What exactly is FPF? First distinguish the difference between it and the metal expansion joint
Non-metallic expansion joint FPF, to put it bluntly, is the kind of expansion joint with fiber fabric, rubber and fluoroplastic composite layer as loop belt. It is completely different from metal corrugated expansion joints-metal expansion joints deform by corrugated thin walls, while non-metals absorb displacement by stretching and twisting of flexible bands. You press the band with your hand and you can press it, that's right.
Corrosion resistant, dust resistant, not afraid of sulfur-containing flue gas. High nickel alloy should be selected for metal expansion joints in front of acidic media, and the cost will rise; Non-metal expansion joint FPF can be carried with ordinary carbon steel flange plus fluororubber lining. The "Non-metallic Expansion Joints (Fabric Fiber Expansion Joints)" and "Rectangular Non-metallic Expansion Joints" of this station all belong to this category. FPF is only a series code, and there is no general standard model. The specific size and number of layers depend on working conditions. So don't want to buy a standard part with the three letters "FPF", you have to report the parameters to the manufacturer.
Typical application scenarios: power stations, cement, desulfurization and denitrification
And guess what? The vast majority of non-metallic expansion joint FPF are buried in the pipes of power plant flue, cement kiln tail and desulfurization and denitrification system. These places have one thing in common-the temperature fluctuates, the medium is full of sulfur dioxide and dust particles, and the pipeline may be displaced laterally due to thermal expansion and contraction.
Metal Expansion Joints In this environment, bellows are prone to corrosion and have limited fatigue life. The non-metallic expansion joint FPF can absorb axial, transverse and angular displacements simultaneously, and the ring belt itself has no metal fatigue problem. With manual plug-in insulation doors, round baffle doors (double seals) and flue gas baffle doors, the thrust of the pipeline to the equipment interface can be reduced. The "soft connection" that the installation team master often says refers to it.
Three Parameters Most Easily Overlooked in Type Selection
The easiest place to overturn is not the pressure, but the temperature, displacement and media composition.
The temperature directly determines the belt material. Neoprene rubber is used below 130℃, silicone rubber is obtained around 200℃, and fluororubber or polytetrafluoroethylene coating is obtained if it is higher. When you report the temperature, don't just say "average temperature". You have to report the highest instantaneous temperature. In case the furnace is opened instantly at 300℃, the ring belt will be directly carbonized.
The displacement should be reported as the combined value of axial, transverse and angular directions. If one is missed, the ring belt may be cracked or pressed. The composition of the medium should also be made clear. Is there any acidic gas? Is it high dust? When the dust concentration is high, a guide tube and a wear-resistant layer must be added inside, otherwise the ring belt is equal to rubbing on sandpaper. Pressure is not the main contradiction. Non-metallic expansion joint FPF generally runs in low-pressure or atmospheric pressure systems. However, one point must be mentioned separately-the negative pressure working condition. If you don't tell me, the belt will be deflated, and that thing will hurt to look at.
Do not underestimate the direction of the guide tube during installation
The function of the guide tube is to guide the flow direction of the medium and protect the ring belt from being washed by high-speed airflow and particulate matter. It is directional, and the arrow must point to the direction of the media flow. Two days ago, I met a customer, and the scene was installed backwards. As a result, the circle belt was worn out for three months. When I remove it, I see that the high-speed smoke directly hits the fabric, which is not bad.
And transport rods. Non-metal expansion joint FPF will bring several tie rods to hold the ring belt for the convenience of transportation when it leaves the factory. After installation, remember to loosen the tie rod nut or adjust it to the working length. Many scenes forgot this, and the expansion joint became a rigid short tube, and the displacement of the pipeline was all held in the equipment interface. If the tie rod is not loose, it means that there is no expansion joint installed.
The core of maintenance is regular inspection of the belt surface
The loop is a wear part, and there's nothing to avoid. Metal expansion joint can also estimate the fatigue life of bellows, but non-metallic expansion joint FPF can't. The aging rate of ring belt has much to do with the actual working conditions, so it can only be seen by human eye.
Turn it around regularly during operation to see if the surface of the ring belt is scratched, aged and cracked, and if the bolts are loose. Once you find a leak, don't panic-the ring belt can be changed separately, and the flange and frame can continue to be used. This is much more economical than metal expansion joints. If the metal bellows leaks, basically the whole set will be scrapped.
So you say that non-metallic expansion joint FPF is worth choosing? In smoke, dust and corrosive situations, it is originally a more cost-effective scheme. The premise is that the parameters are reported accurately, the installation is not reversed, and the maintenance is diligently watched. Do these three things, and it can work honestly in the pipeline for several years. If you are still unsure, ask the manufacturer to dump the working condition data, and let the master who has done power station desulfurization help you calculate it.