Let's start by talking about common misunderstandings
When many people hear about expansion joints, their first reaction is that kind of big guy with several layers of ripples and sturdy look. However, in practice, in the pipeline system, where the installation space is stuck and the displacement is only a few millimeters, it is cumbersome to use multi-wave expansion joints-high cost, soft stiffness and easy instability. Who should play at this time?Circular metal single-wave expansion joint。 To put it bluntly, it is a corrugated, the simplest metal compensator of construction. But it is simple, and there are many ways. Let's break it up and crumble it into pieces in this issue.
Let's talk about the structure first. What is the difference between single wave and multi-wave?
The core difference between a single-wave expansion joint and a multi-wave expansion joint lies in the number of corrugations. A corrugation bears pressure, and the stiffness is relatively greater, but the compensation amount is also small-usually the axial compensation amount of a single wave is within 10mm. Don't underestimate this displacement. The thermal expansion and contraction of steam pipelines in power plants, air ducts in cement plants, and even chemical pipelines are often just a few millimeters. Moreover, because of the small wave number and short overall length, the single wave node is particularly suitable for installation next to the valve and the equipment outlet. In addition, if the "universal corrugated expansion joint" of this site is made of a single-wave structure, it is essentially this kind of product-but when selecting the model, you have to clearly tell the manufacturer to ask for a single-wave version, otherwise you will be given multiple waves by default, so it will be blind.
What are the advantages of single-wave expansion joints? Three hard indicators.
First,High fatigue life。 Some people think that the fewer the number of ripples, the more concentrated the strain each wave bears? No, on the contrary-the stress distribution of single wave node is more uniform because of the large wave pitch and relatively reasonable wave height. According to GB/T 12777 standard, the design fatigue life of single-wave products is usually 15%-20% higher than that of multi-wave products with the same caliber. This data is not made up by me. You can find it by looking through the standards. Second,Strong pressure bearing capacity。 With the same wall thickness material, single wave node allows the pressure to be one grade higher than multi-wave. For example, 304 material, multi-wave node may only go 1.0MPa, and single wave node can go up to 1.6MPa. Once the pressure difference comes out, the selection cost is directly saved. Third,Small installation space。 This is not expanded, everyone knows it, but there is a detail: because the single wave node is short, the distance between adjacent pipe supports can be closer, and the constraints on the pipe layout are small.
Don't step on pits when selecting models. I just ran into an example two days ago.
The customer is engaged in steam pipeline, with a pressure of 1.6MPa and a temperature of 350℃. He said that he wanted to use a universal corrugated expansion joint, but it couldn't be installed on site-the flange spacing was only 200mm, and the multi-wave joint couldn't be stuffed in at all. Later, it was changed to the single-wave version of "high-temperature axial expansion joint", and the problem was solved. Therefore, pay attention to three points in the selection: First,The amount of compensation is not hardIf the compensation amount of the single wave node is not enough, go to the duplex or big tie rod, and don't kill the single wave. For example, if the axial displacement exceeds 10mm, if you use single wave, the fatigue life will plummet. It is better to directly choose "compound hinge transverse expansion joint" or "straight pipe pressure balance expansion joint". Second,The guide tube must be equipped。 The internal flow rate of the single node corrugation is high, and it is easy to erode without the guide tube. This is the specific function of the guide tube in our previous FAQ. Simply put, it is to protect the inner wall of the corrugation and avoid direct erosion of the medium. Third,Pay attention to the end tube materialUse 321 or 347 stainless steel for high temperature working conditions, and use 304 for cheap. 304 is prone to intergranular corrosion above 350℃, and it will crack in less than two years. At that time, the cost of replacing it once is enough for you to buy three new ones.
Installation and maintenance, there are also a lot of attention.
Many people ask how to adjust the tie rod nut of the expansion joint. Because of the high stiffness of the single wave joint, the installation method of pre-tensioning or pre-compression is particularly critical. If you check the "Correct Installation Method of Large Tie Rod Expansion Joint" on this site, although the products are different, the principle is the same: the transport screw must be removed after installation, otherwise the compensation function will fail. Remember, the single wave node itself does not have its own restraint device, and the transport screw is temporarily fixed. If it is not removed, the pipe will expand thermally, and the corrugated node will be jacked to death, which will burst directly. In addition, the single-wave expansion joint tends to ignore the lateral displacement-because of its large axial stiffness, the influence of lateral force on the pipe support is more obvious than that of multi-wave joint. It is recommended to keep sufficient distance between guide brackets in pipeline design. For specific values, please refer to the relevant suggestions of "Service Life of Expansion Joints" on this site. To put it bluntly, if the spacing of the brackets is not accurate, if the single wave node is biased sideways, the corrugated root will crack, and the life will be greatly reduced.
Finally, let me tell you the truth: single-wave expansion joints are not suitable for all working conditions.
For example, large-diameter thick-walled expansion joints require a large amount of compensation, but single wave can't. Or like the corrosion + large displacement environment behind the desulfurization flue gas baffle door, non-metal or multi-wave metal is reliable. Therefore, before selecting, first take your pipeline parameters against the classification of this station: simple working condition, small displacement, tight space,Circular metal single-wave expansion jointIs the king of value for money. Don't blindly follow, and don't take it lightly. If you choose the right one, you will have ten years of worry. If you are not sure, look directly at the product information of this site-metal hose, PTFE-lined metal hose, corrugated expansion joint for power station industry, metal corrugated expansion joint for cement industry... There is a parameter table under each classification, so just take your seat. In this matter of selection, spending ten minutes more reading the information will save 10,000 yuan compared with on-site rework.