How is it different from a regular expansion joint? — — Find out what the word "Wanxiang" means first
To be honest, people who came into contact with this thing for the first time would most likely be misguided by the word "Wanxiang". You think it can turn 360 degrees like a joint? Don't be naive. The core of a real universal metal expansion joint is two sets of hinge structures, one set swinging in the plane and the other set swinging in the vertical plane. When combined, it can absorb the displacement of the pipe in any direction-but note that it is "angular displacement", not "rotation".
Common expansion joints, such as those common in our stationUniversal corrugated expansion jointOrAxial expansion joint, they can only absorb displacement in one direction. You don't expect the axial type to carry the lateral force, and the tube will look at you sooner or later if you hard-fit it. The advantage of the universal type is that once the two hinges cross, it can be folded when the pipe expands and contracts thermally, no matter which side it moves up, down, left and right. To put it bluntly, it is a "flexible joint" to prepare the direction of complex pipelines.
Then it andCompound hinge transverse expansion jointWhat's the difference? The latter is also two hinges, but is relatively simple in construction and is typically used to absorb lateral displacement. The universal type has one more degree of freedom and can absorb angular displacement from two different planes at the same time. Which to choose depends on the actual deviation direction of the pipeline-don't expect one model to dominate the world.
Its core work: multi-directional displacement one shoulder, pipeline stress does not run blindly
What are plumbing systems most afraid of? Stress from thermal expansion. Especially those pipes that turn around. Once the temperature heats up, no one knows where the pipes are squeezed. What is the role of universal metal expansion joint? Simple and crude-swallow all the displacements in multiple directions, let the thrust concentrate on the fixed bracket, and don't let the stress jump at the welds and flanges.
Take the main steam pipe in the power station for example. The temperature can soar to more than 500 degrees, and the pipe can expand by several millimeters per meter. The total displacement of a pipeline of tens of meters is scary to death. If only the axial type is used, the lateral displacement cannot be managed; If two hinges are combined, it takes up too much space. One solution for universal type, two hinges are arranged crosswise, and then cooperatetie rod(Remember the "role of expansion joint tie rod" in the FAQ?) To withstand pressure thrust, bellows only absorb displacement and perform their respective duties.
Deflector tube. This thing is inSpecific Function of Expansion Joint Guide TubeAs mentioned in, the main thing is to prevent high-speed airflow from washing the bellows. The design of the guide tube inside the universal type is more particular, because there are many displacement directions, and the guide tube must swing with the hinge, leaving a large gap to leak air and a small one to get stuck. Many small factories in this piece can't do well, which directly leads to a discount in life.
Which occasions must use the universal type? The real demand of power stations, cement and desulfurization
Before talking about the application scenario, let's first look at a set of data: in the smoke duct system of domestic thermal power plants, the amount of universal expansion joint accounts for more than 30% of the total number of pipeline compensators. Why? Because the flue tends to be winding, and the space is often limited, it is impossible to install large-size double hinges. You go and seeCorrugated expansion joint for power station industryMany of that kind of products are universal.
The same goes for kiln tail pipes in the cement industry. High temperature, dusty, multi-directional displacement, ordinary axial type can't carry two months before leaking. Use the universal type, matchingMetal Corrugated Expansion Joints in Cement IndustryHigh temperature resistant design, there are many problems in five years. Two days ago, a customer who was doing the denitrification transformation of cement kiln tail told me that they used to use a non-metallic compensator, which was replaced every six months. After replacing it with a universal metal bellows, the number of downtime was directly cut in half.
Look at the desulfurization system again. Near the flue gas baffle door at the outlet of the desulfurization tower, the pipeline has to bear both thermal expansion, fan vibration and corrosion prevention. useDesulfurization flue gas baffle doorWith universal expansion joints, it is a common configuration. Note that the desulfurization environment medium contains acidity, and the material must be 316L or higher. At this timePTFE-lined hoseOrPTFE compensatorIt can also go up, but the advantages of universal metal lie in higher temperature resistance and stronger pressure-you can't always use PTFE in 200℃ flue gas, can you?
Don't step on pits when selecting: universal type is not universal type, installation details determine life
The name "Wanxiang" is too easy to let people down their guard. The most outrageous case I have ever seen is that the universal type is used as a long and short telescoper, stuffed directly between two fixed brackets, and as a result, the bellows is pressed into a twist. Remember that the universal type can only absorb angular displacement and a small amount of lateral displacement,Unable to absorb axial displacement。 If the pipe has a large axial expansion and contraction, you need to matchAxial expansion jointOrStraight pipe pressure balanced expansion joint。
Transport screw. In order to fix the bellows when leaving the factory, several screws will be welded-this point is clearly stated in the FAQ "Do the screws of expansion joints need to be disassembled". Many on-site workers try to save trouble and don't dismantle it, or half of it is dismantled. As soon as the system heats up the screw, the bellows gets stuck and it fails directly. Solution: After installation, all must be removed and marked.
Adjustment of tie rod nuts. Gimbal typically hasLarge tie rodWhich is used to withstand the thrust generated by the internal pressure while limiting the excessive elongation of the bellows. The tie rod nut cannot be screwed to death and must be adjusted according to the design pre-compression amount. It is written in the answer of "How to Adjust the Tie Rod Nut of the Expansion Joint" that the nut is usually screwed to the marked position when it is cold, leaving a thermal expansion margin. Screwed to death is equivalent to locking the bellows, and the consequence is that all the stress of the pipeline runs to the equipment.
Talk about something real: fault cases and common misunderstandings, spend less money after reading it
Let's start with a real malfunction. Two universal expansion joints were used in the outlet pipeline of the grate cooler of a cement plant, which burst one after another within half a year. On disassembly, longitudinal cracks appear in the bellows sidewalls — typical lateral displacements exceeding design values. The designer patted his head to measure the thermal expansion of the pipeline, but ignored the forced displacement caused by fan vibration. How to fix it? Replace withCompound straight pipe bypass pressure balanced expansion jointThe vibration displacement is directed to structures with stronger absorption capacity. Hey, I spent an extra two hundred thousand to buy a lesson.
It is believed that the universal type can be installed in any direction. It is true that it is more flexible than a regular expansion joint, but it has its own "neutral face" — the center of the hinge's swing. If the pipe centerline deviates from this neutral plane during installation, the displacement will increase exponentially and the bellows life will plummet. Therefore, pipeline stress analysis must be done before installation, and don't rely on experience alone.
Also, don't combine the universal type withRotary compensatorMix up. The rotary compensator absorbs the displacement by rotation, which is suitable for the thermal expansion of long straight pipes; Universal type mainly solves the scenario of space constraint and multi-directional displacement. You use it on asphalt pipes? Then you have to chooseSleeve type pipe expansion joint。 If you choose the wrong one, you will spend money for nothing.
If your pipe is only displaced in two directions and there is enough space, use two setsHinge transverse expansion jointOften cheaper than a gimbal and easier to maintain. Don't be superstitious about the word "universal", it is only a tool, not a omnipotent. Understanding the displacement boundary conditions of your own pipeline and then selecting the type is better than anything else.