Selection of Uniform Corrosion Resistant Stainless Steel

Selection of Corrosion Resistant Stainless Steel

Stainless steel is a material that has become increasingly popular in a variety of applications due to its corrosion resistance and low cost. As one of the most widely used materials in the world, it is important to understand the differences between types of stainless steel and their relative suitability for use in specific applications.

Essentially, stainless steel is an iron-based alloy that contains a minimum of 10.5% chromium. The chromium forms a passive layer on the surface of the steel which serves to prevent corrosion. As such, stainless steel is frequently referred to as a “self healing” metal due to its ability to continue to protect itself in the presence of oxygen. The addition of other elements such as nickel, molybdenum, or titanium serve to enhance the corrosion resistance of stainless steel, allowing the material to be used in a wide range of applications.

When selecting a stainless steel for use in an application, it is essential to consider the environment in which the material will be used. For instance, if the application will require exposure to a high chloride environment, such as sea water, a stainless steel with high molybdenum content, such as 316L, would be preferable. Similarly, if the application will be in an extremely acidic environment, such as a chemical processing plant, a stainless steel with a higher nickel content, such as 317L, should be used. While there is no “one size fits all” solution for selecting a stainless steel, there are certain types that are more suited for certain applications.

The most commonly used type of stainless steel is austenitic stainless steel. This type of stainless steel contains high levels of chromium and nickel and is resistant to corrosion in most environments. It is frequently used in food processing, chemical processing, and marine applications.

Ferritic stainless steel is another popular type of stainless steel. This type contains lower levels of nickel, but higher levels of chromium, making it more economical than austenitic stainless steel. Ferritic stainless steels provide excellent resistance to corrosion in mildly acidic environments, making it well suited for many industrial applications.

Martensitic stainless steel is the final type of stainless steel. It contains lower levels of chromium, but higher levels of carbon, making it more hardenable than austenitic and ferritic stainless steels. Martensitic stainless steel is best suited for applications that require superior strength and wear resistance, such as knife blades, valves, and compressor blades.

When selecting a stainless steel for an application, the environment in which the material will be used is the most important factor. Based on the environment, a certain type of stainless steel should be chosen to best suit the application. While there are many types to choose from, the three most popular types are austenitic, ferritic, and martensitic stainless steel. Each type of stainless steel is unique and offers its own unique advantages and disadvantages, so it is important to select the appropriate stainless steel that best suits the need.

Stainless steels are widely used in industries such as oil and gas, construction and engineering, and food processing due to their high corrosion resistance and aesthetic properties. Corrosion resistance of stainless steel is, however, dependent on the environment where the material is used, and it can be beneficial to select the appropriate grade for the environment to ensure that the material is effective and long lasting.

The degree of corrosion resistance varies widely between different grades of stainless steel, with some grades providing far superior resistance than others. Ferritic grade stainless steels are generally considered poor for resisting uniform corrosion due to the presence of chromium carbide which can lead to premature failure, but martensitic stainless steels are known to have some of the best levels of pitting, crevice and stress corrosion resistance.

Austenitic stainless steels are the most common type of stainless steel and are usually preferred in higher temperature corrosive environments. Examples of austenitic steels include 304 and 316, which are well known for their ability to resist uniform corrosion. Duplex and super duplex stainless steels are specialised grades designed to combine the advantages of both austenitic and ferritic grades, with greater resistance to corrosion than austenitic types.

For marine and industrial environments where uniform corrosion resistance is required, grade 316 is generally regarded as the best choice. It has excellent corrosion resistance in a range of acid, alkaline and salt solutions, so is well suited to environments such as swimming pool and food processing plants.

For more extreme corrosion environments, super duplex grades are often used. These materials contain a higher proportion of molybdenum and chromium (22-25%) compared to austenitic or duplex grades, giving them improved resistance to pitting and crevice corrosion, intergranular corrosion and stress corrosion cracking.