Why should non-metallic compensators be sealed with glass glue-not just plugging leaks
Run and leak? That's a superficial problem. What really kills is that dust, moisture, and corrosive gases drill down the gaps into the fibrous layers of the non-metallic compensator. Non-metallic expansion joints (such as the non-metallic expansion joints (fabric fiber expansion joints)) are composed of multi-layers of flexible composite materials, which usually rely on the ring belt body to bear pressure. But the seam between the installation flange and the pipe-don't expect a rigid connection like a rubber compensator or metal bellows to fit perfectly-process deviations, thermal expansion and contraction can make that seam "open". The core value of glass glue seal is not to plug that little air leak, but to add a layer of "skin" to the most fragile joint surface of the compensator, so as to isolate the corrosive medium from slowly eroding the fiber cloth layer. To put it bluntly, if the non-metallic compensator you spend a lot of money on is not sealed properly, the life will be directly discounted in half.
Core Principles of Glass Glue Sealing: Balance between Flexible Compensation and Interfacial Bonding
Why do you have to use glass glue? Can't you stick it to death with structural glue? Structural glue is hard. As soon as the pipe expands, the glue layer will directly crack. Glass glue (silicone sealant) is naturally elastic, and the elongation can achieve 300% or even higher. This is the key. The non-metallic compensator itself is designed to absorb axial and angular displacement. If the sealant is not elastic, it is working against the compensator-you expand and I carry it hard, and the result is degumming and cracking. But too much elasticity will not work: the adhesion is not enough, and it will fall off by wind and sun. So balance. Two points should be taken into account when selecting glue: one is the bond strength with the adhered substrate (usually galvanized steel plate, stainless steel or coated surface), and the other is the displacement capacity. Generally, the displacement of the pipeline compensator is within ±15mm, so it is enough to choose a sealant with 25-level displacement capacity. Remember, it's not the more expensive the better, it's matching the working conditions.
Three steps in place: standard construction process for glass glue sealing of non-metallic compensators
Regardless of whether you are maintaining the corrugated expansion joints in the power station industry or the metal corrugated expansion joints in the cement industry, the process is the same, so don't be lazy.
- Step 1: Clean up the interface.Take a wire brush or angle grinder with louver blades, and clean all the aging glue layer, rust and oil stains on the edge of the flange surface and compensator ring belt. Be sure to reveal the true color of metal, and there is no floating ash or oil film on your hands. Finally wipe it over with acetone or industrial alcohol.
- Step 2: Primer + Stick Mask Paper.Silicone glue penetrates too quickly into porous media (such as fibrous fabric), which easily causes the glue layer to become thin and lose elasticity. First, brush a matching primer on the side of the compensator ring band, and wait for 10 minutes for the surface to dry. Then stick masking paper on the edge of the flange-99% of people in this step don't stick it because it is troublesome, and the resulting glue is crooked, ugly, and easy to hide dirt.
- Step 3: Size + Scrape Flat.Use a glue gun to punch evenly along the gap, be careful not to hit too full, and just fill the gap after extrusion. Then use a scraper or a finger dipped in soapy water to scrape it flat to ensure that the glue and the interface on both sides are fully soaked. Finally, tear off the masking paper and wait 24 hours to cure. Don't let the pipe vibrate during the period, and don't have water.
Three main culprits of seal failure: wrong glue selection, interface treatment and curing conditions
This topic is tearful if I talk about it too much. Two days ago, I met a customer who used neutral silicone glue with a nominal temperature resistance of 200℃. As a result, it was installed on a non-metallic compensator next to the flue gas baffle door, and it was powdered in two months. After checking, although the actual operating temperature is only 150℃, there is a large amount of SO2 and condensed water in the flue gas-the acidic environment directly corrodes the glue. Glue selection should not only look at temperature, but also look at chemical tolerance. Interface treatment is even more nonsense: many people clean it up even if they shovel it a few times with a blade. As a result, the residual glue is not cleaned up, and the new glue sticks to the old glue, and it takes off as soon as it is pulled. As for the curing conditions-humidity below 40% or temperature below 5℃, silicone glue cures ridiculously slowly or even does not cure. In winter, outdoor construction in the north must be heated by a shed, otherwise it will be in vain. If any of these three items are not achieved, the probability of failure will increase by 80%.
Glass glue seal vs rubber gasket seal-each has its own field
Does the non-metallic compensator flange seal use glass glue or rubber gasket? This is not a choice of two questions. Rubber gasket (such as the structure of rubber compensator) is suitable for occasions with low working temperature, clean medium and high flatness of flange surface, such as air conditioning water system and low-pressure air duct. However, because the gasket is sealed by compression force, the flange bolt needs to be tightened regularly, and the gasket is easy to harden and shrink after aging, resulting in leakage. The advantage of glass glue sealing lies in its strong adaptability on the spot: uneven flange surface, uneven bolt preloading force, and glue can fill the gaps. It is especially suitable for dirty and messy working conditions such as flue gas, hot air and dust-such as behind the baffle door of desulfurization flue gas and the connection of air ducts in cement industry. However, glass glue is not a panacea: flanges that are frequently disassembled and assembled cannot be glued (they will be wasted once they are torn), and the pressure bearing capacity of glue is limited when sealing under pressure (generally less than 0.01MPa). The suggestion is: use gaskets if you need multiple frequency maintenance, and use glass glue if you install them at once and don't want to move again. If possible, the combination of the two is the most stable-gasket first and glue, double insurance.
Maintenance and Glue Change Cycles: When is it time to reapply glass glue?
Silicone sealants are not done once and for all. Ultraviolet rays, temperature cycles, and medium erosion will make it slowly harden and crack. So when should I change? Two hard indicators: First, visual inspection found tortoise cracks on the surface of the glue, or it felt obviously hard and lost elasticity when pressed by hand. Second, during the operation, it was found that dust accumulated in strips on the edge of the flange, and there was actually a micro leak. The adhesive change cycle is divided according to the working conditions-indoor room temperature pipeline: 3-5 years; Outdoor open air (including UV exposure): 2-3 years; High temperature flue gas (like the area near the corrugated expansion joint used in the power station industry): It is recommended to inspect it once a year and replace it in 2 years. Don't wait until it leaks before replacing it. The air leakage is accompanied by corrosive medium infiltration into the ring belt, and the replacement cost will be 10 times after the compensator body is damaged. Therefore, during regular inspection, take a flashlight to shine on the flange seam to see whether the color of the glue is uniform and whether it is peeled off, and knock it easily-if it is hard, it has to be changed. Get used to it, it's easier than checking air leaks.