Find out which expansion joint is leaking first
When the flue expansion joint leaks, the first step is not to rush to plug it, but to see what material it is made of. Metallic, non-metallic, rubber-the causes of air leakage and repair schemes of the three are very different.
For example,Non-metallic expansion joints (fabric fiber expansion joints)Air leakage is mostly caused by aging or damage to the skin. This kind of compensator is sealed by multi-layer fabric and rubber composite layer. When the high-temperature smoke is baked, the fiber layer will be embrittled, the coating will peel off, and the air leakage will come. WhileMetal rectangular expansion jointAir leakage, with a high probability of fatigue cracking of bellows or weld failure. Used in power stations and cement industriesCorrugated expansion joint for power station industryOrMetal Corrugated Expansion Joints in Cement Industry, long-term bearing large displacement and alternating stress, the root of the bellows is prone to cracks.
Andrubber compensatorAndRubber PTFE compensatorThey are mostly used in desulfurization systems or low-temperature corrosive flue gas pipelines. Aging of rubber and damage of PTFE layer directly lead to air leakage. The material is different, and the repair method is completely different-you can't weld rubber with a welding torch, can you?
The leakage position determines the processing direction
The same air leak, the location is different, and the solution is completely different.
- Bellows body leakage: There are pinholes or cracks in the metal expansion joint bellows, which usually can't be repaired locally, but can only be replaced as a whole. If the non-metallic skin is damaged, it can be repaired temporarily, but it has to be replaced sooner or later.
- Air leakage at flange connection: This is most common. Uneven bolt pre-tightening, ageing or misalignment of gaskets during installation will lead to flange leakage. Check the torque of the bolts first, tighten them evenly again, and change the gasket if it doesn't work. Gasket materials should be selected correctly-graphite pad for high-temperature flue gas and tetrafluorine pad for corrosive media.
- Deflector dropped or worn out：expansion joint guide tubeThe function is to guide the airflow and protect the bellows. Once it falls off or wears out, the high-temperature flue gas directly washes the bellows, and the air leak is only a superficial appearance, and the interior may have been seriously damaged.
- Tie rod nut loose: The loosening of the tie rod nut of the expansion joint will cause the limit failure, and the bellows will be over-stretched or compressed, resulting in leakage. When adjusting the tie rod nut, pay attention to symmetrical tightening, and don't screw it to death unilaterally. refer toHow to adjust the tie rod nut of expansion jointMethod: First loosen the locking nut, adjust it in place and then lock it.
How to quickly judge the air leak point? The easiest way-spray on the suspected area with soapy water or blowing agent, bubbling is the leak spot. For high-temperature pipelines, sweep them with an infrared thermometer, and the temperature at the air leak will be abnormally high.
Emergency treatment scheme for different working conditions
Many times, when an air leak is found, the equipment is still running and can't be stopped. What about that?
High temperature flue gas pipes (e.g.Corrugated expansion joint for power station industry、Metal Corrugated Expansion Joints in Cement Industry) Air leakage, temporary plugging can be usedHigh temperature repair tapeOrCeramic fiber blanketAdd temperature-resistant sealant. Clean up the leakage first, then wrap it and bandage it, which can last for a short period of time. But this is only an emergency, not a permanent solution.
Low temperature or corrosive flue gas pipes, such as desulfurization systems, leakage points often occur inrubber compensatorOrPTFE compensatorOn. For emergency treatment, you can wrap corrosion-resistant tape first, but it is recommended to directly prepare the same model of spare parts for replacement. Desulfurization flue gas contains sulfuric acid droplets, and ordinary tape can't last for a few days.
If the air leak occurs inFlue gas baffle doorOrElectric plug-in insulation doorOn the nearby expansion joint, we have to pay attention to the impact on the expansion joint when opening and closing. Instantaneous pressure fluctuations may make the bellows bulge or even tear-at this time, no matter how good emergency repair is, it will be useless, and the machine must be stopped first.
Long-term radical cure must choose the right replacement parts
Don't be so busy plugging leaks. The leaky expansion joint indicates that the life has arrived, and the symptoms are treated rather than the root cause. When replacing, the type should be re-selected according to the displacement, temperature, pressure and medium of the pipeline.
Frequent fatigue failure, such as in the flue of a power plantUniversal corrugated expansion jointIf you can't handle the cyclic displacement, then replace it withHigh temperature axial expansion jointOrCompound hinge transverse expansion jointThey can withstand greater axial or lateral displacements and have a higher fatigue life.
If the installation space is limited, the traditional expansion joint won't fit? ConsiderationSleeve type pipe expansion jointOrRotary compensator。 The sleeve type is compact and suitable for small spaces; The rotary compensator absorbs displacement through rotation, and requires low installation direction.
For corrosive environments, recommendedPTFE-lined hoseOrPTFE compensatorThe PTFE layer is acid and alkali resistant, and its life is several times longer than that of ordinary rubber.
Displacement, pressure and temperature are three parameters, and it is preferable to leave a margin rather than stuck. Many air leakages are caused by too tight calculation during model selection and exceeding the limit of actual operating conditions.
Key points of daily maintenance to prevent air leakage
Instead of waiting for a leak to fix it, it's better to keep an eye on a few points daily.
- Does the guide tube fall off: Regular shutdown for inspection, the guide tube has to be replaced if it is worn to 1/3 of the original thickness.
- Is the tie rod nut loose：Correct installation method of expansion joint of large tie rodIt is emphasized in that the nut should be symmetrically tightened and an anti-loosening washer should be added.
- Are there scratches on the non-metallic skin: Even a small hole, the high-temperature smoke will expand quickly as soon as it blows. Scratches are found to be temporarily blocked with special repairing agent, and replaced at the next shutdown.
- Impact of opening and closing of flue baffle door on expansion joint：Flue gas baffle door、Electric plug-in insulation doorWhen switching, try to operate slowly to avoid sudden pressure changes. Instantaneous negative pressure or positive pressure impact can easily make the bellows bulge and deform.
In addition, the displacement amount of the expansion joint is periodically recorded. If it is found that the actual displacement is more than 20% larger than the design value, it means that the pipe support and hanger may fail or the calculation of thermal expansion is wrong, and it needs to be recalculated.
In the final analysis, how to deal with the leakage of flue expansion joint, the core is four words: prescribe the right medicine. Recognize the material first, find the leakage point, temporarily block it, change the root correctly, and keep a close eye on it daily. It's not a difficult job, but I'm afraid of fooling around.