Why does the plumbing system need to "rotate" this action? -Thermal displacement is more than linear expansion and contraction
When many people talk about pipe thermal expansion, what comes to mind is that the pipe becomes longer, and then find something to pull it back. But how can the actual working conditions be so simple? Steam pipelines, hot oil pipelines and high-temperature flue gas pipelines, thermal displacement is not only axial expansion and contraction-lateral displacement, angular displacement and even torsional displacement, none of which are fuel-efficient lamps.
Last year, a thermal company complained to me that they used a batch of general-purpose corrugated expansion joints. As a result, less than half a year after they were put into operation, the deflectors wore out. When disassembled, the problem lies in the rotational displacement at the corner of the pipe. The ordinary corrugated joint is not designed to absorb torsion at all, and the corrugated pipe is forcibly screwed out of cracks. You say it was wrong or not?
So, a compensator that can "rotate" is needed in the pipeline system, not because it is fancy, but because the thermal displacement itself is three-dimensional. Straight-line expansion and contraction are just appearances. What really concentrates the stress in the pipe is often those twists and deflections that you can't see. Rotary metal expansion joints (also called rotary compensators) do this job specifically.
Structure and Working Principle of Rotating Metal Expansion Joint (Rotating Compensator)
It's actually quite clever in design. The rotary compensator consists of an inner tube, an outer tube, a sealing packing and a rotary ring. The key is the rolling or sliding rotary structure in the middle. The inner pipe rotates with the thermal expansion of the pipe, and the outer pipe is fixed, and the medium is not leaked by sealing packing between the two. You see, instead of elastic deformation to absorb displacement like bellows, it relies on mechanical rotation to "release force".
Instead of turning. Pipes to twist? Let it turn. The rotary compensator allows the pipe to rotate 360 degrees in the direction of its own axis, while also absorbing a certain amount of axial displacement. Is it much more troublesome to handle two displacements with one set of equipment than to plug two different models of expansion?
And let's talk about the sealing packing-this thing is the lifegate of the rotary compensator. Generally, flexible graphite or polytetrafluoroethylene is used, which has excellent temperature and pressure resistance. If the filler is chosen wrong and it takes less than half a year to start leaking steam, it might as well be used back to the ordinary corrugated joint.
Rotary Compensator vs Other Types of Expansion Joints: Selection Comparison
Universal corrugated expansion joint, high temperature axial expansion joint, sleeve type pipe expansion joint. Let's start with the universal corrugated joint, which is good at absorbing axial expansion and contraction, but has little temper with torsion and lateral displacement. If the pipeline is complicated and displaced in multiple directions, you have to connect several different models of corrugated joints in series, which is overwhelming in cost and space.
Temperature resistance of high-temperature axial expansion joint is a strong point, but it is only suitable for the scenario of single axial displacement. When it meets the angular displacement at the corner of the pipeline, it will still be blinded. Sleeve-type pipe expansion joints can absorb axial displacement, but their sealing performance is poor and the risk of media leakage is high. Now they are gradually replaced by rotary compensators.
What is unique about a rotary compensator? First, it can turn torsional displacement into rotational motion rather than hard resistance-a major benefit for large-diameter thick-walled expansion joints. Second, it can absorb axial, transverse and angular displacements at the same time, and all three kinds of displacements can be done in one stop. Third, long life: because there is no fatigue failure like bellows, as long as the sealing packing is properly maintained, it will not be a problem to use it for ten or eight years.
But it's not without its drawbacks. The rotary compensator requires high installation accuracy. If the pipeline axis is misaligned and the rotary ring is stuck, it will really become a decoration. Moreover, the cost is usually more expensive than the general corrugated joint of the same diameter, so there is no need to use this for small pipelines and low pressure conditions.
Several critical pits in installation and maintenance
I've been running the scene all these years, and I've seen too many examples of accidents when the rotary compensator is installed. The first pit is the wrong position of the "fixed bracket". Guide brackets and fixed brackets must be set on both sides of the rotary compensator, so that the pipeline can only rotate in a predetermined direction and cannot sway. Some construction teams saved trouble and saved the bracket directly. As a result, the compensator deviated under the vibration of the pipeline, and the sealing packing was squeezed out.
The second pit is a cold drawn pre-stretch. When the rotary compensator is installed, it is necessary to pre-rotate the angle according to the working temperature of the pipeline, which is the same as the pre-stretching of ordinary expansion joints. In a petrochemical project, the installer failed to set the pre-rotation angle according to the drawings. As soon as the pipeline heated up, the rotating ring was directly pushed to death, squeezing the sealing packing out. Alas, a loss of hundreds of thousands.
The third pit is the replacement cycle of the seal packing. Many people think that the rotary compensator will be installed once and for all. In fact, the packing will wear out. It is generally recommended to check it every two years and adjust the gland according to the leak. However, some factories lose millions of dollars once they park, so how can they have time to change the packing regularly? Therefore, try to choose the model with self-lubricating filler when selecting the model in the early stage, which can save a lot of trouble.
Which industries are most inseparable from rotating metal expansion joints?
To put it bluntly, there are two core application scenarios of rotary compensator: high temperature, large diameter and multi-directional displacement. The first is the power station industry-the main steam pipeline and the reheated steam pipeline, with a temperature of 500 to 600 degrees, a pipe diameter of more than one meter, and complicated thermal displacement. If you go to the steam turbine room of the thermal power plant, the rotary compensator is basically standard. We have equipped many power plants with rotary compensators, which are used together with corrugated expansion joints used in power station industry, and the effect is leveraged.
Followed by the central heating pipe network. Long-distance directly buried pipeline, the thermal displacement is not only large in the axial direction, but also large in the torque at the corner. Using rotary compensator can reduce the number of fixed piers and save a civil construction cost. Two months ago, there was a northern heating company. It used to use sleeve expansion joints, which leaked hot water all over the floor every year. After replacing it with a rotary compensator, it didn't leak a heating season.
There is also the chemical industry-high temperature and high pressure process pipelines, especially organic heat carrier (heat transfer oil) systems, the medium cannot leak, and the sealing performance of rotary compensators is much better than that of sleeve sections. In addition, the gas pipelines in the iron and steel industry and the kiln tail flue gas pipelines in the cement industry have begun to use a large number of rotary products. Although the metal corrugated expansion joint in cement industry can also be used, when it encounters high-temperature gas with dust, the corrugated pipe is easy to accumulate dust and wear, while the rotary compensator is not easy to get dust because of its smooth inner wall.
You want to ask me what is so good about rotating metal expansion joints? In a word: it can "turn rigidity into softness", turn the flaw of pipeline thermal displacement into a rotating action, saving worry, money and space. Of course, the premise is that you have to be able to choose, fit, and raise.