Field Guide / Hydrometallurgy & Mining
93%-100% H₂SO₄ — the material ceiling for every equipment type in a concentrated-acid system, and two real vendor conflicts this guide does not paper over.
Most published sulfuric acid compatibility charts treat "sulfuric acid" as one line item. It isn't. A material rated fine for 75% H₂SO₄ can crack at 98.3% from a natural sulfur trioxide (SO₃) contaminant in the acid — a failure mode that attacks PVDF and Noryl, two materials commonly assumed safe for "concentrated" acid. Above that threshold, the correct materials are Halar/ECTFE, flanged one-piece PTFE (never threaded — cold-flow leakage fails the joint), or Alloy 20.
Concentrated sulfuric acid forms a protective iron-sulfate film on carbon steel that substantially reduces corrosion — confirmed independently by two tank manufacturers. That makes engineered carbon steel the standard, economical bulk-storage material at 93%-98% concentration. The guide covers the real conditions attached to specifying it, plus a documented vendor conflict over XLPE tanks at 98% that this guide doesn't smooth over.
The worst failure location in a concentrated-acid system usually isn't the storage tank — it's wherever concentrated acid can accidentally meet water: a dilution tee, an injection point, a flushing connection. That transition creates both a lower-concentration acid and a large exothermic heat release simultaneously, which is where materials correctly rated for the bulk process concentration actually fail.
A mining-rated control valve's body and its diaphragm can carry completely different chemical ratings. One real, named example: a common mining-valve diaphragm material is rated for sulfuric acid to only 38°C (100°F) — well below what heap leach solution can reach in warm-climate operation — even though the valve body tolerates much higher temperatures. The guide names the manufacturer, the exact rating, and the documented substitute material.
This guide reflects vendor-published data current as of September 2026. Chemical compatibility and material ratings should always be confirmed with the manufacturer for your exact concentration, temperature, and duty cycle before final specification.
Commercial "98%" sulfuric acid can run above 98.3% on the certificate of analysis. Above that threshold, sulfuric acid carries a natural sulfur trioxide (SO3) contaminant that attacks and stress-fractures PVDF and Noryl — materials that are otherwise completely fine at lower concentrations. Above 98.3%, step up to Halar/ECTFE, flanged one-piece PTFE, or Alloy 20.
Yes — carbon steel is the standard, economical choice for bulk sulfuric acid storage at 93-98% concentration, not a fallback. Concentrated sulfuric acid forms a protective iron-sulfate film on carbon steel that substantially reduces corrosion, confirmed by two independent tank manufacturers. This requires a vent with a desiccant dryer, corrosion allowance, and a real inspection program.
Two named tank manufacturers publish opposite claims — ProTank documents XLPE failing within six months of service at 98% sulfuric acid, while Poly Processing's catalog lists 98% as XLPE-compatible with no caveat. Get the specific manufacturer's engineering group to confirm in writing that their exact liner/antioxidant system is tested and warrantied at your guaranteed concentration before ordering.
The valve body material and the valve diaphragm material can carry completely different chemical ratings. Netafim's own ALD70 diaphragm — used across its mining valve lines — rates sulfuric acid to only 38°C (100°F), well below what heap leach solution can reach in warm-climate operation, even though the valve body tolerates much higher temperatures. Confirm the diaphragm rating specifically, not just the body material.
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James Riggins
LibertyCES — Liberty Chemical Equipment & Supply
30+ years in industrial chemical systems, reviewing real process conditions before a part number ever gets recommended.
(559) 395-5500 ·[email protected] ·[email protected] ·libertyces.com