Find out one thing first: what will happen if the number of ripples is more or less?
A few days ago, a customer who makes steam pipes asked me, saying that the steam pipes in their factoryUniversal corrugated expansion jointIt leaked after less than half a year of use. When I removed it, I found several cuts at the root of the corrugation. I asked him how to select the type at that time, and he said, "I just matched a regular one according to the diameter of the pipe, and I didn't care too much about the number of corrugations". Tsk, this is the typical problem-the number of ripples is not determined by patting the head, and if there is more or less, something will happen.
Let's put it this way, when the number of corrugations is small, the displacement that a single corrugation has to bear will be large, the stress will be concentrated, and the fatigue life will fall by a cliff. Especially in high temperature and high pressure conditions, such as those used in power stationsHigh temperature axial expansion joint, the number of ripples is not enough, and it will crack in a few months. Conversely, what about more ripples? You think more is safer? Wrong. If there are more ripples, the overall stiffness will decrease, the pressure bearing capacity will follow, and instability will easily occur-if the ripples collapse like noodles, it will be completely wasted.
Therefore, the question of "calculating the number of compensator ripples?" is not a simple addition and subtraction, but to find a balance between the compensation amount, pressure, temperature and fatigue life. To put it bluntly,Number of corrugationsIt's a lever: it can't bear pressure a little to the left, and it can't live a little to the right.
What does the calculation formula look like? These are the core variables. Don't be scared by the formula
When it comes to formulas, many people have big heads. But don't be afraid,Compensator Ripple Number CalculationThe core logic is actually four variables: single-wave compensation amount, total compensation amount, pressure conversion coefficient and temperature correction coefficient. The formula looks like this:
Required number of corrugations = total compensation ÷ (single wave compensation × pressure coefficient × temperature coefficient)
Simple right? However, in practical applications, the "pressure coefficient" and "temperature coefficient" are the most easily overlooked.
Take the pressure coefficient, aExternal pressure single axial expansion jointThe design pressure is 1.0MPa, and the actual operating pressure is only 0.6MPa. If you calculate according to 1.0MPa, the number of corrugations will be too large, which will increase the cost in vain and reduce the stability. Conversely, if you useDirect buried (fully buried) type expansion jointOn, the pressure of underground pipelines fluctuates greatly. If you calculate according to the average value, then wait for an accident.
The temperature coefficient is more pit. Many customers take the single wave compensation amount at room temperature to set the 300℃ steam pipeline, which is definitely not allowed. At high temperature, the elastic modulus of the material decreases, and the single wave compensation ability will be discounted. Such asMetal Corrugated Expansion Joints in Cement IndustryThe flue gas temperature is often five or six hundred degrees, so it is necessary to use heat-resistant alloy and reduce the temperature, otherwise the calculated ripple number is a paper tiger.
Under different working conditions, the number of ripples must be adjusted-give you a few real scenarios
Desulfurization flue gas baffle doorMatching corrugated expansion joint. Desulfurization flue gas has high humidity and low temperature (generally about 70℃), but contains a large amount of acidic condensate. The number of corrugations should not be too small because additional axial displacement due to fouling is to be absorbed? No, the key is to ensure that the spacing between the corrugations is large enough to avoid corrosion by fluid accumulation. In this case,Compensator Ripple Number CalculationAdd an additional corrosion margin-it is usually recommended to reserve 15% ~20% more corrugation than pure displacement calculation, and choosePTFE-lined hoseOrPTFE compensatorTo resist corrosion.
Double hinge expansion joint for air-cooled island vacuum pipeline。 The air-cooled island pipeline has a large diameter and a negative pressure operation. If the number of corrugations is too large and the stiffness is too low, the vacuum degree will deflate the corrugations. At this time, it is necessary to reduce the number of ripples or increase the wave distance. I have seen a project that used a 30-wave expansion joint, and as a result, once the vacuum was pumped, the troughs stuck directly together. Later, it was changed to a design with 18 waves and increased wave thickness, and it was done.
Corrugated expansion joint for power station industry, the main steam pipe. Operating temperature 540 ℃, pressure 10 MPa. Under this condition, the single-wave compensation amount is only about one third of that at normal temperature. The creep fatigue interaction must also be considered in the selection. The number of ripples is generally calculated by the manufacturer with finite element, so don't pat your head yourself. Before, there was a power plant diagram to save money, and I calculated it by myself according to a simple formula. As a result, the number of ripples was reduced by 30%, and the pipe burst in two months.
What do these examples illustrate? Formulas are dead, working conditions are alive. The same oneCompound hinge transverse expansion jointUsed in thermal pipe gallery and used in chemical pipeline, the number of corrugations may be twice as different.
Selection and Pit Avoidance Guide: Half of these mistakes have been stepped on by customers I have seen
Just look at the total displacement, not the displacement direction. Many people take the total thermal elongation of the pipe and substitute it into the formula, butCompensator Ripple Number CalculationWhen, the single-wave compensation amount is divided into axial, transverse and angular directions. You use an axial expansion joint to absorb the lateral displacement. No matter how many corrugations are, it will quickly distort and break.
Superstition that "the more ripples, the longer the life". Wrong! An increase in the number of corrugations reduces the displacement that a single wave is subjected to, but at the same time reduces the overall stiffness and stability. ForStraight pipe pressure balanced expansion jointThis kind of structure needs to counteract the pressure thrust, the number of corrugations must be strictly controlled. More, the pressure thrust can't be balanced; Less, main bellows overloaded.
Ignore installing pre-stretch/pre-compression. For example, a steam pipe is installed at 20°C and operates at 280°C. If it is not pre-stretched in the cold state, the expansion joint will withstand additional stretching in the hot state. You calculated the number of ripples according to the actual displacement, without considering the amount of pre-stretching, and the result was that the number of ripples was small. The correct way is to deduct the displacement generated by pre-stretching in reverse when calculating the total compensation amount. For example, if pre-stretching is 50%, the total compensation amount will be calculated as 50% of the actual displacement. Can the number of corrugations be halved? No, it can't be halved, because pre-stretching only changes the zero position, and the fatigue life still has to be calculated according to the total displacement-it is easy to be swirled here, so it is recommended to find the manufacturer to confirm.
Mixed formula for non-metallic expansion joints and metallic expansion joints.Non-metallic expansion joint (fabric fiber expansion joint)Andrubber compensatorThe logic of calculating the number of corrugations (actually bands) is completely different, because they depend on the elastic deformation of fabric or rubber, rather than the plastic deformation of metal. You take the formula of metalRubber PTFE compensatorThe result must be wrong.
UnderstandCompensator ripple number calculation?Actually, it's not that mysterious, but you can't be too confident. In case of complicated working conditions (high temperature, high pressure, corrosion, large diameter), it is much more reliable to contact the manufacturer directly to come up with a plan than to calculate it yourself for half a day. We have a library of cases of various working conditions, fromFlue gas baffle doorToSleeve type pipe expansion joint, can be referred to.