Practical Applications of Nickel-Based Alloy Incoloy 800HT in Different Corrosive Media

Incoloy 800HT — a nickel-based alloy with 30–35% nickel and 19–23% chromium — keeps its corrosion resistance across oxidizing acids, reducing acids, chlorides and alkalis. In aggressive plants the flange gaskets and the alloy parts share the same medium, so both are chosen for the chemistry.

Oxidizing Media: Nitric Acid and Hot Air

High chromium (19–23%) builds a dense Cr₂O₃ layer that heals itself in oxidizing environments, and nickel with iron add high-temperature oxidation resistance.

• 65% nitric acid (HNO₃) boiling at 120 °C — corrosion rate below 0.1 mm/year; 98% HNO₃ at room temperature — below 0.05 mm/year. 304 stainless steel can reach 1 mm/year in the same service.
• Air at 800 °C — oxidation weight gain ≤0.1 mg/cm² after 1000 hours; at 1000 °C — ≤0.5 mg/cm² after 1000 hours.

Applications cover nitric acid production equipment, heat exchangers, furnace tubes and high-temperature steam lines in nuclear reactors.

Reducing Media: Sulfuric and Hydrochloric Acid

Nickel at 30–35% resists reducing acids, and iron with chromium reinforce it.

• 10% sulfuric acid (H₂SO₄) at room temperature — below 0.1 mm/year; 50% H₂SO₄ at 80 °C — below 0.5 mm/year. 316L can reach 1.5 mm/year in the same service.
• 1% hydrochloric acid (HCl) at room temperature — below 0.1 mm/year; 5% HCl at 50 °C — below 0.3 mm/year. Ordinary carbon steel can reach 10 mm/year.

Applications cover sulfuric acid plants, hydrochloric acid storage tanks, pipeline systems, reactors and heat exchangers in chemical service.

Chloride Stress Corrosion Cracking

High nickel also suppresses chloride stress corrosion cracking (Cl-SCC).

• Boiling 42% magnesium chloride (MgCl₂) at 155 °C — time to cracking above 1000 hours; 304 stainless can crack within 100 hours.
• Seawater — no stress corrosion cracking in long-term use.
• Water at 300 °C and 10 MPa with chlorides ≤1000 ppm — no stress corrosion cracking.

Chloride duty in oil and gas covers pipe flanges and production equipment, plus desalination units, offshore platform components and nuclear cooling systems.

Alkalis, Organic Acids and Sulfides

Beyond acids and chlorides the alloy handles alkalis, organic acids and sulfides — which is why it appears across five industries.

• 50% sodium hydroxide (NaOH) at 100 °C — below 0.1 mm/year; 10% NaOH boiling — below 0.05 mm/year. Applications: alkali tanks, alkali treatment equipment, chemical reactors.
• Organic acids such as acetic and formic acid — below 0.05 mm/year. Applications: organic acid plants, food processing equipment, chemical pipelines.
• High-temperature hydrogen sulfide (H₂S) — superior to ordinary stainless and low-alloy steel. Applications: oil and gas equipment in sulfide service.
• Field guide — chemical (reactors, exchangers, pipelines), marine (desalination, offshore), nuclear (cooling, steam generators), oil and gas (extraction and sulfide lines), food (organic acid and sterilization equipment).

Typical values for Incoloy 800HT; comparisons with 304, 316L and carbon steel are given in the text above.

Frequently Asked Questions

Why does Incoloy 800HT resist oxidizing acids?

Its 19–23% chromium forms a dense self-healing Cr₂O₃ layer that blocks further oxidation, even in 65% boiling nitric acid.

How does it behave in sulfuric and hydrochloric acid?

Nickel at 30–35% carries the load: below 0.1 mm/year in 10% sulfuric acid at room temperature and below 0.3 mm/year in 5% hydrochloric acid at 50 °C.

Does Incoloy 800HT resist chloride stress corrosion cracking?

Yes — above 1000 hours in boiling 42% MgCl₂, no cracking in seawater, and none in water at 300 °C and 10 MPa with chlorides ≤1000 ppm.

Where is Incoloy 800HT typically applied?

Chemical plants, marine desalination and offshore units, nuclear cooling systems, oil and gas sulfide service, and food processing lines.