Q: Can I use zirconium bolts in boiling HCl. Concentration would be about 5%?

A: Yes, zirconium fasteners work well in hydrochloric acid but may be a bit overkill at that relatively low concentration but depends on the temperature and other media it may be exposed to. Zirconium screws do not begin to show substantial corrosion in HCl until 130°C (266°F) even up to 37% concentration (reagent grade HCl). You just need to make sure you’re not exposing these bolts to any oxidizing contaminants. Though zirconium is extremely corrosion resistant to acids, if it is exposed to even small amounts of oxidizing media such as ferric or cupric chlorides, it will cause a breakdown in protection, and rapidly corrode. If you are exposing your bolts to oxidizers in addition to the hydrochloric acid you may want to try tantalum bolts which is the combination of harsh chemicals better than zirconium. If not you may also consider Hastelloy C276 bolts.

Q: I have a process that utilizes about 10% hydrochloric acid with trace amounts of other chemicals. I tried zirconium bolts because they are known for HCl but we’re burning through them like crazy and I can’t figure out why they are corroding. Any ideas and what other material may work?

A: I think the key to what you are describing is not the hydrochloric acid corrosion but the “other chemicals” in your process. Zirconium bolts offer excellent resistance to HCl corrosion even upwards of 37%. The problem with zirconium fasteners is that if they are exposed to any oxidizing media. Oxidizers, even in trace amounts can cause zirconium to corrode rather quickly. Depending on the temperature of your process, Hastelloy C276 bolts will be a good fit. For a high temperature application, I would suggest tantalum fasteners. They can handle HCl corrosion even up to the boiling point.