Rubber-lined metal expansion joint: How to choose the "flexible joint" of corrosion-resistant pipeline?
Old masters engaged in chemical industry, desulfurization and hydrometallurgy all know that the biggest headache for pipeline leakage is not the flange gasket, but the compensator that absorbs thermal expansion and contraction. Ordinary stainless steel bellows look like paper paste in front of acid, alkali and salt, and pitting and perforating in a few months. At this time, the rubber-lined metal expansion joint is the role of "rescue"-to put it bluntly, it is in conventional metal bellows (such asUniversal corrugated expansion joint) A rubber liner is attached to the inner wall. It not only has the skeleton ability of metal bellows to absorb displacement and vibration reduction, but also separates the corrosive medium by rubber layer. Is that the truth?
Why do you have to add that extra layer of rubber?
Corrosion and abrasion resistant. Think about it, the wet flue gas pipe behind the desulfurization flue gas baffle door contains sulfuric acid and sulfurous acid in the medium, which is not high in temperature but extremely corrosive. Ordinary stainless steel can't withstand chloride ion stress corrosion, and it will perforate in a few years. However, the rubber-lined metal expansion joint can last for several years under the working condition of 80℃. Another example is slurry transport, where the particles are worn seriously, and the rubber lining is much more wear-resistant than the metal itself. Two days ago, I met a customer who said that they usedrubber compensatorAll-rubber structure, low pressure, rotten in two years, replaced with rubber-lined metal expansion joint after the life doubled. Tsk, this is a typical selection mistake-the rubber compensator is suitable for normal temperature and pressure-free pipelines, and it can't bear the corrosion conditions with pressure and temperature.
Choose a few numbers to get stuck, don't rely on your feeling
Design pressure, working temperature, displacement amount and medium composition, one less of these four parameters can't work. The pressure should not exceed 2.5MPa, and the temperature should not exceed 120℃-beyond this point, the rubber will age and become brittle, so you have to consider itPTFE-lined hoseOrPTFE compensatorYeah. How to calculate the displacement amount? Referring to the common formulas of expansion joints, axial, transverse and angular displacements must be taken into account. In addition, note that the direction of the guide tube must be consistent with the flow direction of the medium. When installing, the arrow is pointed opposite, and the rubber lining will be quickly washed off. The specific function of the guide tube of the expansion joint is to divert and protect, and the wrong direction is equivalent to white installation.
Installation pitting: the tie rod nut is not adjusted, and it is directly wasted
Rubber-lined metal expansion joints usually come with transportation rods when they leave the factory. This thing is called transportation rods, and its purpose is to prevent the deformation of bellows during transportation. Must be loosened after installation! Otherwise, the expansion joint can't move at all and becomes a rigid pipe section, and the thermal expansion and contraction all depend on the pipeline. When adjusting the pull rod, it should be balanced and symmetrical. Don't screw one to death and then screw the other-refer toCorrect installation method of expansion joint of large tie rodFirst, pre-tighten to the initial length, and then tighten symmetrically one after another. And guess what? In order to save trouble at some sites, the tie rod is not loosened directly, and as a result, the weld cracks within a few days of startup. Another point: when welding, be sure to stuff canvas or asbestos board into the bellows to block splashing. If the welding slag burns through the rubber layer, it will be scrapped. The role of the tie rod of the expansion joint is to limit displacement and protection, but it must be adjusted in place after installation.
Compared with similar products, where is the rubber-lined metal expansion joint stuck?
- rubber compensator: All rubber structure, low pressure, not resistant to negative pressure, suitable for normal temperature pressure-free pipeline.
- PTFE-lined hose: Stronger corrosion resistance and higher temperature resistance (200℃ +), but the cost is 3~5 times more expensive, and the bending life of PTFE lining is not as good as that of rubber.
- PTFE compensator: The ultimate solution for high temperature and strong corrosion scenarios, but the price is high and the installation requirements are high.
Moderate price, temperature resistance 80~120℃, suitable for wet desulfurization, chemical pickling, paper bleaching and other scenarios. If the working conditions are both high temperature and strong corrosion, then you have to use a PTFE compensator or PTFE-lined hose. To put it bluntly, selection is about calculating an account-what's the temperature? How strong is the corrosion? What is the budget? You know how to choose if you figure it out.
A practical case to help you avoid detours
Clean flue of wet desulfurization system of a power plant, originalNon-metallic expansion joints (fabric fiber expansion joints)It leaks and corrodes in two years. Changing the stainless steel corrugated expansion joint can't bear the chloride ion stress corrosion. Finally, rubber-lined metal expansion joint was selected, lined with butyl rubber, with design pressure of 0.3MPa, temperature of 65℃ and axial compensation of ±50mm. It has been operating for 18 months since installation and no leaks have been found. Key experience: The thickness of rubber layer is recommended to be more than 6mm, and the medium flow rate should not exceed 10m/s, otherwise it is easy to wear. In addition, if the pipeline needs frequent disassembly and maintenance, you can consider installing manual plug-in plate isolation doors at both ends of the expansion joint to facilitate isolation and maintenance.
Therefore, if you are also struggling with choosing rubber or metal, you might as well take a look at the medium temperature and corrosion strength first-figure out this account, and the answer will come out naturally.