Two High-Performance Alloys, Very Different Applications
In the world of high-corrosion chemical pump materials, two alloys dominate the conversation: Alloy 20 (CN7M) and Hastelloy C-276 (CW2M). Both offer dramatically better corrosion resistance than standard 316 stainless steel — but they achieve it through different metallurgical mechanisms, at different price points, and for different chemical services.
Metallurgy 101: What Makes Each Alloy Special
Alloy 20 (CN7M) — The Sulfuric Acid Specialist
Alloy 20 is an austenitic stainless steel with elevated nickel (29-32%) and additions of copper (2.5-3.5%) and molybdenum (2-3%). The copper content shifts the alloy’s corrosion potential into the passive range in sulfuric acid.
Hastelloy C-276 (CW2M) — The Universal Corrosion Fighter
Hastelloy C-276 is a nickel-molybdenum-chromium superalloy with tungsten. Its exceptionally high nickel content (~57%) and 15-17% molybdenum give it resistance to an extraordinarily wide range of corrosive media.
Corrosion Rate Comparison (mils per year)
| Environment | Temp | 316SS | Alloy 20 | Hastelloy C-276 |
|---|---|---|---|---|
| 10% H₂SO₄ | 150°F | >50 | <5 | <2 |
| 40% H₂SO₄ | 150°F | >100 | <10 | <5 |
| 93% H₂SO₄ | 120°F | >50 | <20 | <5 |
| 10% HCl | 100°F | >100 | >50 | <2 |
| 65% HNO₃ | Boiling | <5 | <10 | >20 |
| 10% FeCl₃ | 100°F | >100 | >50 | <2 |
Decision Matrix: Alloy 20 or Hastelloy C?
| Scenario | Choose | Reason |
|---|---|---|
| Sulfuric acid, 0-70%, moderate temp | Alloy 20 | Excellent H₂SO₄ resistance at ~55% lower cost than Hastelloy C |
| Mixed acid stream with chlorides | Hastelloy C | Chlorides attack Alloy 20; Hastelloy C resists |
| Hydrochloric acid service | Hastelloy C | Alloy 20 has very poor HCl resistance |
| Nitric acid above 150°F | Alloy 20 (or 304L) | Hastelloy C performs poorly in hot HNO₃ |
| Hot chloride environment (>140°F) | Hastelloy C | Alloy 20 susceptible to Cl-SCC |
| Budget-constrained H₂SO₄ project | Alloy 20 | 55% lower material cost |
| Multi-purpose chemical pump | Hastelloy C | Broadest chemical resistance |
Need Help Choosing Between Alloy 20 and Hastelloy C?
We provide both alloys in 100% interchangeable configurations for Goulds 3196 and Durco Mark III pumps. Send us your process conditions — we’ll help you select the right material and quote a competitive price.