What is the role of the circle belt?
To put it bluntly, it is the "flexible joint" of non-metallic compensator. Pipeline thermal expansion and contraction, equipment vibration, installation deviation, these displacements are absorbed by the ring belt. Designing a loop is not about drawing a shape on paper-it has to withstand temperature, pressure, corrosive media, and keep the chain from dropping for tens of thousands of cycles. Many people think that the ring belt is just a few layers of cloth and rubber, but the actual problem is precisely the ring belt. Two days ago, I met a customer. The rectangular non-metallic expansion joint on the flue gas pipe took less than half a year, and the ring belt bulged and leaked. When I disassembled it, I saw that there was no exhaust hole between the layers, and the gas was held inside and directly ejected a big bag.
If the ring belt is designed to roll over, the whole compensator becomes a decoration. So today, let's make it clear which cores should be focused on in the circle design. Don't be too long-winded. If you figure this thing out, it can help you save a lot of rework money on the spot.
Material selection is the first hurdle in ring belt design
What to choose for fabric fibers? Silicone cloth, fluorine tape, ceramic fiber or PTFE? It depends on the working conditions. For example, the flue gas system has high temperature and sulfur content, and fluorine tape plus polytetrafluoroethylene layer is a common combination; If there is more abrasive dust, it is necessary to add a wear-resistant layer. I have seen that some design drawings only write "temperature resistance 200℃". As a result, the temperature of the field medium fluctuates to 250℃, and the ring belt is directly carbonized. Alas, is the margin enough?
Don't forget the intermediate insulation layer-many designs ignore the thermal conduction calculation of multi-layer structures, and as a result, the ring tape surface is hot. From our stationRectangular non-metallic expansion jointAndNon-metallic expansion joint (fabric fiber expansion joint)In the product, the ring belt uses a multi-layer composite structure, and each layer undertakes different functions: the outer layer is anti-aging, the middle is heat insulated, and the inner layer is corrosion resistant. When you design, at least calculate the thickness and thermal conductivity of each layer clearly. Don't pat your head and fill in "5mm".
Structural design is not simply spelling thickness
The geometry of the band, wave height, wave pitch, interlayer overlap length, these parameters directly affect the compensation amount and life. For example: the stress is concentrated at the corners of the rectangular loop band, and if you don't do arc transitions or stiffeners, the tear starts there. And guess what? I removed a failed sample, and the cracks at the corners were neat, like knife cuts. Arc R did not do enough, all the stress gathered there.
In addition, many people have little understanding of the sealing structure-the design of the pressing surface of the ring belt and flange is not in place, and media leakage has become a common occurrence. In the actual project, I saw that the ring belt leaked after half a year of use. When I disassembled it, I saw that the spacing between the strip bolts was too large, and the sealing strips were squeezed out. When designing the spacing of strip bolts, refer to the recommended spacing range in standard JB/T 12235-2015. Don't make a span of 300mm in order to save a few bolt holes. It would be strange if nothing happened.
Failure Mode Analysis is a Compulsory Course for Belt Design
The most common are bulging, delamination, tearing, and aging. Bulge is often caused by the inability of interlayer gas to discharge, so exhaust holes have to be reserved in design. Delamination is mostly a problem with the bonding process or material matching. Another thing that is easy to overlook is the fatigue life of the ring belt-don't just look at static pressure, but count the number of displacement cycles. Our station hasrubber compensatorAndRubber PTFE compensatorProducts, their loop design has special data support in dynamic fatigue test, but many non-standard design users have not done this verification at all. Do you know how many thermal cycles industrial pipes go through a year? The power plant starts and stops once as a cycle. If it starts and stops every day, 365 times a year, the design life of 3 years is 1095 times. Can you hold it with your loop? If you dare to use it without data, that's called gambling on luck.
The ring belt is not an isolated part
It works with metal parts to form a complete compensator. For example, how should the guide tube extend into the loop belt? How much clearance is left? If the guide tube is too short, the air flow directly washes the inner wall of the ring belt and wears out quickly. There are also tie rods and limiting structures-the ring belt can only absorb axial or transverse displacement, and excessive pressure and thrust must be restrained by the tie rod. Don't understand this. No matter how well the ring belt is designed, it will be blown up after installation. We're standingCorrugated expansion joint for power station industryAndMetal Corrugated Expansion Joints in Cement IndustryAlthough it is mainly made of metal, their frame and loop design ideas can be used for reference-every time I design the loop, I will first draw the length of the guide tube, the stroke of the tie rod and the flange compression structure together, and then adjust the wave distance of the loop.
Finally, let's talk about standards
The national standard JB/T 12235-2015 for non-metallic expansion joints clearly specifies the material properties, test methods and inspection rules of ring belts. As a designer, you have to keep an eye on at least three points: whether the temperature resistance grade reaches the highest temperature + margin of the working condition, the blasting pressure is not less than three times the design pressure, and the displacement compensation amount must have measured data. Don't just look at the parameters on the sample, ask the other party to provide the test record-otherwise, if the circle belt has an accident on the project, it will be you who will take the blame. Two days ago, a project manager asked me that the temperature resistance of the band sample was 300℃, but it actually cracked after two years of use. I said did you check the actual medium temperature? At first measurement, the peak value was 335℃, and there was no margin at all. The standard clearly requires that the temperature resistance grade should be at least 30℃ higher than the highest temperature of the working condition. Don't you understand this?
The belt design is difficult to say and simple to say-the four dimensions of material, structure, cooperation and standard are fastened, and it will basically not overturn. If you are still unsure, ask the supplier for a type test report directly. Don't trust verbal promises. After all, it takes several years for the pipeline to be installed, and it is more expensive to replace it if the ring is broken than to buy a new one.