Compression 25mm: Just how much force is required for metal expansion joints?
"I want to press down a metal expansion joint by 25mm. How hard is it?" This question sounded simple, but it would be a trick to give a casually counted question. 25mm is not a small number, especially in some high-temperature and high-voltage power station pipelines or cement lines. This pressure may be directly related to whether the compensator can work normally or even be scrapped in advance. Let's break it down today,How much force can compress a metal expansion joint by 25mmHow to calculate this account.
What does 25mm compression amount mean in engineering?
Don't rush to compute power, we have to find out what the concept of 25mm is first. In the thermal expansion of pipelines, 25mm is roughly equivalent to the length of a 10-meter-long carbon steel pipe extending when the temperature rises by 200℃. Therefore, this compression amount is very common: steam pipes, hot air pipes and flues. As soon as the temperature rises, the pipeline has to find a place to "stretch". The metal expansion joint is the component that carries the displacement of the pipe. The displacement of 25mm is hard pressed onto the bellows, and the bellows is deformed, resulting in reaction force. This reaction force is the "strength" you need. But if the strength is too strong, the pipe frame, flange and equipment foundation may not be able to stand it; If the strength is too small, it also indicates that the expansion joint is too soft, which may not be able to hold the internal pressure or the service life may be discounted. Therefore, this force is not the greater the better, nor is it the smaller the better, it has to be just right.
Stiffness of expansion joint- -the core of determining force
What is the source of force? Stiffness. To put it bluntly,Stiffness of bellowsIs how much Newtonian force is needed per 1 mm of compression. The calculation formula of stiffness, which is specifically mentioned in the common questions and answers in our station, is directly linked to the wave height, wave distance, wall thickness, number of layers and elastic modulus of the corrugation. For example: aUniversal corrugated expansion joint(DN200, single layer stainless steel 304, wave height 40mm, wall thickness 1.5mm), single wave stiffness is about 500~800 N/mm. If it has 4 waves, the overall axial stiffness is the single wave stiffness divided by the wave number (in series), which is about 125~200 N/mm. Then to compress 25mm, the theoretical force is stiffness multiplied by displacement: 125~200 N/mm ×25mm =3125~5000 N, which is about 319~510 kgf when converted into kilogram force. Which is about half a ton. But don't be too happy-this is just an estimate.
Different structures and different parameters of expansion joints have several times difference in force energy
And guess what? For the same amount of compression, with a different expansion joint model, the force may soar from a few hundred kilograms to a few tons. Let's say:High temperature axial expansion jointIn order to withstand high temperatures, Inconel 625 or 321 stainless steel is usually used, with thickened wall thickness and increased number of layers, and the stiffness is more than double that of ordinary 304. Another exampleLarge diameter thick wall expansion joint, DN1000 or above, the wave height is short, the wall is thick, and the single wave stiffness can easily reach 3000 N/mm. Compressed by 25mm, the force ran for seven or eight tons and went. And, in turn, someCompound hinge transverse expansion jointOrStraight pipe pressure balance expansion joint, because multiple bellows in the structure are connected in series and parallel, or there are tie rods and hinges to share the load, the actual axial force acting on the bellows may be much smaller. AndMetal Corrugated Expansion Joints in Cement IndustryOften equipped with a guide tube, the guide tube will eat part of the displacement, and the actual compression amount of bellows is not as much as 25mm. So before asking "how much force", you have to be clear: Which expansion joint are you using?
A Practical Method for Estimating the Required Force
How can you quickly estimate when you don't get the specific parameters of the manufacturer? Remember three elements: wave number, single wave stiffness, displacement. The single-wave stiffness can be roughly calculated according to an empirical formula: for U-shaped bellows, the single-wave stiffness ≈ (1.7× E × t³) / (h³ × n), where t is the wall thickness, h is the wave height, n is the number of layers, and E is the elastic modulus. But to be honest, this formula calculated and the actual deviation of 20% is considered normal. A more reliable way is to directly check the stiffness value on the manufacturer's sample, or ask the manufacturer forMetal expansion joint weight table(There is a certain positive correlation between weight and stiffness), or just look at itModel and size of expansion jointThe axial stiffness parameters of the outside and inside. In our stationUniversal corrugated expansion jointAndCorrugated expansion joint for power station industryIn the sample manual, the axial stiffness value of each specification will be listed, and it will come out as soon as you multiply it. One more thing: don't forget the safety factor. The thrust of the pipeline system also includes the blind plate force generated by internal pressure, which is sometimes greater than the compression force, and has to be superimposed when designing the pipe frame.
Don't go over the limit! Where is the limit for compressing 25mm?
The force is calculated, but can you hard press 25mm? Depends on the design of the expansion joint to allow displacement. Each expansion joint has a rated axial compression when it leaves the factory. For example, ±50mm refers to the total displacement, but the compression may only be 25mm or 30mm on one side. If the rated compression amount is exceeded, the bellows will become unstable, bulge or have uneven wave pitch, and in severe cases, it will tear directly. EspeciallyExternal pressure single axial expansion joint, its bellows is subjected to external pressure, and excessive compression may lead to local buckling. In addition,Direct buried (fully buried) type expansion jointUnder soil constraints, uneven compression can also be problematic. Therefore, before compressing 25mm, confirm whether the product nameplate or technical parameters allow this displacement. If not enough, you have to choose a model with multiple wavenumbers or more compensation, such asDouble straight pipe bypass pressure balanced expansion joint, which can share the displacement through multiple bellows, so that each wave is within a safe range.
Summary: Selection calculation, it is best to let the manufacturer help you calculate
Having said so much, in fact, the last big truth: Don't do your own blind calculations. Leave professional matters to professional people. The force, displacement, fatigue life and pressure thrust of the expansion joint are coupled with each other, and the actual stiffness and allowable displacement are different in each manufacturer's bellows forming process. You send the working condition parameters (pipe diameter, temperature, pressure, displacement, medium) to the manufacturer, and the manufacturer calculates it with special software, so that the resulting force is reliable. Like the one we have hereFlue gas baffle doorSupporting pipelines,Desulfurization flue gas baffle doorThe expansion joints in the system are all reaction forces calculated according to the actual pipeline layout of customers, which are used to design the thrust of baffle doors. You take a general formula to calculate the force. After installing it, the pipe frame deforms and the flange leaks, and it is too late to regret it.
How much force can compress a metal expansion joint by 25mm？ The answer is always one sentence: "Look at the specific expansion joint parameters." But if you are willing to send the working conditions, we can help you calculate it. After all, with the right force and the right compensator, the pipeline can run safely for ten years.