Three parameters that must be killed before installation: temperature, pressure and displacement
Don't think this is nonsense. Two days ago, I met a customer and put a temperature-resistant 200℃Non-metallic expansion joint (fabric fiber expansion joint)It was installed on the flue gas pipe at 300℃, and it burned through in a week. JB/T 12235-2015 clearly states that the design temperature, working pressure, and axial/transverse compensation amount of the compensator must match the actual working conditions. After you get the product, check the parameters on the nameplate first – especially the amount of displacement. Thermal expansion in the air duct system is miscalculated, and the compensator is just a decoration.
A 30-meter-long steel air duct can expand about 72mm (calculated as 0.012mm/m·℃) from normal temperature to 200℃. If the compensator you choose has only 50mm compensation capacity, then installing it is equivalent to making it hard, which is weird if it is not bad. Therefore, after getting the design drawings, take the calculator to calculate it first, and don't be superstitious about the selection table given by the supplier.
Installation position and bracket setting: If you do this right, you will save half the trouble later
Air duct non-metallic compensators are typically installed near pipe direction changes, valve outlets, or equipment interfaces. However, note that fixed brackets must be set on both sides of the compensator, and guide brackets must be set in the middle to prevent lateral instability of the pipeline. If you put the compensator behind the elbow without the guide frame, when the pipe is hot, the compensator will twist into a twist- -I've seen one scene, thatRectangular non-metallic expansion jointAfter a 90° elbow, no guide was added. After two weeks of running, the fabric layer was directly torn, and the flange was misaligned.
In addition, the compensator itself does not bear the weight of the pipe, so the bracket cannot be pressed against it, and sufficient installation space must be left. Generally, it is required to leave at least 200mm clearance on both sides of the compensator for future maintenance. For rectangular air ductsRectangular non-metallic expansion jointAlso pay attention to the direction of the reinforcing ribs in the four corners, don't install them backwards-the exposed side of the reinforcing ribs faces outward, and the lining faces the medium.
Specific installation steps-don't be led off by those fancy tutorials
The first step is to check whether the flange surface is flat and has no burrs. What to choose for flange gaskets? Look at the medium temperature: use asbestos rubber sheet below 200℃, and change PTFE pad beyond this temperature. In the second step, hoist the compensator in place, pre-tighten the bolts first, and don't screw them to death at once-screw them to 50% torque first, and then tighten them symmetrically after adjusting the position. Step 3, adjust the tie rod nut. Attention!The transport screw (that is, the limit screw) must be removed after installationOtherwise the compensator cannot be scaled or retracted. How to tune it? Refer to the question and answer "How to adjust the tie rod nut of the expansion joint" in our station-simply put, let the compensator be at free length, and then tighten the flange bolt symmetrically. The torque is according to the standard, for example, the torque of M16 bolt is usually 80-100N·m. Step 4, if it isrubber compensatorOrRubber PTFE compensator, also check the rubber part for scratches.
By the way, during construction in winter in the north, when the pipeline shrinks greatly, the compensator needs to be pre-stretched or pre-compressed. For example, the ambient temperature is-20℃, the operating temperature of the pipeline is 300℃, and the expansion amount is very large, but it should be stretched a little when installed in cold state. The specific values are calculated and will be stated in the general design documents.
Common Installation Mistake: You Think Just Install It? Absurdly wrong
Install the deflector in the reverse direction. The role of the guide tube is to guide the flow of the medium and reduce the scouring. The arrow must point to the direction of the medium flow. You install it backwards, and the smoke flushes directly into the fabric layer, and it leaks in three months. The question and answer "The specific function of the expansion joint guide tube" makes it very clear. Turn it over yourself.
The bolts were tightened too tightly, causing the rubber or fabric part of the compensator to be fractured. Especiallyrubber compensatorThe compression force of the flange should be even, just screw it until the seal does not leak-don't screw it to death. It is recommended to use a torque wrench and tighten it diagonally in 2-3 times, and the final torque is controlled within the middle and lower limits of the recommended value of the manufacturer.
Cold drawn pre-compression is ignored. As mentioned earlier, the installation must be done in winter in the north. If it is not done, it will either disconnect or die when running. These three pits are stepped on in almost every project. And guess what? Last month, there was a power plant project. Because the limit screw was not removed, the compensator was stuck and the pipe joint was cracked. The production was stopped for one day, resulting in a loss of more than 100,000 yuan.
Inspection and acceptance criteria after installation
Pressure test is necessary, but many air duct systems are low pressure (
Also, don't forget to record the ambient temperature at the time of installation and the initial length of the compensator. These data are of great reference value for future maintenance. For example, after a year, you find that the compensator is elongated. Comparing the initial data, you can calculate the actual thermal displacement and judge whether the pipe support has failed.
Finally, regarding the service life-non-metallic expansion joints are generally 5-8 years, but they will be shortened due to media corrosion and temperature. It is recommended to check the fabric layer every six months for aging cracks, and if so, prepare to replace it. This site'sNon-metallic expansion joint (fabric fiber expansion joint)The product page has a detailed maintenance schedule, which can be performed against it.