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.