What job does silicone cloth carry in a non-metallic compensator?
Let's be honest first-many users ask "How to use silicone cloth for non-metallic compensator?" As soon as they come up, thinking that this thing is like plastering, just tear it open and stick it on. Tsk, it's so simple, the equipment factory has long gone out of business.
Silicone cloth is the core skin material of non-metallic compensators (also called fabric fiber expansion joints). It does three things:Temperature resistance, sealing, displacement absorption。 For example, in the smoke duct of power plant and the hot air duct of cement plant, the medium temperature always soars above 300℃, ordinary rubber can't bear it, and the metal is too hard to absorb large displacement. At this time, silicone cloth comes in handy-the silicone rubber coated on its surface can bear high-temperature oxidation, and the glass fiber base cloth provides strength. After the combination of the two, it can deform softly without being burned through.
But don't think it's all-purpose. Two days ago, I met a customer who used a silicone cloth skin in a flue gas pipe containing concentrated sulfuric acid. As a result, it rotted in three months. Why? Silicone cloth is acid resistant but not strong acids, especially organic solvents. If the corrosiveness of the medium is not clear, it will be useless to change any material.
When choosing silicone cloth skin, don't just look at the thickness: temperature, pressure and medium corrosiveness are the key parameters
Many purchasers ask "How thick is it?" as soon as they pick up the silicone cloth. Every time I want to ask back: Where are you buying a quilt? Thickness is of course important, but what is more critical are the following three parameters. One less is easy to step on pits.
- Temperature: The temperature resistance range of silicone cloth is generally-60℃ ~ +250℃, and the special formula can reach 300℃ for a short time. If the medium temperature exceeds 250℃, composite polytetrafluoroethylene (PTFE) membranes or other high-temperature resistant layers should be considered. Don't believe the nonsense of "almost working". If the temperature exceeds the standard of 100℃, the life may be shortened by 80%.
- pressure: The non-metallic compensator itself is not resistant to high pressure, and is usually used in smoke and air systems with positive pressure ≤0.1MPa. If the pressure exceeds 0.15MPa, it can't be supported by silicone cloth skin alone, so it is necessary to add stainless steel wire mesh reinforcement layer or use metal compensator instead. For specific parameters, refer to this site'sNon-metallic expansion joint (fabric fiber expansion joint)Product page, where detailed pressure-temperature curves are available.
- Medium corrosivity: This is the easiest place to roll over. Silicone cloth has good resistance to weak acid, alkali and salt spray, but when it encounters strong oxidizing acid (such as concentrated nitric acid) and halogen gas (such as chlorine), it will bubble and crack in minutes. At this time, either change the fluorine rubber coating or please come outPTFE compensatorTo the rescue.
Also, don't forget to watchNational Standard for Non-Metallic Expansion Joints JB/T 12235-2015, which clearly stipulates the peel strength, aging performance and other test methods of skin materials. When purchasing, don't just look at the thickness. If you want to open your mouth, ask the supplier for the temperature resistance grade and media compatibility experiment report-this is what veterans should do.
The 3 most overlooked details before installation: storage environment, flange surface treatment, and tie rod pre-adjustment
After the silicone skin arrives, don't rush to the pipeline. These three details are not done properly, and it is also a ticking time bomb when loaded.
First, the storage environment.Silicone cloth is afraid of ultraviolet rays, ozone and humidity. If you leave it in the open yard for a month, and the surface is cracked and then loaded, can it still be called compensation? It should be placed indoors in a cool and dry place at a temperature not exceeding 40℃, away from heat sources and chemicals. It is best to check the production date when entering the factory, and don't use old materials that have been in stock for two years.
Second, flange surface treatment.The non-metallic compensator is sealed by clamping the skin with a flange. If there are welding nodules, burrs and unevenness on the flange surface, it is the air leakage point when pressed. Before construction, it must be polished and smoothed, and the oil and iron debris must be cleaned up. The most outrageous case I have ever seen-the old sealing strip left over from the last overhaul is still stuck on the flange surface, and the new skin bulges when pressed onto it.
Third, tie rod pre-adjustment.Non-metallic compensators generally come with a tie rod (also called a limit device), and the tie rod nut is pre-tightened to the installation length when it leaves the factory. Before installation, make sure that the tie rod is not loose or deformed due to transportation. How exactly to adjust? Refer to the FAQ on our siteHow to adjust the tie rod nut of expansion joint》: First loosen the locking nut, let the tie rod be in a free state, wait for the compensator to be aligned, then re-adjust to the designed length, and finally tighten the lock nut. Don't be too troublesome, this step is saved, and the later compensator may directly break the pipeline.
Installation of non-metallic compensator silicone cloth: From hoisting alignment to bolt tightening torque
OK, now to the chase-how to use non-metallic compensator silicone cloth? Do it hand-by-hand.
Hoisting alignment:Use a sling or soft rope, and it is strictly prohibited to strangle the wire rope directly on the skin. Let the compensator and the pipe flange naturally connect first, and do not force it with bolts. If the misalignment exceeds 2mm, adjust the pipe support instead of hard pulling the compensator. Ensure that the compensator is in a free state (without twisting, deflection) when aligning, otherwise additional stress will occur during operation.
Bolt tightening:This is the most problematic link. Many people used wind cannons to snap tightly when they came up. As a result, the skin was squeezed into deformation and the seal failed. Correct practice: Tighten symmetrically in 3-4 times, and the final torque is according to the design value (usually 40-60N·m, depending on the bolt specification and skin thickness). The tightening sequence refers to the cross diagonal method of flange bolts, first inside and then outside. Remember one principle:Compress but not kill。 The silicone cloth skin requires a certain amount of compression to seal, but excessive compression can reduce the fatigue life.
Tie Rod Adjustment:After the bolts are screwed, check that the tie rod still maintains the factory pre-adjusted length. If the pull rod is unevenly stressed due to pipe displacement, it is necessary to re-adjust the nut position to ensure the normal limiting function. This step can be referred toCorrect installation method of expansion joint of large tie rodKey points in: Keep a 2-3mm gap between the tie rod nut and the ear plate to avoid rigid constraints.
Pressure test and inspection:After the installation is completed, carry out an air tightness test (≤1.25 times the design pressure), focusing on checking whether there is air bubble leakage at the flange joint. If there is no condition to do the air pressure test, you can also do a light inspection-illuminate one side of the compensator with a flashlight, and observe whether or not light is transmitted on the other side. Once light leakage is discovered, stop the machine immediately to re-tighten or adjust the gasket.
Installation is not the end point: aging cycle, leak troubleshooting, and replacement timing of silicone cloth
It's all right when you install it? Wrong. The lifetime of a non-metallic compensator is largely dependent on post-curing.
Aging Cycle:The theoretical life of silica gel cloth is 3~5 years under normal working conditions (temperature ≤200℃, no strong corrosive medium), but it is greatly influenced by environmental factors. For example, in the back section of the desulfurization flue gas baffle door, the humidity is high, the acidic condensate is large, and the life may only be 1~2 years. It is recommended to check the skin surface every 6 months to see if there are blisters, cracks, stiffness or exposed fibers. Once these signals appear, it means that the silicone cloth has entered the end of its life.
Leak Troubleshooting:In daily operation, if there is an abnormal temperature rise around the compensator (more than 10℃ higher than the surface of the pipe) or a hissing sound is heard, the seal failure can be basically judged. At this time, don't rush to change the whole skin. First, check whether the flange bolts are loose and whether the tie rod is stuck. A lot of times tightening the bolts will solve it. If the skin itself is broken, consider replacing it-but be aware that changing only a single skin may cause secondary leakage due to the different expansion coefficients of old and new materials. It is best to replace the whole compensator together.
Replacement timing:Don't wait until it leaks into a jet plane. When any of the following conditions occur on the skin surface, it is recommended to stop the machine immediately for replacement: ① The exposure of the fabric layer exceeds 5% of the total area; ② The peeling depth of the coating exceeds 1 mm; ③ Penetrating holes or cracks appear. Remember to release pressure and vent before replacing. After removing the old skin, check whether there is rust on the flange surface. If necessary, remove rust and paint. Check the batch number before installing the new skin and avoid mixing different batches of products (due to different degrees of vulcanization).
How to use non-metallic compensator silicone cloth? In fact, there are three core points-choosing the right materials, installing the right process and maintaining the right time. Understand these three points thoroughly, and your plumbing system will have at least 80% less leakage problems. Don't believe it? Try it.