How to choose the correct pipeline compensator?
Origin of compensator
The basic meaning of compensation is to make up for defects and offset losses. There is also compensation in science and technology. When there is a temperature change in the pipeline conveying medium or the environment where the pipeline is located, the thermal expansion and cold contraction caused by the temperature of the pipeline is inevitable. If a certain way is not taken to compensate for the size change, a very high stress will be generated in the pipe wall, which will be transmitted to the fixed pipe support or equipment through the pipe. When the temperature difference exceeds a certain range, the temperature difference stress is greater than the pipe can bear In this case, the compensation problem must be considered.
Function of compensator
In the design of pipeline system compensation, the most economical one is natural compensation, which uses the flexibility of natural bending shape of pipeline to compensate thermal displacement. Obviously, the ability of natural compensation is limited. When the natural compensation can not meet the requirements, the metal bellows expansion joint and other compensation devices should be considered.
The load of pipeline system mainly includes external force load (self weight of pipeline and flowing medium, internal pressure, wind load, earthquake load, etc.) and displacement load. The purpose of setting pipeline compensator is to eliminate the force of external load on equipment or pipeline, and can separate complex pipeline into simple shape ratio and independent expansion pipe section, so as to ensure the best use effect of expansion joint. The pipeline compensator can compensate and absorb the axial, transverse and angular thermal deformation of the absorption pipeline, absorb the equipment vibration, reduce the impact of equipment vibration on the pipeline, and absorb the deformation of the pipeline caused by earthquake and ground subsidence. Compensators are used in the entrance and exit of hot and cold pipe system, steel plant, thermal power plant, etc. in large stadiums, such as flue gas desulfurization, dust removal equipment, air heating, air blast and other equipment, so all kinds of compensators have been vigorously promoted and applied.
Analysis of several common compensators
Meaning of corrugated compensator:
Corrugated compensator is a kind of compensation device which uses the effective expansion and contraction of elastic elements of bellows to absorb the size changes of pipelines, pipes or containers caused by thermal expansion and cold contraction.
Classification of corrugated compensator:
Bellows can be divided into axial type, transverse type, angular type and pressure balance type bellows according to displacement forms.
According to whether it can absorb the pressure thrust (blind plate force) generated by the medium pressure in the pipeline, it can be divided into unconstrained bellows and constrained bellows.
According to the waveform structure parameters of bellows, they can be divided into U-shaped, Ω shaped, S-shaped and V-shaped bellows. At present, most of the expansion joints (bellows) at home and abroad adopt U-shaped waveform structure.
Advantages of corrugated compensator:
It has compact structure, less space occupied and can be directly buried; the disadvantages are difficult manufacturing, low pressure resistance and small compensation capacity. The compensation ability is related to the shape size, wall thickness and pipe diameter of the corrugated pipe: the higher the pressure, the thicker the wave wall, the smaller the pipe diameter, and the greater the rigidity, the smaller the compensation ability. The waveform compensator is generally used in the case of nominal pressure ≤ 1.0MPa and nominal diameter ≥ 150mm, and can also be used for atmospheric pressure and low pressure large diameter pipeline. It can reach dn4000mm in the flue gas and air duct of boiler.
Disadvantages of corrugated compensator:
The corrugated compensator has thin pipe wall, can not bear torsion and vibration, and has poor safety; the equipment investment is high, the design requirements are strict, the construction and installation accuracy is high, and the expected life is often not reached; the axial type corrugated compensator produces pressure thrust on the fixed support, which causes the fixed support to have large thrust force and high cost.
Application conditions of corrugated compensator:
The corrugated compensator cannot bear load and should be hoisted separately. Unless the corrugated compensator is reinforced, it is not allowed to be hoisted together with the pipeline after welding. During installation, the degree of bellows compensator should be designed correctly according to the data recommended by the manufacturer. In any case, the bellows should not be stretched or compressed or twisted to compensate the installation deviation, so as to avoid affecting the normal function of the bellows compensator, reducing the service life and increasing the load of the piping system, equipment nozzle and supporting components. Enough space should be reserved around the expansion joint to ensure that the expansion joint can move freely within the design range.
Advantages of rotary compensator
- (1) The product has high safety performance: the product structure is reasonable, the rotary compensator adopts double seal form, one side is end seal, the other side is ring seal;
- (2) Convenient design: in the design of heat supply network, the compensation conditions of bellows compensator are more stringent, and the five golden principles must be followed. The sleeve compensator should be “strictly centered”, and the stress and blind plate force of bellows compensator and sleeve compensator should be considered. There are various types of rotary compensators. According to the different directions of pipelines, the suitable type of rotary compensators can be selected to solve the problem of pipeline compensation;
- (3) Long service life of products: the service life of products can reach more than 20 years;
- (4) Large compensation: the compensation amount can reach 1800 mm (for other compensators, such as bellows compensator, the maximum compensation amount is 300-400 mm), for pipelines above DN 200, unilateral compensation can reach 130-200 m, for pipelines ≤ DN 200, unilateral compensation can reach 100-130 m, which can be used for long-distance steam pipeline compensation;
- (5) High economic efficiency of pipeline operation: due to the increase of compensation distance of compensator, elbow is reduced compared with natural compensation and sleeve compensation, so as to reduce pressure drop and reduce pipe loss of heat supply network;
- (6) Diversified installation methods and types: according to the pipeline direction and the terrain on site, the rotary compensator compensation type is selected to solve the compensation problem of the steam pipeline. The project installation is convenient, and the cold drawing, pre tightening and other construction technologies are not required, and butt welding is enough;
- (7) Less investment: due to the long compensation distance of rotary compensator, the number of compensators used is reduced, and the thrust of fixed pier for civil engineering is small, the number of fixed piers is relatively small, and the scale of fixed pier is relatively small, which greatly saves the investment of civil engineering. Compared with other compensators, the total project investment is saved by 20% – 40%, and the economic benefits are considerable.
Application conditions of rotary compensator:
Generally, one group of rotary compensator is installed on the pipeline according to 200-500m (it can be determined according to the natural terrain). There are more than 10 installation forms, and the layout can be determined according to the pipeline direction. After using this type of compensator, the distance between fixed supports increases. In order to avoid the deflection of the pipe section, the guide bracket should be properly added; in order to reduce the friction resistance of the pipe section, the rolling support should be installed on the sliding support.
The meaning of square compensator
The square compensator is also called square expansion force or expansion bending. The elastic deformation made by the pipe bending absorbs the thermal expansion of the pipe. The square compensator must be made of seamless steel pipe with good quality, and the whole compensator should be made by simmering one pipe.
Advantages of square compensator:
- (1) Compared with sleeve compensator and corrugated compensator, the axial thrust acting on the fixed bracket is smaller and the thermal compensation is larger, which is suitable for various pressure and temperature conditions;
- (2) High safety, no maintenance is needed in normal operation, and no inspection well is needed.
The application conditions of square compensator are as follows:
When installing the square compensator, in order to reduce the deformation elastic force of the compensator and improve the compensation ability, the outer arm of the compensator must be stretched a certain length in advance and then installed on the pipeline.
Installation and use requirements of compensator
- 1. The model, specification and pipeline configuration of compensator should be checked before installation, which must meet the design requirements;
- 2. For the compensator with inner sleeve, the direction of inner sleeve cylinder should be consistent with the direction of medium flow, and the hinge rotation plane of hinge type compensator should be consistent with the displacement rotation plane;
- 3. For the compensator that needs to be “cold tight”, the auxiliary components for pre deformation should be removed after the pipeline installation is completed;
- 4. It is strictly forbidden to use the deformation method of metal corrugated compensator to adjust the installation out of tolerance of pipeline, so as to avoid affecting the normal function of compensator, reducing the service life and increasing the load of piping, equipment and supporting components;
- 5. During the installation, welding slag is not allowed to splash on the surface of the wave shell, and the wave shell is not allowed to suffer other mechanical damage;
- 6. After the piping system is installed, the yellow auxiliary positioning components and fasteners used for installation and transportation on the metal corrugated compensator shall be removed as soon as possible, and the limiting device shall be adjusted to the specified position according to the design requirements, so that the pipeline system has sufficient compensation capacity under environmental conditions;
- 7. All moving components of the compensator shall not be blocked by external components or limit its range of motion, and the normal operation of each moving part shall be ensured;
- 8. During the hydraulic test, the secondary fixed pipe support with compensator pipe end shall be reinforced to prevent the pipeline from moving or rotating. For the compensator and its connecting pipeline used for gas medium, it is necessary to pay attention to whether temporary support is needed during water filling;
- 9. After the hydraulic test, the water in the wave shell should be drained as soon as possible, and the inner surface of the wave shell should be dried quickly;
- 10. The insulation material in contact with the compensator bellows shall be chlorine free.
Source: China Pipeline Compensator Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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