Where are non-metallic expansion joints generally used? These 5 industries can't live without it
What exactly is a non-metallic expansion joint? When many people hear "expansion joint", what pops up in their minds is metal bellows. However, non-metallic expansion joints (also called fabric fiber expansion joints) are made of flexible composite materials, which can resist high temperatures and corrosion, and the key is that they can absorb multi-directional displacement. You flip through the national standard JB/T 12235-2015, and write its technical requirements clearly. This thing is not as hard as metal parts, but it is more suitable for those places where the pipe expands and contracts violently and vibrates heavily.
1. Power plant flue gas system: the most appropriate application scenario
The flue of the power station boiler and the inlet and outlet of the desulfurization tower have high temperature and strong medium corrosion, so they have to start and stop frequently. Rectangular non-metallic expansion joint or non-metallic expansion joint (fabric fiber expansion joint) is used here, which is used together with desulfurization flue gas baffle door and circular baffle door (double seal). Think about it, there are SO₂ and water vapor in the smoke, and metal parts will quickly rust through, but non-metallic materials can hold up. Moreover, the rectangular flue can't use metal bellows, and the non-metal can be customized according to the on-site size, which is convenient to install.
Two days ago, I met a buddy from a power plant, saying that the metal expansion joint exported by their desulfurization tower leaked in half a year, and there was no problem for three years after changing the non-metal one. It's not that the metal is bad, but that the working condition is too ruthless-the temperature fluctuates from normal temperature to 200℃, plus condensed acid, and the metal is fatigued + corroded, which can't be held up. The composite layer structure of non-metallic expansion joint (fabric fiber type), the inner layer is temperature resistant, the middle layer is heat insulated, and the outer layer is anti-corrosion, which is just right for the symptoms.
2. Cement industry: hard bones in high temperature and wind and dust
The preheater, decomposition furnace and grate cooler on the cement production line can have a pipeline temperature of 800℃ or even higher. Although there are metal corrugated expansion joints in cement industry in this station, non-metal expansion joints are used a lot at air duct connections-they can compensate for axial, transverse and angular displacements, and are not afraid of dust accumulation. For example, the pipelines at the head and tail of the kiln should be removed from the thermal stress with non-metallic expansion joints, so that the pipelines will not crack. The construction team likes it lightly, and one person can carry it and weld it well.
Tsk, I don't need to say more about how bad the dust environment in cement factories is? Dust accumulation will jam the corrugations of the metal bellows, resulting in compensation failure. The surface of the non-metallic expansion joint is smooth, and the ash can't hang. Even if it accumulates, it will not affect the displacement. Moreover, the compound three-way expansion joint in the cement industry can also handle complex displacement, but the cost is higher. Non-metallic expansion joints are the cost-effective choice on air ducts.
3. Iron and steel metallurgy: standard configuration of blast furnace hot blast furnace and flue gas pipeline
The supply air temperature of blast furnace hot blast furnace is thousands of degrees, and the thermal displacement at the connection of pipe flange is surprisingly large. Non-metallic expansion joints (especially fabric fiber types) can absorb multi-directional displacements here, and at the same time play a role in vibration isolation. When you look at the head of the sintering machine and the air duct of the ring cooler in the steel mill, there are such flexible connectors everywhere. Cheaper than metal expansion joints and quicker to replace when broken-downtime is money.
And guess what? Some steel mills used to use metal rectangular expansion joints, but as a result, the weld cracked, which was found to be thermal fatigue. After replacing it with non-metallic, it not only absorbs the displacement well, but also isolates the vibration. In particular, the temperature difference between the cold air duct and the hot air duct of the blast furnace hot blast furnace is several hundred degrees Celsius, and the non-metallic expansion joint is equipped with a heat insulation layer to properly hold it. If the double-sealed single-axis circular baffle door is used, the front and rear sections are compensated by non-metal, and the sealing effect can be doubled.
4. Chemical industry and environmental protection: corrosion resistance is king
The acid fog pipeline and waste gas scrubber of chemical plants are acidic and alkaline in medium, and the metal hose can't carry it for several months. Although rubber compensator and rubber PTFE compensator can also be used, it is more cost-effective for large-size pipes or non-metal expansion joints. For example, the rear of the flue gas baffle door in the desulfurization system is not high in temperature but strong in corrosion. It can last for three to five years with non-metallic expansion joints (fabric fibers) and PTFE-lined hoses. In addition, the flue gas pipeline of waste incineration plant also likes it, and the replacement cost is low anyway.
Don't think that non-metallic expansion joints are not afraid of corrosion-the material selection depends on the media composition. For example, ordinary fabric fibers cannot be used for fluorine-containing gas, but PTFE compensator or PTFE-lined scheme must be used. However, for most flue gas and exhaust gas conditions, standard non-metallic expansion joints (fabric fibers) are sufficient. The purchasing supervisor of a chemical plant generally calculates the whole life cycle cost. Non-metallic expansion joints are cheap, easy to change, and have small downtime losses, which is twice as cost-effective as metal ones.
5. Other unpopular but important places: air-cooled islands, vacuum pipes and manual insulation doors
The steam pipeline of the air-cooled island of the thermal power plant has large temperature fluctuations. The double-hinged expansion joint of the vacuum pipeline with the air-cooled island is metal, but the non-metal expansion joint is used to connect the compensation section of the steam distribution pipe and the condensing tube bundle, and the cost is lower. There are also the front and rear sections of manual plug-in type insulation doors and electric plug-in type insulation doors, which also require non-metallic expansion joints to absorb installation errors. Don't underestimate these places. If something goes wrong, the whole system will have to stop.
Non-metallic expansion energy saving in vacuum environment can't be used? The answer is yes-the vacuum of non-metallic expansion joints (fabric fibers) can be maintained as long as the right sealing layer is selected. In the working condition of air-cooled island, negative pressure will be generated after steam condensation. The flexibility of non-metallic expansion joint can make up for the pipeline alignment deviation, and the whole pipeline does not need to be moved when replacing it, which saves a lot of effort.
So you see, where are non-metallic expansion joints generally used? Power stations, cement, steel, chemical industry, air cooling... pipelines with high temperature, corrosion and multi-directional displacement in these industries are basically inseparable from it. A product can span so many industries, not by gimmicks, but by real adaptability to working conditions. If you are also choosing models, don't just look at metal parts. Non-metallic expansion joints may be a better way to go.