1. The body of the non-metallic compensator is fabric fiber. Why do you have to add a stainless steel ring belt? — — Talk about the doorway of structural design
Anyone who has engaged in pipeline compensation knows that the main body of non-metallic expansion joints (that is, fabric fiber expansion joints) is made of flexible materials such as glass fiber cloth and silicone cloth, which are resistant to high temperatures, corrosion resistant and can absorb multi-directional displacement. However, there is a problem-these fabrics have enough tensile strength to withstand high-speed erosion and local pressure concentration in the pipeline. And guess what? The key lies in that stainless steel ring belt.
To put it bluntly, the function of the circle belt is "skeleton + armor". It is wrapped at both ends or in the middle layer of the non-metallic compensator, holding the fabric edge firmly to prevent layering and tearing. Especially under negative pressure conditions, the fabric is easily deflated, and the air flow channel will be stable with a hoop. In addition, the ring belt also acts as a sealing interface-after the flange bolt is compressed, the stainless steel ring belt and the flange surface are close to each other to ensure no air leakage. Without this ring of steel, rely on fabric alone to bear pressure? I will give you a bulge in minutes.
Second, how to choose the material of stainless steel ring belt? 304 or 316L? Don't just look at the grade, it should be determined according to the working conditions and media
Two days ago, I met a customer. The non-metallic compensator was used in the desulfurization flue, and asked me if I could use 304 for the ring belt. I said brother, the concentration of chloride ions in the condensed water in the desulfurization flue gas is not low. It is only a matter of time before 304 encounters chloride ions and stress corrosion cracks. At this time, you have to go to 316L, or simply use a high molybdenum alloy such as 254SMO.
There is no universal answer to material selection. Drying high-temperature flue gas, such as cement kiln tail waste gas (temperature 300-400℃), 304 is completely enough, and the cost is low. However, if it is wet flue gas containing sulfur and chlorine, or there is acid and alkali liquid splashing, 316L starts. If the medium temperature exceeds 600°C? Ordinary austenitic stainless steel is also not very good, and you have to use heat-resistant alloys, such as Incoloy 800. Remember one principle: first measure the composition of the medium and the working temperature, and then determine the material. Don't just look at the brand.
3. Details that are easy to overlook during on-site installation: positioning, pre-tensioning and bolt torque. If one is not screwed correctly, air may leak
Installing this thing looks simple, but most of the problems are that the details are not done in place. Let's talk about positioning first: the mounting hole on the ring belt must be aligned with the flange bolt hole. Even if it is misaligned by 1mm, the ring belt will be scratched when the bolt is penetrated. Let's talk about pre-stretching: When the non-metallic compensator leaves the factory, the loop belt is usually adjusted to the designed length, but the actual spacing of the pipeline on site may be too large or too small. It is necessary to pull the whole with the tie rod or jack compensator to the predetermined position according to the installation instructions, and then tighten the bolts. If you forcibly pull the ring belt, it may directly crack.
And bolt torque. Many workers twist it by feeling. If it is too tight, the ring belt will be pressed out of dents, and even the flange edge will be deformed by pressing it. It screws too loosely and leaks as soon as it runs. It is recommended to use a torque wrench and tighten it diagonally three times according to the torque value given by the manufacturer (generally M16 bolts are between 80-120N·m). By the way, the bolt spacer should use a large flat pad to prevent the surface of the loop belt from being pressed out of imprints.
4. What should I do if the middle circle belt is broken? Analysis of Common Failure Modes and Replacement Judgment Criteria
Wear, corrosion, fatigue cracking. Wear mostly occurs in pipes with particles in the medium, such as the flue behind the dust collector of power plants. The dust polishes the surface of the ring belt like sandpaper, and it wears out over time. Corrosion is common in desulfurization systems. Chloride ions or dilute sulfuric acid pits stainless steel bands into honeycombs. Fatigue cracking is caused by frequent thermal expansion and contraction, and cracks occur at the root of circular wrinkles, which extend slowly.
Then how to judge if you should change it or can continue to use it? Just look at two points: one is air leakage, and the other is structural damage. Slight surface rust spots or shallow scratches, as long as they don't penetrate, they can still be used after sanding. If there are perforations with a diameter greater than 2mm, crack lengths exceeding 30% of the width of the loop band, or there is obvious delamination and degumming between the loop band and the fabric layer, don't hesitate to change. It is best to replace the time during the shutdown and maintenance period, and do not run with illness, otherwise the pipeline leakage will cause safety accidents and the cost will be higher.
By the way, when replacing, you must choose the same model and material ring belt. Don't be greedy for cheap and use miscellaneous brands. The thickness, width and wave height are different, but installing them may affect the compensation amount. It is recommended to purchase from the original manufacturer and keep the spare parts.
5. Should you mention the ring belt parameters separately when selecting the model? Explain clearly the actual case of non-metallic expansion joint (fabric fiber expansion joint) in this site
When many designers choose non-metallic expansion joints, they only write the caliber, temperature and pressure, and the belt parameters are made according to the standard by default. This is actually enough, because for normal working conditions, the manufacturer will match the ring belt according to the national standard JB/T 12235-2015 for non-metallic expansion joints. However, in case of special working conditions, I suggest that you circle the band requirements separately.
We distribute the rotary kiln for the export of a cement factoryNon-metallic expansion joint (fabric fiber expansion joint)The flue gas temperature fluctuates greatly (from normal temperature to 400℃) and contains a large amount of alkaline dust. If you use a regular 304 for the loop belt, the hole will be worn out in two months. Later, a special note was made in the technical scheme: the material of the loop belt was upgraded to 316L, the thickness was increased from 1.5mm to 2.0mm, and the wear-resistant ceramic fiber cloth was lined. This expansion joint has been used for more than two years without any problems. So, do you want to mention the ring belt parameters when selecting the model? Ask yourself three questions: Is there corrosion in the media? Is there a particle scouring? Does the temperature exceed the material limit? As long as there is a "yes", the technical parameters should be written separately.
Similarly, for the rectangular non-metallic expansion joint matched with the flue gas baffle door of the power station, the ring belt also bears the function of closely fitting with the flange of the baffle door, which will leak air if it is slightly deformed, affecting the desulfurization efficiency. At this time, not only the material should be right, but also the wave height and wave distance of the ring belt should be designed according to the manufacturer's standard, which can't be done by just finding a supplier.
As for other products of this site, such as metal hoses, corrugated expansion joints, rubber compensators, etc., they also have similar structural reinforcements, but the ring belt is the only steel line of defense for non-metallic compensators, and its importance is self-evident. Don't be too troublesome to select the model next time. Spend 10 more minutes to figure out the parameters of the ring belt, and the equipment life can be doubled.