Selection of stainless steels for handling hydrofluoric acid (HF)
Introduction
Hydrofluoric Acid is extremely aggressive and attacks most metals and glass.
The approach to the selection of stainless steels is similar to that for hydrochloric acid.
Commercially concentrated acid is around 40wt. %
Corrosion resistance of stainless steels
The iso-corrosion diagram 0.1 mm/year lines are represented for 316 types (red) and a 6% molybdenum austenitic types (green)
See
Corrosion Handbook for source data.
The common stainless steel types, 304 and 316 should be considered non-resistant to hydrofluoric acid at any concentration and temperature.
Higher grades of stainless steel can have limited resistance, up to around 2% maximum at ambient temperatures, but may suffer local attack, mainly as crevice and pitting corrosion, even at such low concentrations.
Plastics are normally considered for handling hydrofluoric acid.
Uses for hydrofluoric acid with stainless steel
Hydrofluoric acid is used, along with nitric acid, in stainless steel pickling solution and paste preparations.
Its main function is to loosen and help remove scale deposits.
Incorrect use can be the cause of pitting problems if the solutions or pastes are left in contact with the stainless steel too long. It is very important that the manufacturers / suppliers instructions are followed to avoid damage to stainless steel products when using products containing hydrofluoric acid.
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