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Chemical processing fasteners must resist specific acids at defined concentrations and temperatures. Hastelloy C-276 (UNS N10276) is the most versatile choice, resisting HCl at all concentrations and H2SO4 to elevated temperatures. For hydrofluoric acid (HF), Monel 400 is the only suitable nickel alloy, resisting all concentrations to 150°C. Hastelloy C-22 provides the broadest resistance across mixed oxidizing and reducing acid environments.
Chemical processing environments expose fasteners to concentrated acids, mixed acid streams, and elevated temperatures that rapidly destroy standard stainless steels. Selecting the correct alloy requires matching the specific acid type, concentration, and temperature to the alloy's proven corrosion resistance data. The wrong choice can lead to rapid pitting, crevice corrosion, or stress corrosion cracking with process safety implications.
The following table matches common process acids to the best-performing fastener alloys based on iso-corrosion data (<5 mpy / <0.13 mm/year). Note that stainless steels (including duplex grades) are generally unsuitable for strong reducing acids like HCl.
| Component | Recommended Alloys | Why |
|---|---|---|
| Hydrochloric Acid (HCl) | Hastelloy C-276, Hastelloy B-3 | C-276 resists all concentrations to moderate temperatures; NOT stainless steel or titanium |
| Sulfuric Acid (H₂SO₄) | Hastelloy C-276, C-22, Inconel 625 | Inconel 625: <5 mpy up to 80% concentration at 38°C |
| Nitric Acid (HNO₃) | Incoloy 825, Hastelloy C-22, Ti Grade 2 | Oxidizing acid — high-Cr alloys excel |
| Hydrofluoric Acid (HF) | Monel 400 | Resists all HF concentrations to 150°C; Hastelloy/Inconel NOT suitable |
| Phosphoric Acid | Hastelloy C-276, Hastelloy B-3 | B-3 specifically designed for phosphoric acid |
| Mixed Acids | Hastelloy C-22 | Broadest resistance across oxidizing + reducing acids |
All alloy-acid resistance data is temperature-dependent. Key limits: HCl with Hastelloy C-276 is effective up to boiling at dilute concentrations (consult iso-corrosion charts for concentrated). H2SO4 with Inconel 625 is limited to 38°C (100°F) at concentrations up to 80%. HF with Monel 400 resists all concentrations up to 150°C. Always consult specific iso-corrosion diagrams for your exact concentration and temperature conditions.
Hastelloy has high resistance to corrosion in both oxidizing and reducing environments. The material has excellent resistance to localized corrosion such as pitting as well as crevice and stress corrosion cracking.
View specificationsInconel is very strong in a wide temperature range from sub-zero to approx. 980°C. The material also has very good resistance to mineral and organic acids.
View specificationsTitanium has the highest strength-to-weight ratio of all metals (60% lighter than steel) and is extremely corrosion-resistant in chlorine and seawater. In natural environments, the material is not affected by corrosion.
View specificationsOur team has decades of experience supplying exotic alloy fasteners for critical applications. Contact us for alloy selection guidance and competitive quotes.