A: Since your process is exposed to both sulfuric and phosphoric acid, I would suggest Hastelloy C276 bolts. C276 performs very well in phosphoric acid at all temperatures below boiling and concentrations to 65%. In addition, Hastelloy bolts also protect against sulfuric acid corrosion even in high temperatures and concentrations.

Q: I’m using HCl in a pickling process and have used Hastelloy C276 bolts to protect my equipment but am still having corrosion issues. Any ideas?

A: In pickling processes ferric chloride is created which is a strong oxidizer and most pickling process are at elevated temperatures – Hastelloy C276 doesn’t perform well in strong oxidizers. Steel placed in HCl, not only removes rust but creates a chemical reaction where iron combines with chlorine in HCl, making FeCl₃. To prevent corrosion from both the hydrochloric acid which is a strong acid and the ferric chloride which is a strong oxidizer, you may want to try Hastelloy C2000 bolts or tantalum bolts. Hastelloy C2000 features strong acid protection of C276, plus its very resistant to oxidizers. Tantalum is the ultimate for corrosion resistance in HCl pickling process but offers less strength.