While hydrochloric acid (HCl) is a common and critical industrial chemical, it often causes significant maintenance issues for fasteners. Due to elevated temperatures, fluctuating concentrations and permeation of its vapors, utilizing the correct material for your fasteners is key to withstanding this potent acid. This article will briefly review some of the most common fastener material solutions for dealing with HCl most effectively.
Engineered Polymers
Depending on the load and temperature requirements of the application, polymer fasteners can perform very well in HCl solutions. Some of the highest performing polymer fasteners are those in the fluoropolymer family which include PVDF (Kynar) and PTFE. In addition, PEEK is also a high performer although not as good as the fluoropolymers. While these polymers are the most corrosion resistant in HCl from a materials perspective, when it comes to utilizing them in the form of a fastener, the key is understanding if they are strong enough for the application.
Generally speaking, in order of corrosion resistance PTFE would be the best choice followed by PVDF and PEEK. However in terms of strength, the opposite is true with PEEK being the strongest, followed by PVDF and PTFE being the weakest. With polymers, its best to first determine the minimum strength needed and then go up the corrosion resistance scale to select the best material.
Specialty Metals
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n HCl environments, typical steel fasteners generally will not suffice as they are rapidly attacked. For these tough corrosive HCl applications, specialty materials should be considered with one of the most common being Hastelloy C276. This high performance nickel alloy performs well in many HCl environments and far outperforms 316 stainless steel.However, as temperatures and concentrations increase, even Hastelloy C276 has its limitations and will be decimated by corrosion. If the fasteners are hard to replace or cannot fail, more exotic materials likeZirconium or Tantalum fasteners could be considered. While these materials are significantly more expensive, there performance, especially tantalum’s, is second to none.
I’m dealing with a Ferrous Chloride chemical system design that may create fugitive HCl vapors in the enclosed space that make it impossible to employ stainless steel alloys or fasteners. I am curious how to extrapolate that hydrochloric acid iso-corrosion curve into an atmospheric vapor environment? Would the Hastelloy fasteners perform acceptably in a room-temperature atmosphere with HCl vapor?
Thanks, Martin
Hello Martin,
Its best to treat HCl vapor as concentrated reagent grade HCl at 36%. HCl vapors could be very concentrated especially when they condense on parts. Because of this, Hastelloy C276 would be safe bet in HCl especially at room temperature.