How critical is lateral displacement compensation in a pipeline system?
Anyone who has worked in power plants or chemical pipelines has encountered this problem: the pipelines are clearly laid in a straight line, but they deviate as soon as they heat up. Thermal expansion and contraction is common sense in physics, but lateral displacement-the misalignment of the pipe perpendicular to the axis-is often the most troublesome. The equipment interface is misaligned, the bracket is unevenly stressed, and the flange leaks... The root cause is often that the lateral displacement is not controlled.
Where did the lateral displacement come from? Thermal expansion is only part of it. Lateral misalignment can also be caused by pipeline turns, equipment settlements, earthquakes or wind loads. You use a normal axial expansion joint to carry it? If you can't carry it, the bellows will twist. At this time, we have to rely on a special transverse displacement compensator-that is, the transverse product of metal expansion joint we are talking about today.
To put it bluntly, the core value of the metal expansion joint horizontally is two words: it can safely compensate the displacement when the pipeline is not walking straight. This is not the icing on the cake, it is just needed. Two days ago, I met the construction party of a desulfurization project, and the pipeline leaked directly after the pressure test. After checking, it was found that the lateral displacement was not counted, and the expansion section was selected as an axial type. You see, if a parameter is selected wrong, it will be followed by pits.
Double hinge transverse vs. large tie rod transverse: structure determines whether you can install
There are two main types of metal expansion joint horizontal products on the market:Compound hinge transverse expansion jointAndLarge tie rod transverse expansion joint。 The structure is different, and the applicable scenarios are completely different.
Compound hinge transverse expansion joint, to put it bluntly, means that two bellows are connected with hinges in the middle to form a "joint". It can only absorb lateral displacement, not axial displacement. What are the advantages? The structure is compact and occupies a small area, so it is suitable for the occasion where the space is limited and the pipeline direction has been fixed. For example, the air-cooled island pipeline of the power plant is tight in space and only has lateral deflection, and the double-hinged structure is very good-the one in our stationDouble hinge expansion joint for air-cooled island vacuum pipelineThat's what we do.
What about the large tie rod transverse expansion joint? The structure is also two bellows, but the middle is connected by a long tie rod, and the two ends of the tie rod are limited by nuts. It both absorbs lateral displacement and limits axial elongation through a tie rod — to put it bluntly, keeping the bellows from being straightened. This product is suitable for scenarios in long straight pipelines where lateral displacement needs to be compensated while axial constraints are required. For example, chemical pipe gallery and cement plant hot air duct.
How to choose? Don't feel it. You first draw the direction of the pipe to see whether the main direction of displacement is horizontal or comprehensive. If the pipe has turned several corners, a duplex hinge may be more handy; Large tie rods are more secure if only one section of straight pipe needs to be staggered horizontally. Remember one principle:The tie rod is not a decoration, but a force-bearing part.If the strength of the tie rod in the model you choose is not enough, the bolts will collapse first, and the bellows will be scrapped.
Type selection and calculation do not step on pits: lateral stiffness, compensation amount, guide tube, tie rod locking
- Lateral stiffness.Many people only focus on the amount of compensation and ignore the stiffness. If the stiffness is too great, the thrust of the pipeline is transmitted to the bracket, and the bracket can't stand it; If the stiffness is too small, the bellows will easily become unstable. On our websiteStiffness and Calculation Formula of BellowsThere are special instructions, so look through them if you are interested. Simply put: the stiffness should match the allowable thrust of the pipe support, don't take it for granted.
- The amount of compensation.The greater the amount of lateral compensation is not better. The cold state prebias should be included in the design. For example: the pipeline operates at 200 °C, the ambient temperature is 20 °C, and the lateral displacement is expected to be 20 mm. You buy an expansion joint with a compensation amount of 30mm, and install it directly in the right position during installation-after operation, the thermal expansion direction is opposite to expected, and the bellows may exceed the limit. The correct way to do it is to pre-bias half and leave an allowance.
- Deflector tube.High-speed gas flow or pipelines containing particulate media (such as desulfurization flue gas), guide tubes are a must. The function of the guide tube is to guide the flow direction of the medium and avoid direct flushing of the bellows. In the FAQ on our siteSpecific Function of Expansion Joint Guide TubeThat article is very detailed, and there are pictures attached to it. Without the high temperature and dusty working condition of the guide tube, the bellows may wear out in half a year.
- Pull rod locked.Large tie rod transverse type expansion energy saving can not lock the tie rod? Many installers go to the site to screw the nut directly, thinking that the tighter the better. Wrong. The tie rod nut is locked in transportation, but needs to be adjusted to the working position according to the design after installation-How to adjust the tie rod nut of expansion jointOur station also wrote it specifically. If you don't adjust it right, the bellows is equal to hard-carrying displacement, and the life is at least halved.
If one of these four parameters is wrong, it will be a hidden danger if it is installed. Don't believe it, there was a cement plant case last year: the deflector tube was not installed, the bellows was perforated in three months, and hundreds of thousands of losses were shut down for maintenance.
Rollover case at installation site: tie rod nut is not adjusted, fixed bracket is not counted correctly
Let me tell you two more real things.
Case 1: The tie rod nut is used as a locking part.The steam pipeline of a chemical plant uses a large tie rod transverse expansion joint, and the workers screw the nuts on both sides to close with the end plate. During operation, the bellows is held firmly by the tie rod, and the lateral displacement is fully pressed onto the bellows, resulting in fatigue cracking at the root of the bellows. Correct practice: The nut is only used to limit the maximum displacement. After installation, it should be loosened to the design gap so that the bellows can deform freely.
Case 2: The fixed bracket is thought to be a standard part.Another project, the design was selectedCompound hinge transverse expansion jointHowever, the fixed bracket is welded with ordinary channel steel, and the stiffness is not enough. As soon as the pipe expands, the bracket deforms first, and the hinge of the expansion joint becomes the fulcrum instead, and the bellows is bent. You see, the expansion joint itself is fine, the bracket is not counted correctly, and the pot still has to be carried. In our stationCorrect installation method of expansion joint of large tie rodThat article specifically emphasized the stent requirements, which can be compared.
The transverse product of metal expansion joint is not an isolated part, it constitutes a system with bracket, guide tube and fixed tube holder. You only count as a part, and if the other links don't keep up, it will still fail.
Working condition extension: Why do air-cooled island pipelines in power plants prefer double-hinged transverse type? How to pick cement, chemical industry and desulfurization scenarios?
Different industries, the fishy smell is different.
Power plant air cooling island.Vacuum pipe, the temperature changes greatly, the space is compact, and the pipe trend is complicated. Double hinge construction (includingDouble hinge expansion joint for air-cooled island vacuum pipeline) can absorb the multi-directional lateral displacement in the horizontal plane, and occupy a small space. In addition, the vacuum condition requires high sealing performance, and the double-hinged bellows itself is designed to have low stiffness, which has little influence on the vacuum degree.
Cement industry.Hot air duct, kiln tail duct, high temperature, large dust, large air volume. The lateral displacement is mainly caused by thermal expansion and foundation settlement. recommendLarge tie rod transverse expansion jointBecause the tie rod can withstand the high internal pressure thrust and avoid the bellows from being blown. At the same time, a guide tube must be added, otherwise the dust will wash every wave peak of the bellows. Our station hasMetal Corrugated Expansion Joints in Cement IndustrySeries, you can see the specific selection cases.
Chemical and desulfurization.There are many corrosive media in chemical pipelines, and desulfurization flue gas contains moisture and sulfur. The material should be high nickel alloy or PTFE-lined structure. In shape, the duplex hinge is suitable for lateral compensation at the elbow; Large tie rod fits long straight pipe sections. Note that the bellows are often worn out in the desulfurization system due to slurry washing, soDesulfurization flue gas baffle doorAndPTFE-lined hoseSuch kits should sometimes be considered together.
There is no universal type, only working condition matching type. If you figure out the medium, temperature, pressure and displacement direction, the selection is more than half successful.