Find out what non-metallic compensator is first: compared with metal compensator, where is it stronger and weaker?
The core structure of non-metallic compensator, also called non-metallic expansion joint (fabric fiber expansion joint), is flexible fabric band, thermal insulation filler layer and metal frame. It is different from the metal corrugated compensator: metal absorbs displacement by the deformation of the corrugated thin wall, while non-metal absorbs displacement by the flexibility of the fabric band.
First, the amount of compensated displacement is large, especially the lateral and angular displacement, which is often several times that of metal; Second, the thrust is small, because the stiffness of the fabric loop is extremely low, and the load requirement on the pipe support is low; Third, it has good corrosion resistance and can resist corrosive media such as sulfide and chloride ions in flue gas. There are also shortcomings-poor pressure bearing capacity, which can generally only be used in low pressure or even slightly negative pressure conditions, and fabric belts are consumables, and their life is not as good as that of metal bellows.
Therefore, the use of non-metallic compensator is not to replace metal, but to make up the shortcomings of metal. The following working conditions are its home field.
Application 1: Large-diameter low-pressure pipes such as air ducts and flues of power plants can be easily compensated by rectangular cross sections
The air ducts and flues of power plants are often two meters, three meters or even larger in diameter, and many of them are rectangular in cross section. Metal corrugated compensator for this occasion? Material and molding costs are ridiculously high, and metal bellows are sensitive to cross-sectional shape, making rectangular bellows extremely difficult to manufacture.
Nonmetallic compensators don't have this concern. Its ring belt is flat, and it is made into a rectangular cross section by the frame. This is how rectangular non-metallic expansion joints come from. Large diameter and low pressure just avoid the short board of non-metal pressure difference, and give full play to its advantages of large compensation and small thrust.
And guess what? A rectangular flue of DN4000, the heat displacement may reach fifty or sixty millimeters, and the non-metallic compensator can easily absorb it. What about the metal ones? Honestly calculate the fatigue life.
Use 2: How can fabric fibers and rubber materials hold high temperature and corrosive smoke environment?
Flue gases and corrosive gases are another typical type of operating conditions. The temperature of the flue gas at the inlet of the desulfurization tower may reach 150℃, as well as corrosive components such as SO₂, SO₃ and HCl, and dust washing in some places.
The band material of the non-metallic compensator is a composite structure such as glass fiber, polytetrafluoroethylene and silicone rubber, which can withstand the temperature above 200℃, and its corrosion resistance is much better than that of metal. Metal bellows are prone to stress corrosion cracking in chloride ion environment, but non-metallic bands become more and more solid.
In addition, the insulation layer of the non-metallic compensator can be designed as a multi-layer structure, which can not only compensate for displacement, but also reduce heat loss. This kind of structural design flexibility, metal compensator can't compare.
Application 3: Vibration and noise reduction of equipment interface, and "fault tolerance" function of installation deviation
The inlet and outlet of rotating equipment such as pumps, fans and compressors can't avoid vibration. If the pipes are connected rigidly, vibrations are transmitted directly to the piping system, and both noise and stress are large.
The fabric band of the non-metallic compensator itself has damping effect, which can absorb part of high-frequency vibration. A non-metal compensator is installed at the outlet of the fan, and the vibration transmission rate can be reduced by an order of magnitude. Rubber compensator and rubber PTFE compensator are the same way, which is suitable for vibration reduction of fluid media pipelines.
There is also a particularly practical use – fault tolerance. During on-site installation, the pipeline alignment deviation is several millimeters or even more than ten millimeters, which is normal. Hard connections can't be installed, so soft connections are much more convenient. The non-metallic compensator can absorb the installation deviation, which saves the user the time of field adjustment, which is considerable.
Application 4: Special applications in desulfurization, dust removal and other systems, used with baffle doors and other equipment
Flue gas baffle door, electric plug-in type insulation door, manual plug-in type insulation door of desulfurization system, these devices will have thermal displacement in the pipeline when switching and starting and stopping. The baffle door body is rigid and cannot absorb displacement, so it must be digested by the peripheral compensator.
Here non-metallic compensators are pretty much the only option. The temperature of desulfurization flue gas is not high but it is extremely corrosive, and the cross section of pipeline is often rectangular, so the space is limited. The non-metal compensator can be made into a flat shape, connected on both sides of the baffle door, and used in cooperation with the desulfurization flue gas baffle door, which just meets the technical requirements.
The same goes for dusting systems. The fabric ring belt compensator at the inlet and outlet of the dust collector can not only compensate the displacement, but also block the vibration transmission and protect the body of the dust collector.
Pits to be avoided in model selection: pressure, temperature, displacement, none of which can be taken for granted
Finally, talk about selection. What are non-metallic compensators most afraid of? Stress. Some people think that the fabric loop is soft anyway, so the pressure should not matter, right? Wrong. Under positive pressure, the ring belt will bulge, and the skeleton will be subjected to additional pressure load, which will tear if the design is not good.
Temperature is also a red line. Silicone rubber bands and fluorine rubber bands have different temperature resistance grades, and they will age and crack if they exceed the upper limit. The displacement is more accurate, and the deformation of the ring belt must be controlled within the safe range, otherwise creep fatigue will shorten the life.
The usefulness of non-metallic compensators?In the final analysis, it is born for specific working conditions such as large diameter, low pressure, high corrosion, large displacement and vibration reduction. When selecting the model, give the working condition parameters to the manufacturer and let the engineer help you check it-don't take it for granted.