Selection of stainless steel in hydrochloric acid and hydrofluoric acid

Selection of Stainless Steel in Hydrofluoric and Hydrochloric Acids

Stainless steel is an alloy metal composed of steel and chromium, and it is, by virtue of its corrosion-resistant properties, used in a variety of applications. In some applications, stainless steel will be exposed to corrosive chemical reagents, including hydrofluoric and hydrochloric acids. In such circumstances, it is of utmost importance to select the correct grade of stainless steel for the specific chemical environment.

Hydrofluoric acid (HF) is a strong acid, which can react quickly and vigorously with metals. Stainless steels are no exception, and HF can cause rapid, localized corrosion resulting from microscopic attack at surface defects or crevices. In most cases, the attack can be avoided through proper grade and design selection. The general rule is to select an austenitic stainless steel, such as 304L or 316L, for contact with HF. These steels contain adequate levels of chromium and nickel to protect them against HF. Martensitic stainless steels, such as 410 and 420, are not resistant to attack by HF and should not be used in HF applications.

Hydrochloric acid (HCl) is a much weaker acid than HF, and is used in a variety of industries, including food and beverage processing, pharmaceuticals, chemical processing and metal finishing. In general, all stainless steel grades are resistant to attack by HCl, and nickel-containing grades are particularly useful in aqueous solutions of HCl up to 5%. In more concentrated solutions, references should again be made to austenitic stainless steel grades, such as 304L and 316L, which provide increased corrosion resistance.

In general, stainless steel is one of the most rain stable materials used in process plant applications, and with the correct grade selection can provide years of trouble-free service. However, correct grade selection for hydrofluoric and hydrochloric acid applications is essential for long-term performance. Austenitic stainless steel are the grade of choice for use in these environments, and care must be taken to ensure that their resistance to attack is not compromised through improperly applied surface coatings or plating.

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Introduction

Stainless steel is an alloy of iron, chromium and other metals, and is suitable for use under a variety of corrosive conditions. In particular, stainless steel is capable of resisting corrosion from hydrochloric acid and fluorosilic acid, and is thus an excellent choice for use in these acidic environments.

Types of Stainless Steel

The primary benefit of stainless steel is its ability to resist corrosion and abrasion, and there are many different types of stainless steel available for different applications. The grades of stainless steel which are most suitable for use in hydrochloric acid and fluorosilic acid environments will depend on the concentrations of those acids and the temperatures in which they are used.

Austenitic Grades

Austenitic grades of stainless steel are generally the most corrosion resistant and are ideal for use in hydrochloric acid and fluorosilic acid environments. Examples of these grades include 304, 316, 317 and 316L. These grades of stainless steel tend to be very tough and can also resist scaling at elevated temperatures.

Ferritic Grades

Ferritic grades of stainless steel are also suitable for use in hydrochloric acid and fluorosilic acid environments, but are typically less resistant to corrosion than austenitic grades. Examples of these grades include 409 and 430. These grades of stainless steel are more susceptible to pitting and crevice corrosion, and are therefore better suited for use in low concentration and low temperature environments.

Conclusion

Overall, stainless steel is an excellent choice for use in hydrochloric acid and fluorosilic acid environments. The most suitable grade of stainless steel will depend on the concentration and temperature of the acids as well as the desired properties of the final product. Generally speaking, austenitic grades of stainless steel are the most corrosion resistant, while ferritic grades are more suitable for use in low concentration and low temperature environments.