What Is a Stainless Steel Fitting?
Stainless steel fittings are used to join stainless steel pipes together.
In most cases, they are SUS304 stainless steel. Stainless steel is characterized by its resistance to rust, so it is often used in piping and water, etc., where rust contamination is to be prevented.
In addition, austenitic stainless steels such as SUS304 do not develop low-temperature brittleness even at extremely low temperatures; rather, their strength increases. For this reason, they are also used for liquid nitrogen (-196°C) piping.
Applications of Stainless Steel Fittings
Stainless steel fittings are used for piping where rust should not be allowed to form. Specific applications are as follows:
- Water supply piping
- Sulfuric acid transfer piping
- Strong alkali liquid transfer piping
- Liquid nitrogen transfer piping
- Liquid oxygen transfer piping
- Steam transfer piping
Principle of Stainless Steel Fittings
As mentioned above, stainless steel fittings are made of stainless steel. Among them, austenitic stainless steel contains chromium, which prevents rust by forming a non-conductive film. Therefore, it can be used as a fitting for piping where rust is a problem.
However, care must be taken to avoid sensitization. Sensitization refers to a phenomenon in which chromium oxide is formed when welding stainless steel joints, resulting in chromium deficiency. Heat control during welding and solidification heat treatment should be performed to ensure that a non-conductive film is formed.
In addition, austenitic stainless steel becomes martensitic at low temperatures, resulting in an increase in tensile strength. Therefore, stainless steel fittings can be used for cryogenic piping without any problems.
Connection Method of Stainless Steel Fittings
There are different types of stainless steel fittings, depending on the shape of the fitting and the method of connection.
1. Screwed Type
The threaded type is a stainless steel fitting that has a threaded groove in the fitting itself. Unlike welding, they are not completely fixed and have the advantage of being easy to maintain.
2. Welding
Welding is a method of connecting pipes and fittings. There are two types of welded joints: butt welding (SW), in which the ends are butt-welded together, and insertion welding (BW), in which the pipe to be used, is inserted into the joint and welded.
3. Flange
In this connection method, the flanges at the ends of the pipe and fitting are butt-welded together, and a gasket is inserted between them and secured with a bolt and nut. Compared to the threaded type, the flange type is not only more reliable in terms of strength and workability but also easier to maintain.
Types of Stainless Steel Fittings
Stainless steel fittings are classified according to the purpose of connecting pipes.
1. Elbow
Elbow fittings are characterized by their curved shape. The direction of flow can be changed, and the angle of bend, such as 45°, 60°, 90°, etc., can be selected according to the application. In particular, L-shaped 90° joints are used in places where there is a right angle, such as floors and ceilings.
2. T-Shaped
T-shaped fittings are used to merge two flowing fluids or to split a pipe in two. Y-shaped laterals, which have a low water head loss, are sometimes used.
3. Reducers
Reducers are fittings used to connect two pipes of different diameters; if one fitting cannot accommodate the diameter of the pipes, two or more may be used simultaneously.
4. Nipple Socket
A nipple is a fitting used to connect pipes with internal threads. On the other hand, a socket is a fitting used to connect pipes with external threads. Each of these fittings is used to extend pipes of the same type.