Q: I was planning on using Hastelloy C276 in hot sulfuric acid. It would be approximately 50% concentration around 100F +/- 10 degrees. Will this be okay? I’m just concerned because I read that it cannot handle strong oxidizing environments and I’ll be using it in an application where its exposed to air? Does Hastelloy C276 need to be in a vacuum? What does an oxidizing environment mean?

A: All grades of Hastelloy can handle air environments. C276 is also fine in moderately oxidizing environments. What is meant by a strong oxidizer is when it is exposed to oxidizing chemicals like ferric chlorides or highly concentrated nitric acid. This is due to it’s lower chromium content than say Hastelloy C22 which can handle these types of strong oxidizers. Air is not considered a strong oxidizer so you  will be perfectly fine using C276 in sulfuric acid at these concentrations and temperatures. For additional corrosion information on using C276 in sulfuric acid reference the C276 / Sulfuric Acid Iso-Corrosion chart.

Q: I have a waste water purifying situation where I’m using chlorine to treat the water. In addition to the acidic solution produced the fastener will also experience high loads, so I’m also concerned with stress corrosion cracking. Currently Super Duplex 2507 is not doing the job. Any recommendations on materials?

A: One material worth considering is Hastelloy C22 fasteners. These fastener are excellent in wet chlorine environments and can be used if ferric chloride is produced incidentally (Hastelloy B2 and Hastelloy B3 cannot handle ferric chloride). In addition, Hastelloy C22 is also know for providing resistance to stress corrosion cracking as well as pitting and crevice corrosion and has a typical ultimate tensile of 111ksi and yield strength of 52ksi