Wear is the number one reason for early scrapping of metal expansion joints
Cement plants, power station flue gas pipelines, desulfurization systems-the high-concentration dust in these places is wrapped in high-speed airflow, and the bellows can be worn out in a few months. Do you think the manufacturer is cutting corners? In fact, there is a high probability that wear resistance was not taken seriously when selecting the model. The wall thickness of the bellows is only about 1.0mm, so it is strange to use it as a shield without perforation.
I ran into a customer in the cement industry before, newly installedMetal Corrugated Expansion Joints in Cement IndustryAfter only three months, the guide tube was first ground out of the hole, and then the bellows was scrapped. When it is removed, the inner wall of the cylinder is ground by cement raw material as if it has been scraped by a knife. Later, I changed the scheme of thickening the guide tube + lining with wear-resistant ceramics, and it was fine after more than two years. Therefore, the wear-resistant design of metal expansion joint is not an elective course, but a compulsory course.
The guide tube is the first line of defense for wear resistance, and the life of the right material will be doubled
Direct the media away, and don't let it go directly into the bellows. Usually 304 or 316L stainless steel is used, but when it encounters abrasive media, stainless steel alone can't hold it. What to do? There are two directions: one is physical thickening, such as increasing the wall thickness of the guide tube from 3mm to 6mm or even 8mm; The second is to do surface strengthening on the inner wall, such as surfacing cemented carbide, or simply lining wear-resistant ceramics and polymer materials.
The cost of lining ceramics has indeed gone up, but the lifespan can be multiplied several times. Like inCorrugated expansion joint for power station industryIn, the flow rate of pulverized coal pipeline is as high as 25m/s, and the effect of simply thickening the guide tube is limited. After lining with alumina ceramic, it can last for more than three years. Polymer materials are suitable for desulfurization flue gas with low temperature, which is corrosion-resistant and wear-resistant, but don't think about it if the temperature exceeds 200℃.
There's a pit here-many people think that the thicker the deflector, the better. In fact, thickness will increase the weight and cost, and the gap between the guide tube and the bellows should be left enough, otherwise it will be bad for thermal expansion to get stuck. When selecting the type, the flow rate, particle hardness and temperature of the medium should be calculated clearly, and then the scheme should be determined.
There is a big gap in the selection of types under different working conditions, so don't take the general-purpose hard sleeve
Both the cement industry and the power station industry look like dust, but the details of the working conditions are different. The flue gas on the cement production line has high alkali content and large temperature fluctuation.Metal Corrugated Expansion Joints in Cement IndustryWhen, wear-resistant sheathing must be added on the outside of the bellows, and wear-resistant ceramics or surfacing welding is recommended for the inner lining of the guide tube. It is recommended to use pulverized coal pipeline and smoke air duct of power stationWhen the corrugated expansion joint is used in the power station industry, pay attention to the gap design of the guide tube-if the gap is too large, it will easily cause eddy current erosion, and if the gap is too small, it will get stuck.
The desulfurization system is more complicated, grinding and corroding. The expansion joint near the smoke baffle door has to bear acid corrosion in addition to wear resistance. At this time, useDesulfurization flue gas baffle doorThe matching expansion joint is often lined with bidirectional stainless steel or PTFE, but PTFE is not wear-resistant, so many manufacturers add wear-resistant layers on the guide tube. Alas, this requires a combination of punches-both corrosion-resistant and wear-resistant, and can't just stare at one hurdle.
Installation and routine maintenance can also influence the wear resistance effect
The most common problem is that the deflector is installed in the reverse direction. There is an arrow direction on the expansion joint, pointing to the direction of media flow. If it is installed backwards, the medium will directly rush the bellows, and no matter how good the material is, it will not be able to bear it. Two days ago, I encountered a customer who spat that the expansion joint always leaked. When I went to the scene, I found that the guide tube was installed backwards. And guess what? The inside of the bellows is ground to fish scales.
What about routine maintenance? Check the deflector regularly for the amount of wear. Measure the wall thickness with a gauge or caliper, and repair it in time if there is a risk of perforation. Don't wait until it leaks before shutting down-the loss of a day's shutdown is enough to replace several expansion joints. EspeciallyLarge diameter thick wall expansion jointOnce the guide tube is worn out and the medium passes to the bellows, the whole assembly has to be replaced, which is very expensive.
What to do when you encounter extreme wear cases?
Ordinary schemes in some working conditions simply can't stand. For example, the large-diameter expansion joint used in pulverized coal pipeline has fast pulverized coal flow rate and high temperature, so it is useless to simply thicken the guide tube-the abrasion rate is faster than the thickening rate. What about that? Lined tortoise shell mesh castables may be considered. The tortoise shell net is fixed on the inner wall of the guide tube, and then the wear-resistant material is poured to form a hard shell with a thickness of 20-30mm. The disadvantage is that it is heavy and costly, but compared with changing the assembly every three months, it is actually cost-effective in the long run.
Replace withWear-resistant alloy bellows。 Make the bellows itself wear-resistant directly, such as duplex stainless steel or hard chrome plating on the surface. But this thing is expensive, and bellows are naturally afraid of wear, so it can only be considered a last resort. To be honest, in most cases, it is enough to make the deflector liner well.
The core of the wear-resistant design of metal expansion joints is not to stack materials, but to harden the places where it should be wear-resistant. Guide tube, sheath, liner, perform their duties, don't let the bellows directly contact the medium, you may wish to ask the manufacturer before selecting the type.