Valves for Strong Acids

Hello,

I have an application that requires acid resistant ball valves in a solution that is mostly sulfuric acid. We have had mild success with Hastelloy valves but after a few months it is impossible to get leak tight shutoff or seal. The valves will continue to slowly leak which generally worsens with time. At that point in time we will need to replace the valves. If we get 3-6 months that typically good.

What I am not understanding is Hastelloy should be good in application according to the corrosion curves (220F and 70% H2SO4) but something is obviously accelerating this significantly. I am assuming that Ultra-Metal tantalum surfaces on our valves will perform better? Could you explain why it would or would not?

Jim

Thanks Jim,

There are a couple of things to consider for acid resistant ball valves that may not be a factor in other process equipment you have. First, a ball valve has tight tolerances. Evan though you are using a Hastelloy ball valve, which is corrosion resistant in many applications, the allowable corrosion rate is much less due to the tight tolerances needed for a leak tight seal in a ball valve.

Additionally you must remember the corrosion curves published are always produces in perfect and pristine lab environments without contaminants. In reality many "contaminants" are unavoidable like iron and actually will accelerate the corrosion of many metals in highly corrosive environments. So use the corrosion curves as a best case scenario as most materials will corrode at actually a faster rate.

The good news with tantalum metal is there is usually a nil corrosion rate in most conditions of sulfuric acid. So for corrosion resistant valves at the conditions you described, 220F and 70% H2SO4, the Utlra-Metal tantalum surfaces would be an excellent choice.

Ultramet CPT Corrosion Experts