1. Find out first: What role does the skin play in the fabric nonmetallic compensator?
To put it bluntly, the skin is the core seal of the fabric nonmetallic compensator. It directly contacts the medium, is responsible for absorbing the thermal displacement of the pipeline, vibration isolation and noise reduction, and at the same time firmly seals the smoke, dust and corrosive gas in the pipeline. Think about it, the whole set of equipment costs tens of thousands. If the skin leaks first, the compensator will be wasted-almost like the broken screen of the mobile phone, and the money for replacing the screen is almost catching up with the price of the mobile phone.
Once the skin is damaged, it will leak from running air and soar energy consumption, and in the worst case, high-temperature smoke will be sprayed out, burning out the surrounding instrument cables and even causing safety accidents. Two days ago, a cement factory customer complained to me that the rectangular non-metallic expansion joint at the tail of their kiln was used for less than half a year, and the skin bulged and cracked. When I removed it, I saw that the inner PTFE had been worn down by high-temperature coke particles. It is not expensive to replace a skin, but it loses hundreds of thousands a day when it is discontinued. Do you think it is worth it?
2. One floor or five floors? The structure of skin and the matching of materials are a discipline
Don't think the skin is just a piece of cloth. Regular fabric non-metallic compensator skin, usually a five-layer structure, each performing its own duty:
- outer layer: Silicone coated fiberglass cloth or fluororubber cloth, weather-resistant, corrosion-resistant, UV, acid rain and temperature shocks.
- Thermal insulation: Ceramic fiber blanket or aerogel felt with a thickness of 10~50mm, blocking high temperature conduction to the metal frame.
- Sealing layerPolytetrafluoroethylene film or PTFE cloth to ensure zero gas leakage, especially in sulfur-containing working conditions.
- Reinforcement layer: Stainless steel wire mesh or high-strength glass fiber mesh cloth, which provides tensile strength and tear resistance, and depends on it to support negative pressure conditions.
- inner layer: High temperature resistant silicone or fluororubber cloth, directly facing the pipeline medium, must be resistant to erosion and wear.
Is it that more layers are better? Not. For example, at the entrance of the desulfurization tower of a power plant, the medium has high humidity content and low temperature. You have to pile five layers of ceramic fibers, but it is easy to absorb moisture and collapse. It is better to use a three-layer structure + reinforced core material. In turn, the temperature of the hot air duct of the blast furnace in the steel mill is 800℃, and you only use two layers of silica gel cloth, and it will be carbonized in three months. When selecting a model, matching is a hundred times more important than thickness.
3. Can the skin bear under high temperature, corrosion and negative pressure conditions?
Generally, silicone cloth can withstand 250℃, fluorine rubber cloth 300℃, and ceramic fiber blanket can achieve more than 1000℃. But don't forget, the skin is a composite, and the temperature resistance of each layer must be matched-you use fluororubber for the outer layer, but ordinary glass fiber for the inner layer. As soon as the temperature rises, the inner layer turns to ash first. A domestic petrochemical project once stumbled in this pit, and later it could only be replaced with a non-metallic expansion joint (fabric fiber expansion joint) model with higher temperature resistance.
Sulfur oxides and hydrogen chloride in flue gas are dilute sulfuric acid when they meet condensed water. Conventional fiberglass lasts less than half a year in this environment and must be lined with PTFE compensator grade or fully isolated with PTFE cloth. Some manufacturers fool customers into using "acid-resistant coating", but in fact, the coating is finished as soon as it falls off. The negative pressure working condition is more insidious-the pipeline management suction is large, and if the reinforcing layer of the skin is not enough, it will be directly concave and squeezed to death, resulting in the failure of the expansion joint. We encountered an air-cooled island project. The negative pressure of the vacuum special hose system reached-50kPa, and the ordinary skin deflated in 3 days. Later, the customized skin with stainless steel wire mesh reinforcement was changed to stabilize.
4. Installation and routine maintenance: Where is the "dead hole" of the skin?
Non-metallic expansion joints are usually pre-compressed when they leave the factory to compensate for pipe cold shrinkage. Some installation teams plan to save trouble, and it is done as soon as the screws are screwed. In winter, the pipeline shrinks and the skin is directly cracked. The correct way is to adjust the flange spacing according to the installation length provided by the manufacturer, and then lock it with the tie rod nut.
Let's talk about bolt tightening torque. The skin flange is a soft connection, the bolts are tightened too tightly, the pressure ring is deformed and even the skin root is crushed; Screw too loosely, leak and run out of gas. The standard practice is to tighten diagonally three times with a torque wrench, and the torque value is controlled at 20~40N·m, depending on the skin thickness and material. Daily maintenance focuses on two points: first, appearance inspection to see if there is any bulge, crack and delamination on the surface; The second is to listen to the air leak sound and test the leak with soapy water or smoke. If you find a small damage, plug it immediately with silicone repair agent. Don't wait until there is a big smoke before changing it.
5. When choosing the skin, don't just look at the thickness: it is a serious thing to select the type according to the working conditions
Many people ask "how thick is the skin" when they buy it. It seems that if it is thick, it will be durable. However, in reality, the life of 2mm thick imported fluororubber cloth plus ceramic fiber composite skin may be 10 times longer than that of 8mm thick inferior silicone cloth. The core of the selection is three points: temperature, medium composition, pressure/negative pressure. For example, the pipeline behind the desulfurization flue gas baffle door has a temperature of 80℃, saturated humidity and chloride ions. The best solution is PTFE layer + silica gel cloth +316 stainless steel mesh reinforcement. If the high-temperature pipeline of cement kiln head is 800℃, then you have to use ceramic fiber blanket + high-temperature resistant alloy wire mesh, and the outer layer is thick coated fluororubber.
In the same working condition, the skin structure of different manufacturers may be very different. Regular manufacturers generally provide detailed material specifications, including the material, thickness and temperature resistance limit of each layer. When you compare it with the actual working parameters, you will know that it is a mule or a horse. In the final analysis, choosing a skin is choosing a fitting protective clothing for the pipeline system. Fit is more important than good-looking, and durability is more important than cheap.
When the skin is broken, the whole fabric non-metallic compensator is wasted. Therefore, next time you choose or replace, spend more time on this "cloth", which is definitely not a loss.