Q: I’m running a steam surface condenser which is installed on a steam turbine in a thermal power station. I’m using sea water that could be contaminated with chemical pollutants cooling water side of the condenser. Any ideas on a good fastener for the tubes and water boxes?
A: Duplex 2205 screws are commonly used in sea water situations as the provide excellent protection from chloride stress corrosion cracking, as well as pitting and crevice corrosion. However Duplex 2205 does have a temperature limit of 300°C, after which you would experience embrittlement which might be limiting for your application.
A more fitting option worth considering as you are not only dealing with salt water corrosion but also corrosion from chemical pollutants is AL6XN. AL6XN screws are often used in steam surface condensers. This alloy was developed for salt water corrosion applications and offers excellent resistance to stress corrosion cracking, pitting and crevice corrosion in a broad range chloride environments. In addition to its resistance to chloride based corrosion it has also be widely used in chemical processing for resistance to various acids. Plus it has a usable temperature limit over 500°C. Since you have both salt water and chemical pollutants, AL6XN may be a better fit.