Valves for HCl

Hello,

My application deals with hot hydrochloric acid (HCl) at about 27% and 50C. Typically we use Hastelloy ball valves and Hastelloy plug valves but after a few months it is impossible to get leak tight shutoff or seal. PTFE valves do not work in this application as the HCl seems to permeate the liner and causes corrosion on the back side and swelling of the PTFE liner. This the creates issues with the actuation of the valves. This corrosion problem occurs on both ball valves and plug valves and after a few months in service I could no longer obtain a leak tight shut off. At that point in time we will need to replace the Hastelloy valves or at least the trim. If we get 3-6 months that typically good.

Will the Ultra-Metal tantalum surfaces on our valves will perform better or help with this problem? What about the costs?

Thanks
Jim

Hello Jim,

HCl at 27% and 50C will certainly corrode Hastelloy C276. I have attached a corrosion curve to help you better understand the corrosion rates of the different materials. On the Hydrochloric Acid Iso Corrosion Curve, essentially you want your operating point to be as far below the line as possible as each line represents a 5 mil corrosion rate per year. The further you are away from the line, the corrosion rate will either be exponentially better or worse. In your case, you are operating right on the borderline of the Hastelloy (depending on what grade) and in real-world process conditions all the curves generally shift downward due to other elements and conditions (flow, temp swings, crevices etc.) that accelerate corrosion.

So in the case of valves, ball valves or plug valves, a small amount of corrosion will quickly effect how well the valve can seal. Because of the valves need to seal properly, the corrosion allowance for a valve is very small and this why you are seeing this problem so often.

Looking at the HCl Iso Corrosion Curve, tantalum's corrosion rate is orders of magnitude less than Hastelloy. At you HCl operating condition the Ultra-Metal tantalum surface would definitely improve the life at a cost that would be comparable to a Hastelloy C276 valve.

Best Regards
Ultramet CPT Corrosion Experts