STAINLESS STEEL FLANGES

In systems carrying liquids, chemicals, or food, corrosion of joints not only causes leaks but can also contaminate the entire production line. The stainless steel flange emerged as a flexible, detachable connection solution that withstands high pressure and offers outstanding rust resistance compared with carbon steel flanges.

This product line is usually made of stainless steel 304 or 316, to the connection standards BS4504/EN 1092-1 and JIS B2220. Sizes range from DN10 to DN2000, meeting the diverse requirements of large and small piping systems.

General information on industrial stainless steel flanges

Like carbon steel flanges, stainless steel flanges form a bolted joint that connects valves or other equipment to the pipeline. The only difference is the material: stainless steel. Stainless steel has a thin chromium oxide layer that forms naturally on the surface and resists rust, so it needs no galvanizing or protective paint as carbon steel does.

Advantages and disadvantages of stainless steel flanges

The main advantages of stainless steel flanges are stable rust resistance and a clean, easy-to-clean surface that does not contaminate water or food with rust. They also keep their strength over a wide range of operating temperatures and require almost no coating maintenance over their service life.

However, stainless steel flanges cost more than carbon steel flanges of the same size. In environments rich in chlorides, such as seawater, brine, or some cleaning chemicals, pitting corrosion can still attack stainless steel, including grade 316. In addition, stainless steel joints require matching bolts; mixing in other materials forfeits the rust-resistance advantage.

Common applications

Stainless steel flanges are commonly chosen for the piping systems of:

• Food, beverage, dairy, and pharmaceutical plants
• Clean water, RO water, and demineralized water systems
• Water treatment and mild chemical lines
• Coastal projects, seafood plants, and seafood processing
• Hot water, steam, and condensate lines
• HVAC systems, fire protection systems, and buildings with high aesthetic requirements

Classification of stainless steel flanges by steel grade

When should you choose 304 stainless steel flanges? When should you choose 316?

• 304 stainless steel flanges are generally used for clean water, air, and food without high chloride content.
• 316 stainless steel flanges should be considered for systems in coastal areas, in contact with brine or chloride-containing cleaning chemicals, or where hygiene requirements are high, such as pharmaceuticals.
• For welded joints, the L versions (304L, 316L) should be preferred to limit corrosion at the weld zone.

Classification by dimensional standard

For the same pipe size, flanges under different standards have different outside diameters, bolt circles, and numbers of holes, so you must choose the standard of the valves and pumps they will be fitted to.

Classification by flange type

Besides grade and standard, the flange type determines how the joint is welded or attached to the pipe. The six most common types of stainless steel flange today:

With the lap joint flange, the flange ring can be carbon steel, while the stub end in contact with the medium is stainless steel. This approach helps reduce installation costs for large pipelines.

Notes when buying and installing stainless steel flanges

A stainless steel flange delivers its rust resistance only when the entire joint is selected as a matching set. Please note the following 5 points before making a purchase decision:

• Bolts and nuts. Use stainless steel of the same group as the flange, usually A2-70 for the 304 system and A4-70 for the 316 system. Galvanized steel bolts in damp environments will rust first and make the joint hard to take apart. Stainless steel tends to gall on the threads when tightened, so apply anti-seize grease before assembly.
• Gaskets. Choose PTFE, EPDM, or graphite depending on the medium and temperature. For high-temperature systems, choose a gasket with low chloride content.
• Galvanic corrosion. When a stainless steel flange is connected to carbon steel or cast iron in an environment with conductive water, the carbon steel part corrodes faster. An insulating kit (insulating gasket, sleeves, and washers) can be used, or the carbon steel part can be protected with paint.
• Welding. Choose a welding rod or wire suited to the stainless grade (308L for 304 and 316L for 316 are common choices). After welding, pickle and passivate the weld to restore the rust-resistant oxide layer, and use tools dedicated to stainless steel to avoid contamination by carbon steel dust.
• Do not use a magnet to tell grades apart, because 304 stainless steel can still be slightly attracted after cold working, and 201 stainless steel can also be attracted. When certainty is needed, use a PMI analyzer or test the composition in a laboratory.

For stainless steel flanges, the material documentation is as important as the dimensions. A reliable supplier needs to provide complete CO and CQ documents, and also supply the matching bolts and gaskets for the type of flange supplied. At An Phu Thanh, we are confident in meeting all of these requirements, ensuring peace of mind for customers when they buy.

If you need a quotation for stainless steel flanges, or want to check a flange against the valves and pumps you are using, please contact Hotline 0946 729 913 or message An Phu Thanh’s Zalo OA. The An Phu Thanh team is always happy to support you.