How do welding flanges and non-metallic ring strips fit together?
To put it bluntly, the welding flange non-metallic compensator is to screw the rigidity of the metal flange and the flexibility of the non-metallic ring band together. The structure is actually very simple to disassemble: there are grooved carbon steel or stainless steel flanges on both sides, and multi-layers of composite non-metallic fabric bands are sandwiched in the middle-fluororubber, silica gel and polytetrafluoroethylene are laminated and pressed, and then wrapped with stainless steel wire mesh for reinforcement. The flange and the ring belt are fixed by mechanical compression or welding, but the key is that the flange itself is welded to the pipe, not the ordinary flange connection that is clamped by bolts.
The ordinary flange connection relies on the bolt preloading force to compress the gasket. Over time, the gasket will age, the bolt will be loose, and the risk of leakage will rise linearly. Although the direct welding connection is well sealed, it has no compensation ability when the pipe expands and contracts, and the pipe is directly cracked by hard pulling and hard pulling. The welded flange non-metallic compensator stacks the advantages of the two: the flange is welded to the pipeline, which prevents the leakage path of the gasket; The non-metallic band in the middle is specifically designed to absorb thermal displacement and vibration. This combination can withstand pressure within 2.5MPa, and the upper temperature limit can reach above 600℃ according to different materials. Leaks? Unless the ring band is broken, the weld position will not leak at all.
What occasions must it be?
In the desulfurization system of the power plant, the flue gas carries sulfuric acid and sulfurous acid, and the temperature is not low. You let metal corrugated expansion joints carry the corrosion? Piercing in a few days. However, the non-metallic ring belt is naturally immune to acidic media, and with a welding flange, the installation position is at the connection between the inlet and outlet of the desulfurization tower and the flue. With this compensator, the desulfurization flue gas baffle door on our station has passed the actual measurement of sealing and corrosion resistance. The temperature of the hot air duct in cement plant fluctuates greatly, and there is much dust. The metal rectangular expansion joint is easy to accumulate dust and get stuck. If it is replaced with a rectangular non-metallic expansion joint, the fabric ring belt itself does not accumulate dust, and the hot air will be clean when it blows.
Chemical plants are more typical-strong acid and strong alkali media, and pipeline displacement is also complicated. The non-metallic compensator of the welded flange can absorb both axial and transverse displacements at the same time, such as the large angle swing of the transverse expansion joint of the compound hinge. The non-metallic ring belt can be done by the elastic deformation of the fabric itself, so there is no need to calculate the fatigue life layer by layer like the metal bellows.
The Three Details That Are Most Prone to Rollover When Installing
First, the temperature control is not good when welding the flange, and the end face of the flange is deformed and warped. The welding sequence should be jump welded in sections from the inside to the outside, and the heat preservation should be slowly cooled immediately after welding, otherwise the sealing surface will be uneven, and the non-metal ring belt will still leak when pressed. Second, the bolt tightening sequence is reversed. Many people twist diagonally casually, and as a result, the flange tilts up while being stressed. The correct way is to use a torque wrench to twist symmetrically from the middle to both sides, and gradually apply force to the specified torque value in three times-this is a similar principle mentioned in the question and answer of adjustment of expansion joint tie rod nut. Third, the lack of a guide tube induces vortex wear. When the medium flow rate is high, without the protection of the guide tube, the air flow directly washes the inner layer of the non-metallic ring belt, and the hole will be worn out in a few months. The function of the guide tube is to divert and protect the flow. The related problems of the expansion joint guide tube in this station are very clear. Remember to check whether the length and thickness match the inner diameter of the pipe when installing.
Don't just look at the sample when you select the model
Welding flange non-metal compensator is generally suitable for PN0.25~ PN2.5, beyond this range, metal corrugated expansion joint should be considered. The upper temperature limit depends on the material of the band: fluororubber can withstand 200℃, silica gel can withstand 300℃, and polytetrafluoroethylene can reach 250℃ but is more corrosion resistant. What really rolls over is the compensation amount matching-axial compensation is easy to calculate, but lateral and angular displacement is complicated. Refer to JB/T 12235-2015 National Standard for Non-metallic Expansion Joints, which clearly stipulates the maximum compensation amount of each structural form, and also requires type test. Don't take the maximum value on the manufacturer's sample directly, which is measured under ideal working conditions, and the actual discount is 0.7%.
Speaking of which, by the way, mention the difference between rubber compensator and rubber PTFE compensator. The rubber compensator relies on elastic deformation to reduce vibration and is suitable for water system; The rubber PTFE compensator is lined with polytetrafluoroethylene, which is more corrosion resistant but less elastic. The nonmetallic compensator with welded flange mostly uses fabric fiber composite structure, which is more resistant to high temperature and high pressure than pure rubber, but the cost is also high. When selecting the type, it must be according to the actual medium temperature, pressure and displacement. Don't think about one product packaging the world.
Compared to a metal compensator, where's this guy's temper?
Corrosion resistance is its trump card. Metal bellows are afraid of chloride ions and sulfides, and non-metallic bands don't care about these things at all. Vibration and noise reduction is also good. The fabric itself has great damping, which is not as easy to resonate as metal bellows. But weak pressure is also a dead hole-if it exceeds 2.5MPa, you have to consider metal. In large displacement occasions, it does not need corrugation, but all depends on the plane stretching and twisting of fabric bands. For example, in the hot air duct of cement industry, we replace the traditional metal corrugated expansion joint with rectangular non-metallic expansion joint, and the compensation amount is twice as large as that of metal parts of the same size, and there is no stress concentration point.
The outlet pipeline of the rotary kiln of the cement plant has a temperature of 800 ℃, a slight negative pressure and a large displacement. With the metal corrugated expansion joint in cement industry, multi-layer stainless steel corrugated pipe has to be used, which has large thickness and high cost, and is afraid of high-temperature oxidation and peeling. Replace with a rectangular non-metallic expansion joint with welded flange, the inner layer is made of ceramic fiber + stainless steel wire mesh, and the outer layer is made of silicone coated glass cloth. It has been running continuously for two years without any problems. There are also disadvantages-it can't be used in vacuum conditions, and it is easy to deflate. Therefore, this product is suitable for scenes of low pressure, corrosion and large displacement. If the high-pressure vacuum deviates, don't put it hard.