What is good about the duplex metal corrugated expansion joint? Understand these points and make no mistake in your selection
The thermal displacement of the pipeline is too large, and the single expansion joint is not enough to live and die. What should I do? I just threw him a word — changeDouble metal corrugated expansion jointUgh. To put it bluntly, the duplex structure is to string two or more bellows together, connect them with pipes in the middle, and cooperate with the tie rod system to deal with those super-large axial displacements or combined displacements that can't be handled by the single type. This thing is particularly common in high-temperature and high-pressure pipelines such as power stations, cement and petrochemicals. It is similar to the ones in our stationsCorrugated expansion joint for power station industry、Metal Corrugated Expansion Joints in Cement IndustryThey're all a family. So what does it look like? Simply put, if one bellows is not enough, add another. Like a series battery, the displacement is directly doubled, but the pressure and thrust have to be carried by a tie rod or hinge. Is that the truth?
What is the difference between duplex and single?
For example, a single axial expansion joint can only absorb linear expansion and contraction in one direction, and the displacement is a big deal. The bellows will explode as soon as it is supported. What about the duplex? You can make itCompound hinge transverse expansion jointabsorbing lateral displacement; Can also be made intoCompound straight pipe bypass pressure balanced expansion joint, balanced pressure thrust, the main fixed bracket design is much easier. There is also a double tie rod type, in which a tie rod is installed in the middle of two corrugated pipes, which specifically solves the angular displacement of Z-shaped pipes.
Remember, the duplex is not simply two bellows piles together. The length of the middle section and the arrangement of the tie rod hinge directly affect the compensation ability. A few days ago, I helped a cement factory to select a type. They had many pipeline turns and small space. Finally, they were equipped with a double hinge transverse expansion joint, which finally suppressed the problem of thermal expansion and contraction. Why don't you just use single style, you ask? The single lateral compensation amount is almost zero, and the hard can only make the bellows twist into a twist.
Application scenario: Large displacement, large pipe diameter, high pressure
The compound metal corrugated expansion joint is the best in large displacement, large diameter and high pressure pipeline system. For example, the main steam pipeline of the power station has a temperature of five or six hundred degrees and an expansion amount of tens of millimeters. It can't be used in a single type, so it can only be used in a double type. There are many duplex structures in the corrugated expansion joints used in the power station industry in our station. In the kiln tail pipeline of cement industry, there is much dust and high temperature, and the compound guide tube can effectively prevent wear. For the function of the guide tube, you can refer to the question and answer "The Specific Function of the Expansion Joint Guide Tube" in the station. The high-speed airflow carries solid particles, and without the guide tube, the bellows will wear out in one month.
There are also desulfurization flue gas pipelines, which have severe low-temperature corrosion. The duplex is matched with suitable materials (such as stainless steel 316L or duplex steel), which can last for many years. And guess what? Many people confuse the duplex with the pressure balanced type-the pressure balanced type is also two bellows, but its design goal is to eliminate pressure thrust, while the duplex mainly pursues displacement compensation. The two sometimes combine, such asCompound straight pipe bypass pressure balanced expansion joint, both balancing thrust and compensating for large displacements, which can be regarded as killing two birds with one stone. In addition,Curved tube pressure balance expansion jointIt is also a similar idea, but the curved pipe structure is more suitable for the curved pipe section with limited space.
Selection, installation and maintenance, don't step on these three pits
Most Common Mistakes in Model Selection
I have seen a project in which the engineer directly strung together two single expansion joints. As a result, no tie rod was installed, and the bellows was directly twisted into twists. The tie rod of the duplex expansion joint is not an ornament, it is responsible for absorbing the pressure thrust and preventing the bellows from over-stretching or compressing. Refer to the article "How to adjust the tie rod nut of expansion joint" in our station. When installing, the tie rod nut should leave a gap and cannot be screwed to death, otherwise the expansion joint will be wasted. In addition, the guide tube can't be saved-the high-speed airflow carries solid particles, and without the guide tube, the bellows will wear out in a month. There is also fatigue life. There are a large number of double bellows, and the stress borne by each wave should be evenly distributed. If the design is unreasonable, one of the bellows will break first, and the whole will be scrapped. When selecting the model, be sure to give detailed working condition parameters: pressure, temperature, displacement (axial, transverse and angular), number of cycles, don't be vague.
Installation details make or break
Compound expansion joints are usually relatively long, so pay attention to the setting of guide brackets when installing to ensure that the pipeline can only displace in the expected direction. Refer to "Correct Installation Method of Large Tie Rod Expansion Joint". Like the double hinge hinge type, the hinge pin must be flexible and not stuck. In addition, the direction of the arrow on the expansion joint refers to the flow direction of the medium. Don't install it backwards, otherwise the guide tube can't play a protective role-this point is clearly stated in the question and answer "What is the direction of the arrow of the expansion joint" in the station. Regularly check for loose tie rod nuts and corrosion spots or cracks on the bellows surface.
Two days ago, a customer said that the bellows leaked after three years of use. After checking, it was found that it was not pre-stretched during installation. As a result, the bellows was in a compressed state after operation, and the fatigue life was greatly reduced. Tsk, this kind of mistake can actually be completely avoided. In the final analysis, the duplex metal corrugated expansion joint is a good thing, but it has to be selected, installed and used correctly, otherwise the expensive equipment will be useless.