Flue expansion joint skin leakage? Don't panic, follow these 5 steps to troubleshoot and fix

Two days ago, I met a customer, and I called in a hurry to say that the skin of the flue expansion joint leaked again, and the ash at the scene turned into "artificial fog". Tsk, this is too common in power plants, cement plants, chemical plants. If the skin leaks, you will be fined for shutdown at least, and your scalp will be numb if you are found by environmental protection at worst. What about that? Don't panic, follow these 5 steps and you can take care of it yourself.

First, find out why the skin leaks: common causes and on-site self-inspection methods

Skin leakage, to put it bluntly, means that the soft connection part of non-metallic expansion joint (also called fabric fiber expansion joint) can't bear it. The reasons are as follows:

• Temperature over limit:Designed to withstand 200℃, you dry to 280℃ for a long time, the fluororubber layer is directly carbonized, and it will break when you pinch it.
• Chemical corrosion:The desulfurization flue gas contains sulfuric acid dew point, and the PTFE film in the inner layer of the skin is slowly bitten through.
• Mechanical damage:During installation, the guide tube is not aligned, or the pipe vibrates too much, and the skin is rubbed out of the hole.
• Aging Natural Cracking:After three or five years of use, UV + thermal oxygen aging, it's weird that it doesn't crack.

After shutting down, spray soapy water on the surface of the skin to see if any bubbles string out. If so, the leakage is there. If it leaks badly, you can directly see smoke or dust spraying out. There is another trick-feel it with the back of your hand close to the surface of the skin. If you feel pumping, you will leak (be careful not to burn it).

2. Preparation before hands-on: What tools and replacement parts are needed

Tools, don't come to the scene and find out that it's lacking this or that. The list goes away:

• Replacement:Make sure you're usingRectangular non-metallic expansion jointIt is still a round model, and the skin size, number of layers and thickness must be the same as the original. Common non-metallic expansion joint skin is made of fluororubber, silicone rubber, PTFE membrane, glass fiber cloth, etc. When ordering, it is best to ask the manufacturer whether it can provide the factory inspection report.
• Tools:Wrench (open, plum), crowbar, utility knife, wire brush (rust removal), angle grinder (with hundred impeller), putty scraper, rivet gun and rivet (or bead screw).
• Auxiliary materials:High temperature sealant (recommended temperature resistance ≥300℃), bolt anti-jamming agent, asbestos gasket (if flange surface is uneven).
• Safety Equipment:Dust masks, goggles, high temperature resistant gloves. Don't bother, the lungs are your own.

3. Three steps of emergency leak plugging: temporary measures do not allow the leak to expand

If the site can't be stopped immediately to change the skin, do temporary leak plugging first to minimize the loss.

1. Looking for missing points:Use a small mirror + flashlight to check all around the skin, especially the corners and the connection with the flange. Many times the leakage point is near the beading screw.
2. Patch:Cut a piece of skin scrap of the same material (or use high-temperature silicone rubber cloth), coat it with high-temperature sealant, directly stick it outside the leakage point, and then fix it with a metal pressure plate with self-tapping screws. Note: The patch must be one turn larger than the leakage point, with at least 5cm margin.
3. Tie-up reinforcement:Temporarily tie the patch tightly with fiberglass tape or stainless steel cable ties. Belle was too dead, and the skin itself had to have a certain displacement compensation ability.

This method is fine for a few days, but don't expect it to be done once and for all.

4. Practical operation of replacing the skin: dismantling the old, cleaning the surface and installing the new, there are pits in every step

It's the practical session again. After changing the skin for more than a decade, I have stepped on more pits than you guys have ever eaten salt. One by one said:

Demolition:

• First, support the pipes on both sides of the expansion joint to prevent the pipes from sinking and crushing people after removing the screws.
• The bead screws on the old skin usually rust to death. Don't twist hard, spray loosening agent first, wait 10 minutes before twisting. Really can't screw it off? Use an angle grinder to cut off the bolt head, but not to the flange.
• Don't throw the removed old skin, keep it as a sample, and show it directly to the manufacturer when buying a new skin.

Clear Noodles:

• Old sealant, rust and oil stains on the flange surface must be cleaned up. Polish with a wire brush or angle grinder to reveal the natural color of the metal.
• Check the flange for any deformation after cleaning. If the flange warps more than 2mm, it is useless to install a new one-it leaks again after three weeks.

Install new:

• Before the new skin is laid on, apply a layer of high temperature sealant evenly on the flange surface. Note: Do not apply too thick, otherwise the glue will squeeze out when screwing.
• Once the skin is laid, cover with the pressing strip. The bead holes must be aligned with the flange holes – this is the biggest difference between veterans and newbies. Many people try to save trouble, and if the hole position is wrong, it will be hard screwed. As a result, the strips will tilt up and there will be more air leakage points.
• The screws should be tightened in diagonal order and gradually tightened in 2-3 times. Don't have too much torque, otherwise the strip will deform. Finally, check it with a wrench, and it feels even.

If the site hasElectric plug-in insulation doorOrManual plug-in insulation doorIt is recommended to turn it off completely during replacement to prevent smoke from suddenly rushing out and hurting people.

5. Don't go after installation: testing and routine maintenance can be managed for a long time

Just put it on and you're done? Beautiful thought. Only after taking this last step would the job be truly handed over.

Testing:

• First pass low-pressure flue gas (or compressed air), the pressure cannot exceed 50% of the design pressure, and check whether there is any air leakage around the skin. Test with soapy water or a smoking pen.
• If there is no leak, slowly rise to normal pressure and hold pressure for another 30 minutes. Listen to whether there is a hissing sound during the period.
• At the same time, check the expansion joint for abnormal deformation-especially the four corners of the rectangular non-metallic expansion joint, which are most prone to bulging.

Routine maintenance:

• Use infrared thermometer to measure the skin surface temperature every quarter, and be vigilant if it exceeds the design value of 10℃.
• Check the flange screws for loosening. Thermal expansion and contraction will cause the screw to loosen, and it is recommended to re-screw it every six months.
• If the vibration of the pipeline is large, it can be considered to install it near the expansion jointrubber compensatorOrRubber PTFE compensatorTo dampen the vibration.
• Record replacement date and model number. The service life of non-metallic expansion joints is generally 3-5 years, and they should be replaced actively when they expire. Don't wait for leaks before repairing them.

Skin leakage is not a big deal, but it can be expensive and time-consuming to deal with it badly. Follow these 5 steps, and 90% of the problems can be solved by yourself. If you really can't get it, it's not too late to find a manufacturer.