What Are the Materials of Stainless Steel Flanges?

I. Introduction

In the industrial field, stainless steel flanges play a vital role. They are widely used in many aspects such as pipeline connections and mechanical equipment, and their performance largely depends on the materials. Stainless steel flanges made of different materials can meet the requirements of various working environments.

II. Common Materials for Stainless Steel Flanges

Stainless Steel 304 (SS304)

Composition and Characteristics:

Stainless steel 304 is an austenitic stainless steel. Its main elements include approximately 18% chromium (Cr) and about 8% - 10% nickel (Ni). The presence of chromium enables a dense chromium oxide protective film to form on the surface of the stainless steel, thus endowing it with good corrosion resistance. The nickel element helps to stabilize the austenitic structure and improves the toughness and machinability of the material.

In terms of mechanical properties, 304 stainless steel has good strength and ductility. Its yield strength is generally above 205 MPa, and its tensile strength can reach above 515 MPa. This allows it to maintain its shape stability under certain pressure.

Application Occasions:

Due to its relatively good comprehensive performance, it is widely used in general industrial settings. In the construction industry, it is often used for indoor pipeline system connections, such as air conditioning water systems and water supply and drainage systems. In the food processing industry, it is also used for the connection parts of food conveying pipelines because of its relatively safe and non-toxic characteristics. In the automotive manufacturing field, some pipeline connections in non-critical internal parts can also adopt 304 stainless steel flanges.

Stainless Steel 316 (SS316)

Composition and Characteristics:

Stainless steel 316 adds molybdenum (Mo) element on the basis of 304, with a content of about 2% - 3%. The addition of molybdenum significantly improves the corrosion resistance of stainless steel. Especially its corrosion resistance to chloride ions makes it perform excellently in marine environments.

At high temperatures, 316 stainless steel can also maintain relatively good mechanical properties. Its coefficient of thermal expansion is low, which can reduce deformation under the condition of large temperature changes.

Application Occasions:

The marine field is one of the main application scenarios for 316 stainless steel flanges. It is used for the pipeline systems of ships, such as seawater cooling systems and ballast water systems, and can resist the corrosion of seawater. In the chemical industry, when dealing with pipeline connections containing corrosive chemical substances, 316 stainless steel flanges are also the preferred choice. In the medical equipment manufacturing industry, for example, the external connection parts of some implantable medical devices also need to use 316 stainless steel flanges to ensure biocompatibility and corrosion resistance.

Stainless Steel 321 (SS321)

Composition and Characteristics:

Stainless steel 321 contains titanium (Ti) element. Titanium combines with carbon (C) to form titanium carbide (TiC), which can stabilize the austenitic structure at high temperatures. This characteristic makes 321 stainless steel have good high-temperature resistance.

In a high-temperature environment of 700 - 900 °C, 321 stainless steel can maintain sufficient strength. Its antioxidant performance is also good, and it is not easy to oxidize at high temperatures.

Application Occasions:

In the energy industry, such as the furnace tube connections and heat exchangers in thermal power plants, which are high-temperature components. In the metallurgical industry, the pipeline connections of high-temperature furnaces can also adopt 321 stainless steel flanges. In addition, in the aerospace field, for the pipeline connections of some engine components that need to withstand high-temperature environments, 321 stainless steel flanges will also be chosen.

Stainless Steel 904L (SS904L)

Composition and Characteristics:

Stainless steel 904L is a super austenitic stainless steel. Its composition contains a relatively high proportion of chromium (Cr) at about 20% - 21%, nickel (Ni) at about 10% - 12.5%, and molybdenum (Mo) at about 4% - 5%, and it also contains a small amount of copper (Cu) element.

The synergistic effect of chromium, nickel, and molybdenum makes 904L have extremely high corrosion resistance. It has good resistance to corrosive media such as strong acids, strong alkalis, and chlorides. In an acidic environment, its corrosion rate is extremely low, and it also performs well in an alkaline environment.

Application Occasions:

In the chemical industry, especially for chemical devices that handle highly corrosive chemical substances such as strong acids and strong alkalis, such as sulfuric acid production equipment and sodium hydroxide production equipment, the pipeline connections of 904L stainless steel flanges are indispensable. In the oil exploration and processing fields, when it comes to corrosive well fluids or corrosive media in the oil refining process, 904L stainless steel flanges will also be used.

III. Stainless Steel Flanges Made of Special Materials

Stainless Steel 310

Composition and Characteristics:

Stainless steel 310 is a high chromium-nickel austenitic stainless steel with a chromium content of as high as about 25% and a relatively high nickel content. Such high contents of chromium and nickel make 310 stainless steel have excellent high-temperature resistance and antioxidant properties.

In a high-temperature environment above 1000 °C, 310 stainless steel can maintain relatively good strength and stability. Its oxidation rate at high temperatures is very low, and it can be used in a high-temperature environment for a long time without serious oxidation.

Application Occasions:

In the construction of high-temperature industrial kilns, such as ceramic kilns and glass furnaces, 310 stainless steel flanges are used to connect the pipelines and equipment parts of the kilns. In some pipeline connections in high-temperature exhaust gas treatment systems, 310 stainless steel flanges may also be adopted.

Stainless Steel 317

Composition and Characteristics:

Stainless steel 317 is similar to 316, but its molybdenum content is higher, usually around 3% - 4%. This makes 317 stainless steel have better corrosion resistance than 316, especially in high-temperature and highly corrosive environments.

It has better tolerance to some special corrosive media, such as in an environment containing sulfides.

Application Occasions:

In offshore oil exploration, especially in the seabed environment where there may be high sulfide content, 317 stainless steel flanges can be used for the pipeline connections of exploration equipment. In some chemical production processes involving pipeline connections with complex corrosive media such as sulfides, 317 stainless steel flanges can also be selected.

Stainless Steel 347

Composition and Characteristics:

Stainless steel 347 adds niobium (Nb) element. Niobium can combine with carbon to reduce the enrichment of carbon at grain boundaries, thereby improving the intergranular corrosion resistance of stainless steel.

After welding, 347 stainless steel can maintain relatively good corrosion resistance, especially excellent corrosion resistance in the welded area.

Application Occasions:

In some pipeline systems that require frequent welding operations, such as large pipeline installation projects in construction engineering or temporary pipeline modification projects in chemical plants, 347 stainless steel flanges can avoid problems  such as strength reduction caused by intergranular corrosion after welding.

IV. Considerations for Selecting the Material of Stainless Steel Flanges

Corrosive Nature of the Working Environment:

If the working environment is an ordinary indoor environment with basically no corrosive media, stainless steel 304 flanges may be sufficient to meet the requirements. However, if it is a marine environment or a chemical environment where there are corrosive gases or liquids, materials with stronger corrosion resistance such as 316, 317 or even 904L need to be considered. For situations where there is high temperature and corrosion, such as the acidic gas environment in high-temperature exhaust gas treatment, materials that are both high-temperature resistant and corrosion resistant, such as 321 and 310, need to be selected.

Temperature Requirements:

In a low-temperature environment, most stainless steel flanges can work normally. But if it is in a high-temperature environment, materials with good high-temperature resistance such as 321 and 310 are required. For example, in the high-temperature pipeline connections during the steel smelting process, if 304, which is not high-temperature resistant, is selected, it will lead to deformation or even damage at high temperatures, affecting the normal operation of the entire system.

Pressure Requirements:

When bearing relatively large pressure, not only the strength of the flange material needs to be considered, but also the toughness and fatigue properties of the material. Although the strength of stainless steel materials can generally meet the requirements, different materials have different performance in high-pressure environments. For example, in some deep-sea oil exploration pipeline connections, the high-pressure environment requires the use of stainless steel flange materials with high strength and high toughness, such as 904L.

V. Conclusion

There are various materials for stainless steel flanges, and each material has its unique properties and application ranges. From the common ones like 304, 316, 321, 904L to the special ones like 310, 317, 347, etc., enterprises need to comprehensively consider various factors such as the corrosive nature, temperature requirements, and pressure requirements according to the specific requirements of the working environment to select the most suitable stainless steel flange material. Only in this way can it be ensured that stainless steel flanges play their due durability and safety roles in pipeline connections and mechanical equipment, and guarantee the stable operation of the entire industrial system.