Don't be in a hurry to draw a picture. Find out what components a non-metallic compensator consists of
Many people paint fiercely in front of CAD as soon as they come up, and only when they finish painting do they find that the structure is wrong-ring beam, skin, insulation layer, frame, pressure plate and guide tube. None of these six components can be missed. The ring beam is responsible for the end sealing and stiffness support, the skin is the flexible main body, the heat insulation layer shields the high temperature, the frame carries the external load, the pressure plate presses the skin, and the guide tube guides the airflow. One less, and the device will either leak air or just be scrapped. For example, if the guide tube is installed backwards, the high-temperature smoke directly washes the inner wall of the skin, and it will be perforated in two days.
Selection of skin material is a science: Different temperature range, different corrosiveness of media, if the wrong selection is directly burned through or leaked
Two days ago, a customer used the 250℃ flue gas pipe as an ordinary silicone skin, and the result was wasted in a week. The temperature resistance range of silicone cloth is-60℃ ~200℃. Beyond this range, fluorine tape (temperature resistance-20℃ ~280℃) or polytetrafluoroethylene film (temperature resistance-40℃ ~260℃, and extremely strong corrosion resistance) must be applied. If the medium contains acidic gas (such as desulfurization flue gas), a layer of PTFE film must be added for anti-corrosion isolation. The skin is usually a multi-layer composite structure: the outer layer of silicone cloth/fluorine tape provides weather resistance, the middle layer of polytetrafluoroethylene serves as an anti-corrosion barrier, and the inner layer of fiberglass cloth or ceramic fiber cloth resists high temperatures. The number of layers, thickness, and lamination order have to be calculated according to the working conditions-it is not just a few layers of cloth pressed together.
Insulation design is the easiest to roll over
Many people think that the packing is stuffed, but in fact, the compression rate, layer thickness and airflow flushing direction have to be calculated. Ceramic fiber or aluminum silicate wool is commonly used for heat insulation layer, and the compression ratio is controlled between 15% and 25%. If it is too tight, the heat insulation effect will be poor, and if it is too loose, the filler will easily be taken away by air flow. More importantly, the layered design is: a high-density layer of fine fiber is used near the skin side to block the heat radiation, a low-density layer is used in the middle to reduce heat conduction, and a scour-resistant layer is added on the medium side. When installing, pay attention to the direction of airflow-if the medium flushing direction is just facing the filler joint, the filler will be blown out in less than three months, and the inner skin will be directly exposed to high temperature, so it will be a matter of time before it burns through. We handled a cement industry project before. The customer installed the insulation layer by himself, without adding anti-scour baffles, and changed the skin three times within half a year.
The framework is the skeleton, but don't make it into a lump
The treatment of rectangular non-metallic expansion joints and round non-metallic expansion joints in the corner stress concentration zone is completely different. The four corners of a rectangular frame are the weak points, and usually triangular rib plates or circular transition plates are added to disperse the stress to the adjacent edges. For circular frames, we should pay attention to the spacing of flange bolt holes-excessive spacing of standard anchor bolt holes will lead to deformation of pressure plate and lax skin seal. The stiffness of the ring beam must match the pipeline flange: for example, if the thickness of the ring beam matched with DN1000 pipeline is less than 8mm, the ring beam will be directly twisted when the wind load blows, the end face of the flange will be tilted, and air leakage will be inevitable. In addition, the frame material should also be selected according to the environment: Q235B hot-dip galvanizing for outdoor open air, 304 stainless steel for high temperature areas and 316L for corrosive environment. Don't save this little money, the frame rust through the whole expansion joint will be waste.
Deflector is not an optional accessory
The root cause of many leakage accidents is that the guide tube is too short or not installed at all. The insertion depth of the guide tube should exceed the inner wall of the skin by at least 50mm, otherwise the high-temperature airflow will directly scour the fold of the skin-that position has the highest stress and is easiest to scour through. In terms of wall thickness, the common air duct is 4mm ~6mm Q235 steel plate. If the medium contains particulate matter (such as fly ash in the flue of power plant), the thickness should be increased to 8mm ~10mm, or the wear-resistant layer should be welded on the inner wall. The angle of guiding the flow direction is also very critical: the front end of the guide tube should be designed as a bell mouth of 45 ° ~60 °, so as to guide the airflow smoothly to the center and avoid vortex erosion. The expansion gap must be allowed during installation-the front end of the guide tube cannot be pushed against the opposite flange, otherwise the guide tube will be bent during thermal expansion. We have seen a rectangular non-metallic expansion joint at the outlet of a desulfurization tower. The guide tube was installed backwards (the bell mouth faced outward). As a result, the airflow backwards washed the pressure plate bolts, and the bolts were all broken three months later.
Don't forget the design of the pre-compressed structure
During installation, the adjustment amount of the tie rod, the factory pre-compression amount, and whether the expansion joint can smoothly absorb displacement during operation, these parameters must match the test method specified in JB/T 12235-2015. The pre-compression structure is usually composed of a tie rod and a limit nut: the expansion joint is compressed to half of the design displacement before leaving the factory, and then the tie rod is loosened to allow it to expand and contract freely after the pipe is installed. If the tie rod is adjusted incorrectly, either the expansion joint is compressed to the limit and cannot absorb the thermal expansion further, or it is stretched too long and causes the skin to tear. Pay special attention to the thread specifications of the tie rod-M16 or M20, and how big the adjustment stroke is, it has to be checked according to the pipeline calculation book. By the way, many installers try to save trouble by cutting off the tie rod or screwing the nut directly after installation, which is equivalent to scrapping the expansion joint. The standard practice is to loosen 50% of the pre-compression amount after installation, and then adjust to the design compensation amount after the temperature of the pipeline system stabilizes. Don't forget to write every step clearly in the operation manual, otherwise there will be another pile of after-sales if you make mistakes on the spot.
From ring beam to guide tube, from skin to tie rod, the structural design of non-metallic compensator is essentially competing with the parameters of temperature, pressure, medium and displacement. Every detail is a pit, and you have to rework it if you take a wrong step. If you have a project at hand, you might as well take JB/T 12235-2015 and compare it with the items we mentioned above to see if there is anything missing.