Don't be in a hurry to look at the price: Find out what problems non-metallic expansion joints solve first
Many people ask "How much is a meter of non-metallic expansion joint" as soon as they come up. This question is really impossible to answer. You haven't even said clearly whether the smoke or acid-alkali medium is running in your own pipeline, so no matter how low the quotation is, it is useless. The core task of non-metallic expansion joint is to absorb thermal displacement, reduce pipe stress, and carry vibration and noise by the way. Instead of carrying hard by corrugation deformation like metal bellows, it digests displacement through a flexible fabric layer. Therefore, the first step in model selection is not to look at the price, but to find out the temperature, pressure, medium and displacement in your system.
Two days ago, I met a customer. The rectangular flue at the exit of the desulfurization tower was not high in temperature but extremely corrosive. He insisted on taking the universal corrugated expansion joint to top it. As a result, the fabric layer rotted out in two months. Alas, this is a typical example of random selection without knowing the working conditions.
Select materials according to working conditions: fabric fiber, rubber and PTFE, and what occasions are they suitable for
The skin material of non-metallic expansion joints directly determines the life. Fabric fiber expansion joints are resistant to high temperatures, can hold flue gas above 300℃, and are most used in exhaust gas pipelines of power plants and cement kilns. Rubber compensator (also called rubber joint) has good elasticity and is suitable for low-pressure and normal-temperature pipeline systems, such as fan inlet and outlet and water pump connection, with obvious vibration reduction effect. However, rubber is afraid of oil and ozone, and it ages quickly at high temperatures.
PTFE compensator is different. PTFE material is resistant to almost all strong acids and alkalis, and it is correct to choose corrosive media containing sulfur and chlorine in desulfurization systems and chemical pipelines. However, PTFE has poor flexibility and cannot withstand too much displacement. There is also a rubber PTFE compensator, which combines the elasticity of rubber and the corrosion resistance of PTFE, which is a compromise scheme, but the price is also a little higher.
Therefore, the more expensive the material is, the better, but the more matched the better. If you take PTFE to do high-temperature smoke, it can't bear it; You take the fabric to make a strong acid medium, and it won't last for a few days. This principle is the same as picking shoes. You have to wear running shoes for running and hiking shoes for climbing.
Structural design is the key: rectangular and circular, single-layer and multi-layer, don't wait for it to be installed before you find it wrong
The structure was chosen wrong, and the back was full of pits. Rectangular non-metallic expansion joints and round non-metallic expansion joints are much different in appearance, and their applicable scenarios are completely different. Rectangular expansion joints are used on rectangular flue and air ducts, such as the flue and air duct system of power plant boilers. Both axial displacement and transverse displacement should be considered. Circular expansion joints are used for circular pipelines, which are compact in structure and have relatively better pressure bearing capacity.
Another easy overlook is the number of layers. Single-layer skin is cheap, but the insulation effect is poor, the surface temperature is high, and the rubber or PTFE of the outer layer is easy to bake. Multi-layer skin is composed of thermal insulation layer, sealing layer and reinforcing layer, such as aluminum silicate cotton for thermal insulation, tetrafluorine film for anticorrosion, and glass fiber cloth for reinforcement, each doing its own work. You think multi-layer is just a bit more expensive? Wrong, it may last two or three times as long as a single layer. When selecting, don't just look at the total thickness, but ask the material and order of each layer clearly.
Common installation and maintenance pits: deflectors, tie rods, compensation amounts These details determine life
Many expansion joints can't be used, which is not a product problem, but an installation problem. Is a deflector a must? It is a life-saving device in a dusty airflow. There is no guide tube, and the high-speed smoke directly washes the inner wall of the skin, which wears very quickly. The guide tube can guide the medium to flow inside and protect the skin from direct impact.
The pull rod is also a key player. The tie rod can limit the maximum displacement of the expansion joint and prevent the skin from being torn by excessive tension and compression. However, having a tie rod does not mean that it can be adjusted at will. The nut position has to be set according to the design compensation amount. If it is adjusted too much, it will imprison the expansion joint. As for the compensation amount, it must correspond to the actual thermal expansion calculation value. Don't pat your head to set a number.
The most afraid thing in maintenance is not to inspect. Abnormal bulging, air leakage and loose screws on the skin surface should be dealt with in time. For example, near the flue gas baffle door of the desulfurization system of a power plant, the fabric layer of non-metallic expansion joints must be regularly checked for corrosion by slurry. If you wait until shutdown for maintenance to find out, the damage will be great.
Recommended list: Common configuration and selection reference in power plants, cement, desulfurization and other industries
Finally, give a few sets of common configurations for your reference. They are all verified collocations in the industry, but the specific projects have to be based on the actual working conditions.
- Smoke duct system of power plant: Rectangular non-metallic expansion joint is recommended, and the skin adopts multi-layer composite structure (aluminum silicate wool + glass fiber cloth + tetrafluorine membrane), with guide tube and tie rod. Corrugated expansion joints can also be used in power station industry, but the vibration and noise reduction effect of non-metal is better.
- Kiln head and kiln tail in cement industry: When the temperature is high and the dust is large, choose non-metallic expansion joints (fabric fiber expansion joints), and the temperature resistance is not less than 400℃. Be sure to bring a guide tube, otherwise it will wear too quickly. Metal corrugated expansion joints in cement industry are not as resistant to dust accumulation as non-metals here.
- Desulfurization system: For slurry pipelines and flue gas pipelines of wet desulfurization, choose rubber PTFE compensator or polytetrafluoroethylene compensator, which is resistant to acid and alkali corrosion. At the same time, pay attention to whether there is slurry accumulation and blockage inside.
- Universal fan duct: For low-pressure and normal-temperature ventilation pipelines, rubber compensator is enough, which is cost-effective and can reduce the vibration transmission of the fan.
In the final analysis, the recommendation of non-metallic expansion joints is not to give a model, but to exchange for working condition data. You list your temperature, pressure, medium, displacement and installation space clearly, so that the manufacturer can match you with a reliable structure. If you only quote a caliber to save trouble, the cost of rework later can be much more than the difference in price saved.
That's it for this time. Do your homework before choosing and save real money. If you are unsure of the specific working conditions, you can also refer to the existing product information of this site, such as non-metallic expansion joints (fabric fiber expansion joints), rectangular non-metallic expansion joints and rubber PTFE compensators. There are detailed structural diagrams and application cases in the corresponding pages.