How is it different from a metal expansion joint? Don't wait for something to go wrong to regret not choosing the right one
Two days ago, there was a power plant customer, whose flue temperature was only 350℃, and he had to put on a metal expansion joint. As a result, it leaked in three months-it was replaced with our fabric fiber expansion joint (that is, non-metallic expansion joint), and there was nothing wrong for two years. The upper limit of temperature resistance of non-metallic expansion joints is indeed not as good as that of some metals, but in the scenes of medium and low temperature, corrosive flue gas and large-diameter rectangular pipes, its compensation ability, vibration isolation effect and cost performance are really incomparable to those of metals. How high do you say metal is capable? High-temperature axial expansion can save energy above 800℃, but what about the price and installation requirements? Non-metallic expansion joint In desulfurization flue, cement kiln tail, power station boiler and other places, any rectangular non-metallic expansion joint can handle several times the displacement of metal, and it is light in weight and easy to install. To put it bluntly, the selection is not about who is "high temperature resistant", but about who is "suitable".
The most afraid of type selection is "almost enough"-temperature, pressure and medium can't be missed
The desulfurization flue is contained with acid condensate, the cement industry is high-temperature dusty gas, and the power station boiler is negative pressure and large displacement. You can't take it all with the same model. Taking our rectangular non-metallic expansion joint as an example, three numbers will be stuck in design: the temperature does not exceed 600℃ (the upper limit of conventional fabric fibers), the pressure is not higher than 0.1MPa (negative pressure is safer), and the displacement depends on the superposition of axial and transverse directions. Another example is the rubber compensator. The working medium has oil or acid and alkali, so the oil-resistant or corrosion-resistant rubber formula must be specified. If you make a mistake, it will explode directly. The standard refers to JB/T 12235-2015, in which the test pressure, sealing performance and fatigue life are all written to death, so don't take it as a child's play. There is another small detail: rubber PTFE compensator, the thickness of PTFE lining must reach the specified value, otherwise corrosion resistance is a joke. When you buy it, it is a hundred times more reliable to ask the supplier to issue a material report and a type test report than to read a brochure.
One wrong step of installation will cut the life by half
Do you think the non-metal expansion joint is just a soft cloth, just pull it casually? Wrong. There are three most common pits: First, the guide tube is installed backwards, and the medium directly washes the fabric layer, which is worn out in two weeks. The specific function of the expansion joint guide tube is to guide the airflow and protect the skin. If it is installed backwards, it is equal to self-harm. Second, the mounting bolts are too tight, leaving no margin for pre-tensioning/pre-compression. When the system is hot, the expansion joint is cracked. The third is to ignore the adjustment of the tie rod nut-many of the expansion joints on the edge of our circular baffle door and flue gas baffle door have limit tie rods. After the installation bolts are welded, the tie rod nut must be loosened to the design position. How to adjust the expansion joint tie rod nut? Simply put, first adjust to the installation length, and then loosen the corresponding number of turns according to the design displacement, otherwise the expansion joint is equal to dead pulling and hard pulling. Refer to the question and answer of our expansion joint tie rod nut adjustment. If you make a mistake, wait for air leakage. The correct installation method of the expansion joint of the large tie rod is the same: the tie rod is only a limit protection, not a force-bearing part.
Routine maintenance is easy, but these two details must be kept an eye on
The skin of non-metallic expansion joint is a weak link. When inspected, it should be seen with eyes and touched by hands-bulging, wrinkling, and seepage of water and ash on the surface, indicating that the internal structure has been damaged. In addition, if it is a rectangular non-metallic expansion joint used in power plants or cement plants, it is best to check the torque of the flange bolts after running for about one year, because the thermal cycle will cause the bolts to loosen. I have a customer who is lazy and doesn't tighten the bolts, and the whole expansion joint is disengaged from the flange surface, and it loses millions after three days of shutdown. The rubber compensator is more afraid of ozone aging, so it should be covered with a protective sleeve when installed in the open air, otherwise it will crack for one or two years. The lifespan of expansion joints largely depends on installation and maintenance, don't expect to do it once and for all. Tighten the bolts regularly and observe the condition of the skin, this little effort can't be saved.
Don't be cheap, how deep is the "non-standard" pit of non-metallic expansion joints?
On the market, recycled rubber or inferior glass fiber cloth is impersonated, which saves half the cost and leaves one tenth of the life. Our rubber PTFE compensator, PTFE lining must reach the specified thickness, otherwise corrosion resistance is a joke. According to national standards, airtightness test and dimensional inspection are required when leaving the factory, but many small factories don't even use pressure gauges. You ask why the price difference of non-metallic expansion joints is three times? The difference lies in the invisible places such as base cloth, coating and sealing ring. It is a hundred times more reliable to ask the supplier to show the material report and type test report before buying than to read the brochure. In addition, if the expansion joint of the flue gas baffle door is not sealed well, the leakage of flue gas will corrode the baffle door body and peripheral equipment. Therefore, when selecting the model, don't just look at the expansion joint itself, but take the whole system into account.
To say a thousand words, where is the practical use of non-metallic expansion joints?
Corrosion resistance, large displacement, vibration isolation, low cost, this is the metal expansion joint in rectangular pipes and flue gas systems can not replace. Look at the desulfurization flue gas baffle door, manual plug-in insulation door and electric plug-in insulation door. The compensation on both sides of these valves is almost all the world of non-metallic expansion joints. Choose the right one, keep up with the maintenance, and use it for five or six years without a problem; Wrong choice, three months of air leakage is purely self-inflicted. Therefore, next time you encounter the pipeline compensation problem of "low temperature, low pressure, but difficult medium", think about non-metallic expansion joints first, and don't blindly put on metal. Remember the standard of JB/T 12235-2015, and the selection, installation and acceptance are all compared, so that you won't step on pits.