National Standard of Non-metallic Fabric Compensator JB/T 12235-2015: Understanding these is an introduction
Many purchases confuse non-metallic fabric compensators with rubber compensators, thinking that they are all soft connections-which is ridiculously wrong. The national standard JB/T 12235-2015 clearly states that the main body of non-metallic fabric compensator is fiber fabric layer, which is not the same species as rubber. The rubber compensator absorbs the displacement by the deformation of the elastic body, and the one we are talking about is carried by the superposition of multi-layered fabrics and the sealing structure. If the product nameplate you get is not marked with JB/T 12235, nine times out of ten, it is fooled by a small workshop with fiberglass cloth, and there is no national standard at all.
Three hard bars, the most ignored
There are three iron rules hidden in the national standard that many people don't know at all. I said them one by one.
First, the combustion performance of the fabric layer.Don't think that if you write "Flame Retardant" in the product manual, everything will be fine. The national standard clearly requires that the oxygen index be no less than 26%-this is a hard target. An oxygen index of 26% means that it can't ignite in the air, and it has to be burned in an environment where the oxygen concentration exceeds 26%. Many cheap products may have an oxygen index of only 22%. Once there is a little spark in the flue or the temperature is abnormal, it will take a few minutes to burn. Last year, there was a fire in the flue of a steel mill. After disassembling it, the fabric layer had not been flame retarded at all, leaving a pile of ash.
Second, the number of fatigue life tests.Metal bellows often have tens of thousands of fatigue life, and the national standard of non-metallic fabric compensator only requires 1000 cycles without failure. Do you think the standard is too low? In fact, it is not that it is weak, but that its application scenario determines it. This thing is mainly installed in the smoke duct, desulfurization system, and the inlet and outlet of dust collector-these places have only a handful of displacements all year round, relying on low-frequency and large displacements. 1000 cycles are more than enough to cover the entire device lifecycle. If you force it into the frequently vibrating fan outlet, it will be a selection accident.
Third, the structural requirements of the guide tube.Many people think that the deflector is just a baffle, just weld the iron sheet casually. The national standard has detailed regulations on the thickness, insertion depth and fixing method of the guide tube. Many accidents on the scene are because the guide tube is not installed, or the guide tube is too short, and the high-temperature smoke directly washes the fabric layer, which is perforated in a few days. You can flip through our website aboutSpecific Function of Expansion Joint Guide TubeThat article is clearly marked in the picture.
Type selection is not to look at the diameter, it is to count three numbers
When it comes to model selection, just looking at the path and patting the head, there are nine times out of ten that there will be problems. You have to count three numbers: temperature, pressure, corrosive medium.
Temperature.Below 300℃, silica gel cloth and glass fiber layer can be done. Over 400℃, sorry, must be on ceramic fiber. When the higher point is above 600℃, all-ceramic fiber and high-temperature resistant coating have to be used. Don't think about saving money. If the temperature is selected one level lower, it will be brittle for you to see in a few months.
Stress.The design pressure of non-metallic fabric compensator in the national standard usually does not exceed 0.1MPa-to put it bluntly, it is often called flue negative pressure condition. If you encounter a positive pressure pipe, such as the fan outlet section, you must add additional frame stiffeners, otherwise the bulge will take minutes. Two days ago, a customer of a cement factory took one of our rectangular non-metallic expansion joints to install steam pipelines, with a pressure of 0.3MPa. He thought that he could use it with the same diameter, but it bulged in half a month. It's not that the product is not good, it's that I don't understand the pressure level matching at all.
Corrosive media.The sulfur-containing flue gas in the desulfurization system has acidic condensate, which ordinary glass fiber can't bear, so PTFE coating or acid-resistant rubber composite layer has to be used. On our stationNon-metallic expansion joint (fabric fiber expansion joint)In the product page, each model is marked with a medium-resistant list. It is better than anything to turn it over before choosing a model.
Installation link, hardest hit area
I estimate that most of the field workers haven't even turned over the pages installed in the national standard. Arrow Direction – The arrow on the expansion joint indicates the direction of media flow, which is the bottom line. And guess what? Many workers weld it directly, no matter where your arrow is pointing, which one is welded easily. As a result, the airflow recoils, the fabric layer is lifted, and the seal fails.
And the mounting length. The national standard requires that the amount of cold pre-stretching or pre-compression should be calculated according to the thermal displacement of the pipeline. What about the actual scene? Often just leave a seam, or don't leave it at all, and weld it to death. When the pipe heats up and expands, the fabric layer will either be cracked or squeezed out. The most outrageous time, the customer screwed the tie rod nut to death, saying "afraid of air leakage". The pull rod is for limiting, not locking! You screw to death, and as soon as the temperature goes up, the pipe displacement is all pressed on the fabric layer, tearing directly. This is illustrated in the appendix of the national standard, and there should be an adjustment margin after the tie rod nut is installed. We're standing on the articleHow to adjust the tie rod nut of expansion jointThe question and answer, it is recommended that all the on-site masters have a look.
Inspection and replacement, don't just look at the surface
The surface of the fabric layer is white, hardened, and cracked. Needless to say, this must be changed. But some of the damage is hidden inside-such as layering between layers of fabric, sealing strips aging and falling off, and the appearance can't be seen. The national standard recommends visual inspection every six months and airtightness test every year. Actually? Few users of power stations and steel plants we contact can do quarterly inspections. Wait until the scene smoked before I remembered to change it. The downtime loss was enough to buy more than a dozen compensators. You taste, you taste.
When overhauling, take a flashlight from the side of the fabric layer to see if there are any light-transmitting spots. Light transmission means that the fabric layer has been worn thin, so hurry to arrange a replacement. This method works better than any precision instrument.
National standard is not a decoration, it is the bottom line
JB/T 12235-2015 gives the complete path from design, manufacture, inspection to installation and maintenance. But there are few enterprises that really implement it in place. As a manufacturer, we often encounter customers asking to "go to national standard products", and then we take out the type test report, and the other party is confused-they don't know that national standard products need fatigue life test reports and fabric layer oxygen index test sheets. To be honest, those who have the confidence to stamp JB/T 12235 steel stamp on the nameplate have at least done a complete type test, and they can't just take a sample.