Why can't ordinary metal corrugated expansion joints last for two or three years in high-temperature dusty pipes?
In high-temperature dusty pipelines, the average life of ordinary metal corrugated expansion joints is often only two to three years, and sometimes it can't even carry a maintenance cycle. The problem lies in the geometry of the bellows-the peaks and troughs themselves are "traps" of airflow. High-speed dusty airflow forms vortices on the corrugated surface, and dust particles repeatedly hit the troughs like grinding wheels. After a few years, the bellows wall is worn out.
The ceramic liner makes up for this short board. The hardness of wear-resistant ceramics is much higher than that of metals, and the resistance to particle erosion is several times that of ordinary stainless steel. But this thing is not just installed-ceramics are afraid of thermal shock and mechanical impact, and when the expansion joint absorbs displacement, the ceramic sleeve must "move freely" in it, and it will get stuck or crack if it is not done properly. Therefore, ceramic lining is the last line of defense and the last trouble for high-temperature wear-resistant pipelines.
How do you combine ceramics and metals? Three processes, three ways
The integral ceramic sleeve is to assemble the ceramic sheet into a sleeve structure in the mold first, and then assemble it into the bellows. This structure has the best wear resistance and is suitable for the working conditions of high dust concentration and large temperature fluctuation in the kiln tail and kiln head, but the cost is also the highest.
Ceramic fiber filling is not used to prevent wear. It mainly relies on the thermal insulation performance of ceramic fiber cotton to form a thermal insulation buffer layer between the guide tube and the bellows. Don't expect it to block sand and gravel, the dust will scatter as soon as it washes.
Surface thermal spraying is spraying a layer of alumina or chromium oxide coating on the surface of bellows and guide tube, which has simple process and low cost. However, the thickness of the coating is limited, and it is already good for two or three years. It is suitable for air ducts with less severe wear and short maintenance period.
Which one to choose? Depends on the working conditions. Don't focus on ceramic sleeves. Just spray the places where the wear is not serious. The money saved can buy several pieces of equipment.
Three typical locations of cement plants: where they must be used, where they suffer instead
In the cement industry, the kiln tail is the worst position. With high temperature, large dust concentration and large air volume, ceramic lining must be used here, and the metal corrugated expansion joint of cement industry designed with high temperature resistance should be matched, otherwise the corrugated pipe will not be overhauled.
The kiln head is slightly better, but the thermal shock when the kiln is opened and shut down is particularly severe, and the ceramic sheet is easy to collapse. The air duct of the grate cooler is even more interesting-the wind speed is high, but the dust particles are coarse and the impact angle is single. Many factories use non-metallic expansion joints here, which is more cost-effective. The non-metallic fabric fiber itself is not afraid of dust washing, and it is cheap and convenient to change. You have to stick a ceramic sleeve in the air duct of the grate cooler, and the ceramic block falls off by the thermal stress top and sticks the bellows, which is asking for trouble.
Can the expansion joint absorb the displacement normally after adding the ceramic liner?
Yes, but you have to re-check it, or you will have to step into a pit. The ceramic sleeve has high rigidity and cannot be welded directly to the bellows, so sufficient clearance must be reserved to allow the bellows to deform freely. The setting of the guide tube is equally critical-it is fixed at one end, and the other end is free to expand and contract, so that thermal expansion and displacement can occur within a controlled range.
When checking the stiffness, the weight of the ceramic lining should be counted, especially the large-diameter expansion joint. The density of ceramic materials is not small, and tens of kilograms of lining are hung on the bellows, which has a very obvious influence on the stiffness. In terms of fatigue life, the friction resistance between the liner and the guide tube should not be too large, otherwise the local stress of the bellows will increase, and the design life will be directly folded in half.
How to solve it? Set a limit pull rod to limit the displacement within the design range, and use a guide tube to guide the air flow to the direction that does not flush the bellows. This keeps both displacement and life.
Selection and installation: Ceramic lined expansion joints are not standard at all
Don't think about quoting a pipe diameter. When ordering, we should provide the manufacturer with caliber, medium, temperature, pressure, displacement, and more importantly, dust concentration, particle size, flow rate and space size of installation position. It is best to attach the pipeline layout drawing, so that the manufacturer can design according to the actual trend. The lining schemes of high-temperature axial expansion joints and general-purpose corrugated expansion joints are different, and accidents will happen if they are mixed.
There are also quite a few pits installed on site. When hoisting, the ceramic sleeve is bumped and directly scrapped; During welding, the welding flowers splashed on the ceramic surface, and the thermal shock cracked and could not be seen by the naked eye, and it broke as soon as the machine was turned on. After installation, be sure to check that the direction of the arrow of the guide tube is consistent with the direction of the airflow, otherwise it will not only protect the bellows, but will lead the airflow to the dead corner.
Finally, as a reminder, after the liner is installed, give it a circle with a flashlight to see if it is loose, cracked or misaligned. If this line of defense goes wrong, the rework cost is enough for you to buy ten new expansion joints.