1. Why does the non-metallic compensator leak? Find out what is leaking first
When it comes to the leakage of non-metallic compensators, many engineers come up and ask, "Can we achieve zero leakage?" This matter is clearly scored-what kind of medium are you referring to?
The ring body of non-metallic expansion joint (fabric fiber expansion joint) is flexible fabric, and its air permeability is not zero. However, the "leakage" that really gives customers a headache is mostly that the medium runs out of the compression surface of the interface between the ring body and the pipeline. Smoke, hot air, dust, run out is an accident; But if you set the standard for leakage as "breathability", then no fabric can be absolutely sealed.
So talking about leakage, you have to be clear first: are you concerned about trace air permeation through the fabric body, or penetrating leakage at the compression of the flange? The former is material physical properties, the latter is structural and mounting issues. If these two were not clearly broken up, there would be no way to talk about the later selection.
2. What factors affect the leakage? The number of fabric layers, the compacting structure and the temperature of the medium should not be less
The number of fabric layers is naturally the first factor affecting the leakage amount of non-metallic compensators. The more layers, the longer the gas penetration path, and the amount of leakage decreases exponentially — but at the cost of worse flexibility and higher costs. Whether four layers are enough or six layers are guaranteed depends on the working conditions.
The second is the compression structure. The sealing performance of non-metallic compensators depends half on the fabric itself, and the other half on the locking force of plates and bolts. The bolts are too spaced apart, or the platen is not stiff enough, and the fabric is like an untied tie under pressure, leaking to you. I have seen many scenes, and there is no problem with the compensator body, but the screw is twisted perfunctorily, and the leakage exceeds the standard.
The third is the medium temperature. With a temperature of 100℃ per liter, the viscosity of the gas increases, the permeability coefficient changes, and the leakage rate increases not linearly but exponentially. If you take the normal temperature data to set the high temperature working conditions, you will have to pay tuition fees.
Third, the standard basis and measurement method of the leakage amount of non-metallic compensator, don't be fooled by the manufacturer's parameters
Manufacturers like to report "leakage rate 0.5%", but when you ask him what standard he measured, most of them hesitate.
In the current industry standard, the non-metallic expansion joint refers to JB/T 12235-2015, but the standard does not give a uniform value of "allowable leakage"-it mainly specifies the material, strength and fatigue performance. The amount of leakage is calculated when designing and measured when making products, but the measurement method has to be determined by yourself. A reliable factory will use a flowmeter to encrypt the cover, measure the air permeation per unit time and unit area under the set pressure, measure one group at room temperature and one group at high temperature, so that the data can have reference value.
It makes no sense just to look at the "leakage rate" on the manufacturer's sample. You have to ask three questions: What is the test medium? What is the test pressure? Is the temperature normal or working temperature? After asking these three, most of the parameters can't stand up to scrutiny.
4. How to weigh the leakage under different working conditions? The requirements of flue gas, hot air and desulfurization systems are very different
Non-metallic expansion joints are installed on the flue gas pipelines of thermal power plants, and the leakage is large, which is nothing more than the escape of dust, and it is troublesome to check the environmental protection tightly; But in the desulfurization system, the flue gas contains SO₂ and corrosive droplets, and when it leaks out, it is not only dirty, but also that the equipment is bathed in sulfuric acid-the requirement for leakage is directly filled.
Look at the hot air system again. The working temperature is above 600℃. Once the number of fabric layers is small, the hot air will penetrate the ring body, and the outer silicone rubber will immediately age and crack, and it will be scrapped in less than half a year. In this case, instead of pursuing low leakage, it is better to consider a double-layer structure with an intermediate guide tube, which is common on rectangular non-metallic expansion joints.
Therefore, the essence of weighing the upper limit of leakage is to calculate economic accounts: how much is the value of the leaked medium, how much maintenance cost it brings, and how many unplanned downtimes there are. The flue gas baffle doors at the entrance of the desulfurization tower are all designed with double seals. Can the compensator still expect a single layer of fabric to block everything? It's not realistic.
V. Practical Means to Reduce Leakage: Key Details from Structural Design to Installation and Maintenance
Structurally, the selection of plates and bolts is the most immediate point. The leakage rate can be reduced by an order of magnitude by changing the platen to a continuous frame type instead of a segmented joint. Another is the guide tube-although it is inconspicuous, it can separate the high-speed airflow from the fabric surface, which not only protects the ring body but also reduces the leakage driven by differential pressure.
When installing, the bolt torque should be evenly divided two to three times diagonally tightened. The flange surface of non-metallic compensator must be flat, the welds of pipe flanges should be polished clean, and the selection of gaskets should be matched with the medium-don't use asbestos rubber pad to deal with sulfuric acid flue gas, that is not to save money, but to dig a hole for yourself.
On maintenance, regularly check whether the compression bolts are loose and whether the fabric surface is fluffed or cracked. Many leakage problems are not poor design, but no one cares about them after three or five years of use. You paid a lot of money for a low-leak non-metallic expansion joint, but the bolt came loose and no one tightened it. What's the difference between holding a leaking pipe with your hand?
In the final analysis, there is no standard answer to the question of non-metallic compensator leakage. It is the comprehensive result of selection parameters, structural details and field management. Next time you make a plan, don't just listen to the manufacturer's report of a beautiful value, put out the working conditions, ask the test basis clearly, and then decide the number of layers and compression form-this account is not lost no matter how it is calculated.