How much does it cost to wear through pipes? Let's talk about why we should care about "wear resistance" first
Two days ago, I met the equipment supervisor of a cement plant, who told me that the metal expansion joints on their production line couldn't last a maintenance cycle on average-the bellows was directly worn down by particulate matter, and it cost 100,000 yuan to shut down and change a set of labor. This is not the worst. The brothers in the next power plant are even more exaggerated. The high-temperature dusty flue gas directly dries through the guide tube, the debris falls into the downstream pipeline, and the whole set of SCR catalysts is scrapped. Do you think it costs a lot?
The fact that metal expansion joints are wear-resistant has never been a metaphysics. There are solid particles, high-speed airflow and high-temperature steam in the pipeline medium. The combination of these factors makes the erosion and wear of the bellows and internal components real. When you choose a model, you spend an extra 2,000 yuan on wear-resistant design, which may save hundreds of thousands of maintenance fees later. Then what is "wear-resistant"? Guide tube, liner, material, three things are indispensable.
The deflector is not a display: it is the first line of wear defense for the metal expansion joint
Many customers come up and ask, "Are metal expansion joints wear-resistant?" I usually ask first: Do you have a guide tube installed in this working condition?
The function of the guide tube is definitely not as simple as "an extra piece of iron". It is mounted on the inside of the bellows, directly facing the direction of media flow. When the airflow or slurry with particulate matter is washed over, the guide tube first carries this part of the impact force down, so that the bellows body can avoid the direct impact of high-speed particles. The principle is like wearing a layer of armor into a bellows-you can't expect the cotton-padded jacket inside the armor to block the knife, can you?
I have seen some sites make the guide tube short or cancel it directly in order to save costs. As a result, the bellows will wear out in three months. The correct approach is that the length of the guide tube must cover the effective compensation section of the bellows and be thickened on the media inlet side. For high wear conditions, the material of the guide tube can be upgraded from 304 to 316L or harder wear-resistant alloy steel, and even a cemented carbide layer can be welded on the inner wall.
The guide tube is the most basic and effective means in the wear-resistant structure of metal expansion joint。 Without it, talking about lining and material upgrades later is half the result.
Liners and Material Upgrades: From General Purpose to Specific Corrugated Expansion Joints for the Cement Industry
The deflector carried the big head, but it wasn't enough. When the particle size is small and the flow rate is fast, it will still drill into the crest and trough of the bellows for micro-wear. At this time, the liner is needed to fill the position.
General-purpose corrugated expansion joints generally only have guide tubes, which are suitable for gaseous media or slight particulate matter conditions. But when it comes to the cement industry, it is necessary to go to specializedMetal Corrugated Expansion Joints in Cement IndustryYeah. This product usually adds a wear-resistant liner to the inside of the bellows-it can be a wear-resistant ceramic sheet adhesive layer or a high-temperature resistant aluminum silicate fiber felt plus stainless steel wire mesh wrap. The function of the liner is to isolate the bellows from the flowing medium, while absorbing a part of the kinetic energy of the particles.
Material upgrades are also the last word. The conventional 304 bellows is fine at room temperature, but when it encounters high-temperature flue gas containing chloride ions or high-hardness mineral powder, corrosion and wear are two-pronged, and the life span is directly fractured. Replace it with 316L or duplex stainless steel, the corrosion resistance is good, the hardness is also up, and the wear resistance is naturally improved. If the temperature was a little higher (such as the flue duct of a power station boiler), you would have to use a superalloy, such as Incoloy 800 or 625-the price is high, but the life is several times longer.
To put it bluntly, there is no universal wear-resistant scheme, only superposition combination for working conditions. Guide tube + liner + material upgrade, all three dimensions are in place, so that it can be called truly wear-resistant.
High Temperature and Particulate Matter Double Killing Scenario: How to Select Power Station and Cement Industry
Power plants and cement plants are the high incidence areas of wear resistance problems of metal expansion joints, but the emphasis of the two scenarios is completely different.
In the power station industry, the medium is mainly high-temperature flue gas (the temperature is usually 350℃ ~600℃), and the flue gas carries coal ash particles and sulfur oxides. At this time, the selection should first maintain temperature resistance — —Corrugated expansion joint for power station industryUsually designed as high-temperature axial type, the bellows material is Incoloy 800 or 825, and the guide tube material is also heat-resistant alloy steel. Don't forget the liner: ceramic fiber felt is much more reliable than rubber or PTFE in high temperature environments, but pay attention to the fixing method, and don't let the liner fall off and block the pipeline.
In the cement industry, the problem lies in the high concentration of particulate matter and wide particle size distribution, ranging from tens of microns to several millimeters of clinker particles. The design of metal corrugated expansion joints in cement industry focuses on the wear-resistant thickness of the guide tube and the impact resistance of the liner. I have seen a case where a cement factory increased the wall thickness of the guide tube from 3mm to 6mm, and laid wear-resistant ceramic sheets on the inside. Other expansion joints on the same line were changed for two rounds, and it is still in service. When selecting the type, it should also be noted that there are often alternating positive and negative pressures in the air duct of cement line, and the lining must be fixed firmly, otherwise the negative pressure will fall off as soon as it is sucked.
What about the scene of high temperature and particulate matter double killing? For example, the denitrification inlet of power plant or the flue gas pipeline at the tail of cement kiln. This kind of working condition basically requires "special customization": thickening of the guide tube + wear-resistant castable for the lining layer + high-temperature resistant alloy for the corrugated pipe + heat insulation layer on the exterior. The price is really high, but compared with downtime losses, the price/performance ratio is the best. "
Installation details determine wear life: Don't be sloppy with flow direction arrows, pre-stretching and tie rod adjustments
If you choose the right equipment and mess up the installation, you'll still spend money for nothing. A large part of the wear life of metal expansion joints depends on whether the "arrows" are respected during installation. The flow direction arrow on the expansion joint housing is not randomly drawn, it indicates the opening direction of the guide barrel. When installed backwards, the opening of the guide tube faces away from the incoming flow, which is equivalent to exposing the bellows to the impact of particles, and the wear rate doubles. Therefore, be sure to see clearly before installation: the arrow points to the direction of media flow, don't rely on feeling.
Pre-stretching is also a pit. When manufacturers leave the factory, they usually compress the expansion joint to the installation length and lock it with a tie rod. After installation, it is necessary to adjust the pre-amount of tie rod nut release according to the design temperature. If you forget to loosen the tie rod, or if you loosen it too much, not only will the ability to compensate for displacement be lost, but also will cause additional friction between the guide tube and the bellows, which will accelerate wear. How to tune it? Refer to the adjustment method of expansion joint tie rod nut: first loosen the locking nut, rotate the adjustment nut according to the design value, and finally lock it. Never knock with a sledgehammer, it will damage the lining of the inner wall of the guide tube.
Speaking of pull rods,Large tie rod expansion jointThe installation is more particular. The function of the tie rod is to bear the blind plate force of the pipeline and protect the bellows from being pulled by axial force. However, improper adjustment of the length of the tie rod will cause the expansion joint to deflect during work, and the guide tube and bellows will be scratched and directly worn out. The correct method is: during installation, ensure that there is a gap between the tie rod nut and the ear plate, so that the expansion energy saving can expand and contract freely; However, the clearance should not be too large, otherwise the tie rod will not play a limiting role.
What are customers with high buyback rates asking? Disassembly of Three Common Wear Resistance Problems
I talked to customers who bought and bought more, and found that the questions they asked were highly concentrated. Disassemble the three most common:
1. How long can the metal expansion joint be wear-resistant?
A: There is no unified answer, but you can refer to an empirical value-the general expansion joint with guide tube + lining + stainless steel, which can be used for 2~3 years in air-fed pulverized coal pipeline; The clinker dust pipeline in cement industry can have a life of 1.5~2 years under the configuration of thickened guide tube and ceramic lining. The key is to look at the average particle flow rate and concentration of your actual working conditions. The data speaks for itself, and don't trust verbal promises.
2. What should I do if the guide tube is worn out? Can I just change the guide tube?
A: Theoretically it can be, but in practice it is rare. Because the guide tube and bellows are usually welded and fixed, cutting and replacing will damage the bellows body, and the labor cost of disassembling and assembling once is not much cheaper than buying a new one. Therefore, many old customers will choose to make the guide tube thick and wear-resistant in the early stage, and get it in place in one step.
3. Do you use ceramic or metal wear-resistant plates for lining?
A: Look at the temperature and particle impact angle. The ceramic sheet is easy to fall off under high temperature (> 400℃), so it is better to use wear-resistant castable or metal surfacing layer instead. The ceramic sheet has the highest cost performance when the particle impact angle is close to 90 ° at normal temperature or medium-low temperature. However, the sticking process of ceramic sheets is very critical. If the glue is not resistant to high temperatures, it will fall off in three months. It is recommended to find manufacturers with mature lining technology, not cheap.
At the end of the day, there is no shortcut to wear resistance of metal expansion joints. The guide tube does not steal work, the lining is not fooled, the material is not degraded, and the installation is not sloppy, so that the equipment can hold firmly in bad working conditions. The extra thought you spend when choosing a model will turn into money saved in the maintenance ledger.