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Selection, processing, and installation of hydraulic steel pipes

With the development of hydraulic technology, how to correctly select, process, and arrange hydraulic steel pipes to make hydraulic systems work more energy-efficient, reliable, and have a longer lifespan.



With the development of hydraulic technology, how to correctly select, process, and arrange hydraulic steel pipes to make hydraulic systems work more energy-efficient, reliable, and have a longer lifespan has become a research topic for hydraulic system designers. This article discusses the selection, processing, and installation of hydraulic steel pipes.

Pipe Selection

The selection of pipes should be based on the system pressure, flow rate, and usage situation. It is necessary to pay attention to whether the strength of the pipe is sufficient, whether the pipe diameter and wall thickness meet the system requirements, and whether the inner wall of the selected steel pipe must be smooth, free from rust, oxide skin, and other defects. If the following situations are found to be unusable: the inner and outer walls of the pipe have been severely corroded; The depth of scratches on the pipe body is more than 10% of the wall thickness; The surface of the pipe body is recessed to more than 20% of the pipe diameter; Uneven wall thickness and obvious ovality of the pipe section. Seamless steel pipes are generally used for piping in medium and high pressure systems, which are widely used in hydraulic systems due to their advantages such as high strength, low price, and ease of achieving leak free connections. Ordinary hydraulic systems often use cold drawn low-carbon steel seamless pipes of sizes 10, 15, and 20, which can be reliably welded to various standard pipe fittings during piping. Hydraulic servo systems often use ordinary stainless steel pipes, which are corrosion-resistant, have smooth inner and outer surfaces, and have precise dimensions, but their prices are relatively high.

Pipe processing

The processing of pipes mainly includes cutting, bending, welding, and other contents. The processing quality of pipes has a significant impact on the parameters of the pipeline system and is related to the reliable operation of the hydraulic system. Therefore, scientific and reasonable processing methods must be adopted to ensure the quality of processing.

1) Cutting of pipes

The pipes of the hydraulic system with a diameter below 50mm can be cut using a grinding wheel cutting machine, while pipes with a diameter above 50mm are generally cut using mechanical methods, such as specialized machine tools. Manual welding and oxygen cutting methods are strictly prohibited, and manual sawing is allowed when conditions permit. The end face of the cut pipe should be kept perpendicular to the axial centerline as much as possible, and the cutting surface of the pipe must be flat and free from burrs, oxide skin, slag, etc.

2) Bending of pipes

The bending process of pipes is better carried out on mechanical or hydraulic pipe bending machines. Generally, pipes with a diameter of 38mm and below are cold bent. Using a pipe bending machine to bend the pipes in a cold state can avoid the generation of oxide skin and affect the quality of the pipes. Hot bending is not allowed during the production of bent pipes, and pipe fittings such as stamped elbows can be used as substitutes, as deformation, thinning of pipe walls, and the generation of oxide skin are prone to occur during hot bending. Bending pipes should consider the bending radius. When the bending radius is too small, it can cause stress concentration in the pipeline and reduce its strength. The radius of the bend should not be less than 3 times the pipe diameter. The higher the working pressure of the pipeline, the larger its bending radius should be. The ellipticity of the bent pipe after production should not exceed 8%, and the deviation of the bending angle should not exceed ± 1.5mm/m.

3) The welding of pipes and hydraulic pipelines is generally carried out in three steps:

(1) Before welding the pipe, the end of the pipe must be beveled. When the weld groove is too small, it can cause the pipe wall to not be fully welded, resulting in insufficient welding strength of the pipeline; When the groove is too large, it can also cause defects such as cracks, slag inclusions, and uneven welds. The angle of the groove should be executed according to the types of welding that are favorable according to the national standard requirements. Beveling machine shall be used for better groove processing. The mechanical cutting method is economical, efficient, simple, and can ensure the processing quality. Common grinding wheel cutting and beveling shall be avoided as far as possible.

(2) The selection of welding methods is a crucial aspect of pipeline construction quality and must be highly valued. At present, manual arc welding and argon arc welding are widely used. Among them, argon arc welding is suitable for hydraulic pipeline welding. It has the advantages of good weld junction quality, smooth and beautiful weld surface, no welding slag, no oxidation of weld junction, and high welding efficiency. Another welding method can easily cause welding slag to enter the pipe or generate a large amount of oxide scale on the inner wall of the welding joint, which is difficult to remove. If the construction period is short and there are few argon arc welders, it can be considered to use argon arc welding for one layer (backing) and electric welding for the second layer, which not only ensures quality but also improves construction efficiency.

(3) After pipeline welding, weld quality inspection should be carried out. The inspection items include: whether there are cracks, inclusions, pores, excessive biting, splashing, and other phenomena around the weld seam; Check whether the weld bead is neat, whether there is any misalignment, whether the inner and outer surfaces are protruding, and whether the outer surface is damaged or weakened during the processing of the pipe wall strength.

Installation of pipelines

Hydraulic pipeline installation is generally carried out after the installation of the connected equipment and hydraulic components. Before laying the pipeline, it is necessary to carefully familiarize oneself with the piping plan, clarify the arrangement order, spacing, and direction of each pipeline, determine the positions of valves, joints, flanges, and pipe clamps, and mark and locate them.

1) Installation of pipe clamps

The base plate of the pipe clamp is generally welded directly or through brackets such as angle steel to structural components, or fixed with expansion bolts on concrete walls or wall side brackets. The distance between pipe clamps should be appropriate. If it is too small, it will cause waste. If it is too large, it will cause vibration. At right angles, there should be one pipe clamp on each side.


2) Pipeline laying

The general principles for pipeline laying are:

(1) The pipes should be arranged horizontally or vertically as much as possible, paying attention to neatness and consistency to avoid pipeline crossing; A certain distance must be maintained between the walls of two parallel or intersecting pipes;

(2) Large diameter pipes or pipes close to the inner side of the piping support should be prioritized for laying;

(3) The pipe connected to the pipe joint or flange must be a straight pipe, and the axis of this straight pipe should coincide with the axis of the pipe joint or flange, and the length should be greater than or equal to 2 times the diameter;

(4) The distance between the outer wall of the pipeline and the edge of the adjacent pipeline fittings should not be less than 10mm; The flanges or unions of the same row of pipelines should be staggered by more than 100mm; The joint position of the through-wall pipeline should be at least 0.8m away from the wall surface;

(5) When laying a group of pipelines, two methods are generally used at turns: 90 ° and 45 °;

(6) The whole pipeline is required to be as short as possible, with few turns, smooth transition, reduce up and down bending, and ensure proper Thermal expansion of the pipeline. The length of the pipeline should ensure the free disassembly and assembly of joints and accessories without affecting other pipelines;

(7) The pipeline laying position or fitting installation position should be convenient for pipe connection and maintenance, and the pipeline should be close to the equipment for fixing the pipe clamp; The pipeline shall not be directly welded to the bracket;

(8) During the interruption of pipe installation, all pipe orifices shall be strictly sealed. During the installation of the Plumbing, there shall be no sand, oxide scale, scrap iron and other dirt entering the pipeline; Do not remove all pipeline protection before installation, as it may contaminate the pipeline.


The hydraulic system is composed of various hydraulic components that are organically connected through pipelines, pipe joints, and oil circuit blocks. There are many connecting steel pipes used in the hydraulic system. Once these pipelines are damaged and leaked, they can easily pollute the environment, affect the normal functioning of the system, and even endanger safety. The selection, processing, and installation of hydraulic steel pipes is a very important step in the transformation of hydraulic equipment. Mastering the correct methods will be beneficial for the stable operation of the hydraulic system.

Post time: Aug-01-2023