Under what working conditions are non-metallic expansion joints most prone to aging?
High temperature, corrosive media, frequent displacement, these three factors superimpose, and the aging rate doubles. Many users think that non-metallic expansion joints are cheap, so they don't care when they are installed. As a result, the fiber layer is brittle, the surface cracks, and even the tear leaks in two or three years. In the actual case, the non-metallic expansion joint used in the desulfurization flue of a power plant has a large area of cracks on the skin surface because it is in the sulfur-containing flue gas of about 80℃ for a long time. When it is removed, it shows that the inner PTFE film has been powdered, and slag falls when touched by hand. If you think about it, if this is not discovered in time, it will be a downtime accident.
You have to know the stages of aging
At the beginning, the surface color changes, such as yellowing and darkening of the fabric layer, and the elasticity of finger pressing decreases. At this time, many people didn't take it seriously and thought it could still be used. In the medium term, you can see fine cracks, or local bulging, and the sealing performance has begun to decline, but it has not leaked yet. It will be troublesome in the later period-crack propagation, fiber fracture, media leakage, and the whole expansion joint is basically scrapped.
Scratch the surface of the skin with your nail. If it leaves obvious marks and does not rebound, it means that the material has lost its elasticity. Remember, don't wait until it leaks before dealing with it. At that time, even the pipeline bracket may be damaged. The money for replacing the expansion joint is small, while repairing the bracket and missing work period is big.
Core Factors Affecting the Aging Rate
One is the temperature and the other is the medium. Take non-metallic expansion joints (fabric fiber expansion joints) as an example. The design temperature is usually selected according to the working conditions. For example, the skin structures with temperature resistance of 200℃ and temperature resistance of 400℃ are completely different. In actual use, overtemperature operation is a taboo. Even if it occasionally exceeds 20 or 30 degrees, it looks fine on the surface, but the polymer chain inside the material has been broken, and the life span has been directly reduced by half.
Corrosive gases are harder. Especially behind the desulfurization flue gas baffle door, there are acidic droplets in the flue gas, which ordinary silicone coating can't bear at all, so it is necessary to use the composite structure of acid-resistant PTFE or rubber PTFE compensator. And guess what? Some customers told the manufacturer that "the working condition is not corroded", but when they were removed, the metal mesh inside was all rusty.
Then how to extend the service life?
Don't be cheap in choosing models. Strictly according to the working condition temperature, pressure and displacement, especially for non-metallic expansion joints, the matching of skin, frame and guide tube is very critical. In order to save two thousand dollars, someone chose a small one, but it tore within a few months of installing it, which was not worth the loss.
Pay attention to pre-displacement during installation, don't pull hard, flange surfaces should be aligned, and bolts should be evenly tightened. This point is easily overlooked by the installation team, and it is okay to tighten it. Keep an eye on the daily inspection, and check whether there are any abnormal deformation, wear or chemical corrosion traces on the skin surface every month. When shutting down for maintenance, clean up dust and scale easily, and don't let corrosive substances accumulate in the skin folds for a long time-this place is the easiest to hide dirt and evil, and it is also the easiest to be overlooked.
There is also a big pit: treating non-metallic expansion joints as all-purpose
In order to save trouble, some customers want to directly use ordinary non-metallic expansion joints on the pipelines of the cement industry with high temperature and dust, but the result is worn out in a few months. This kind of working condition should choose metal corrugated expansion joint or high-temperature axial expansion joint in cement industry, which has stronger wear resistance and pressure bearing capacity.
On the other hand, if large displacement compensation and vibration isolation and vibration reduction are needed, metal is not as good as non-metal. At this time, rectangular non-metal expansion joints or rubber compensators have to be used. Used in the wrong place, fast aging is inevitable. It's not that something is bad, it's that I didn't choose the right thing.
One last word
Aging is not terrible, it is terrible to not pay attention to it. Establish a ledger, record the installation date, working condition parameters, and the results of each inspection, and encrypt the inspection frequency in the middle and late stages of life. If you are not sure of the current state of the expansion joint, go directly to the manufacturer to see photos or send samples for testing. Don't pat your head to judge.
After all, the cost of replacing non-metallic expansion joints is not high, but if it is shut down due to aging leakage, the loss will be great. This kind of thing has been seen too much-usually reluctant to change it, and after leaking it, it will be repaired for days and nights, and it will cost more money.