Q: How does 254 SMO compare with Alloy 20 and AL6XN? Can it handle sulfuric acid?

A: To answer your first question, I’ve ranked each of these specialty alloys in terms of their  general corrosion resistance to sulfuric acid:

1. Alloy 20 Most

2. AL6XN Moderate

3. 254 SMO Least

Overall these alloys all perform well in saltwater and chloride environments, but for an acid application like sulfuric acid, you would likely want to choose a more robust alloy like Alloy 20 fasteners (though it always depends on the concentration and temperature of the acid environment). For strong sulfuric acid environments  254 SMO bolts are not a good fit. Alloy 20 bolts are designed to provide a moderate range corrosion resistance to sulfuric acid, specifically in the range of 20% to 40% in concentration. In hot sulfuric acid Alloy 20 bolts are known for their resistance to stress-corrosion cracking. If you are dealing with a harsher sulfuric acid environment, I’d recommend Hastelloy bolts as they can be used in much higher sulfuric acid concentrations and at elevated temperatures.

Q: I have a hot sulfuric acid application that utilizes approximately 25-32% sulfuric acid. I really need a corrosion resistant bolt but due to the vastness of the operation, I’m wondering if there is a lower cost option than Hastelloy.

A: For hot sulfuric acid in your concentration range, we would need to know the operating temperature to make a recommendation. However generally the most economic option would be Alloy 20 bolts, but for Alloy 20 bolts to be successful in your application the temperature would need to be below 150F.  Beyond 150F, you are better off with Hastelloy C276 bolts otherwise you will suffer a significant corrosion rate in Alloy 20 and likely premature failures.