What's so good about non-metallic compensators? Don't be confused with metal expansion joints
Two days ago, a friend who is a cement production line complained to me, saying that the flue gas pipe compensator in their factory leaked after less than half a year of use, and the metal expansion joint didn't work after replacing it several times. It was a lot of torment. As soon as I heard it, I knew what the problem was-the occasion was not the right one, and the good thing was useless.
Many people think of bellows when they hear "compensator", thinking that metal ones are definitely stronger than non-metal ones. However, the industrial site is not tougher than who is, but who "knows" the working conditions better. Non-metallic compensators (that is, what we often callNon-metallic expansion joint (fabric fiber expansion joint)The core advantages of) are that it can absorb multi-directional displacement at the same time, reduce vibration and noise, and is corrosion-resistant and high temperature-resistant. Metal expansion joints are deformed by corrugation, while non-metallic joints are deformed by flexible deformation of fabrics and rubbers. To put it bluntly, the metal one is "hard to carry", while the non-metal one is "soft to overcome rigidity".
Is the metal expansion joint useless? Of course not. For example, in high-pressure steam pipelines, where it needs to bear a large axial force, metal is still the main force. However, if you encounter sulfur-containing flue gas, dust medium, or the complicated pipeline needs multi-dimensional compensation, then the metal is prone to fatigue cracking. Is that the truth?
Which occasions must use non-metals? — From flue gas pipelines to hard demand in the cement industry
Having said so much, on what occasion are non-metals just needed? I'll list you a few of the most common ones:
- Flue gas pipeline system: The desulfurization and denitrification pipelines of power plants and steel plants have high temperature, strong corrosion, and have to absorb fan vibration. When you put on the metal at this time, the weld will crack in less than three months. From our stationDesulfurization flue gas baffle doorCooperateRectangular non-metallic expansion jointIt has become a standard configuration in the industry.
- Cement industry: The exhaust gas pipeline at the outlet of the preheater and the tail of the kiln has large temperature fluctuations and lots of dust. The metal expansion joint is easy to be stuck by dust and fail, while the non-metal has good elasticity and is convenient to clean dust. LikeMetal Corrugated Expansion Joints in Cement IndustryIt can also be used in some locations, but the high-temperature section still has to rely on non-metals.
- Chemical and environmental industries: Treatment of acid-containing, alkali-containing waste gas, corrosion resistance of non-metal rolling metal. Especiallyrubber compensatorAndRubber PTFE compensatorIt is extremely cost-effective in low pressure and large displacement scenarios.
By the way, there is another point that many people overlook: space is constrained. Some pipes are arranged like a maze, with axial, transverse and angular displacements. A model of metal expansion joint can only take care of one end, and the non-metal one can do it all. Do you think it will save trouble?
The core indicators of high-quality non-metallic compensator: material, structure, temperature and pressure resistance
Since you have decided to use non-metals, how can you pick "high-quality" ones? Don't just look at looks, you have to keep an eye on three core metrics.
Material: Don't be fooled by the words "fabric fiber"
Fluororubber/silicone rubber lining, multi-layer fiberglass cloth, PTFE film, stainless steel wire mesh reinforcement layer. What really determines the life span are the middle layers-in order to save money, some factories use ordinary fiberglass cloth instead of high-temperature resistant fiberglass, and as a result, they smoke as soon as they turn on. Remember, the temperature resistance level directly depends on the continuous use temperature given by the manufacturer. OurNon-metallic expansion joint (fabric fiber expansion joint)In the material selection, strictly according to JB/T 12235-2015 standard, the number of layers and thickness have clear requirements.
Structure: rectangular or circular? Flange or skin?
Rectangular pipes must be made withRectangular non-metallic expansion jointFor rounded shapes, use rounded. The structure is divided into skin type (integral fabric) and frame type (with metal frame). The skin type has good sealing performance and is suitable for low-pressure pipelines; The frame type is more resistant to negative pressure and suitable for fan outlets. You must not take a round hard set rectangle, when the air leaks to doubt your life.
Temperature and pressure resistance: Don't just look at nameplate numbers
Many manufacturers mark "temperature resistance 300℃". Is it an instantaneous peak or a long-term operating temperature? You have to ask clearly. Under high pressure conditions, the non-metallic compensator needs to add an external pressure ring or a metal support ring, otherwise it will be crushed and exploded. When selecting the model, we must give the three parameters of medium temperature, pressure fluctuation range and displacement to the manufacturer together. The lack of one may lead to the selection rollover.
The three easiest pits to step on during model selection (with real cases)
I have been in this business for more than ten years, and I have seen too many people stepping on pits. Share three of the most common ones that you take as a warning.
Pit 1: Treating non-metals as omnipotent
A chemical plant used a non-metallic compensator on the main steam pipeline, but it was burst by steam pressure in less than a month. And guess what? The rubber compensator they used has a withstand pressure of only 0.5MPa, and the actual pressure of the steam pipe is 1.2MPa. This is the typical product selection error. The correct method is: high-pressure steam application High temperature axial expansion jointOrExternal pressure single axial expansion jointDon't try to be cheap.
Pit 2: Ignore the guide tube
The aforementioned cement factory friends, the non-metallic compensator they used before had no guide tube, and the dust in the pipeline directly washed the fabric layer, which was worn out in half a year. Install a guide tube (refer Specific Function of Expansion Joint Guide Tube) After that, the lifespan tripled directly. The deflector not only directs the flow direction of the medium, but also protects the inner wall of the compensator-this detail cannot be omitted.
Pit 3: Do not remove the transport screw during installation
Many non-metallic compensators leave the factory with transport screws to prevent transport deformation. However, some people forgot to dismantle it and run it directly. As a result, the compensator couldn't expand and contract normally, and the deadlift broke. It's like buying a new phone without tearing the protective film, joke. Remember: Always check and remove the transport fixings after installation.
Installation and routine maintenance: Don't let the details ruin your compensator
Picking the right thing and pretending to be wrong is equal to wasting money. Note three points when installing:
- Coaxiality: The pipe interface should be aligned. If the deviation exceeds 2mm, it is easy to eccentric load, resulting in local tear.
- Pre-stretching/pre-compression: Adjust the pre-deformation amount of the compensator according to the ambient temperature during installation, and the specific value will be given to you by the manufacturer. Don't feel it.
- Fixed bracket: There must be fixed brackets or guide brackets on both sides of the compensator, otherwise the pipe thrust will push it into a twist.
In routine maintenance, inspect once a month to see if the skin has bulging and aging cracks. Non-metallic compensators on flue gas pipes are prone to dust accumulation and are regularly purged with compressed air or steam. If you find a leak, don't wait for it to collapse before replacing it. Generally, the service life of non-metallic compensators is 3-5 years, depending on the working conditions. Refer to this siteService life of expansion jointQ&A, the actual life is closely related to the medium temperature and start-stop frequency.
Don't believe in a "once and for all" compensator, any mechanical part has a life span. Regular inspection and on-demand replacement are the king of stable operation of pipeline system.