Q: I’m running a chemical cleaning process on stainless steel to remove the oxides and to enrich the chromium depleted areas again surface. It’s an acid pickling process, where mixtures of hydrofluoric acid (HF) and nitric acid (HNO3) are used. I’ve tried Hastelloy C276 bolting on my tanks because I thought it was corrosion resistant but its now working. Is this normal?
A: Yes, this is completely normal for Hastelloy C276 to corrode in hydrofluoric acid. HF is extremely corrosive to most metals however Monel and Hastelloy C2000 fair far better than most. Though Monel bolts are very resist to HF, the highly oxidizing nature of nitric acid will corrode them. In this situation, I would suggest the Hastelloy C2000 bolts. This is a unique material because of its ability to resistant not only Hydrofluoric acid and other strong acids, but it has a high chromium content which also makes it very resistant to oxidizers like nitric acid.