What is a pipe elbow?

What is a pipe elbow?

A pipe elbow is a pipe fitting used in plumbing systems to connect two pipes of the same or different nominal diameter. It’s bent at an angle to allow straight pipes to be joined at an angle, thereby realizing a change of direction. Of all pipe fittings, pipe elbow is the most widely used one, which is used in a variety of applications in industries such as electrical power, marine, heating, paper making, metallurgy, petrochemical, chemical, oil, gas and so on.

Husteel's pipe elbows are made of a variety of materials, such as alloy steel, carbon steel, stainless steel, etc. The material used depends on the function of the pipe unit. According to the angle, there are three most commonly used elbows: 45°, 90° and 180°. In addition, according to project needs, other abnormal angle elbows such as 60° are also included.

The methods of connecting to pipes include: direct welding (the most common method) flange connection, hot melt connection, electrofusion connection, threaded connection and socket connection, etc.
According to the production process, it can be divided into: welding elbow, stamping elbow, push elbow, casting elbow, butt welding elbow, etc. Other names: 90-degree elbow, right-angle bend, etc.

Elbow usage:
Connect two pipes with the same or different nominal diameters to make the pipes turn at 90° elbow, 45° elbow, 180° elbow and various degrees.

Elbow vs bend pipe: A bend radius less than or equal to 1.5 times the pipe diameter is an elbow, and a bend radius greater than 1.5 times the pipe diameter is a bend pipe.

Standard specification for pipe elbow:

The standard specification for carbon steel pipe fittings is an important guarantee for ensuring the safety and quality of pipeline system operations. Various standard-setting organizations at home and abroad have formulated corresponding standards, such as the international pipe fitting standard ASME B16.9, the domestic steel pipe fitting standard GB/T12459, etc. There are corresponding regulations on the specifications, dimensions, surface treatment, pipe wall thickness, etc. of pipe fittings.

The internationally accepted pipe flange standards can be summarized into two different and non-interchangeable pipe flange systems: one is the European pipe flange system represented by Germany; the other is the American pipe flange system represented by the United States. 

Classification of pipe elbows:

1. Divide by material
Carbon steel: ASTM/ASME A234 WPB, WPC
Alloy steel: ASTM/ASME A234 WP 1-WP 12-WP 11-WP 22-WP 5-WP 91-WP911, 15Mo3 15CrMoV, 35CrMoV
Stainless steel: ASTM/ASME A403 WP 304-304L-304H-304LN-304N
ASTM/ASME A403 WP 316-316L-316H-316LN-316N-316Ti
ASTM/ASME A403 WP 321-321H ASTM/ASME A403 WP 347-347H
Low temperature steel: ASTM/ASME A402 WPL3-WPL 6
High Performance Steel: ASTM/ASME A860 WPHY 42-46-52-60-65-70
Cast steel, alloy steel, stainless steel, copper, aluminum alloy, plastic, argon phosphate, PVC, PPR, RFPP (reinforced polypropylene), etc.

2. According to the production method, it can be divided into pushing, pressing, forging, casting, etc.
3. According to manufacturing standards, it can be divided into national standard, electric standard, ship standard, chemical standard, water standard, American standard, German standard, Japanese standard, Russian standard, etc.
4. According to its radius of curvature: it can be divided into long radius elbow and short radius elbow. A long-radius elbow means that its radius of curvature is equal to 1.5 times the outer diameter of the pipe, that is, R=1.5D; a short-radius elbow means that its radius of curvature is equal to the outer diameter of the pipe, that is, R=1.0D. (D is the elbow diameter, R is the radius of curvature).
5. If divided by pressure level: there are about seventeen types, which are the same as the American pipe standards, including: Sch5s, Sch10s, Sch10, Sch20, Sch30, Sch40s, STD, Sch40, Sch60, Sch80s, XS; Sch80, SCH100, Sch120, Sch140, Sch160, XXS; the most commonly used ones are STD and XS.
6. According to different shapes and uses, it can be divided into: grooved elbow, ferrule elbow, double-bearing elbow, flange elbow, reducing elbow, dead seat elbow, internal and external tooth elbow, stamping elbow , push elbow, socket elbow, butt welding elbow, inner wire elbow, etc.

Features:
1. Since most pipe fittings are used for welding, in order to improve the welding quality, the ends are beveled, leaving a certain angle and a certain edge. This requirement is also relatively strict, how thick the edge is, what the angle is, and the deviation. The scope is specified. The surface quality and mechanical properties are basically the same as those of pipes. For ease of welding, the steel grade of the pipe fittings and the pipes being connected should be the same.

2. All pipe fittings must undergo surface treatment. The iron oxide scale on the inner and outer surfaces must be shot blasted and then coated with anti-corrosion paint. This is for export needs. Moreover, domestically, it is also to facilitate transportation and prevent rust and oxidation, so work in this area must be done.

3. It is the requirement for packaging. For small pipe fittings, such as export, they need to be made into wooden boxes, about 1 cubic meter. It is stipulated that the number of elbows in such boxes cannot exceed one ton. The standard allows sets, that is, large sets and small sets. But the total weight generally cannot exceed 1 ton. For large items, they must be packaged individually, such as 24" items. The other is the packaging mark. The mark should indicate the size, steel number, batch number, manufacturer's trademark, etc.

Application fields of elbow:
Elbow is a pipe connecting device, which is mainly used to change the direction of pipes. Its design allows pipes to be connected in horizontal, vertical or oblique positions and to change the flow direction of the pipes. Elbows are widely used in many fields. The following are some common application fields:

1. Construction projects: Elbows are often used in water supply, drainage, HVAC and other systems in construction projects to adjust the direction of water flow and connect different pipes.
2. Chemical engineering: In the chemical process, the flow direction of pipelines needs to be changed frequently. Elbows are used to connect different parts of pipelines to facilitate operation and maintenance.
3. Electric power engineering: Elbows are widely used in power plants, substations and other power systems to connect transmission lines, heat dissipation systems, cooling systems, etc.
4. Petroleum and natural gas engineering: Elbows play a key role in the extraction, transportation and storage of oil and natural gas, and are often used for the connection and flow direction adjustment of oil and gas pipelines.

5. Shipbuilding industry: In shipbuilding, elbows are widely used in pipeline systems, such as water supply and drainage, fire protection, cooling and other systems.
6. Food processing: Elbows are mainly used in pipeline systems for transporting liquids, gases and powder materials in the food processing industry to meet the requirements of different processes.
7. Sewage treatment: In sewage treatment plants, a large number of elbows are used to connect pipes in different parts to facilitate treatment and maintenance.
8. Metallurgical industry: Elbows are widely used in the metallurgical industry, such as steel plants, railway transportation and other fields, to adjust the flow of ore, coke and smelting products.

How to make pipe elbow?

There are three ways to make pipe elbows: hot pushing forming, stamping forming and medium plate welding.

1. Hot push forming
It requires the use of a pushing machine, a mandrel and heating equipment. The finished tube blank is placed on the mandrel and pushed, heated and shaped at the same time. This production speed is fast, suitable for mass production, and the manufactured elbow is , beautiful appearance and relatively uniform thickness.

2. Stamping molding
Depending on the material, you can choose cold pressing or hot pressing. Put the tube blank into the outer mold. After the upper and lower molds are merged, under the push of the press, the tube blank moves along the gap reserved between the inner mold and the outer mold to complete the forming process.

3. Medium plate welding
Medium plate welding is for the production of large elbows. First, cut two middle plates, then use a press to press half of the elbow section, and then weld the two sections together, so that the manufactured elbow will have two welds. Therefore, the welds must be inspected after production to ensure that they meet the standards.

Quality control of pipe elbow fittings:
Quality control of pipe elbow fittings is the key to ensuring the quality and safety of the pipeline system. The quality inspection of pipe fittings includes appearance quality inspection, chemical composition analysis, physical performance testing, non-destructive testing and other aspects. Only pipe fittings that have passed the inspection can be put into use to ensure the safe and effective operation of the pipeline system.

Go here to learn more: Stainless steel pipe fittings vs Carbon steel pipe fittings