Is the non-metallic expansion joint wire layer inside or outside? Wrong location, the consequences are serious
The wire layer is usually not in the outermost layer, but hides in the middle or inside. Many people look at the picture and think that the shiny layer outside is steel wire. In fact, it is an outer protective cloth or metal mesh sleeve. To be honest, I have encountered many customers who regard the steel wire layer as an anti-wear layer and have to ask for it to be put outside. As a result, it wore out in less than half a year. The real steel wire reinforcement layer-which we often call stainless steel wire mesh or galvanized steel wire mesh-is sandwiched betweenNon-metallic expansion joint (fabric fiber expansion joint)Between fluorine tape, silicone cloth and fiberglass cloth. The purpose is to give it a skeleton so that the soft non-metallic layer can withstand the positive and negative pressures in the pipeline, without bulging or deflating like a balloon.
Why do you have to add this layer of steel wire? To put it bluntly, the non-metallic expansion joint itself is a pile of fabric and rubber, and has limited tensile strength. When the internal pressure of the pipeline runs, there is no steel wire layer to cover the bottom, and the expansion joint will deform and fail directly. Wire layers are like steel bars in concrete, dispersing axial and radial forces. For specific data, you can refer to this siteNational Standard for Non-Metallic Expansion Joints JB/T 12235-2015Which clearly specifies the material and arrangement of the reinforcing layer. Also, something likeRectangular non-metallic expansion jointFor this large cross-section, the steel wire layer has to be densified and thickened, otherwise the stress at the square corners will be concentrated and it will be easy to tear.
However, the position of the steel wire layer is not static, it depends on the working conditions. For example, in the desulfurization flue gas pipeline, the medium contains acid and humidity. At this time, the steel wire layer usually leans against the inner layer, and several layers of corrosion-resistant polytetrafluoroethylene or EPDM rubber are wrapped outside to prevent acidic gas from directly corroding the steel wire. On the other hand, if the pipeline is running under negative pressure (such as the air cooling system of a power station), the steel wire layer has to be close to the outer surface, and the inner layer is used with a more flexible silicone cloth to absorb the negative pressure deformation. Two days ago, a customer in the cement industry asked, saying that they usedMetal Corrugated Expansion Joints in Cement IndustryGet used to it, and I am afraid that it will not be durable if it is replaced with non-metallic. I told him that if the layout of non-metallic steel wire layer is reasonable, the life span is not bad at all.
What are you most afraid of? I am most afraid of installing the steel wire layer in the wrong position. There was a power plant project before, and the installer saved the trouble by installing the non-metallic expansion joint in reverse, with the steel wire layer facing outward. As a result, within two months of operation, the outer fabric was worn out, the steel wire was exposed, rusted and broken, and the whole expansion joint directly leaked and stopped. In addition, there is also a situation that the steel wire layer is designed too inward and too close to the medium, and the high-temperature gas (over 400℃) burns the steel wire soft and loses its reinforcing effect. Therefore, when you buy, you must tell the manufacturer clearly about the medium temperature, pressure, positive and negative pressure, and don't just stare at the price. In the industry customer cases of this site,Flue gas baffle doorThe matching non-metallic expansion joint is specially aimed at the high-temperature dusty air flow to optimize the position of the steel wire layer.
Then how do you judge which category you should choose? Simple and rude method: Look at the nameplate or drawings. Regular manufacturers like us will make arrows on the flange on the non-metallic expansion joint to indicate the flow direction of the medium. If you are really worried, take a bright flashlight and take a look at the cross section-the reflection of steel wire mesh and the diffuse reflection of fiber cloth can be distinguished at a glance. If you buy it back and find that the steel wire layer is outside, and there is dust washing under the working condition, install the external sheath quickly. Finally, a reminder: Don't believe the nonsense that "the steel wire layer is universal inside and outside". The structural design of non-metallic expansion joints is calculated by stress. If the position is wrong, no matter how large the compensation amount is, it will be useless.