"Can't expand energy saving be used instead of metal hoses?" Many people asked, and I pondered that this question was definitely not an exception. The day before yesterday, I met a customer who put the general-purpose corrugated expansion joint directly at the pump outlet, and it leaked in less than two months. He patted his thigh and asked me what was going on. The reason is simple-it looks like it on the outside, but it is not the same thing at all. Today, I will make this matter clear. What should and shouldn't be used under the three working conditions, and explain it thoroughly at once.
1. Why do people always ask this question?
The expansion joint and the metal hose are both corrugated pipe structures from the appearance, and the stainless steel corrugated section by section, which looks like brothers at first glance. But the original intention of the design is very different:Metal hose(For example, the PTFE-lined hose of this station) The core function is flexible connection, solving installation deviation, absorbing vibration and adapting to arbitrary swing in three-dimensional space; Whileexpansion joint(For example, high-temperature axial expansion joint) is specially used to absorb the axial displacement caused by thermal expansion and contraction of pipelines-pushing forward and pulling back, which is its special skill.
You let an expansion joint do the work of a metal hose, like letting a weightlifter do ballet, not out of the question, but you have to stifle internal injuries. The customer mentioned earlier had a large vibration at the pump outlet and a slight lateral swing in the pipeline, but he used a universal corrugated expansion joint to carry it. As a result, the corrugated pipe was repeatedly tortured by lateral forces, and it was only a matter of time before fatigue cracked.
2. Core difference: one can "bend" and the other can "push"
Take the products of this site for example, the reason why the metal hose can be bent at will is the keymesh sleeve。 The wire braided mesh sleeve is subjected to the internal pressure of the pipe, and the bellows are only responsible for deformation, providing flexibility. In terms of pressure level, the pressure resistance of metal hoses is usually much higher. For details, you can check the pressure standard of metal hoses in this station. And the expansion joint? Its bellows have to withstand pressure and absorb displacement by compression or stretching, so the structure does not consider lateral bending. If you insist on making it bend, the local stress of the bellows will increase sharply, and the fatigue life will be directly discounted.
Metal hoses are often equipped with flanges or joints, which are convenient to assemble and disassemble, and are suitable for occasions that require frequent maintenance; After the expansion joint is equipped with attachments such as pull rod and guide tube, it is basically fixed dead, which is not suitable for turbulence. This is also something to consider when choosing a model.
3. Which situation can be substituted? — — Large diameter, long straight pipe, single displacement
Not completely irreplaceable. For example, on the steam pipeline of the power station, the pipeline is thick and long, and the axial displacement caused by thermal expansion and contraction is very large. Moreover, the site space is narrow, and the pipe frame layout is limited. At this time, useDirect buried (fully buried) type expansion jointReplaces metal hoses and works great. The reason is: this kind of pipe has almost no vibration, and the displacement direction is a simple axial push-pull, which is just the appetite of the upper expansion joint. In addition, the cement industry is also commonMetal Corrugated Expansion Joints in Cement IndustryTo replace the metal hose, the flange connection is simple, saving money and space.
But the premise is-the pipe must be carefully arranged with hangers to ensure that there is no lateral force. The hanger should be guided by adding the guide, and the limit of the limit, otherwise once the pipeline deviates, the expansion joint will stop.
4. In which case should you never replace it? — — High-frequency vibration, need to bend, corrosive media
To be honest, in high-frequency vibration occasions such as pump outlet and compressor inlet and outlet, honestly use metal hoses. The fatigue resistance of the expansion joint is limited (refer to this siteService life of expansion jointRelated questions and answers), in the vibrating environment, the bellows may crack after tens of thousands of cycles, while the metal hose can carry hundreds of thousands or even millions of times because the net sleeve shares the stress. If you have to top it with an expansion joint, that is to make it "short-lived".
Also, when dealing with strongly corrosive media,PTFE-lined hoseThe lining PTFE is more resistant to corrosion than ordinary stainless steel bellows. If the expansion joint is not lined, it will quickly be corroded and perforated. As for the occasion where three-dimensional random swing is required, the expansion joint is even more important-its design does not consider multi-directional displacement.
5. How to choose the model?
- Is the displacement axial or multidirectional?-Pure axial direction, consider expansion joints (such as general-purpose corrugated expansion joints, compound hinge transverse expansion joints); Multidirectional or frequent bending, metal hoses.
- Did the temperature and pressure exceed the standard?— — Expansion joints are usually used in high temperature and low pressure (refer to corrugated expansion joints used in power station industry). The application range of metal hoses is wider, but reinforced mesh sleeves should be selected under high pressure.
- Is there enough installation space for tie rods?— — Expansion joints sometimes need tie rods to limit lateral displacement. If there is not enough space, don't force it. It is more worry-free to use metal hoses instead.
If you are not sure, you can flip through the FAQ of this site, which contains aboutExpansion joint tie rod nut adjustmentAndInstallation MethodThe instructions are very detailed. Wrong choice? The cost of shutdown and repair is enough to buy dozens of right parts, and everyone will calculate this account.
6. One-sentence summary
There is no universal alternative, only the correct selection to match the working conditions. Expansion joints and metal hoses each have their own expertise-don't blindly replace them to save trouble. Next time someone asks, "Is it okay to replace a metal hose with an expansion joint?", throw this to him, and it will work better than anything else.