Corrosion-Resistant Alloy Valves for Acid Service

ted wang
Jun 5
1 min read

Acid service environments subject valve materials to highly aggressive corrosion that can rapidly degrade carbon steel and standard stainless steel. Selecting appropriate corrosion-resistant alloys (CRAs) is essential for safe and reliable operation in acid handling systems.

Common Acid Service Environments

Sulfuric acid (H2SO4): used in fertilizer, chemical, and refining industries; highly corrosive especially at concentrations 50-99%
Hydrochloric acid (HCl): pickling, chemical synthesis; attacks most metals aggressively
Hydrofluoric acid (HF): alkylation units, glass etching; extremely hazardous
Phosphoric acid (H3PO4): fertilizer production; moderately corrosive
Nitric acid (HNO3): chemical manufacturing; strongly oxidizing

Alloy Selection Principles

Alloy selection requires matching the alloy's corrosion resistance to the specific acid concentration and temperature. Isocorrosion curves from corrosion engineering references provide corrosion rate data as a function of acid concentration and temperature for candidate alloys.

Recommended Alloys by Acid Type

Concentrated sulfuric acid: cast iron or carbon steel (passive film forms at high concentration)
Dilute sulfuric acid: Hastelloy C-276, Inconel 625, duplex stainless 2205
Hydrochloric acid: Hastelloy C-276, Hastelloy B-3, titanium
Hydrofluoric acid: Monel 400, carbon steel, specialized HF alloys
Phosphoric acid: 316L stainless, duplex stainless, Alloy 20
Nitric acid: 304L, 310 stainless steel, zirconium

Non-Metallic Options

For some acid services, plastic-lined valves (PVC, CPVC, PP, PVDF, PTFE) provide cost-effective corrosion resistance. Lined valves are limited to moderate pressures and temperatures but are widely used in chemical processing.

Inspection and Monitoring

Acid service valves should be included in corrosion monitoring programs with defined inspection intervals. Ultrasonic thickness measurement, visual inspection of seat and disc surfaces, and periodic disassembly inspections detect corrosion damage before it becomes a safety or environmental hazard.