It is also wear. Why do some non-metallic expansion and energy saving use five years, while others leak in half a year?
The non-metallic expansion joints on their flue gas pipes were worn out less than half a year after they were replaced, and the current of the induced draft fan floated upward after air leakage. The expansion joint in the next workshop with the same working conditions can still hold up after five years. The same factory, the same flue gas, why is the gap so big?
Don't rush to scold the manufacturer yet. This matter of wear, on the surface, is "broken", and the root difference is big. If you can't tell whether it is particle scour, fiber aging, or mechanical scratching, ten changes will be useless.
The wear of non-metallic expansion joints can be divided into at least three types: the first is erosion wear caused by high-speed impact of hard particles, and the surface of the ring belt is like being hit by sandpaper, and the fibers are broken one by one; The second is the fatigue fracture of the fabric layer under repeated flexing, and the crack goes along the root of the corrugation, which is not necessarily dried by the particles; The third is scratching by foreign objects, such as the misalignment of the guide tube, the welding slag left during installation, and the edge of the baffle door blade hanging to the ring belt. The three marks of wear are completely different, and the methods of treatment are completely different.
Three high-frequency failure sites: flue gas dust scour, deflector failure, installation centering deviation
Scenario 1: Smoke dust hits the circle directly.When the dust concentration in the flue gas pipeline is high and the flow rate is fast, the non-metallic ring belt is like standing at the air vent of the sandblasting machine. Especially when the expansion joint is arranged downstream of the elbow and upstream of the dust collector, the airflow does not go straight, and the particles are directly thrown to the inner wall of the ring belt with inertia. The corrosive gas is added again, and the life of the band is visibly shortened.
Scenario 2: Deflector failure.Many non-metallic expansion joints are equipped with guide tubes, the purpose is to let the medium go in the middle, and don't directly grind the ring belt. However, the guide tube is either short, or it is not firmly fixed, and it falls off or deflects during operation. As a result, the flue gas drills out from the gap and rushes straight to the ring belt. Whether this thing is installed or not, and whether it is installed correctly, you can only see when you disassemble it.
Scenario 3: Install centering deviation.The flanges were misaligned during on-site installation and the expansion joints were subjected to additional shear and torsion. The band is unevenly stressed, one side is stretched and the other side is compressed, and the fabric layer quickly fluffs and cracks under alternating stress. In another case, the expansion direction of the pipe is blocked by the guide tube, and all the displacement that should be absorbed by the expansion joint becomes a local squeeze of the ring belt.
Wear doesn't happen suddenly: Every step has warning signs
Non-metallic expansion joint wear never leaks into a sieve overnight. It has a process.
At first, the surface of the fabric layer is dark and fluffy, which is a signal that the fibers are beginning to break. After some time, the inner lining layer appears to fall off in a small area, and glass fiber or PTFE film can be seen exposed. Immediately afterwards, corrosive components in the gas began to penetrate the fiber layer, and rust marks slowly appeared on the edges of the metal flanges. If you find rust water flowing out of the flange bolts, or there is a local bulge on the surface of the ring band, you can basically tell that the interior has been delaminated.
The most veiled warning is a change in airtightness. At the same frequency of induced draft fan, the negative pressure of the system is more difficult to maintain than before, or the amount of flue gas leakage is obviously increased. Don't doubt the baffle door first. Take a speedometer to measure around the expansion joint. The air leakage position is often the wear breakthrough.
Don't rush to get a new one, do three things first
When the equipment is broken, people's first reaction is to place an order for spare parts. But if you don't find out the root cause of wear, you will still die in the same way. To save this money, do three things first:
First, take it apart to see the wear marks. Cut the band off and see if the opening is rounded or sharp. There are powdery particles adhering to the edge of the break, that is, erosion wear; The breach goes in the direction of the corrugation, which is fatigue cracking; There are scratches and scratches at the breach, which is mechanical interference. Second, check the working condition parameters. Flip out the operating record to see how different the actual temperature, flow rate, dust concentration and design parameters are. Many "overdue service" non-metallic expansion joints, the actual operating wind speed is 40% higher than the design value, and it is normal for the wear speed to double. Third, check that the deflector tube and the baffle door fit. Is the deflector loose? Can the blades fit perfectly when the flapper door is closed? If the baffle door is not tightly sealed, the high-speed airflow will spray out of the gap and cut the loop strap directly.
Different wear degrees correspond to different maintenance schemes
The degree of wear is different, and the maintenance strategy is different. Don't replace it as a whole at every turn.
If it is only partial surface fluffing and small area perforation, just make a partial patch. Clean the damaged area, patch it with a non-metallic layer of the same material, and then vulcanize or sew it to reinforce it, and it can resume operation in half a day. Pay attention to the edge of the patch to be beveled overlap, otherwise the stress concentration will still tear in the original position.
If the loop tape becomes thin in a large area and the multilayer fibers have been delaminated, the local patch will not last long, and the non-metallic loop tape will be replaced directly. When changing the ring belt, be sure to check whether the flange surface is corroded and the bolts are elongated. By the way, clean the flange sealing surface, and don't let old foreign bodies stay in it.
If this position has been broken two or three times in a row, or the working conditions have been greatly upgraded (the temperature, negative pressure, and dust concentration have all changed), then it is time to consider the overall upgrade. When the flue gas temperature exceeds 200℃ and the dust concentration is high, replace the ordinary non-metallic expansion joint withHigh temperature axial expansion jointOr more wear-resistantRectangular non-metallic expansion jointAlthough the initial investment is a little larger, the comprehensive downtime loss is much more cost-effective.
Reduce wear from the design side, which is much more cost-effective than after-the-fact repairs
Wear problems, in essence, are many buried mines during design selection. When choosing non-metallic expansion joints, don't just look at the diameter and compensation amount, but have to take out the medium characteristics, flow direction and particle concentration.
Structurally, a scheme with a flow guide tube is preferably preferred. The guide tube directs the airflow to the center of the expansion joint, allowing the loop to avoid direct flushing. If the dust is particularly heavy, you can also add a wear-resistant lining plate to the inner wall of the guide tube, which is equal to one more line of defense. Flow speed control is also very crucial. The wind speed in the flue gas pipeline should not exceed 18m/s. If it exceeds this value, the wear amount will soar with the cubic speed, and no material can bear it. In addition, if the particle size in the flue gas is greater than 200 mesh, or it contains hard gypsum particles, it is best to install pre-dust removal or wear-resistant elbow upstream of the expansion joint to reduce the impact of particles on the expansion joint from the source.
Flue gas baffle doorIt is matched with the expansion joint. If the baffle door has poor sealing, wear, scouring and vibration will be transmitted to the expansion joint. When choosing the expansion joint, check the type and sealing grade of the baffle door by the way. Don't let a leaky baffle door destroy a whole non-metallic expansion joint.
At the end of the day, non-metallic expansion joint wear is no trivial matter. It is not a consumable, but a pipe protection component that needs to be taken seriously. Distinguish the type of wear, find the real cause, and then decide whether to repair, replace, or upgrade, so that you can stabilize the system with the least amount of money. Next time you encounter an expansion joint leak, don't scold the quality yet, take it apart and have a look-it may have told you why.