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.