Find out why you want to choose a non-metallic expansion joint first-what is the difference between it and metal?
Two days ago, a customer who was a cement factory called and asked, saying that the temperature of their dust removal pipeline was not high but the medium was highly corrosive. They chose the metal corrugated expansion joint, but it leaked after half a year. In this case, non-metallic expansion joints (fabric fiber expansion joints) should be applied. The biggest advantages of non-metals are corrosion resistance, good vibration reduction, can absorb multi-directional displacement, and the price is relatively cheap. However, many people are planted in the configuration: either the temperature is incorrectly calculated during selection, or the direction of the guide tube is reversed during installation. Let's start with the underlying logic of configuration today.
Configuration Level 1: Find out the working condition parameters, one less won't work
To configure non-metallic expansion joints, you have to get four numbers first: maximum operating temperature (both continuous and instantaneous), media composition (acid and alkali flue gas? Dust content?), pipe displacement (axial, transverse and angular displacements respectively), and diameter size. Taking the rectangular non-metallic expansion joint used in power station industry as an example, the temperature of desulfurization flue gas is usually 80-120℃, but it can rush to 180℃ instantly when starting and stopping. When configuring, the band material has to be fluororubber-coated glass fiber cloth with a temperature resistance of more than 200℃ instead of ordinary silicone cloth. In addition, the pressure is generally very low (0.05-0.1MPa), but if used in positive pressure pipelines, anti-pull-off wire ropes or limit rods must be installed. If one of these parameters is missing, there will be problems during later installation.
Material configuration is the real test of expertise
The innermost layer is a temperature-resistant and corrosion-resistant layer (PTFE or fluororubber), the middle is a reinforcing layer (fiberglass cloth, aramid cloth), and the outer layer is a protective layer (silicone coating or stainless steel wire mesh). There is a common misunderstanding when configuring: many people only look at the total thickness, not the matching of layers. For example, the metal corrugated expansion joint in the cement industry is replaced with non-metal, and the medium contains hard particle dust. You must add a layer of wear-resistant ceramic fiber felt in the inner layer, otherwise it will be worn out in three months. There are also sealing gaskets at the connection of flanges. Don't use asbestos pads for cheap, but replace them with PTFE-coated pads or flexible graphite pads, which will last twice as long. In addition, the rubber compensator and rubber PTFE compensator of this station also belong to non-metallic categories, but the materials of the ring belts are different, so don't mix them-rubber has limited temperature resistance, and PTFE has stronger corrosion resistance, each with its own strengths.
Dimensions and connections: You don't just measure the diameter and you're done
The configuration logic of rectangular non-metallic expansion joints and round non-metallic expansion joints is not quite the same. The stress at the corner of the rectangular part is concentrated, so the radius of the fillet should be counted in the configuration. Generally, R ≥50mm, otherwise the ring belt will easily tear at the corner. The connection mode is divided into flange type and plug-in plate type: flange type is suitable for large diameter, and the bolt spacing cannot exceed 150mm, otherwise the seal is not tight; Plug-in style is suitable for small space installation, but care should be taken to reserve enough operating space. In addition, the installation length should allow for the amount of pre-stretch-the exact amount of stretch depends on the pipe thermal displacement calculation, usually the amount of pre-stretch is half the total compensation. Don't believe in "just put it on". Without pre-stretched expansion joints, the life will be halved directly. In the product information of rectangular non-metallic expansion joint of this site, the standard length and pre-stretching coefficient are marked, so it is correct.
Installation Details: 99% of Leaks Are Wrong Here
Install deflection and deflector backwards. The guide tube must be facing the direction of media flow. If it is installed backwards, the vortex will directly scour the inner wall of the ring belt, which will take less than two months. Another type of high-incidence fault is the uneven bolt tightening torque-the specification requires that the torque wrench be tightened diagonally 2-3 times, and many people directly hit the wind cannon to the end, resulting in flange deformation and leakage. One more point: non-metallic expansion joints cannot bear the weight of the pipe and must be provided with separate brackets on both sides. Most of the on-site failure cases are related to this inattention. And guess what? A master of a power plant told me that they used the expansion joint as a support before, but the band was directly torn and repaired for half a month.
Don't slap your head on the maintenance cycle, set it according to the working conditions
A customer disassembled it and inspected it once every six months, and found that the ring belt was intact, which was a waste of labor. The actual maintenance cycle can be determined according to the corrosiveness of the medium and the start-stop frequency: clean flue gas once a year, sulfur flue gas once every six months, and cement mill dust collection pipeline once a quarter. Inspection focus: the loop has no blistering, delamination and hardening; Whether or not the flange bolt is loose; The guide tube is perforated with or without wear. If the band is found to be partially damaged, it can be patched in an emergency manner (glued with the same material), but the whole strip must be replaced within three months. Don't think about patching for a year-non-metallic material aging is holistic, and local patching won't solve the underlying problem. It can also be seen from the common QA of this site that the service life of the expansion joint is directly linked to the configuration, installation and maintenance, so don't expect it once and for all.
In the final analysis, the configuration of non-metallic expansion joints is a systematic project, with parameters, materials, dimensions, installation and maintenance linked one by one. Whichever step you skip, you'll have to fix it later. Next time, when you encounter dust removal pipeline, desulfurization flue or fan inlet and outlet, don't rush to place an order. First, clarify these four elements. Right configuration, the cost performance of non-metallic expansion joints is absolutely beating metal bellows.