Concentrated Sulfuric Acid Materials Field Guide

A Material Ceiling Most Compatibility Charts Don't Show

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.

Carbon Steel Tanks — Standard, Not a Fallback

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 Failure Point Most Engineering Attention Misses

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 Heap-Leach-Specific Failure Mode Most General Guidance Misses

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.