCl deposited by sea spray along the way. This runoff water then gets on the bolts, and especially behind the hanger. When the rain stops and the water evaporates, the Ca and Mg cations from the limestone combine with the Cl in the seawater to form both CaCl2 and MgCl2. After several rain/dry cycles the MgCl2 (Magnesium Chloride) and CaCl2 (Calcium Chloride) become highly concentrated on the bolt. It is these high levels of Chlorides that are causing Stress Corrosion Cracking (SCC) at ambient temperatures in ALL Series 300 stainless steels. I have no reports of SCC in marine Granite at this time. We have credible reports of SCC in marine Basalt, one from the Northern hemisphere and one from the Southern. Formal analysis will be done this summer. Koen is also correct about titanium. Currently, Ti bolts are the only material proven to resist these conditions with 14 years of perfect service.


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