Why use a non-metallic compensator? These five scenes metal really can't do
Dry pipeline compensation has been in the business for a long time, and you will find a heartbreaking fact: metal expansion joints (such as metal corrugated expansion joints and metal hoses) are indeed solid, but when encountering high-temperature flue gas, corrosive media and super-large displacement, the shortcomings of metal are completely exposed-short fatigue life, high cost and limited installation. At this time, non-metallic compensators (that is, non-metallic expansion joints, including fabric fiber expansion joints, rectangular non-metallic expansion joints, rubber compensators and rubber PTFE compensators) have become life-saving straws. Why? Look down.
If metal can't carry it, why can non-metal carry it?
The greatest confidence of non-metallic compensators comes from the materials themselves. The temperature resistance range is ridiculously wide-some fabric fibers expand and save energy to work for a long time above 1000℃, and metal bellows start to swing when they reach 600℃. In terms of corrosion resistance, in the face of acidic and alkaline flue gas and desulfurization system, stainless steel can't bear pitting corrosion, but PTFE compensator is like nothing. More importantly, non-metals can absorb multi-dimensional displacements-eating them all in axial, transverse and angular directions, unlike metal bellows, which are prone to fatigue cracking. Think about it for yourself, as soon as the pipe vibrates, the metal bellows bends back and forth, and the stress concentration point will crack sooner or later; The non-metal loop belt is flexible and can be twisted how you want.
In addition, the weight is light, the load on the pipe support is small, and the installation is also hassle-free. The vibration and noise reduction effect is much stronger than that of metal-this is not metaphysics, fiber fabric itself has damping properties. Two days ago, I met a buddy in a cement factory. He used to use metal corrugated expansion joints, and the noise made workers complain. After replacing them with non-metal expansion joints (fabric fiber expansion joints), the noise directly dropped by 10 decibels.
Five scenes, metal is really bad
Specific to actual projects, non-metallic compensators are almost just needed in several industries, and hard metal is to find trouble for yourself.
1. Power station industry: front and rear of boiler flue duct and desulfurization flue gas baffle door
The flue gas temperature of the power station is high, and the sulfur-containing corrosion is heavy. In the desulfurization system, the temperature of the pipelines in front and behind the flue gas baffle door fluctuates greatly, and there is still a large amount of acidic condensate in the medium. Would you try it with a metal corrugated expansion joint? Corroded perforations in a few months. Non-metallic expansion joints (specifically rubber PTFE compensators or PTFE compensators) are acid and alkali resistant and can absorb large displacements. The desulfurization flue gas baffle door of this station is a standard flue configuration with non-metallic compensator.
2. Cement industry: hot air ducts at the head and tail of the kiln
At the head and tail of the cement rotary kiln, the temperature fluctuates drastically and the amount of dust is extremely large. The surface of metal bellows is easy to accumulate dust. Once the ash block falls off and gets stuck in the corrugation, the expansion joint will be wasted. The surface of the non-metallic compensator is smooth, the dust is not easy to adhere, and it can adapt to frequent temperature changes. Cement industry metal corrugated expansion joints are also available, but only in branch pipes with lower temperatures and less dust. Trunk hot air duct, honestly use non-metal.
3. Iron and steel industry: blast furnace gas pipeline, dust removal system
Blast furnace gas pipeline contains a lot of dust and corrosive gas. Although the temperature is not high (usually 300-500℃), the medium is extremely corrosive. The life of metal bellows here is generally less than a year. The non-metallic compensator (fabric fiber expansion joint) with the guide tube can effectively isolate the medium and easily double the life. The dust removal system is the home field of non-metals-low pressure, large displacement, serious wear, and the rubber compensator is cheap and doesn't feel distressed to change.
4. Chemical industry: acid-base media pipeline
Concentrated sulfuric acid and concentrated hydrochloric acid run in the chemical pipeline, and even if the metal hose is lined with PTFE, it is inevitable that there is a risk of pinhole leakage. The rubber PTFE compensator in the non-metal compensator is made of PTFE composite material as a whole, which is corrosion resistant and has no dead angles. Moreover, low-pressure pipelines do not need to bear much pressure, and non-metals are completely enough.
5. Rectangular large section flue
Many flue gas pipelines are rectangular, such as the inlet and outlet of desulfurization towers in power stations. Although the metal rectangular expansion joint can be made, it is expensive, heavy and difficult to install. Designed for rectangular flues, the rectangular non-metallic expansion joint is lightweight and compensates for less than half the price of metal. Which do you want to choose?
The structure is not so mysterious, and the core of the selection is a few points
Non-metallic compensators typically consist of non-metallic loop belts (fabric fiber, rubber or PTFE composite) and metal frames (deflectors, platens, bolts, etc.). The rectangular non-metallic expansion joint in our product line is specially equipped with rectangular flue, while the rubber compensator and rubber PTFE compensator are biased towards low-pressure, corrosive liquid or gas pipelines. Don't look at the fancy name when selecting the model. The core is to look at the medium temperature, pressure, chemical properties, and the displacement required by the pipeline. For example, the desulfurization system should not use ordinary rubber, but use an acid-and alkali-resistant PTFE compensator. Otherwise, the rubber will be softened by corrosion, and it will leak in less than two months.
It's not a panacea. High pressure and low temperature still depend on metal
Nonmetallic compensators aren't panacea either. If the pressure is too high (say over a few MPa) or the temperature is extremely low (cryogenic embrittlement), it won't be able to handle it. What about that? Metallic, such as general-purpose corrugated expansion joints or high-temperature axial expansion joints. There is no absolute choice of who is better or worse, only whether it is suitable or not. After all, the national standard JB/T 12235-2015 also makes it clear that non-metallic expansion joints have clear technical boundaries. What we do in engineering is to choose the most cost-effective plan within the boundaries.