Find out what it is doing first
Many customers ask how to make non-metallic expansion joints as soon as they come up, but they don't even understand the basic principles of this thing. Non-metallic expansion joints (fabric fiber expansion joints) are different from metal bellows-they do not rely on corrugation deformation, but rely on the flexible layer of skin material and the compression of insulating cotton to absorb thermal displacement, vibration and installation errors. Therefore, rectangular non-metallic expansion joints are suitable for pipelines with low temperature, low pressure and large displacement such as flue gas, dust and desulfurization tower inlet and outlet; If you use it to dry high-temperature and high-pressure steam pipes, you are causing yourself trouble. Choose the wrong type, the back is all for nothing.
Selecting materials is the first step of the practice, and it is also the easiest place to roll over
The outermost side is a fluororubber or silicone rubber coated fiberglass cloth, which is responsible for corrosion and aging resistance; In the middle is thermal insulation cotton (aluminum silicate wool or rock wool), and the thickness is calculated according to the medium temperature, such as 80mm for 200℃ and 120mm for 400℃. These have empirical formulas, so don't pat your head; The inner layer also has steel wire mesh and PTFE membrane for support and insulation. Whether Q235 galvanized or 304 stainless steel should be used for flange beading depends on the corrosiveness of the medium and the environment. Alas, I have seen people replace aluminum silicate wool with ordinary rock wool in this link, and it is powdered in three months, so all the money saved is put into maintenance.
Doorways in the manufacturing process
Skin blanking size must consider the interlayer slip of multi-layer materials, and cannot be directly calculated according to the cross-sectional area of pipeline, otherwise the skin will be wrinkled after installation, and the service life will be greatly reduced. High-temperature sewing thread should be used for sewing, the needle length should be controlled at 5~8mm, and the two stitches should be staggered to prevent disconnection. The bolt hole distance between the bead and the flange is according to the standard, generally not more than 150mm, but the corners should be encrypted. There is also the guide tube-in the low-temperature flue gas pipe, the guide tube can prevent the air flow from directly washing the skin. This component is often omitted in the non-metallic expansion joint practice. Save it? Equals chronic suicide. When the skin is worn out, don't blame me for not reminding me.
Installation practices are more important than production
The first thing to do when installing on site is to check the amount of pre-deformation of the expansion joint. There will be a positioning screw when it leaves the factory, and it must be loosened after installation! If you don't release it, the whole expansion joint is a rigid body, and there is no compensation effect at all. What do you buy it for? Secondly, the flange connection should be symmetrically tightened, and the torque should be hit to the specified value twice. Don't screw to death once on one side to cause deformation. For rectangular pipes, the installation position of the expansion joint should avoid joints and obstacles, and keep it coaxial with the pipe. A common mistake is to use the expansion joint as an installation adjustment piece, hard-pull and hard-pull to align it-the skin has initial stress as soon as it is installed, and it won't take long to tear. And guess what? That's how many "quality accidents" come about.
Pressure test and acceptance should not be confused
According to the standard of JB/T 12235-2015 "Non-metallic Expansion Joint", the appearance inspection and dimensional deviation detection should be carried out after leaving the factory, and the airtightness test should be carried out after installation. The airtightness test pressure is usually 1.1 times of the design pressure, but not more than 0.1MPa. Hold the pressure for 5 minutes. Brush the joint surface of the weld and flange with soapy water to see if there are bubbles. Conditional projects suggest to do displacement compensation performance verification-heat the pipeline to the working temperature, and whether the displacement of the measured expansion joint is within the design range. This step can screen out many hidden installation hazards. Don't be too troublesome. If the pressure test fails, it will be really troublesome if the air leaks later.
Pits for aftermarket and remodeling
The skin of non-metallic expansion joint belongs to wear parts, with a normal life of 3~5 years. If the environment is harsh, it may have to be replaced in two years. Customers often say "your quality is not good". In fact, it is because the skin material was selected low at the beginning, or the positioning screw was not loosened during installation. If the project has already been run, you can only change the skin without changing the frame, but the old skin must be cleaned, the flange surface must be removed from rust and smoothed, and the new skin openings should be re-measured. You can't directly punch holes according to the old parts-the old holes may have been worn and deformed. Remember one sentence: the practice of non-metallic expansion joint is not a rigid process, but a comprehensive understanding of materials, working conditions and installation errors. Only by understanding every step can it work for you honestly.