How are pipe elbows made?

The pipe elbow is a metal pipe fitting that changes the direction of the pipeline on the pipeline, and plays a vital role in the pipeline system. Among all the pipe fittings used in the pipeline system, the proportion of pipe elbows is relatively large, about 80%. Usually, elbows of different materials or wall thicknesses use different forming processes. This article will introduce several main methods of making pipe elbows in detail, including pushing, stamping, butt welding and extrusion, in order to provide a comprehensive reference for technicians and readers in related industries.

1. Hot push forming process

Pushing is the most important forming and production process for carbon steel elbows. The hot push elbow forming process is to use a special bending pusher, core mold and heating device to make the steel billet on the mold move forward under the push of the pusher, and heat, expand and bend during the movement. The deformation characteristics of the hot push elbow are determined according to the constant volume law before and after the plastic deformation of the metal material to determine the diameter of the pipe billet. 

The diameter of the pipe billet is smaller than the diameter of the elbow. The core model is used to control the deformation process of the billet, so that the compressed metal flow at the inner arc is compensated to other parts of the expansion and thinning, thereby obtaining a uniform wall thickness elbow. Heating methods usually include medium frequency or high frequency induction heating, flame heating and reverberatory furnace heating. The specific choice depends on the product requirements and energy conditions.

The hot push elbow forming process has fast production speed and continuous operation, which is suitable for mass production. The manufactured elbows have beautiful appearance and uniform thickness. This process has become the main forming method for carbon steel elbows and alloy steel elbows. It is also suitable for the forming of certain specifications of stainless steel elbows. The heating methods of the forming process are medium frequency or high frequency induction heating (the heating ring can be multiple or single turns), flame heating and reflective surface heating. The heating method depends on the requirements and energy conditions of the formed product. When forming alloy steel, stainless steel and carbon steel elbows, the hot push forming process shows extremely high efficiency and good forming quality, with uniform wall thickness, which is very suitable for continuous mass production.

2. Stamping forming process

Stamping is an early forming process used for mass production of seamless elbows. Cold stamping or hot stamping can be selected according to different materials. Put the tube blank into the outer mold. After the upper and lower molds are merged, the tube blank moves along the gap reserved by the inner and outer molds under the push of the press to complete the forming process.

Stamping elbows can be cold stamped or hot stamped according to different materials. Cold stamping or hot stamping is usually selected according to material properties and equipment capacity. Put the tube blank into the outer mold, and after the upper and lower molds are merged, the tube blank moves along the gap reserved by the inner and outer molds under the push of the press to complete the forming process.

The forming quality of the tube elbow formed by stamping is not as good as that of the push elbow. The wall thickness deviation of the elbow is large and the appearance of the formed elbow is not beautiful. In addition, when forming larger specifications of elbows, the mold cost required is also very high. However, in some specifications of elbows, due to the small production volume, the wall thickness is too thick or too thin, the stamping process can be selected.

Although the stamping process has been gradually replaced by push or other manufacturing methods, it is still a viable option in some special cases. For example, for the manufacture of small batches and thick-walled elbows, the stamping process has the advantages of low cost and flexible operation.

3. Butt welding process

The manufacturing process of butt welding elbows is relatively complicated, but it has high strength and sealing. First, use steel plate to draw the expansion diagram of the butt-welded elbow, and then cut the material by gas cutting. Next, heat and press it on a press to get two and a half pieces of elbows. Then cut the edges, splice and weld them, and finally make a butt-welded elbow.

Butt-welded elbows are mainly used for large elbows, and large-diameter elbows can also be made by pushing or stamping. The advantages of butt-welded elbows are their high strength and good sealing performance, which are suitable for pipeline systems under harsh environments such as high pressure and high temperature. However, the manufacturing process of butt-welded elbows is relatively complicated and the cost is high, so they are usually only used in specific scenarios.

4. Extrusion process

The pipe elbows formed by the extrusion method have good forming quality and beautiful appearance. This method is usually used when manufacturing some thin-walled elbows. The extrusion process forms the elbow by extruding the upper and lower dies. The precision requirements of the upper and lower dies are very high, and the wall thickness size deviation is strictly controlled.

The pipe elbows manufactured by the extrusion process have high forming quality and beautiful appearance, and are especially suitable for the manufacture of thin-walled elbows. However, the extrusion process has high requirements for molds, high costs, and is not suitable for mass production. Therefore, when choosing an extrusion process, factors such as product requirements, production scale, and cost need to be considered comprehensively.

Other manufacturing processes:

In addition to the above-mentioned main manufacturing processes, other methods can also be used to make carbon steel elbows, such as the shrimp waist elbow manufacturing process. The shrimp waist elbow is made by welding multiple sections of rolled pipes at different angles, and is suitable for making large elbows of any specification greater than 1.5D. This process is relatively complex, cumbersome to operate, and the forming quality is not as good as the aforementioned process, but it still has application value in specific scenarios.

In addition, the production of pipe elbows can also adopt casting, medium plate welding and other processes. The casting process is suitable for making large and complex elbows, but the cost is high and the production cycle is long. The medium plate welding process is to press the steel plate into half of the elbow body, and then weld the two halves into a complete elbow, which is suitable for making medium and small diameter elbows.

Application and selection of pipe elbows:

Pipe elbows are widely used in pipeline systems in industries such as petroleum, natural gas, chemical industry, hydropower, construction and boilers. When selecting elbow fittings, multiple factors need to be considered, including the medium, pressure, temperature, diameter of the pipeline, and the material, specification and connection method of the elbow.

Read more: American standards for pipe elbows or Pipe elbow size selection