Find out first: What does the metal mesh sleeve do in the expansion joint?
Many people contact the expansion joint of the metal mesh for the first time, thinking that the stainless steel mesh outside is to play a protective role to prevent bumps and scratches. It is small to think so-the net sleeve is responsible for bearing pressure and restraint, not as simple as wearing armor.
The metal mesh sleeve is usually sleeved outside the bellows and is woven with stainless steel wire. Its core role is to limit the radial deformation of the bellows while withstanding the axial tension generated by internal pressure. To put it bluntly, the bellows itself is flexible. When the pressure is high, it wants to bulge and expand outward. The net sleeve is the thing that hoops it. Without the corrugated expansion joint of mesh sleeve, the corrugated pipe is easy to bulge or even burst when the pressure is high. If you've ever seen the bellows explode under high pressure conditions, you know how important the mesh jacket is. In the final analysis, the net sleeve is to "support" the bellows.
How do mesh sleeves and bellows work together?
The mesh sleeve does not work alone. It forms a complete expansion joint with bellows, end tube and guide tube. For example, the general-purpose corrugated expansion joint and the high-temperature axial expansion joint of this station are inseparable from these cooperation in structure.
The weaving density, the number of strands and the wire diameter of the mesh jacket directly determine how high the pressure of expansion energy saving is. Think about it, can the specifications of the mesh sleeve be the same for the same expansion joint of DN100, PN1.6 and PN2.5? Definitely different. Under the working condition of PN2.5, the number of strands of the net jacket is more, the wire diameter is thicker, and the weave is denser, otherwise it can't be carried at all. There is no head-slapping in this, every parameter is calculated.
Which parameters should I look at when selecting?
Everyone who engages in engineering knows that when choosing expansion joints, you can't just look at the caliber. Pressure, temperature, medium and compensation amount, none of these four parameters can be less. The metal mesh expansion joint should pay special attention to the pressure grade, because the mesh sleeve is mainly for the service of pressure.
For example, the expansion joint used on the steam pipeline has a working pressure of 1.6MPa and a temperature of 300℃. At this time, the corrugated expansion joint with mesh sleeve is candidate, and the mesh sleeve has to be woven with multiple strands of stainless steel wire, and the end must be reliably welded or fixed by snap ring. If the installation position is still limited by space, it may be necessary to consider the double hinge transverse type or the external pressure single axial type. Both of these structures have product data at the site. The former is suitable for the occasion of large lateral displacement, and the latter is suitable for the working condition of large axial compensation and stable external pressure.
Medium. If the medium is corrosive, the stainless steel wire material of the mesh sleeve has to be adjusted. The corrosion resistance of 304 and 316L is a bit worse, and it is all troublesome to choose the wrong one.
What is the relationship between metal mesh expansion joint and metal hose and corrugated expansion joint?
To be honest, these three concepts are often mixed, and there are many cases where the wrong name is written on the purchase order. There are metal hose products in this site, as well as general-purpose corrugated expansion joints, all of which may have mesh sleeves.
What's the difference? Metal hoses are mainly used to absorb vibration and displacement, and mesh sleeves are standard; The corrugated expansion joint is mainly used for pipeline thermal compensation, and the mesh sleeve is selected according to the pressure working condition. When you look at the model of the expansion joint, the one with the mesh sleeve will usually be marked in the code, for example, metal braided mesh is added outside the bellows. If you can't figure this out, it's easy to buy the wrong one when purchasing. Buying the wrong is not a problem of returning or exchanging goods, but a problem of pipeline system safety.
What to pay attention to during installation and maintenance?
The worst fear of mesh sleeves is wear and local stress. When installing, the pipes at both ends of the expansion joint must be centered, and the mesh sleeve cannot be subjected to twisting force. Many people don't care about this detail, and think it is OK to install it. In fact, if the pipeline is misaligned, the net sleeve will wear off, and it won't take long to break the wire.
Also, if there are scratches or broken wires on the surface of the mesh sleeve, you have to be careful. Broken wire is not a trivial matter, which means that the local part has been overloaded. If you need to change it, don't think about making do. In addition, the function of the guide tube should not be ignored, especially in pipelines with granular media. The guide tube can protect the inner wall of the bellows, and the net sleeve can protect the outer wall. Only when the inside and outside are protected, can the expansion joint last for a long time.
In the final analysis, metal mesh expansion joints are not all-purpose
But when you use it in the right place, it can do a lot. If it is a pipeline with low pressure and normal temperature, ordinary corrugated expansion joints are enough, but adding mesh sleeves will increase the cost. However, if it is high-pressure steam, hydraulic system or shock vibration, the expansion joint with mesh sleeve is just needed.
Before selection, it is best to send the working condition parameters to the manufacturer and let the engineer help you calculate. In the product information of expansion joints in this site, such as straight pipe pressure balance type and curved pipe pressure balance type, these structures are particularly matched with net sleeves, so don't pat your head to decide. Pressure level, compensation amount, installation space, these factors are related to each other, and they can't be solved by a simple formula.
Before, there was a customer with a steam pipeline pressure of 2.5MPa and a temperature of 350℃. At first, he chose an ordinary corrugated expansion joint without mesh sleeve, and the bellows bulged after less than two months. Later, it was replaced with a metal mesh sleeve expansion joint with a mesh sleeve. Under the same working conditions, it ran for more than a year without any problems. The wire diameter of the mesh jacket was thickened from 0.3mm to 0.5mm, the number of strands was increased from 12 strands to 24 strands, and the weaving density was also increased from 70% to 85%. When the parameters change, the effect is completely different.
So, the metal mesh sleeve expansion joint does not work? It works, but only if you choose the right type and install it in the right place. Pressure, temperature, medium and compensation amount, these four numbers are given to the manufacturer, and professionals can help you calculate them, which is much more reliable than patting your head yourself.