What exactly does the same corrugated expansion joint, with a layer of metal braided mesh, change?
Don't rush to look at the path and pressure yet. The biggest difference between metal woven corrugated expansion joints and ordinary corrugated expansion joints lies in the mesh sleeve woven with stainless steel wire. This layer of net is not decoration. It mainly does three things: pressure, protection and restriction of displacement. The wall thickness of the bellows itself is usually only a few tenths of a millimeter to a few millimeters, and its pressure bearing capacity is limited. The metal woven net sleeve is like a piece of armor, which hoops the bellows, and the internal pressure is shared through the net sleeve, so that the bellows will not burst like a balloon.
At the same time, the net sleeve can also block external mechanical damage and splatters. But you have to understand that adding a mesh sleeve is equivalent to putting a "tightening spell" on the bellows-the flexibility will decrease. For the same wave, the bare tube can be extended by 10mm, but the braided net may only be extended by 8mm. Therefore, the metal braided corrugated expansion joint is not a universal reinforced version, it is used in situations that need to withstand higher pressure, harsh external environment, or require additional safety protection.
Don't copy the model number first when you select the model, the working condition is the father
"How much is the metal braided corrugated expansion joint of DN500?" Can't answer. You have to clarify the medium, temperature, displacement direction, fatigue life requirements and installation space first. For the same model, the diameter pressure is the same, and the medium is changed from water to high-temperature steam, and the life may be reduced by half. Temperature directly changes the allowable stress and fatigue curve of materials. If the temperature is not calibrated during type selection, no matter how thick the woven net is, it will be useless.
The structure is also divided into three, six and nine classes. The universal corrugated expansion joint is suitable for ordinary low-pressure pipeline, and mainly absorbs axial displacement. Thermal insulation layer and guide tube are added inside the high-temperature axial expansion joint, which is used on the high-temperature flue gas pipeline, and a protective sleeve has to be added outside the woven net. The bellows of external pressure single type axial type expansion joint bears external pressure and has better stability, which is suitable for high pressure and large diameter axial compensation.
You find out the working conditions before talking about the model, otherwise it will be scrap iron when you buy it back.
The thicker the woven net is not the better, the design should be reasonable
The wire diameter, the number of layers, the number of strands and the way of connecting the end of the net sleeve of the woven net affect the stiffness. In the formula of bellows stiffness, the stiffness is proportional to the cubic of wall thickness. Adding a layer of braided net is equivalent to increasing the equivalent wall thickness, but the cost is a sharp decrease in compensation amount. The most typical overdesign is the hard sleeve of small diameter expansion joint with four layers of mesh sleeve. As a result, the compensation amount is only 30% of the design value, the thermal displacement of the pipeline can't be pulled, and the bellows is forcibly torn.
Cutting corners in turn is even scarier. A customer in a chemical plant used metal to braid corrugated expansion joints on compressed air pipelines. The supplier reduced the wire diameter of the mesh sleeve from 0.3mm to 0.2mm, and the number of braided strands was reduced by half. After less than two hundred days of operation, the net jacket will loose and the bellows will burst directly. Therefore, the parameters of the net jacket should be calculated according to the pressure grade and fatigue life, which is not stacking or saving materials.
If you install this step wrong, the gods can't save it
When the equipment goes to the site, the installation link is the hardest hit area. Pre-stretching is not done-originally, the expansion joint is preset with 10mm pre-deformation, so you can install it directly, take over a heat, and let the bellows carry all the elongation by itself, which greatly reduces the life span.
The placement of the guide bracket is also particular. The corrugated expansion joint can only move in the axial direction or in a plane. When you turn the pipe, you don't add a guide frame, and the lateral force is all eaten on the corrugated pipe. The tie rod nut is more typical. In order to prevent transportation damage when leaving the factory, the tie rod nut is locked, and the nut must be loosened to the specified size after installation. Two days ago, a customer called to say how the expansion joint leaked. In the past, the nut was still locked-the expansion joint was regarded as a rigid short tube, and the thermal expansion and contraction all depended on the hard top of the bellows, so it was strange that it didn't crack.
Don't expect one expansion joint to dominate the world
Metal braided corrugated expansion joint is resistant to high temperature, high pressure, corrosion resistance and long life, but it does not mean that it should be used in all working conditions. Rubber compensator and rubber PTFE compensator are cheaper when low pressure, large displacement and high demand for shock absorption, such as the inlet and outlet of water pumps. The vibration absorption effect of rubber compensator is better than that of metal, and it is half cheaper.
What about non-metallic expansion joints (fabric fiber expansion joints)? It can't withstand high pressure, but it can withstand high temperature above 1000℃, and the compensation amount is huge, especially suitable for large-diameter low-pressure pipelines such as rectangular flue and inlet and outlet of desulfurization tower. Metal rectangular expansion joint can be made on rectangular pipeline, but the cost is high and the weight is heavy; The fabric fiber expansion joint is lightweight, easy to install, and does not transmit force to the bracket.
Similarly, DN400 pipeline, 150℃ hot water, axial compensation 50mm, metal braided corrugated expansion joint life of about 2000 times, price about 3200 yuan; The life of the rubber compensator is about 800 times, and the price is 1200 yuan; The fabric fiber expansion joint is not temperature resistant enough, so it is directly excluded. However, if the medium is 300℃ flue gas and the pressure is only 0.05MPa, then the non-metallic expansion joint is the optimal solution, and the metal braided net can't bear the combination of high-temperature corrosion and dust wear.
In short, selection is not about looking for the model by turning through the manual, but about figuring out the working conditions, and then letting the manufacturer calculate it for you. Metal braided corrugated expansion joints are used correctly, and they don't have to be cared for for ten years; Use it wrong and play it out in three months. Do you know it yourself?