Splash cold water first: No standard answer
The pressure resistance of metal expansion joint is never a fixed value. It is linked to the corrugated material, the number of layers, the wall thickness, the presence of reinforcing ring, the working temperature and the diameter. You ask "maximum withstand voltage", just like asking how fast a car can go-can Ferrari and Wuling Hongguang be the same? There are general-purpose corrugated expansion joints and large-diameter thick-walled expansion joints in this station. The latter is specially designed for high-pressure scenarios, and the pressure level differs by several orders of magnitude. Two days ago, I met a customer, and he said, "Give me a DN200 expansion joint that can carry 10MPa". I said you should tell me the temperature, what the medium is and how big the displacement is first, but he was still impatient. As a result, steam pipeline, 500℃, 3.5MPa, guess what? Choose a corrugated expansion joint for power station industry, and the conventional design pressure of 2.5~6.4MPa is enough. If it is hard to 10MPa, the fatigue life will directly cut to the ankles.
Core parameters affecting withstand voltage
Corrugated material is the first threshold. The allowable stress of 304 stainless steel is about 137MPa at room temperature, which is slightly higher than that of 316L. However, at 600℃, Inconel 625 can still maintain its strength, and 304 is already as soft as noodles. Number of corrugated layers-the compressive capacity of single layer is limited, and multi-layer corrugation can distribute stress through interlayer friction, but at the cost of increasing stiffness and poor ability to compensate displacement. The wall thickness from 0.5mm to 2.0mm, with every increase of 0.5mm, the withstand pressure can be increased by about 30% ~50%, but the fatigue life may also be decreased, because the thick-walled corrugation is more likely to produce stress concentration in the trough. The reinforcement ring, to put it bluntly, is to add a hoop between the corrugations to prevent excessive deformation of the trough, which is almost necessary under high pressure conditions.
Medium temperature is a hidden killer. The yield strength of the material decreases by 20% ~30% for every 100℃ increase in temperature. For example, the single-layer corrugated expansion joint of DN200 can carry 1.6MPa at room temperature, but may only leave 1.0MPa at 400℃. You select the model according to normal temperature, and the expansion joint will bulge directly when the scene runs at high temperature. If this account is not clear, the design will be in vain.
Which products of this site can carry high pressure?
Corrugated expansion joints used in power station industry, with a common design pressure of 2.5MPa ~6.4MPa, are specially matched for steam pipelines and steam turbine units in power plants. Stainless steel or Inconel are mostly used as materials, and some have lining cylinders and guide cylinders. Large diameter thick-walled expansion joint, the wall thickness is more than 3mm, plus multi-layer corrugation and reinforcing ring, the maximum can reach 10MPa or even higher. In addition, there is a kind of artifact-external pressure single axial expansion joint. Structurally, the bellows is placed outside, so that the medium pressure can resist a rigid inner cylinder from the inside. The bellows only bears the bending stress caused by axial displacement, and does not directly bear the internal pressure. Therefore, its pressure resistance is much stronger than that of ordinary internal pressure expansion joints. But don't think that high pressure is invincible-the higher the pressure, the shorter the fatigue life, which is a dead hole.
The game between pressure resistance and fatigue life
You have to let the expansion joint carry 10MPa, OK, but the number of cycles may drop from 10,000 to 2000. In actual engineering, many customers ask "What is the highest resistance?" I usually ask: "How long do you plan to use it?" Under high pressure conditions, the material is prone to cracks in the trough stress concentration zone. A real case: A high-temperature and high-pressure pipeline in a chemical plant selected an expansion joint with a pressure of 8MPa, but it leaked in half a year. Check the reason, the design pressure is 5MPa, but the pressure fluctuates frequently during actual operation, starting and stopping once a day, and the fatigue life is only enough for 300 cycles. Later, the external pressure single axial expansion joint was changed, and the pressure level was reduced to 4MPa, but the life time was increased to 10,000 times, and there was no problem after three years of use. When selecting a model, you should balance design pressure with life expectancy, rather than staring at a number.
Selection suggestion: Don't pat your head
First, clarify the working pressure, temperature, medium and displacement-for example, for steam pipelines, the temperature is 500℃ and the pressure is 3.5MPa at full load, so you have to use a high-temperature axial expansion joint or a special model for power stations, and check the fatigue life. The best way is to send the working condition parameters to the manufacturer and let them calculate. The rotary compensator and double hinge transverse expansion joint of this station also have their own applicable scenarios. Don't take high pressure as the only standard. The rotary compensator is suitable for long-distance directly buried pipelines, and the double hinge transverse expansion joint can absorb lateral displacement and angular displacement, but their pressure resistance is generally not as high as that of large-diameter thick-walled expansion joint. If you are in the cement industry, the flue gas pipeline has high temperature and dust, and the metal corrugated expansion joint in the cement industry is lined with wear-resistant lining. Pressure resistance is not the main contradiction, but wear resistance and temperature resistance are. In summary, what is the highest pressure resistance of metal expansion joints? Ask about design life and working conditions first, then talk about pressure.