What are rjx non-metallic expansion joints? What is the difference between it and ordinary fabric fiber expansion joint?
To be honest, there are at least dozens of products called "non-metallic expansion joints" on the market, but those who really dare to mark the model as rjx usually mean that it has been strengthened by a specific process. Ordinary fabric fiber expansion joint, to put it bluntly, is several layers of glass fiber cloth pressed together, which is temperature-resistant, but it will be exposed when it is washed by acid, alkali and dust. What about the rjx non-metallic expansion joint? Instead of changing its name on the ordinary model, it changed its thinking from the material formula and structural design-more fluororubber layer, PTFE layer and even stainless steel wire mesh interlayer. The difference is not just the price, but the longevity and reliability.
Structural disassembly: rubber layer, PTFE layer, metal frame-what is each layer doing?
You take apart an rjx non-metallic expansion joint and you see the typical sandwich structure:
The outermost layer is a rubber elastic compensation layer, which is responsible for absorbing the axial and lateral displacement of the pipe. To put it bluntly, it means "letting the pipe take a breath". There is a tetrafluorine film (PTFE) sandwiched in the middle, which is for corrosion resistance-the desulfurization flue gas of power plants is full of sulfuric acid and sulfurous acid, and ordinary cloth bites through it in one or two months, and the PTFE layer can last for several years. The innermost layer is a metal frame, generally 304 or 316L flat steel welded, plus a guide tube. What does the deflector do? I specifically checked the question and answer of our station. The guide tube is to prevent high-speed airflow from directly washing the flexible part of the expansion joint, so as to reduce wear and vibration. Each of these three levels performed their duties, and even one layer less would not be able to hold on.
Which operating conditions must be used with rjx? — — Real cases in flue gas, cement kiln tail and desulfurization system of power plants
Let's talk about power plant flue gas first. The temperature of the flue gas coming out of the coal-fired boiler is 150℃ ~200℃, with a lot of dust and SO₂. Ordinary non-metallic expansion joints have to be replaced in three months, and the maintenance cost is more expensive than the equipment. Last year, a power plant in Shandong used rjx, which was installed next to the stainless steel rectangular expansion joint and used with the flue gas baffle door. The deflector has not been worn out for two years.
The cement kiln tail is more ruthless. The temperature rushes to 350℃, the dust concentration is dozens of grams per cubic meter, and there is alkaline gas. If you use regular fabric fiber expansion joints in this place, the thread will open in a month. We have a customer who uses rjx non-metallic expansion joints at the kiln tail outlet, and matches high-temperature axial expansion joints for secondary compensation, which has been running stably for a maintenance cycle.
What about the desulfurization system? The net flue gas after wet desulfurization has low temperature but high humidity, with a large amount of liquid water. Under this working condition, metal expansion joints are afraid of chloride ion corrosion, and non-metal expansion joints are afraid of hydrolysis. However, the PTFE layer + rubber layer of rjx can hold it. When selecting the model, pay attention to adding anti-corrosion lining, which is used with the desulfurization flue gas baffle door, and it doesn't have to be moved for five years.
Selection and rollover scene: miscalculation of size, confusion of pressure level, neglect of deflector, how many of these pits have you stepped on?
Let's talk about a few rollover cases that I have seen with my own eyes.
The first one: miscalculated size. Someone measured the outer diameter of the pipe, but did not calculate the thickness of the insulation layer. As a result, the rjx non-metallic expansion joint was not tightly installed, and the air leakage was a mess. The correct way to do this is to measure the inner diameter of the pipe, or follow the drawing of the pipe connection dimensions.
Pressure level mix-up. Generally, the withstand pressure of non-metallic expansion joints is only a few tens of kPa. Some people use it in a 0.3MPa steam system, and it explodes directly when it is started. Remember, rjx non-metallic expansion joints are only suitable for low-pressure pipes (usually ≤0.1MPa), and you have to use metal corrugated expansion joints or general-purpose corrugated expansion joints in high-pressure places.
Ignore the deflector. There is a cement factory without a guide tube, and the dust directly hits the fabric layer, which takes three months to wear and perforate. Deflectors are required, not optional. In the product page of our station, all rectangular non-metallic expansion joints are designed with guide tubes, so you must check them when selecting the model.
Don't be sloppy in installation and maintenance: Do you want to remove the tie rod nut? Where does the expansion joint arrow point?
Do you want to remove the tie rod nut? The answer is: in the transportation state, the pull rod is in a locked state to prevent shaking and deformation during transportation. After installing and fixing the pipeline, the tie rod nut should be loosened, and the adjustable margin should be kept, but it cannot be completely removed-there will be no limit if it is removed. In case the displacement of the pipeline exceeds the standard, the expansion joint will be directly pulled out. For specific operation, refer to the question and answer of our station "Does the screw of the expansion joint need to be disassembled", which has a diagram.
Direction of arrow on expansion joint. That refers to the direction of media flow, not the direction of installation. The arrow must be in the same direction as the airflow in the pipe, otherwise the guide tube will trap dust and liquid, accelerating corrosion. You play backwards, let alone five years, you can't hold it for five months.
It's not broken after five years of use? — — Judgment criteria and replacement timing of service life of non-metallic expansion joints
Many people ask how long the rjx non-metallic expansion saves energy. According to JB/T 12235-2015 standard, the design life is generally 10 years, but the actual working conditions are very different. Judging whether to change or not, look at four points:
- Whether there are cracks or aging visible to the naked eye (cracked, hardened surface);
- Whether there is a leak (detect it with soapy water or compressed air);
- Whether the guide tube is worn out (take a look at the insulation layer);
- Whether the amount of displacement compensation is sufficient (measure the size difference before and after installation).
If anything goes wrong with any of the above, don't hesitate to change it quickly. Don't wait until it explodes before shutting down for emergency repair. The damage is dozens of times greater than an expansion joint. Our rubber PTFE compensator products support customized non-standard sizes and fast delivery, so you can consider preparing an inventory.
Choose rjx non-metallic expansion joints, don't buy three no products for cheap, power plant and cement plant equipment shut down for one day, enough to buy a hundred qualified expansion joints.