After many people get the expansion joint, the first thing they ask the manufacturer is: Where does this thing fit? Honestly, this question hit the nail on the head. Installing the expansion joint in the wrong position is more fatal than choosing the wrong model. If the selection is wrong, the service life will be shorter at most, and the position will be wrong. The bellows will be stretched, twisted and unstable, ranging from abnormal noise in the pipeline to tearing the bellows and leaking the medium. We have done pipeline compensation schemes all the year round, and have seen too many such cases. Today, we will break up the location and make it clear.
Which section of the pipeline should the expansion joint be installed: first distinguish the fixing bracket and the guide bracket
To find out where the expansion joint is installed, two roles must be recognized first: the fixing bracket and the guide bracket. The fixing bracket is the anchoring point of the pipe, it locks the pipe firmly and does not allow displacement in any direction. The guide bracket only limits lateral displacement and allows axial sliding. The mission of the expansion joint is to absorb the displacement caused by thermal expansion and contraction between these two types of brackets.
The expansion joint must be located between the two fixed brackets and mounted close to one of the fixed brackets. Leave enough straight pipe segments on the other side to cooperate with the guide bracket to allow the pipe to expand and contract in a predetermined direction. In other words, the expansion joint is not installed wherever you want, it is a link in the pipe support system. You set the fixed bracket first, and the position of the expansion joint will be set by 70% to 80%.
Is the expansion joint close to the fixed bracket or the device end? Force differences between two typical layouts
Pipe layouts typically come in two typical forms. One is that the expansion joint is close to the fixed bracket, which is called "single axial layout". At this time, the expansion joint bears pure axial compression or stretching, and the bellows has the most uniform force and the longest service life. LikeHigh temperature axial expansion jointUnder this layout, the maximum compensation ability can be exerted.
The other is that the expansion joint is close to the equipment end, such as connecting sensitive equipment such as steam turbines, pumps and fans. In this case, the expansion joint has to not only absorb the thermal displacement of the pipe, but also bear the additional displacement caused by the thermal expansion of the equipment. The stress state is much more complex, and sometimes it is necessary to useCurved tube pressure balance expansion jointOrCompound hinge transverse expansion jointTo defuse. Which one you choose depends on whether the equipment can withstand pipe thrust.
Selection of connection position under different working conditions: How to determine high-temperature steam, large-diameter flue gas and corrosive medium
Different working conditions have different ideas for location selection.
High-temperature steam pipelines, such as the main steam pipeline of power stations, have a temperature above 400℃. At this time, the expansion joint should be as close to the fixed bracket as possible, and enough guide brackets should be set in the middle straight pipe section. If the straight pipe section is too long, the bellows will be unstable, and if the straight pipe section is too short, the fixed bracket will bear excessive blind plate force.Corrugated expansion joint for power station industryThe installation spacing is generally controlled at 20~40 meters for a compensation unit, depending on the pipe diameter and medium temperature.
Large-diameter flue gas pipelines, like the inlet and outlet flues of desulfurization towers, have low pressure but large cross-section, and are usually rectangular structures. At this time, where to install the expansion joint depends more on the drop point of the flue support and the arrangement of the baffle door. Generally, it is recommended to set a fixed point on both sides of the flue, and the expansion joint is placed in the middle section, so that the displacement in both directions is concentrated in the middle.
What about corrosive media pipes? The position of the expansion joint must avoid dead angles and fluid accumulation sections. When the medium flow rate is low, corrosive liquid is easy to accumulate at the bottom of the bellows, so in addition to selecting the correct position, it is also necessary to selectRectangular non-metallic expansion jointOr a structure with a guide tube to ensure smooth passage of the medium without staying in the bellows area.
How the expansion joint is connected to the pipe: welded, flanged or sleeved? Position Determines Joint Form
The connection method is not randomly determined, but is directly related to the spatial conditions of the installation position.
The welding connection is the most reliable and suitable for high temperature and high pressure pipelines, but it requires welding conditions and flaw detection means at the site. The flange connection is convenient for loading and unloading, and is suitable for pipelines that need regular maintenance and cleaning, such as desulfurization flue and sewage treatment pipe. The sleeve connection is not welded, without flange, and is sealed by packing. It can be selected in compact spaceSleeve type pipe expansion joint。
If the expansion joint is installed in a narrow pipe gallery with limited access space, preference should be given to flange or sleeve connections. If the position is at the end of the overhead pipeline, which is convenient for hot work, welding is a better choice.
Common installation error: What happens if the expansion joint is installed near the elbow and the distance between the two expansion joints is insufficient
Install the expansion joint near the elbow. The elbow is where the pipe produces lateral displacement and bending moment, where the expansion joint will bear additional lateral forces and bending stresses, and the bellows will soon fatigue crack. The correct way is to set fixed brackets at both ends of the elbow, and the expansion joint is placed on the straight pipe section away from the elbow.
The two expansion joints are too close to each other. Some designers put two expansion joints next to each other in order to save space in the pipeline. This will lead to the middle pipe section becoming a floating unit, the two expansion joints push each other, the displacement distribution is uneven, one is overloaded and the other is idle. The specification requires that the length of the straight pipe section between the two expansion joints, usually not less than four times its nominal diameter, and that an intermediate fixing bracket be provided to distribute the displacement.
Practical recommendations for type selection and positioning: Final installation point determined by combining the design of fixed bracket and manufacturer's data
The positioning of this matter, in the final analysis, depends on the layout plan of the fixed bracket. When making compensation design, first clear the direction of the pipeline, set the positions of all fixed brackets, and then calculate the compensation amount needed for each compensation section according to the thermal expansion amount and allowable span. Then compare the displacement parameters provided by the manufacturer to determine the specific installation point of the expansion joint.
Are temporary supports installed during the pipeline pressure test? Is the amount of pre-stretch adjusted to ambient temperature? Is there a protective sleeve on the outside of the bellows? These details can affect the quality of the installation. As a reminder,Direct buried (fully buried) type expansion jointThe installation method is completely different from the overhead pipeline and cannot be mixed.
Which position the expansion joint is connected to the pipeline is not worked out by the construction team on the spot, but it has to be calculated clearly in the design stage. If the location is selected correctly, there will be no problems with the pipeline for twenty years; Wrong choice, rework is a small matter, safety accidents are a big deal. It is recommended to send the pipe drawing to the manufacturer before purchasing, and let the technicians help you review the positioning. Many problems can be avoided in the drawing stage.