Tag: AL6xn chloride resistance

Duplex Bolt Corrosion

Q:  I need some bolting to attach some surface steam piping for a power industry project. They’re using duplex bolts now but its showing some slight corrosion. Chlorides are involved and maybe some other contaminants. Ideas?
A:  Surface steam condensers and other power industry elements that are exposed to salts and chlorides often use AL6XN fasteners which offer a step up in chloride resistance from Super Duplex 2507 steels. Though AL6XN bolts will improve upon corrosion protection it is slightly less strong offering 53ksi vs 82ksi yield strength. If higher yield is needed to match the Duplex bolts, I would then suggest you use Monel K500 (110ksi yield). While AL6XN will be you most economic choice, Monel bolts will give you even further improvement on chloride resistance and higher strength.

Titanium or AL6XN Fasteners for Salt Water & Acids

Q: We’re setting up a salt brine application for a chemical project. There may be some minimal exposure to some acids. Can I uses titanium bolts?

A: Titanium Gr2 and Titanium Gr5 (6Al-4V) fasteners are excellent for almost all salt related environments, but here since you may have exposure to acids, I would suggest you use a different material. Though I don’t know the specifics on the acids and concentrations your process is exposed to, since you said its “minimal”, you may want to try AL-6XN bolts. AL-6XN fasteners were originally developed to combat salt water corrosion, is also useful as a mid-range corrosion resistant alloy. It contains higher nickel content than Duplex steel but less than Hastelloy so it should work in salt brines that are exposes to low levels of acids.