Hydrofluoric Acid (HF)
Surprisingly tolerable at low concentration, aggressive at high concentration and anhydrous form — and a real stress-crack risk independent of chemical resistance.
Hydrofluoric acid compatibility is heavily concentration-dependent in a way that's easy to get wrong: at 10% concentration, common elastomers (FKM, EPDM) and PP/PVDF all remain resistant through relatively high temperatures — better tolerance than several other acids show at similar dilution. But by 70-85% concentration, only true fluoropolymers survive, and anhydrous HF gas is materially more aggressive than any aqueous form tested. HF at 30-50% is also independently flagged as a stress-crack risk, a separate failure mode from chemical resistance.
What Survives, By Concentration
10%
PVC/CPVC good to 104°F, failing by 140°F. PP, PVDF, FKM, and EPDM all remain resistant through 140-212°F — HF at this concentration is real tolerable territory for common elastomers, distinct from most other acids.
30-50%
PVC/CPVC drop faster (failing by 104-140°F). FKM and EPDM both drop to conditional by 176°F. HDPE conditional throughout, failing by 176°F.
70-85%
Only PVDF, ECTFE, FEP, and PFA are tested/resistant. HDPE and PP are both conditional-to-failing.
Pure / anhydrous HF gas
HDPE and PP both fail even at 68°F. PVDF is only conditional. FKM fails and EPDM is only conditional even at 68°F — the anhydrous/gas form is real, distinctly more aggressive than any aqueous concentration tested.
Source: combined chemical resistance chart, 858 real data rows. Confirm current ratings with the manufacturer before final specification.
A Second Failure Mode, Independent of Chemical Resistance
HF at 30% and 50% concentration is independently flagged as a Known Stress Crack Agent — meaning it can accelerate cracking under mechanical stress even where the chemical-resistance rating alone looks acceptable. See the full Chemical Tank Stress Cracking analysis for why this matters and where these failures actually start.
Frequently Asked Questions
Is hydrofluoric acid always more aggressive to materials than other acids?
Not at low concentration — this is a real, counterintuitive finding. At 10% HF, PP, PVDF, FKM, and EPDM all remain resistant through 140-212°F, which is meaningfully better tolerance than several other acids show at similar dilute concentration. HF becomes aggressive at higher concentration and especially in anhydrous/gas form, not uniformly across the board.
Why is stress cracking a specific concern for HF service?
Hydrofluoric acid at 30% and 50% concentration is independently flagged as a (A) Known Stress Crack Agent on polyethylene — meaning it carries both a chemical-resistance risk profile AND a separate mechanical stress-crack risk. At 50% concentration, Nitrile, Santoprene, and 316 stainless steel also all rate not-resistant, making it a chemical where multiple failure modes compound.
What material is required for anhydrous HF gas service?
The anhydrous/gas form is materially more aggressive than any aqueous concentration — HDPE and PP both fail even at room temperature, PVDF is only conditional, and even FKM fails outright. This service requires the most resistant fluoropolymers available and should never be assumed compatible based on aqueous HF data alone.
Is hydrofluoric acid relevant to semiconductor manufacturing?
Yes — HF is used in semiconductor etching processes (HF etching, HF pickling), which is why it appears in this project's engineering rules tied to high-purity/semiconductor equipment specification, alongside the general industrial storage/transfer compatibility data above.
Confirm your exact concentration before you specify
Send LibertyCES your real HF concentration, form (aqueous or anhydrous), and temperature — we'll confirm the right material.
Ready to buy or need a fast answer? Call, text, or email James directly — (559) 395-5500 · [email protected].