What exactly are the types of integral non-metallic compensators? Understand these 4 categories before selecting a model
Two days ago, I met a purchaser who was doing a desulfurization project. When I came up, I asked, "What are the overall non-metallic compensators?" I ran through the four types of products for him, and he directly eliminated two types from the selection table in his hand on the spot. If the wrong compensator is chosen, the pipeline stress is not absorbed, and it has to be replaced in half a year, doubling the cost. Therefore, this article does not go around the bends, but directly writes the applicable scenarios, temperature resistance limit and corrosion resistance of these four types of products clearly. You will basically not overturn if you pick them.
Find out first: What is the difference between non-metallic compensators and metallic compensators?
The flexible section of the non-metallic compensator is made of non-metallic materials such as fabric fiber, rubber and polytetrafluoroethylene, while the metal compensator relies on stainless steel bellows. To put it bluntly, the three biggest advantages of the non-metallic version are high temperature resistance (the fabric fiber type can carry more than 600℃), corrosion resistance (pure PTFE can resist almost all strong acids and alkalis), large compensation, and cheap. It is commonly found in flue gas pipelines and air duct systems of power plants, cement plants and chemical plants. Note that the low-pressure working condition is its home field. If the pressure exceeds 0.1MPa, it is necessary to discuss the selection.
Category I: Fabric fiber type non-metallic expansion joint-the most mainstream and temperature-resistant
It is also called non-metallic expansion joint or fabric fiber expansion joint in the industry. The structure is composed of multi-layer fabric (silicone cloth, fluorine adhesive cloth, ceramic fiber, etc.) plus thermal insulation cotton, which can withstand temperatures of 600 ℃ or even higher. It is mainly used in flue duct and desulfurization system. The rectangular non-metallic expansion joint of this station is this kind of product, which is specialized in matching rectangular pipes. When selecting the model, keep an eye on the medium temperature, pressure (usually low pressure) and the direction of displacement (axial, transverse, angular). The stress at the corners of the rectangular structure is concentrated, so the seal should be strengthened additionally during design, otherwise the air leakage rate will exceed the standard. And guess what? Many customers hard-install round non-metallic expansion joints on rectangular tubes, but the flanges don't match, and the on-site change fee is more expensive than the product itself.
Category 2: Rubber type compensator-low voltage resistance, no high temperature, but cheap
Comprises a rubber compensator and a rubber PTFE compensator. Rubber compensator mainly absorbs displacement by elastic deformation of rubber, and its pressure resistance is stronger than that of fabric type (it can reach about 1.0MPa), but the upper limit of temperature resistance generally does not exceed 100℃. Suitable for water, weak acid and alkali medium. If you have 80℃ circulating water in your pipeline, choosing a rubber compensator is completely enough. The rubber PTFE compensator is lined with PTFE in the inner layer, which further improves the corrosion resistance and is suitable for chemical pipelines. However, there is an Achilles heel: rubber will age in long-term high temperatures or highly oxidizing media, and it needs to be checked regularly. It is recommended to take it apart and look at it once every three years. If the rubber is hard, replace it. Don't wait for it to leak before treating it.
Category 3: Polytetrafluoroethylene compensator (PTFE compensator) -the king of corrosion resistance, but delicate
Made of pure PTFE material, it is extremely corrosion resistant and can resist almost all strong acids and alkalis (including aqua regia). But has low mechanical strength and is commonly used as a flexible connection section in piping systems, absorbing small amounts of displacement. There is PTFE-lined metal hose in the product information of this site, that is, the metal hose is lined with PTFE, which belongs to another structure; The body of PTFE compensator is pure PTFE bellows, and the application scenarios of the two are overlapping and different. Focus on media corrosivity, temperature and pressure when selecting the type-PTFE withstand pressure is generally ≤1.0MPa. In addition, note that PTFE will creep at high temperature, and its strength will decrease rapidly when it exceeds 200℃, so don't use it in high-frequency vibration occasions.
Category 4: Rectangular non-metallic expansion joints-actually rectangular versions of fabric fibers
It is still textile fiber type in nature, but the cross section is rectangular, and it is specially used for rectangular smoke ducts in power plants and steel plants. This site has rectangular non-metallic expansion joint this product, and the circular non-metallic expansion joint structure principle is the same, but the shape is different. The stress concentration and sealing problems of rectangular corners should be considered during design-the four corners are most prone to air leakage, so reinforcing ribs or special sealing structures are usually installed. If your pipe is rectangular, don't worry about it. Go directly to the rectangular non-metal expansion joint, and don't change the mouth with the round shape.
Summary: There are just four categories, and the selection is only three sentences
There are no fancy models of integral non-metallic compensators, just these four mainstream types-fabric fiber type (round/rectangular), rubber type, rubber PTFE composite type and pure PTFE type. Selection steps:
1. Look at the medium temperature first: if it exceeds 200℃, consider the fabric fiber type;
2. Look at the medium again: highly corrosive tetrafluorine or rubber tetrafluorine;
3. If the shape of the pipe is rectangular, directly attach the rectangular non-metallic expansion joint.