The gas pipeline looked thick and bulky, but it was actually very delicate. Especially the pipe joint, thermal expansion and contraction, vibration, corrosion, which is bad is air leakage. At this time, you have to rely on the expansion joint to cover the bottom. But many people choose metal when they come up. Alas, it's not impossible, it's easy to step on pits. Let's talk todayNon-metal expansion joint of gas pipelineShe broke up the door inside and crumbled it to pieces.
Why do gas pipelines have to have non-metallic expansion joints? Don't let the metal become a hidden danger
Think about it, what's in the medium of gas pipelines? Hydrogen sulfide, moisture, tar, ammonia…typical corrosive mixtures. No matter how good the metal expansion joint is, it can't bear this kind of environment. Stress corrosion cracking and electrochemical corrosion will make you have to change it in half a year in minutes. Two days ago, I met a steel mill customer. In order to save hundreds of pieces, I chose a general-purpose corrugated expansion joint. As a result, the weld seam leaked in three months, and the shutdown loss was enough to buy dozens of non-metallic pieces. Is that the truth? Non-metallic materials themselves are not afraid of these chemicals. The inner layer is made of fluororubber or polytetrafluoroethylene, and it is okay to contact gas directly.
Disassembly to see the structure: How fabric fibers and rubber layers can withstand the corrosion of gas
The structure of a non-metallic expansion joint is not a layer of skin. Take our usualNon-metallic expansion joint (fabric fiber expansion joint)For example, there are at least three layers from the inside to the outside: the inner lining layer is usually fluororubber or butyl rubber, which is dense and impermeable; The middle is a reinforcing layer, high-strength glass fiber or aramid fabric to ensure pressure bearing; The outer protective layer is silicone rubber coated fiberglass cloth, which is resistant to aging and weather. It's kind of like wearing armor, with each layer doing its job. And there's alsorubber compensatorAndPTFE compensatorIt is essentially a kind of thing-absorbing displacement by flexible materials. Why dare you say to carry corrosion? Because the lining material has an aging life of at least five years when the concentration of hydrogen sulfide is several hundred ppm and the temperature is below 100℃, this is supported by the national standard-the corrosion resistance is clearly stipulated in the National Standard for Non-metallic Expansion Joints JB/T 12235-2015.
Don't just look at the caliber when choosing the type. Temperature and medium concentration are the decisive factors
Many people come up and ask "How much is DN500", as if the caliber is set and it is done. Tsk, so wrong. The killer of non-metallic expansion joints of gas pipelines lies in selecting lining materials for different working conditions. The medium temperature is lower than 80℃, the hydrogen sulfide concentration is less than 500mg/m³, and butyl rubber is enough. Temperature scurrying to 120°C? You have to replace it with fluororubber or PTFE. If there are aromatic solvents in the medium, thenPTFE-lined hoseThat full PTFE lining. How to judge? Don't pat your head, throw the working condition parameters (temperature, pressure, media composition, displacement) to the manufacturer, and let them calculate the design life according to JB/T 12235. Also don't forget the pipe arrangement: horizontal pipe or riser? Is there any lateral displacement? These directly determine whether you want to limit the tie rod or not.
Installation and routine maintenance: What position is right to adjust the tie rod nut
I've seen too many rollovers in the installation process. Many people get the expansion joint and watch the tie rod nut screw to death directly, just to save trouble. As a result, as soon as the pipeline heats up, the expansion joint has no space to compensate, and the flange is forcibly pulled and deformed. How to adjust the tie rod nut? The standard practice is to first calculate the pre-tension or pre-compression value according to the design displacement, and then twist the nut to keep the expansion joint in this position, while ensuring that the flanges at both ends are parallel. After the installation is completed, will these tie rods be removed or not? Depends on the situation-if it is a tie rod used for limiting position, it must be loosened after installation, so that the expansion energy saving can expand and contract freely; If it is a tie rod for transport protection, remove it directly. Routine maintenance is simpler: Visually inspect the fabric surface every month for bulging, scratches, and see if the nuts are loose. If you find an air leak, don't hesitate to contact the manufacturer directly to change the liner, don't take the glue yourself.
Compared with metal expansion joint, what is the advantage of non-metal in gas pipeline
In fact, there is no need to compare this question, and the conclusion is obvious. The biggest flaw of metal expansion joint on gas pipeline is corrosion and stress concentration. Why? Metal bellows (whetherUniversal corrugated expansion jointStillCorrugated expansion joint for power station industry) By the deformation of thin-walled stainless steel to absorb displacement, the wall thickness is only a few tenths of millimeters, and it will leak once the pinhole is corroded. WhileNon-metal expansion joint of gas pipelineThe lining thickness is usually 3-5mm, and there is no welding heat affected zone like metal, and the overall corrosion resistance is one order of magnitude higher. In addition, non-metal has low elastic modulus, and its ability to absorb multi-directional displacement (axial, transverse and angular) is much stronger than that of metal. Especially for the common deflection and vibration of gas pipeline, it has self-damping effect and can reduce noise.
You say the metal expansion joint is useless? Of course, it is useful. High-temperature and high-pressure steam pipelines and supercritical media have to rely on metals. However, gas pipelines are generally low-temperature (≤300℃) and low-pressure (≤0.5MPa), and non-metals are completely sufficient, and the cost performance is high. Don't be stuck following the trend.
All in all, when it comes to model selection, knowing the working conditions is more important than anything else. Reelection next timeNon-metal expansion joint of gas pipelineFirst, take a piece of paper and write down the media composition, temperature, pressure and displacement, then set the lining material according to JB/T 12235, and adjust the tie rod nut according to the specification, so that it will basically not overturn. If you are still unsure, ask the manufacturer for a confirmation sheet, write it clearly in black and white, and everyone is practical.