What is Stainless Steel Flange?

Stainless steel flanges are metal component used for connection between pipelines, valves, pumps and other equipment with good sealing and mechanical strength. Its main materials include 304, 316, 316L and other stainless steel, with excellent corrosion resistance, widely used in petroleum, chemical, food, pharmaceutical, water treatment and other industries. Stainless steel flanges can be categorized into weld neck flanges, slip on flanges, threaded flanges, blind flanges and other types according to the connection method and structural form, which are suitable for pipeline systems with different pressures and working conditions. Due to its corrosion resistance, high temperature resistance, beautiful appearance and long service life, it is an indispensable and important connecting part in all kinds of fluid transportation systems.

Advantages of Stainless Steel Flanges:

Excellent corrosion resistance: This is the most important feature of stainless steel. Due to the high chromium content, the surface of stainless steel can form a layer of stable and invisible chromium oxide protective film, effective resistance to a variety of corrosive media, such as water, steam, chemicals and so on.

Good strength and toughness: different types of stainless steel has different strength and toughness, but in general, they can withstand a certain pressure and mechanical stress.

High and low temperature resistance: Many grades of stainless steel maintain good mechanical properties and corrosion resistance at both high and low temperatures.

Hygienic: Stainless steel has a smooth surface that does not easily accumulate scale and is easy to clean and sanitize, so it is widely used in food, pharmaceutical and other industries that require high hygiene.

Aesthetics: Stainless steel has a modern glossy surface, which makes it also used in some occasions where appearance is required.

Recyclability: Stainless steel is a recyclable and environmentally friendly material.

Common types of Stainless Steel Flanges and Characteristics

Weld Neck Flange (WN)

Connection: The neck of the flange is butt-welded to the pipe, and then the flange is bolted to another flange or equipment.

Characteristics: long and tapered neck, gradually transition to the pipe diameter, reduce stress concentration, improve the strength of the flange.

Pressure resistance level: high, suitable for high pressure, high or low temperature environment, as well as occasions with large pressure fluctuations.

Material Characteristics: Usually adopt the same or compatible stainless steel materials with the pipeline, such as 304/304L, 316/316L, etc.

Applicable media: widely used in petroleum, chemical, electric power and other industries, transportation of flammable, explosive, toxic media.

Installation Precautions: Butt-welding connection requires high welding quality and professional welder operation.

Socket Weld Flange (SW)

Connection: The pipe is inserted into the socket of the flange and connected with fillet weld on the outside.

Characteristics: The pipe is inserted into the socket of the flange and welded. This type of connection provides good alignment and is typically used for small diameter, high pressure piping systems.

Pressure Rating: Medium to high, suitable for small diameter, high pressure piping systems, but not suitable for severe temperature cycling.

Material Characteristics: Stainless steel compatible with piping, such as 304/304L, 316/316L.

Applicable Medium: Commonly used in the chemical industry, fluid transportation and other fields, especially for the higher sealing requirements of the system.

Installation Precautions: It is necessary to leave an expansion gap between the pipe and the flange to prevent the stress caused by thermal expansion during welding.

Slip-On Flange (SO)

Connection: The flange is placed on the outside of the pipeline and connected to the pipeline by two fillet welds on the inside and outside.

Characteristics: The inner diameter of the flange is slightly larger than the outer diameter of the pipe, and the pipe is connected by welding on the inside and outside of the flange. Relatively easy to install and low cost.

Pressure Rating: Medium to low, suitable for low to medium pressure, non-critical piping.

Material properties: Stainless steel compatible with piping.

Applicable media: widely used in water, steam, air and other general industrial fluids.

Installation Precautions: Compared with butt-welding flange, its fatigue strength is lower, and it is not suitable for vibration, impact or alternating load occasions.

Threaded Flange (TH)

Connection: The inner hole of the flange is processed into a thread, which is directly connected with the pipe with external thread.

Characteristics: Connected to pipes with external threads through internal threads. Easy to install, no need to weld, but lower strength, sealing is relatively poor.

Pressure rating: low, mainly used for non-sealing requirements of strict or low-pressure piping.

Material properties: stainless steel matching the piping material.

Applicable media: water, non-corrosive gases, compressed air, etc., usually used for small-diameter pipelines or temporary connections.

Installation Precautions: Sealant or sealing tape should be used at the threaded connection to ensure sealing; not applicable to vibration, shock or cyclic load occasions.

Blind Flange (BL)

Connection: No hole in the center of the flange, used to close off the end of a pipe or valve opening.

Characteristics: No hole, used to close the end of the pipe or the opening of the equipment, play the role of blocking.

Pressure Rating: High, as its primary function is to withstand the internal pressure of the pipeline and provide a reliable seal.

Material Characteristics: Usually the same material as the pipeline or connected flange.

Applicable media: any piping system that requires temporary or permanent closure.

Installation Precautions: Make sure the sealing surface of the blind flange matches with the connecting flange, and use suitable gaskets and bolts.

Lap Joint Flange (LJ)

Connection: It consists of a stub end with flanges and a loose flange ring that can slide freely on it. The stub end is butt-welded to the pipe and the loose flange ring is bolted.

Features: Used in conjunction with a stub end, the flange itself is not welded to the pipe and can be rotated. This design facilitates alignment of the bolt holes and allows for easy assembly and disassembly of the pipe.

Pressure rating: low to medium.

Material Characteristics: The stub end is usually made of the same material as the pipe, and the flange ring can be made of carbon steel, stainless steel or other alloys.

Applicable media: commonly used in corrosive media pipelines, in which the short pipe material is corrosion-resistant materials.

Installation Precautions: The welding quality of the flanged short pipe is very important.

Common Stainless Steel Materials

304/304L

Highly versatile, excellent corrosion resistance, easy to process and form, good welding performance. 304L is a low carbon version with better intergranular corrosion resistance, suitable for applications where annealing is not possible after welding.

316/316L

Molybdenum (Mo) is added to 304 to provide greater corrosion resistance in corrosive media such as chlorides, and better resistance to high temperatures. 316L is a low carbon version with better weldability and resistance to intergranular corrosion.

321

Intergranular corrosion resistance at elevated temperatures is improved by stabilizing the carbide with the addition of titanium (Ti).

347

Carbide stabilized by the addition of niobium (Nb) elements, similar to 321, with good intergranular corrosion resistance at elevated temperatures.

2205 (S31803/S32205)

Characteristics: High strength, good resistance to chloride pitting and crevice corrosion, excellent resistance to stress corrosion cracking.

2507 (S32750)

Characteristics: Super duplex stainless steel with higher chromium, molybdenum and nickel content, good corrosion resistance and higher strength.

Martensitic Stainless Steel : such as 410, 420, etc., can be hardened by heat treatment, with high strength and hardness.

Ferritic Stainless Steel : such as 430, etc., higher chromium content, corrosion resistance is better than carbon steel, but the strength and weldability is not as good as austenitic stainless steel.

Stainless Steel Flanges for Industrial Applications

Oil and gas industry

Chemical and petrochemical industry

Power industry

Water treatment and desalination

Food and pharmaceutical industry

Ship and marine engineering

Architecture and structure