How on earth do you build that large non-metallic compensator? It's more than two meters wide at every turn, and it can withstand hundreds of degrees of high temperature. Is it reliable? I told him that this thing looked like a cloth cover, but it actually had many ways. Today, I simply break the whole process apart and crush it, from material selection to factory delivery to installation, and explain it clearly bit by bit.
Find out the details first: temperature, pressure, medium and displacement. These parameters determine what materials are used
The first step in building a compensator is not to draw a picture, but to settle accounts. You have to know whether smoke or hot air runs in the pipeline, whether the temperature is 200℃ or 600℃, whether the pressure is slightly positive or negative, and whether the displacement is axial stretch or lateral offset. These data directly determine the number of layers and materials of non-metallic bands, and also determine the thickness and corrosion protection grade of metal frames.
The flue gas pipeline used in the cement industry has a temperature of around 350℃ all the year round, containing sulfur and dust. Therefore, a temperature-resistant layer and an airtight layer must be added to the belt, and the skeleton must be made of weather-resistant steel and high-temperature paint. If it is used on the pipeline before and after the desulfurization flue gas baffle door, and the medium is still corrosive, the anti-corrosion grade has to be raised. To put it bluntly, the parameters started to cut the material without figuring out, and the rest was all in vain-there are many people in this industry who have stepped on this kind of pit.
The skeleton is the beam of the house: how can the metal frame be designed, welded and prevented from corrosion to hold it?
The skeleton of the non-metallic expansion joint (fabric fiber expansion joint) is, to put it bluntly, a steel structure frame. This thing has to hold the entire ring, and it has to withstand pipe thrust and external loads. When designing, calculate the cross-sectional moment of inertia of the frame according to the displacement and pipe diameter, and the place of the stiffened plate cannot be saved.
For welding, I have seen many factories do not polish or do non-destructive testing after welding in order to catch up with the construction deadline. As a result, the frame is deformed, and it can't match the flange when installed, so it can only be smashed with a sledgehammer. Do you say it is upsetting or not? The good practice is to spot welding the frame first, then fully welding, and annealing to relieve stress or vibration aging after welding. Don't be sloppy in anti-corrosion-hot-dip galvanizing, epoxy zinc-rich primer plus topcoat, or directly use stainless steel, depending on the working conditions.
Non-metallic tape is the soul: How to match fabric lamination, adhesive process and temperature resistant layer
The loop band is the heart of a large non-metallic compensator. And guess what? Many laymen think it's just layers of cloth sewn together. In fact, the band is a multi-layer composite material: the outermost layer is usually silicone rubber cloth or fluorine rubber cloth, which is used to insulate the temperature and wind; Add glass fiber felt or ceramic fiber blanket in the middle for heat insulation; The inner layer is made of tetrafluorine membrane or a material similar to a polytetrafluoroethylene compensator as an airtight layer. Each layer should be pressed with high-temperature adhesive, no bubbles, no wrinkles.
The lamination process is also very particular. Staggered seams should be made between layers to avoid overlapping weak points. The pressing temperature, pressure and time must be supported by data-for example, when silicone rubber cloth and glass fiber felt are compounded, the temperature is controlled at about 150℃ and the pressure is 0.3MPa for 20 minutes. Each manufacturer of these parameters has its own process manual, but the factory that fooled people directly brushed the matter with cold glue, and the ring belt cracked in layers within half a year.
It is not so simple to install: sealing strips, pressure plates, tension structures, one less all leak
How to fix the loop band to the skeleton when it is done? The usual practice is to use plates and bolts to press the ring belt to the frame flange. But here's the problem-if the platen is not designed well, the edge of the loop band will be crushed or slip off. Therefore, the inside of the pressure plate should be rounded, the bolts should be evenly tightened, and the torque wrench should be adjusted properly, so that no air leakage can be made.
Sealing strips are equally critical. Between the contact surface of the ring belt and the skeleton, a temperature-resistant sealing gasket, such as graphite sandwiched metal mesh or PTFE coated gasket, must be padded. In addition, the four corners of rectangular non-metallic expansion joints are most likely to leak, so special corner sealing strips should be used, or the ring belt should be made into an integral corner in advance to avoid splicing seams. It is also very important to tighten the structure, especially the negative pressure pipeline. The ring belt will be deflated, so it is necessary to add an internal support ring or external tension bar. One less detail and the site has to be reworked.
Before leaving the factory, you have to go through the court one by one: withstand pressure test, air tightness test, displacement simulation, one can't be missed
Factory trials are not a formality. Before leaving the factory, the large non-metallic compensator must be tested for pressure resistance, inflated to 1.5 times of the design pressure, and held for 10 minutes to see if the ring belt is bulging and the frame is deformed. The airtightness inspection is stricter-use soapy water or helium to detect leaks, and the leakage points must be repaired and redone.
Displacement simulation is a link that many factories are unwilling to do because it is troublesome. But there is a big difference between having done it and not having done it. Install the compensator on the test bench, pull and compress it to the designed displacement, then offset it laterally, and charge it at the same time, and observe whether the ring belt is twisted and the pressure plate is rubbing. I have personally seen a manufacturer who didn't do displacement simulation. When it was installed at the site, the guide tube interfered with the ring belt, and it was directly scrapped. Alas, is this money not injustice?
Doorways installed on site and pits stepped on in those years: How to adjust pre-stretching, guide tube and expansion gap
Finally on the scene. When good things arrive at the construction site, if they are not installed correctly, they will be finished. Let's talk about pre-stretching first: if there is thermal expansion when the pipeline is running, the compensator should be pre-stretched by a certain amount when it is cold, equal to half the amount of thermal expansion. How much to pull? The data is marked on the drawing, so don't feel it.
The deflector is also an easy place to overlook. What is the specific function of the expansion joint guide tube? It allows the medium to flow smoothly through the interior of the compensator and prevents the vortex from washing the ring belt. The direction of the deflector must be the same as the direction of the media flow when installed-the direction of the arrow is the direction of flow. Never install it backwards. If it is installed backwards, the loop belt will wear out quickly.
The expansion gap needs to be more attentive. If there is no sufficient gap between the frame and the pipe, the compensator will fail when it is directly pushed to death during thermal expansion. In addition, it is mentioned in the correct installation method of the expansion joint of the large tie rod that the tie rod nut should be loosened for a certain stroke after installation, so that the compensator can expand and contract freely. Don't screw the nut to death, that's a common mistake for newbies.
How to make a large non-metallic compensator? It is not knocked out by one person, but an engineering work from parameters, materials and processes to testing and installation. Those who want to save trouble often end up trouble. Those who want to save money tend to burn more money in the end. Is that the truth?