How to choose the universal metal expansion joint? From structure to installation
Many people call the expansion joint a compensator, but it's actually the same thing. General metal expansion joint, to put it bluntly, is a flexible element that absorbs the thermal expansion, contraction and vibration displacement of the pipeline by the deformation of metal bellows. The structure is not complicated-bellows, end tubes, deflectors, tie rods these are standard. But there are many "general" on the market. Which one is general? This site'sUniversal corrugated expansion jointIt is a typical representative. It can absorb axial displacement and has a certain angular capacity. It is suitable for temperature-20℃ to 400℃ and pressure from 0.25MPa to 2.5MPa, basically covering 80% of the conventional working conditions of chemical industry, heating and steam pipe networks.
What is the difference from the "special" expansion joint?
For example, you have a high-temperature axial expansion joint, which is specialized in carrying above 600℃;External pressure single type axial typeSuitable for high pressure and large diameter;Compound hinge transverse typeSpecializing in lateral displacement. The universal metal expansion joint is like a screwdriver in a tool box-most screws can be screwed, but when you hit a plum screw, you have to change the special head. When selecting, don't save trouble. First, calculate the thermal displacement, medium temperature and pressure grade of the pipeline. For example: the steam pipeline is 50 meters long, the temperature difference is 150℃, and the thermal elongation is about 90mm. The single wave compensation of the general corrugated expansion joint is generally 15-30mm, so 3 waves are needed, and a safety margin has to be left. Doesn't it count? When the bellows cracks or crushes to death, it's too late to cry.
Buried? Don't bury blindly!
General metal type expansion energy saving can not be buried directly? This question needs to be kindly advised-don't bury it blindly. Direct buried pipelines have specialDirect buried (fully buried) type expansion joint, the shell has been made anti-corrosion and thermal insulation, and there is a moisture drain pipe. The general-purpose expansion joint does not have this configuration, and it will rust out after two years of burial. Installation is also particular: tie rod bolts play a fixing role during transportation and installation, so don't remove them directly! After the pipeline pressure test is completed, confirm the displacement direction, and then loosen the nut to the design distance. How to tune it? According to the article on this siteExpansion joint tie rod nut adjustment answerFirst, measure the cold tightness, loosen the back mother of the tie rod, and then lock it after adjustment. Tsk, many people found it troublesome to remove the tie rod directly. As a result, the bellows deformed during transportation and was wasted when installed.
If the material is not selected correctly, no matter how good the design is, it will be useless
Material This piece, the most common corrugated pipe material of general metal expansion joint is 304 stainless steel, which has average corrosion resistance. The medium contains many chloride ions (such as seawater and some chemical media), so 316L or 254SMO should be used.PTFE-lined hoseAndPTFE compensatorThey are specially designed to deal with strong corrosive media, and they are different from general metal expansion joints. You made the wrong choice and pierced it in half a year. Calculating the labor cost of changing it once is enough to buy several right products.
Deflector-a neglected life-saver
Deflector tube. The guide tube inside the general metal expansion joint is not a decoration. It has two functions-reducing the erosion of the bellows caused by the medium flow, and guiding the medium to the center of the pipe to avoid vibration caused by turbulence. High-flow steam pipes can cut the life of bellows in half without it. For specific dimensions and installation direction, refer to this siteThe article on the specific function of the expansion joint guide tubeNote that the direction of the arrow must point to the direction of the media flow. And guess what? I have seen a factory install the deflector backwards, and as a result, the steam tore the bellows directly, and it stopped for emergency repair in half an hour. Is that the truth? If the direction is wrong, it is equivalent to not installing.
Maintenance? Pull it open and check it once a year
Finally, talk about maintenance. There is no advanced maintenance for the general metal expansion joint, just check it regularly: see whether there are cracks and corrosion pits on the corrugated surface, whether the tie rod nut is loose, and whether there is any abnormal noise in the guide tube. If the expansion joint is installed in the outdoor insulation layer, it has to be opened and inspected once a year. Many accidents are caused by water accumulation and corrosion of the insulation layer. Well, the design life is 10-15 years under normal working conditions, but in fact, depending on the number of fluctuations-steam pipelines that start and stop frequently may be fatigued in 5 years. When the time comes, don't hesitate to replace it with a new one directly, saving money and life. If you think about it, once the bellows bursts and hot steam spews out, that's no joke.
Therefore, there is no worry-free link in the selection, installation and maintenance of general metal expansion joints, but it is just that. Remember: Don't bury it blindly, don't disassemble the tie rod randomly, don't choose the wrong material, and don't ignore the direction of the guide tube. If you do it, it will work safely for you for ten years.