Q: I am needing to replace some hex heads and nuts on an HCL tank lid. It appears they were originally coated and due to a previous leak, they are starting to corrode. What would be the best alternative bolt type for this situation? HCL concentration is 37% and is at normal room temperature.
A: Coatings in concentrated HCl is very risky. If the coating gets breached, the bolt will fail rapidly and this could easily happen with HCl as its vapors can usually penetrate most coatings. To have a solution that will be more robust would be to go with a nickel alloy like Hastelloy C276 fasteners. Hastelloy C276 is designed for HCl service and will perform very reliably assuming your HCl is at ambient temperatures. You could see this by looking at the HCl iso-corrosion curve below.
