Alloys that can be used in Hydrochloric acid solutions

Hydrochloric acid is a reducing acid in its whole concentrations. It has strong acidic character and the vigorous effect of the chloride ion combines to make it an extremely severe. The super alloys containing high nickel are the only materials that provide significant resistance to hydrochloric acid solutions.

In the presence of oxidizing contaminants, the vigorousness of the hydrochloric acid can change drastically hence this fact should be considered while choosing a service material. Alloys recommended for use in hydrochloric acid are Hastelloy bars C276, Inconel 600, Inconel 625, and Incoloy 825.

Function of Nickel 200 and Monel 400

These alloys show similar performance in hydrochloric acid. With acid concentration up to 10%, both alloys show similar performance with corrosion rates in air-free solutions below 10 mpy. When the concentration is increased such as above 15%, the corrosion of Monel 400 increases steeply hence its applications are limited to room temperature for concentrations below 10% in aerated solutions and within 20% in air-free solutions.

The applications of Nickel 200 are feasible in acid concentrations to 30%, in aerated or non-aerated at room temperature. The function of nickel in concentrated hydrochloric acid may be influenced by relatively low solubility of its corrosion products, care should be taken at high paces.

Uses of Monel 400 and Nickel 200 in air-saturated hydrochloric acid above room temperature are limited to concentrations below 3 – 4%. Monel 400 provides significant performance in dealing with 2% concentration at 120oF and of 1% at 180oF

Increased temperature more severely affects Nickel 200 than Monel 400 in 5% acid. These alloys specifically Monel 400 is commonly used in acids at lower temperatures at higher temperatures. In many process formation of hydrochloric acid occurs as a result of hydrolysis of chlorides or chlorinate solvents, acid concentrations are below 0.5%. Nickel 200 and Monel 400 can serve in these concentrations adequately up to 300 to 400oF.

Inconel 600

However Inconel 600 provides significant resistance to dilute hydrochloric acid solutions, its service is adequate unlike to Monel 400. Inconel 600 shows suitable resistance to cold aerated below 2% concentration and good performance at room temperature to concentrations to 20%.

Incoloy 825

Incoloy 825 provides supreme resistance to HCl solutions. Its resistance is widely enhanced by adding copper and molybdenum as well as higher nickel concentration in Incoloy 825.

Inconel C276 offers outstanding resistance to hydrochloric acid because of its high molybdenum concentration and nominal addition of tungsten. Incoloy C276 provide suitable resistance to corrosion in hydrochloric acid solutions up to 3% at boiling point. 

Inconel alloys with presence of molybdenum, offer supreme resistance to hydrochloric acid, specifically in strong concentrations or oxidizing conditions. These alloys offer better performance than Nickel 200 as well as Monel 400. Inconel 625 provides supreme resistance to hydrochloric acid by 9% molybdenum concentration.

Hence high nickel alloys provide significant performance in powerful acids based applications.