From Rectangle to Rounded Corner: A Structural Evolution Forced by Stress
The stress is concentrated at the corners, and the bellows is easy to crack first. The equipment engineer in the factory complained to me that every time the machine is shut down for maintenance, the first bad place is always those right angles. Think about it, as soon as thermal displacement in the flue duct comes up, the local stress energy of the weld and the corrugated plate at right angles is two or three times higher than that in the flat area, and the fatigue crack starts there. The rounded corner design is aimed at this-replacing sharp corners with transitional arcs to allow more even stress distribution. To put it bluntly, it is not thought up by patting the head, but the optimization forced out by the actual project. Our commonMetal rectangular expansion jointIf it is used in the working condition with large temperature fluctuation, the life is often held back by right angles, andRectangular metal fillet expansion jointDirectly make up for this shortcoming.
How exactly do rounded corners work? Just take it apart and see the structure
The bellows part is still pressed and molded with stainless steel sheet. Like our metal rectangular expansion joint, it absorbs heat displacement by the elastic deformation of the corrugation. But the connection between the end flange and the side plate is made with a circular arc transition, and the weld avoids the high stress zone. Plus the internal guide tube (ref.Specific Function of Expansion Joint Guide Tube-Guide the flow direction of the medium to prevent the high-speed scour from directly impacting the corrugation), and the medium scour does not directly ripple. With such a set of combination punches, the life can be prolonged a lot under the same working conditions. You might ask: Is an arc transition enough? Tsk, more than that. The larger the fillet radius, the lower the stress concentration factor. However, due to the size of the flue, it is generally R30~ R50, and the space allowance must be confirmed with the customer during design.
This thing is especially used in power plant desulfurization and cement industries
Take the flue matched by the desulfurization flue gas baffle door as an example, the temperature fluctuates greatly, the medium is corrosive, and the rounded rectangular expansion joint can bear more than the ordinary rectangle. Two days ago, there was a customer who was doing power station renovation. He used to use an ordinary rectangle, and he had to change it in two years. After changing the rounded corner structure, it is still running for 4 years. Not blowing, rounded corners rely on this reputation to stand in the industry. Used in the cement industryMetal Corrugated Expansion Joints in Cement IndustryThere are similar problems. Right-angle stress concentration in high-temperature dust environment directly leads to air leakage, and the reliability is obviously improved after replacing it with rounded corners. So you see, this is not some fancy, real performance improvement.
There are only two places where the car is easy to overturn when selecting the model
One is to ignore the installation direction-the arrow direction of the fillet expansion joint (refer toThe direction of the arrow of the expansion joint refers toMedia flow direction) must be pointed to the media flow direction. If the guide tube is installed backwards, it will fail. When the ripples are directly washed and worn out, don't blame the product for not working. Second, tie rod nut adjustment (refer toHow to adjust the tie rod nut of expansion joint) Not in place. Did the limit pin remove before transportation?Large tie rod expansion jointThere are cold tightness requirements during installation, and these details directly determine whether the displacement can be compensated normally. I have seen many sites, and the installer drawing saves trouble, but the cold tightness is not enough. As a result, the bellows is overstretched and directly cracked after it is put into operation. The size and pressure level are marked on the selection table, and it can be matched according to the working conditions, but the installation link is the key to success or failure.
Compared with non-metallic and round expansion joints, how to choose?
FollowNon-metallic expansion joints (fabric fiber expansion joints)Compared with, the metal rounded rectangle has higher temperature resistance and more stable pressure bearing, but the disadvantage is that it cannot absorb large lateral displacement. If the lateral displacement of your flue exceeds 20mm, consider usingCompound hinge transverse expansion jointOr simply go on non-metallic. FollowCircular expansion jointRectangle fits the flue section more and does not take up space. If your pipe section is square, don't forcibly use a round one to change it. You need to add a reducer pipe, which not only takes up space but also increases resistance, which is not worth the loss. This matter of selection, to put it bluntly, is just one sentence: the working conditions are clearly listed first-temperature, pressure, displacement, media composition, and then the product information is selected.
Maintain the core of just one point
Regularly inspect corrugated surfaces for corrosion spots and dust accumulation. Especially in the desulfurization condition, smoke and dust are easy to accumulate in the rounded transition zone. Don't beat with hard objects when cleaning dust. High-pressure water gun flushing is the safest. Why? Because corrugated plates are thin, knocking will cause local deformation, which instead will induce new cracks. The matter of lifespan, let's referService life of expansion joint— — There is no problem for 8-10 years under normal working conditions, but the premise is that the cold tightness is in place during installation and there is no excess displacement during operation. If you find corrugated pits or micro-cracks in welds, change them quickly. Don't wait until smoke leaks before shutting down. To summarize in one sentence:Rectangular metal fillet expansion jointIt is not a panacea, but in the subdivision scenario of smoke duct compensation, it maximizes the reliability and long life of metal expansion joints.