Find out what a "large-size" nonmetallic compensator is first
Many people ask "What are the large-size non-metallic compensators?" as soon as they come up, but they have to figure out the concept first. Large size, in the industry usually refers to pipe or air duct connections with a diameter or side length of more than 1 meter, or even to 5 meters or 10 meters. It is completely different from metal compensators-metal compensators absorb displacement by bellows, non-metal compensators use flexible bands, and the main body is made of fabric, rubber or PTFE composite. To put it bluntly, non-metallic is a layer of "soft connection", which can cope with multi-directional displacement at the same time, and is corrosion-resistant, high-temperature-resistant and light in weight.
And guess what? In places such as desulfurization flue of power plant and cement kiln tail, metal compensators can't bear corrosion and dust accumulation at all, while non-metallic compensators have become just needed. Therefore, don't stare at the selection of metal parts as soon as you come up, but first see if the working conditions are right.
By shape: What are the doorways of rectangle and circle?
Rectangular non-metallic expansion joint
Rectangular structure is mainly used in square flue and air duct. For example, the hot and cold air ducts of power station boilers and the inlet and outlet of desulfurization towers. OurRectangular non-metallic expansion jointThe frame is usually welded with angle steel or channel steel, and the loop belt is compounded with multi-layer fabric + insulating cotton + sealing film. This shape has the advantage of absorbing large lateral displacements and facilitating on-site installation. The disadvantage is that the pressure bearing capacity is weak, and it is generally only used in low pressure (≤0.1MPa) occasions. Two days ago, I met a cement factory customer. The size of the kiln tail flue was 3m ×4m, and the temperature was 350℃. Finally, I chose a rectangular non-metallic expansion joint, which took three years without any problems.
Circular non-metallic expansion joint
The circular structure is suitable for pipeline butting, with diameters ranging from several hundred millimeters to several meters. Unlike the metal bellows, the circular non-metallic compensator has no corrugated body, but is deformed by the wrinkles of the loop belt. It has the advantage of large axial compensation and is suitable for long straight pipes. Note that circular shapes also have to be connected with flanges or sleeves, so don't confuse them with metal hoses.
According to the material: fabric fiber, rubber, PTFE composite-how to choose different working conditions
- Fabric Fiber Expansion Joints (Non-Metallic Expansion Joints): The main material is glass fiber cloth, polyester fiber cloth, and then superimposed silicone rubber or fluororubber coating. The temperature resistance range is-40℃ to 450℃, and it can reach 600℃ in a short time. It is suitable for the high temperature and weak corrosion environment of power plant air duct and boiler flue. OurNon-metallic expansion joint (fabric fiber expansion joint)This is the type, the loop belt can be customized in layers and thickness.
- rubber compensator: The main body is synthetic rubber (e.g. butyl, chloroprene, EPDM). The temperature resistance is generally lower than 120℃, but it has excellent elasticity and can absorb vibration and noise. It is more used in pump inlet and outlet and air conditioning pipes. Note that rubber is afraid of oil and ozone, and lightning should be protected under working conditions.
- Rubber PTFE compensator: The rubber is lined with a layer of PTFE, which combines the elasticity of rubber with the corrosion resistance of PTFE. The upper temperature resistance limit is about 200℃, especially suitable for pipelines with strong acid and strong alkali media. This product is common in the chemical and pharmaceutical industries, such as ourRubber PTFE compensatorAndPTFE compensatorThe former is soft and the latter is rigid.
Select fabric fiber for high temperature and dust, select rubber for low temperature vibration, and select PTFE compound for strong corrosion. Don't be greedy and choose randomly, otherwise it will leak in three months.
Special scenario: desulfurization flue gas, cement kiln, power station air duct-what are the non-metallic compensators in these industries
Every industry has its own weird temper. Take desulfurization flue gas as an example. The temperature is not high (50-80℃), but the humidity is high and the acid-containing dew point corrosion is serious. At this time, anti-corrosion film (such as FEP or PFA) must be added to the fabric fiber band, otherwise it will rot for half a year. OurDesulfurization flue gas baffle doorIt is often used in conjunction with non-metallic compensators to form a sealed system.
In the flue of cement kiln, the temperature fluctuates greatly, from 200 ℃ to 500 ℃ instantaneously. The non-metallic compensator must choose high-temperature resistant ceramic fiber cloth, and increase the thickness of heat insulation layer. I have seen some manufacturers use ordinary glass fiber, and as a result, it hardens and cracks in a month.
The air duct of the power station is oversized (5 meters ×5 meters at every turn), and it needs to absorb axial, lateral and angular displacements. At this time, rectangular non-metallic expansion joint is the first choice, and the ring belt should be pre-compressed and installed, otherwise it is easy to tear during thermal expansion. Our product information also includesCorrugated expansion joint for power station industryBut that is for metals, and the selection logic of non-metals is completely different.
Selection and pit avoidance guide: size, compensation amount, temperature, pressure, one parameter is wrong, it is useless
- Dimensions: Measure the spacing between the outer wall of the pipe, do not press the inner diameter. To calculate the peripheral length of the rectangular piece, the width of the ring belt must be greater than the design displacement, otherwise it will be broken.
- Compensation amount: Axial, lateral and angular displacements should be listed separately. The compensation ability of non-metals is greater than that of metals, but it depends on the number of belt layers. In general, a single layer of fabric can compensate for ± 50 mm, and a multi-layer can compensate for ± 150 mm. Don't just look at the maximum value of the sample, but actually leave a margin.
- Temperature: Continuous operating temperature and instantaneous peak temperature are two concepts. When selecting the material of the ring belt, the peak value must not exceed the material limit. For example, silicone rubber coating is ≤250℃, and fluororubber is ≤280℃. If it exceeds, polytetrafluoroethylene or all fabric must be used.
- pressure: The withstand voltage of non-metallic compensators usually does not exceed 0.1MPa (about 1kg), but some reinforced types can reach 0.25MPa. Above this value, don't consider non-metals, and honestly go to metal expansion joints.
A steel mill chose a rubber compensator for use on a 300℃ flue gas pipeline, but it burst in two weeks-because rubber couldn't withstand the high temperature at all. Therefore, the parameters are not accurate, and no matter how cheap it is, it is a waste.
Installation and maintenance: Why are non-metallic compensators more delicate than metallic ones?
Non-metallic compensators are delicate because the bands are flexible and susceptible to mechanical damage. There are a few points to note when installing:
- The loop belt cannot touch sharp objects and is best protected when transported.
- Check that the loop strap is in good condition for scratches or air bubbles before installation. Don't wait until the bolts are finished to find an air leak.
- The flange connection should be symmetrically screwed, and the torque should not be too large, otherwise the ring belt will be crushed. Generally, it is sufficient to screw M16 bolts to 50N·m.
- After installation, adjust the tie rod or limit bolt to ensure that the initial pre-compression amount meets the design requirements. You can refer to our question and answer "How to adjust the expansion joint tie rod nut", which has the same principle.
In terms of maintenance, regularly check the surface of the ring belt for aging cracks, and measure the wall thickness every six months. Don't wait for a leak before replacing it. At that time, the flue is full of smoke, and it is difficult to repair it. Many factories will prepare a set of ring belts as wear parts and replace them at any time. Compared with the metal compensator, which needs to be replaced as a whole, the non-metal ring belt can be replaced separately, which is a money-saving advantage.
So, don't think it's delicate, use it in the right place, and it can save you a lot of downtime costs. The key is to select the type accurately and install it fine.