1. What's the matter with skin opening? Let's talk about the non-metallic expansion joints first
Who in our flue system hasn't encountered skin ungluing? To put it bluntly, it is where the non-metallic expansion joint is soft connected. The adhesive layer at the interface is cracked, warped, or even the whole piece falls off. And guess what? This thing looks scary, but most of the time it is not a fatal malfunction.
Non-metallic expansion joints (also called fabric fiber expansion joints) rely on multilayer composite materials to absorb the thermal displacement of pipes, and the skin is its "skin". Under normal working conditions, it should be firmly attached to the flange surface to separate the smoke from the outside world. Once the glue is opened, air and smoke leakage will be slight, and the pressure of the whole system will be unbalanced. But don't rush to scold the manufacturer, first find out why it opened glue.
2. Why does the interface open glue? Temperature, pressure, installation, which is the real murderer?
To be honest, most of the gluing was done by a partnership of three "killers". The first is the temperature-the flue always moves two or three hundred degrees. If the skin material is not temperature-resistant enough, or it runs at overtemperature for a long time, the adhesive layer will carbonize first and then lose its viscosity. The second is the pressure fluctuation, especially when the furnace is started and stopped, the instantaneous positive and negative pressure switch, which pulls the skin interface to death. The third most injustice-the installation is not in place. Have you ever seen one of those installers stretch the skin like a drumhead? Or paste the flange surface without cleaning it up? If you don't care about this, no matter how good the product is, you can't hold it.
Some non-metallic expansion joints are used on the spot, but the matched strips and bolts are made of wrong materials, and they are corroded and loose at high temperature, so the interface naturally opens. Therefore, don't just stare at the skin itself, but also check the peripheral attachments.
3. What should I do if the glue is opened? Don't be in a hurry to change, see if you can "make up" first
Don't panic if you find that the glue has opened. Assess the opening size and location. If only the edge is raised in a small area, and the medium temperature in the flue does not exceed 200℃, you can try on-site repair. Use professional high-temperature resistant silicone glue or repair tape to clean the opening area (be sure to be dry and oil-free), and then compact and stick firmly. It is best to add another metal strip to reinforce it, which is equivalent to putting a "band-aid" on it.
But pay attention, if the opening area has exceeded 30% of the total area, or the skin itself has aged and brittled, then don't make it up, just change it. In addition, when the flue gas contains acidic medium (such as the flue gas that has not been purified after desulfurization), the repair effect is very poor, because the residual acid will continue to corrode the glue layer.
By the way, we have the product information of "Rectangular Non-metallic Expansion Joint" and "Non-metallic Expansion Joint (Fabric Fiber Expansion Joint)" in our station. For repair materials and beading specifications, you can refer to the parameters of the accessories inside, so don't buy them blindly.
4. How to prevent glue opening? From selection to installation, a few details can avoid big pits
Prevention is much more worry-free than patching. When selecting a model, don't just figure cheap, ask about the temperature resistance grade and pressure resistance. For example, if the flue temperature is above 350℃ for a long time, you have to choose a multi-layer composite skin of silicone cloth + fluorine tape, which will definitely not be able to bear the ordinary rubber-based skin. In addition, the interface form is also critical-is it flange or plug-in? In the case of flange type, is the width of the bead sufficient? Is the bolt spacing too large? These details have been talked about in the "Industry Article", which can be turned over.
The flange surface must be flat, and the welding slag and burrs must be polished clean; When the skin is installed, leave a relaxation of 5-10mm, don't stretch too tightly; The bolts should be tightened in diagonal order, and the force should be gradually applied in 2-3 times to ensure that the pressure bar is evenly stressed. In addition, 80% of the cases of opening the skin interface of the flue expansion joint are related to reversing the direction of the skin during installation-pay attention to the arrow where the flue gas flows, and wait for the opening if it is reversed.
5. If it doesn't work, you have to change it. How to choose the right product? To show you the way
If the glue is so serious that it must be changed, don't fall into the pit when choosing a new piece. First, be sure to provide accurate flue operating conditions: temperature (maximum/sustained), pressure (positive/negative), media composition (with or without corrosive gases). Second, there are various brands and models of non-metallic expansion joints, but the core depends on the temperature resistance grade and layer structure. There are two series of non-metallic expansion joints (fabric fiber expansion joints) on sale in this site: standard type and high-temperature type, the latter of which can carry the instantaneous impact to 600℃. You'd better choose products that have third-party testing reports, and don't trust verbal promises.
In addition, if your system has both axial displacement and lateral displacement, you can consider using "Compound Hinge Transverse Expansion Joint" or "Rectangular Non-metallic Expansion Joint" for comprehensive compensation. When changing, check whether there is any problem with the sealing surface of the adjacent "Flue Gas Baffle Door" or "Desulfurization Flue Gas Baffle Door" by the way-many times, if there is a problem in one place, the next place will be injured.
In short, the opening of the skin interface of the flue expansion joint is not a terminal illness. Find out the cause and prescribe the right medicine, and it should be replaced. If you are not sure, just take a picture and send it, and we can help you consult.