Steel flange

The most important reason for using flanges is their ability to be separated, which means that if two pipes are welded directly to each other, cutting must be done to separate them from each other. But if flanges are used, this can be done by opening and closing the bolts and nuts.

In this method, a flange is welded to each pipe and these two flanges are placed in front of each other and are compressed and tightened by bolts and nuts. In order to prevent leakage, a gasket is used between them.

Application:

– Connecting pipes to equipment (such as pressure Vessels, pumps, compressors, etc.)

– Changing the material in the pipe

– Connecting to valves and other items that are in the pipe path and need possible repairs

– Connecting to instrument devices that need possible repairs or calibration

– All other items that need to be separated.

Flanges are divided into different classes depending on the pressure they withstand. This classification is different in different standards, which is described in detail below:

1- Pressure classification according to ANSI B16.5 standard

According to this standard, steel flanges and its alloys are divided into classes 150, 300, 400, 600, 900, 1500, 2500. In this standard, temperature and pressure tables are presented for different materials and classes.

2- Pressure classification according to ISO standard

According to this standard, steel flanges and its alloys are divided into PN6, PN10, PN16, PN25, PN40, PN63, PN100 classes.

Types of steel flange based on face

Flat face flange (FF)

In this type of flange, the forehead surface is smooth and without protrusions. These flanges are usually used for lower pressures and applications that do not require precise sealing.

Raised face flange (RF)

These types of flanges have a prominent surface in the front part, where the gasket between the flanges is placed on this part. With the help of connecting screws, the raised surfaces transfer the pressure to the gasket between the flanges and provide optimal sealing. These flanges usually have circular grooves that are determined based on the standard, and their depth also depends on its pressure class.

Ring Type Joint Flange

These flanges have a groove on their sealing surface, where the metal ring between the flanges is placed inside this groove. These flanges are used for high pressures and temperatures.

Types of steel flanges based on connection type

Welding Neck Flange

Weld neck flanges have a conical hub. This conical hub is connected to the pipe or fittings by butt welding. Weld neck flanges are used for high pressures, high or sub-zero temperatures, high stresses and fluctuating and vibrating loads. These flanges prevent erosion or corrosion caused by pressure changes or fluid fluctuations.

Orifice Flange

This flange is a type of weld neck flange that is used to measure or limit the pressure or flow of gases and liquids in pipelines. The main application of orifice flange is to measure the fluid flow rate in the piping system.

Slip On Flange

Slip-on flanges are used in normal service. It is simple to install. Their resistance to internal pressure and fatigue is lower than of weld neck flanges, so that its resistance to internal pressure is two thirds and to fatigue load is one third of weld neck flanges. To connect them to the pipe, the pipe is placed inside the flange and welding is performed from the outside and inside using the fillet method so that it has more resistance and prevents fluid leakage.

Socket Weld Flange

This flange is similar to the slip-on flange, except that it has a chamber for placing the pipe. This flange is connected to the pipe from the outside using a fillet weld, but if it is welded from the inside, its fatigue resistance is 1.5 times the resistance of the slip-on flange. These flanges have better sealing than slip-on flanges. But they are less efficient than other flanges. These flanges are usually used for high pressure and small size and non-corrosive fluids, because this type of flange is prone to corrosion in the gap between the pipe and the flange.

Threaded Flange

These flanges are connected to the pipe with a thread. These flanges are produced for different pressure classes and different sizes, but they are usually used in small sizes. Although these flanges are connected with threads, if necessary and to prevent leakage, they can be welded together after connecting the pipe to the flange to have better sealing.

Lap Joint Flange

This flange has the ability to rotate around its axis, so it is easy to adjust its screws. This flange is not in contact with the fluid. Therefore, one of its cost-effective applications is for systems that are exposed to high erosion and corrosion. But its resistance to fatigue is much lower than the weld neck flange.

blind Flange

Blind flanges are used to block fluid flow, for partial pipe repairs, and when piping expansion is possible in the future. These flanges are disc-shaped. At high temperature and pressure, a combination of blind flange and weld neck flange is used. Also, the resistance of blind flanges is higher than other flanges.