What are single and triple waves? Find out the structure before choosing
The core of the metal expansion joint is that bellows, and the wave number is the number of corrugations. Single-wave expansion joints have only one ripple, and three waves are three ripples-it sounds like crap, but many people run to ask for the price without even figuring it out.
Structurally, the single-wave expansion joint is more like a "spring sheet", and the wall thickness, wave height and wave distance are all fixed. The three-wave expansion joint is formed by three single waves welded in series or integrally, and there is a transition section between each wave. To put it bluntly, a single wave is "one section" and a three wave is "three sections strung together".
But don't think that three waves are as simple as three single waves stacked. The wave number has changed, and the stiffness, compensation amount and pressure resistance of the whole expansion joint are all another set of logic. And common products on the market, such as ourUniversal corrugated expansion jointSingle-wave and three-wave are also different in end structure and guide tube design.
Performance Differences: How Different Are Compensation Amount, Stiffness and Pressure Resistance
The axial displacement absorbed by single wave energy is usually only a few millimeters to more than ten millimeters, and the three wave energy is up to tens of millimeters. But what about the cost? The stiffness drops with the wave number-single wave stiffness is high, three wave stiffness is low. Some people think that low stiffness is so soft and wrong.
Low stiffness means that under the same pressure, the bellows is easier to deform, and it is easy to fatigue if the deformation is large. What about pressure resistance? Because the wall thickness of single wave is relatively thicker (under the same caliber), the withstand voltage is usually higher than that of three wave. For example, with the same design of DN200 and 0.6MPa, the blasting pressure of a single wave can reach more than 3MPa, while the blasting pressure of three waves may only be 2.5MPa. It's not an absolute value, but the trend is there.
When the three-wave expansion joint is subjected to lateral displacement, each wave will "share" the deformation, but at the same time, it is also prone to inter-wave interference. We doExternal pressure single axial expansion jointIt has been encountered that if the wave distance design of the three waves is unreasonable, the outer wave will be deflated. That's a real thing.
Application scenario disassembly: Which working condition must use single wave? Which scenario is more stable with three waves?
Is the medium in your pipes under high pressure? Does the temperature fluctuate a lot? If the answer is "high pressure, small displacement", then a single wave is the lifeblood. For example, the compact space on the steam pipeline has a displacement of 5mm and a pressure of 1.6MPa. If you use three waves, it will be easy to tremble. We've done it for the power station industryCorrugated expansion joint for power station industry, the main steam pipeline is all single wave plus external pressure structure, why? Because the safety margin is sufficient.
On the other hand, if it is low pressure and large displacement-such as flue gas pipes and air-cooled islands, three waves are the right way. For example,Double hinge expansion joint for air-cooled island vacuum pipeline, the tube is tens of meters long, the thermal expansion and contraction are tens of millimeters, and the single wave can't hold it at all. The three waves cooperate with the hinge structure, which is stable. There are also hot air ducts in the cement industry, which have high temperature but low pressure, and three-wave belt guide tubes, which can double their life.
The pressure is not high but frequent vibration compensation is required. For example, the pump outlet can absorb multi-directional displacement with three waves, but be careful not to choose the wrong model — —Compound hinge transverse expansion jointThis is what it does specifically, and it has nothing to do with wave number.
The most common mistake made in model selection: blindly pursuing wave number or looking only at price
Two days ago, I met a customer and said, "I want three waves because the compensation is large"-as a result, his pipeline pressure was 2.5MPa and the temperature was 400℃, and the three waves cracked after three months. Later, the columnar instability caused by internal pressure was checked. You say it was wrong or not?
Just look at the price. Single wave is cheap and three wave is expensive, so choose single wave. As a result, the displacement was not enough, and the tube deformed the expansion joint by hard pulling, and the guide tube flew. Tsk, we see too many of these things.
Selecting the wave number is not a pat on the head. You have to calculate the compensation requirement first, then inverse the stiffness, and then check the pressure and fatigue life. We have an internal formula: single wave for small displacement and high pressure, three waves for large displacement and low pressure, and double waves or multi-layer waves for the middle zone. Oh, yeah,Large diameter thick wall expansion jointSometimes single wave is also used, because the wall thickness can be very thick and the pressure resistance is easy.
Professional advice: Introduce the wavenumber from the pipeline parameters, and place an order after calculating it clearly
How on earth is that calculated? The first step is to get the pipeline design parameters: medium, pressure, temperature, pipe diameter, pipe length and fixed bracket position. The second step is to calculate the amount of thermal displacement. Step 3, determine if you need axial, lateral, or angular compensation.
A section of DN300 steam pipeline with a length of 20 meters, a temperature difference of 200℃ and an axial displacement of about 30mm. Pressure 0.8 MPa. If a general-purpose corrugated expansion joint is used, the rated compensation amount of single wave is up to 10mm, and three single waves need to be connected in series, but the stiffness increases after series connection, and multiple sets of tie rods are required. It's better to go straight to three waves and get it done in one. However, it should be noted that the three waves at 0.8MPa should be checked whether plane instability will occur. Usually, we will add a guide sleeve or selectStraight pipe pressure balanced expansion joint。
Don't believe that "three waves are definitely better than single waves" or "single waves are safer". Each wavenumber has its reason for existence. We doHigh temperature axial expansion jointWhen, the wave number will be adjusted for different temperature segments: three waves below 600℃, and a single wave is used to thicken the wall above 600℃, because the material creeps at high temperature, and multiple waves are easy to be uneven.
If you are still unsure, send the pipeline parameters to our technical department, and they will calculate it with finite element, which is ten times better than slapping your own head. After all, which is better, single-wave or three-wave metal expansion joints, is never a multiple-choice question, but an arithmetic question.