The valve group of the control valve (instrument professional regulating valve), including the control valve and the shut-off valve, the bypass valve, etc., the most common arrangement is the façade arrangement, and the bracket is arranged below the pipe elbow. In addition to considering the weight of the support, the brackets of this type of valve block also consider the thermal expansion of the pipe and the force to withstand vibration. When the pressure difference between the inlet and outlet of the valve is large, or when the gas is decompressed during the decompression process, it is more likely to cause severe vibration, which should be paid special attention. For two-phase flow pipelines, the possibility of water hammer should be considered. When the vertical pipe section is long and has upward flow, the water hammer is prone to occur. The situation is improved if the upwardly flowing pipe section is placed before the control valve. For pipes with thermal expansion, one of the brackets shall be set as a fixed frame and the other as a sliding bracket or guide frame according to the requirements of its flexible calculation. If the thermal expansion stress permits, it is advisable to provide a fixing frame on the outlet side of the control valve and a sliding frame on the inlet side. If necessary, a guide frame is also provided on the vertical pipe end of the outlet side of the control valve.
2 tower equipment pipe support
The tower's pipelines can generally be divided into tower top pipelines, tower side pipelines and tower bottom pipelines. The top pipe includes a return pipe, a feed pipe, a side draw pipe, a stripping steam pipe, a reboiler inlet and a return pipe. The bottom pipeline includes a bottom draw pipe and a bottom drain pipe. These pipes are connected to the openings in the tower body, and are generally arranged along the circumference or up and down of the tower body. For the design of the bracket of the bottom reboiler, a more detailed design scheme has been given, and the pipeline descending along the upper part of the tower is mainly discussed here. Tower-type pipes are usually provided with supports on the tower wall to minimize their relative displacement. Tower equipment piping support. Tower equipment piping support The first bracket descending along the upper part of the tower is usually provided with a sliding load-bearing frame or a fixed bracket, and as close as possible to the equipment nozzle to reduce the relative thermal expansion displacement of the equipment port and the support point. The reaction force of small thermal expansion. If the pipe between the first bracket and the nozzle is not flexible enough, the way of changing the direction of the pipe can be taken to appropriately increase the flexibility of the pipe. If the load on the first load-bearing frame is too large, a second load-bearing frame can be provided.
When performing stress analysis on such pipelines, various conditions such as parking, no-load, normal operation, and water-to-air transportation should be considered. Since the temperature difference between the tower equipment and the pipeline will be different under various working conditions, the thermal displacement and thermal stress should be analyzed according to the difference between the thermal expansion of the tower wall and the pipeline. For example, it is necessary to provide a bracket at the elbow of the vertical pipeline, whether it is supported from the tower wall or not, it should be set as a spring bracket. It should be noted that otherwise, due to insufficient flexibility of the pipeline, the rigid bracket closest to the elbow will be caused. Excessive force or emptying will inevitably affect the force of the bracket on the tower wall and the force on the nozzle. Combined with the requirements of the pipe bracket of the control valve group, it is not difficult to see that it is generally not appropriate to set the control valve group too close to the elbow in the upper tower line. The temperature difference between the return line of the tower and the tower wall is large, and the regulating valve group is generally set. The stress analysis should be paid enough attention.
3 centrifugal pump pipe bracket
The inlet and outlet positions of the pump are divided into four types according to the nature, state, flow rate and head of the treatment fluid, which are divided into top, top, side and side. When designing a centrifugal pump piping, the inlet and outlet piping must be flexible enough to reduce the forces and moments that the piping acts on the pump port. For centrifugal pumps that have not been subjected to the force requirements of the manufacturer, the nozzle pressure is generally required to meet the requirements of API610.
The piping arrangement and pipe bracket setting of the centrifugal pump are shown in Fig. 3. Fig. 3 The inlet and outlet pipe arrangement of the centrifugal pump and the inlet pipe of the pipe support pump are stricter, and the export problems are relatively less. In order to make the pump nozzle force as small as possible, a hanger should be installed near the valve to prevent the valve quality from acting on the pump nozzle. If there is a vertical thermal displacement near the branch point at the pump nozzle, consider using a spring holder. For the horizontal inlet and outlet pipelines of the pump, rigid support should be used as much as possible, and the first bracket close to the pump port should normally be made into a height-adjustable load-bearing frame. For the rigid sliding bracket, if the distance from the elbow is too small, It will be empty, or under the load-bearing condition, the heat of the pump nozzle will be greatly affected. Consider using a spring frame. It should be noted that when the inlet pipe of the pump is connected horizontally to the pump port, sometimes the pump body is larger. There is vertical thermal expansion at the pump port. If the sliding bracket is too close to the pump port, flexible analysis often cannot pass. In order to avoid the horizontal thrust of the distal pipe acting on the pump nozzle, a limit bracket or guide bracket should be placed near the symmetrical position of the pipe system. It should be noted that there is no uniform standard in the domestic adjustable brackets, and the designers are required to propose relevant parameters, which are specially manufactured by the manufacturer. When multiple pumps are arranged side by side, the force generated by the thermal expansion of the pipe between the pumps and the axial thrust caused by the friction of the pipe are often the important reasons for the excessive force of the pump port. If the stress analysis results show that the above reasons cause the pump port to be unable to meet the requirements, then the flexibility should be considered to absorb the thermal expansion of the connecting section and reduce the friction coefficient at the sliding point. The more common method is to add a layer of PTFE pad. The friction coefficient of steel to steel is reduced to 0.3 for stainless steel to PTFE. In addition, for large pump outlet pipes, attention should be paid to the thrust action when the check valve is closed. A solid bracket should be placed near the check valve and shut-off valve to withstand water and gravity loads.
4 steam turbine and centrifugal compressor nozzle line bracket
Centrifugal compressors are continuously discharged and can be almost ignored. However, since the gas is small in weight, the rotor speed is high, and it is multi-stage, the alignment requirement of the shaft is very high. Because the operating temperature of steam turbine pipelines is higher and the force requirements are more stringent, the flexible design of steam turbine pipelines is one of the more difficult problems in pipeline stress analysis.
When the machine manufacturer does not propose to allow the force limitation, the general gas turbine nozzle stress calibration standard is NEMASM23, and the centrifugal compressor nozzle pressure calibration standard is API617. The flexible design of the centrifugal compressor and the steam turbine pipeline has Similarities, the following mainly describes the steam turbine pipeline as an example.
(1) The thermal displacement of the machine nozzle must be considered in the calculation, and the most unfavorable working conditions should be considered.
(2) When carrying out the force check analysis of the steam turbine, it should include the inlet and outlet and the extraction port; the steam seal pipe may not be analyzed in detail, but it should be flexible enough.
(3) The calculation should take into account the quality of the pipe flange at the nozzle of the machine. It should be noted that the flanges that are paired with the machine nozzles typically have a higher pressure rating than the pipe pressure rating.
(4) The influence of the branch pipe connected to the main pipe should be considered in the calculation. Under normal circumstances, the safety valve line is connected to the steam pump suction port and the centrifugal compressor outlet line. The external load demanded by the safety valve nozzle is as small as possible to avoid deformation of the valve body and affect the performance of the safety valve. The pipeline is required to have a certain flexibility. Since the bracket can withstand the gravity, it should also be able to withstand the reaction force generated when the fluid is discharged. Therefore, some guides, limit positions and fixing brackets are generally arranged on the safety valve outlet line. Have a big impact. When these restrictive brackets make the machine nozzle unable to pass, it is conceivable to use an anti-safety valve exhaust reaction type damper instead of the restrictive bracket near the safety valve outlet.
(5) Several sets of hangers near the nozzle of a steam turbine generally use spring support hangers to reduce the thermal force of the nozzle caused by the thermal expansion of the vertical pipeline and reduce the influence of friction. The horizontal distance between the first spring support and the nozzle should be controlled within 4 times of the nominal diameter, so that the self-weight and thermal expansion thrust and torque of the compressor pipe should not be applied to the compressor nozzle as much as possible.
(6) The overall comprehensive check of the force and moment of each nozzle of the machine is often the most difficult to pass. Therefore, the force and moment of each nozzle should be considered comprehensively, so that the forces and moments at different nozzles can cancel each other. For multi-stage compression centrifugal compressors, manufacturers generally propose segmentation for overall calibration to allow for force limitations. The CAESAR software itself has NEMASM23 and API617 check modules. When the number of nozzles for the overall calibration of the centrifugal compressor exceeds 4, manual calibration is required.
(7) The pipe of the steam turbine is preferably arranged around the fixed point of the machine, and a limit bracket is arranged near the intersection of the coordinate axis of the pipe and the fixed point of the machine, so that the thermal expansion of the nozzle of the machine is substantially equivalent to the thermal expansion of the pipe to reduce The force of the pipe on the nozzle of the machine.
(8) If the support position, form and direction of the pipeline are adjusted, the turbine is still difficult to meet the requirements. It is considered to use a metal bellows expansion joint on the vertical pipe at the steam turbine outlet.
Some steam turbine inlet pipes use high pressure steam, and the steam temperature even reaches 540! When using CAESAR software for stress analysis, if the software's default cold elastic modulus is still conservative, the thermal elastic modulus will be closer to reality. When the overall check of item 2 is carried out according to the machine stress check standard, the force and torque should be synthesized at the center of the largest nozzle, the steam turbine is generally the exhaust port, and the centrifugal compressor is generally the air inlet. Centrifugal compressors with multi-stage compression have many nozzles, and sometimes there are more than one nozzle with the largest diameter. In this case, the reference point should be selected, and the relevant standard specifications are not clearly defined.
In order to ensure the normal operation of the machine, GB50235 industrial metal pipeline engineering construction and acceptance specification # and SH3501 petrochemical highly toxic, flammable medium pipeline construction and acceptance specification # are the spacing between the pipe flange and the machine flange when installing the rotating machine Parallelism and coaxiality have been strictly required. In order to facilitate the realization of these requirements during construction, in the flexible analysis of the rotating machine pipeline, not only should the mechanical nozzles under the operating conditions be subjected to the requirements of the corresponding standards, but also the force of the pipeline to the machine nozzles in the installed state should be as far as possible. Close to zero. In addition, the first spring support hanger near the machine nozzle on the pipeline should be as close as possible to the machine nozzle. If necessary, the first spring support point can be set to three uniform constant forces with a certain load setting rate. Springs to facilitate adjustment of the spacing, parallelism and concentricity between the flanges during construction. It is not advisable to use cold tightness when the pipe of the rotating machine is close to the nozzle of the machine, otherwise the construction requirements will be difficult to meet.
5 brackets for pipes on the pipe gallery
The pipelines laid on the pipe gallery include the grades and types of various process pipes, and the corresponding school approvals are selected. For example, the current large-scale chemical plants usually use high-pressure steam with a parameter of 9.81 MPa and 540, which belongs to the GD1 class power pipeline. The stress analysis should be checked according to the power pipeline specification ASMEB31.1, and the various process pipelines should be ASMEB31.3 is checked.
The spacing of the pipe supports on the pipe gallery is limited by the beam and column spacing of the pipe gallery structure. The spacing of the large pipe supports is usually 6m, and the spacing of the small pipe supports is usually 3m. When designing the pipeline, whether or not detailed stress analysis is required, First meet the allowable span requirements. Sinking of the pipeline means that the water is not smooth. The local part of the high-temperature pipeline may cause large temperature difference stress due to the hydrophobic problem. In severe cases, the pipeline will be partially deformed, and the span of the bracket is more strict.
The bracket design of the pipe on the pipe gallery focuses on various restraining brackets, especially the brackets. The fixed point position of the pipe should meet the following requirements.
(1) For complex pipelines, it can be divided into several simple-shaped pipe sections by fixed points, such as L-shaped pipe section, U-shaped pipe section and Z-shaped pipe section, and then analyzed and calculated.
(2) When determining the position of the fixed point of the pipeline, it should be beneficial to the natural compensation of the pipe section between the two fixed points.
(3) The fixed point should be placed close to where it is necessary to limit the displacement of the branch pipe.
(4) The fixed point shall be set where it is required to withstand pipe vibration, impact load or need to limit the multi-directional displacement of the pipe.
(5) The process piping of the inlet and outlet devices and the very warm common material piping should be provided with fixed points at the boundary of the device.
(6) The fixed point of the pipeline should generally be placed on the main beam of the column axis. Do not set it on the secondary beam, and try to make the thrust difference between the two sides of the fixed frame not too large. The load acting on the fixed point in the pipeline should be considered. Friction reaction force of each sliding bracket on both sides.
(7) When an axial expansion joint is arranged between the two fixed brackets, one end should be close to the fixed bracket, and the distance between the first guide bracket and the compensator at the other end should be set at 4 times the nominal diameter (4DN), and the second guide bracket The distance from the first guide bracket is set at 14 times (14 DN) of the nominal diameter, and the remaining guide brackets can be set according to the guide bracket spacing allowed by the horizontal pipe.
(8) When there is a U% type compensator, it should be set in the middle of two fixed points, and guide brackets must be provided on both sides. The distance between the first guiding bracket and the elbow should not be too close, so as to avoid excessive horizontal thrust. The A value is generally 32DN~40DN, the B value should not be less than 2m, and the maximum distance between the fixed points should be U%. Depending on the size of the compensator, the bracket with the axial expansion joint pipe should be arranged side by side for multiple pipes requiring U% type compensator. The high temperature and large diameter pipes should be placed on the outside, low temperature and small diameter pipes. Should be placed on the inside. The branch pipe should not be led out on the U% compensator. When the branch pipe is led out on a straight pipe near both sides of the compensator, the branch pipe shall not obstruct the deformation or displacement of the main pipe. The displacement of the branch outlet point due to the thermal expansion of the main pipe shall not subject the branch pipe to excessive stress or excessive displacement. When the pipeline is naturally compensated, the three-dimensional shape is better than the planar shape.
Pipe-restricted bracket type on the pipe gallery When the bracket point only needs to limit the displacement in one or several directions, and allows other directions to be free, it should be set as a limit bracket, and the gap can be appropriately placed as needed.
6 coal gasification frame water vapor system pipeline bracket
Since the coal gasification frame water vapor system pipeline enters, the outlet height difference is large, and the pipeline temperature is also high, most of the brackets on such pipelines are arranged as spring support hangers. When driving, the temperature rises slowly, and the density of the medium in the tube will change greatly, especially in the PCW2 system pipeline. The medium specific gravity of the pipeline in normal operation is less than 0.3. Since the spring is based on the thermal displacement under normal operating conditions. And the installation load design, if you do not take any protective measures, it is likely to cause multiple springs to be crushed.
In order to prevent the spring hanger from being damaged due to overload, it is better to select some suitable positions on such pipelines to add some rigid sliding bearings, but these points must be vertically upward during normal operation. In addition, when stress analysis is performed on such pipelines, the density of the medium can be appropriately enlarged, and the rate of change of the spring load is strictly controlled.
7 Conclusion
(1) In the investment of the whole pipeline engineering, although the proportion of the support and hanger system is small, the correct setting of the support and hanger plays a vital role in the safe operation of the entire pipeline system. Only when the pipeline layout is reasonable and the position and form of the bracket are selected, the pipeline design can be economical, reasonable, safe and reliable while meeting the process requirements.
(2) The above contents have necessary discussion on the position determination and selection of the support and hanger. The design should also pay attention to the strength of the support and hanger parts and the selection principle of the materials.
(3) With the development of the petrochemical industry, the scale of the equipment has increased, the number of large-diameter pipelines has increased, and the support and hangers have become larger and more complicated. The pipe rack standards have yet to be further updated and improved.
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