How much does the metal expansion joint DN250 expand and contract exactly? Stop being fooled by parameter tables
Expansion and contraction amount of metal expansion joint DN250, no fixed value。 You are holding a model and wondering how long it will stretch? That's the same as asking "how fast can this car go"-depends on whether it's a 1.5L self-priming or a 4.0T twin-turbo. The DN250 is only a nominal diameter, and the amount of expansion and contraction depends on wave number, wave height, wall thickness, material, pressure class, and temperature. Take the usual ones on our stationUniversal corrugated expansion jointFor example, the axial compensation amount is usually between a few tens of millimeters and two hundred millimeters, but when changed toHigh temperature axial expansion jointOrExternal pressure single axial expansion jointAnd the data is completely different.
"Why can your DN250 only compensate 80mm, but that one can reach 150mm?" I said you should first see whether the working pressure of his target is 0.1MPa or 1.6MPa, and whether the temperature is normal temperature or 500℃. The same pipe, the working condition is three times different, can the expansion and contraction amount be the same? This is not a fraud of the parameter table, but the selection logic is not right at all.
To understand the scaling amount, first understand these key parameters
The first one iswavenumber-The number of twists and turns on the bellows. The more waves, the greater the expansion and contraction, but the pressure bearing capacity will decrease. The second isWave height and wall thicknessThe higher the wave and thinner the wall, the better the flexibility, but the fatigue life will be shortened. And the third isMaterials-Stainless steel 304, 316L or high temperature resistant alloy? When the temperature exceeds 400℃, the allowable stress of ordinary 304 should be folded in half, and the temperature correction coefficient must be included in the calculation of expansion and contraction.
The same DN250 is used on 0.25MPa flue gas pipeline and 1.0MPa steam pipeline, and the design safety factor is completely different. Think about it, if the low-pressure expansion joint is forced into the high-pressure pipeline, and the bellows will crack as soon as it deforms, it will be useless no matter how much expansion and contraction is. We have a customer in the cement industryMetal Corrugated Expansion Joints in Cement Industry, the medium temperature is 600℃, ask if DN250 can achieve 120mm compensation amount-of course, but you have to use double-layer bellows and guide tube, and you have to pressPressure balance typeDesign. Simply heap wave number? If it can't bear the high temperature and internal pressure, it will be scrapped in three months.
How to calculate the expansion and contraction amount of DN250 expansion joints with different structural types?
This is the easiest place to overlook.Single axial type(For example, the general corrugated expansion joint) can only absorb axial displacement, and the expansion and contraction amount mainly depends on the wave number stacking. But if you need to absorb lateral displacement or angular displacement at the same time, you have to useCompound hinge transverse typeOrDouble straight pipe bypass pressure balance type。 For example, for the same DN250, the axial compensation amount of the single axial type may be 150mm, but if it is replaced with the double hinge type, its axial compensation may only be 30mm, but it can absorb the angular displacement of ±5°-these are completely two kinds of compensation logics.
AndStraight pipe pressure balanced expansion jointIt relies on two sets of bellows to offset the internal pressure thrust, and no matter how large the expansion and contraction is designed, the pipe will not fly. When you choose a model, you have to ask clearly what direction of displacement the pipeline should compensate, otherwise you can't install it when you buy it back, and the rework cost is much more expensive than the expansion joint itself.
Actual selection: How to determine the expansion and contraction according to the thermal displacement of the pipeline?
Don't check Baidu, calculate the thermal elongation first. The formula is simple: Δ L = α × L × Δ T. Carbon steel pipeline α ≈0.012mm/m·℃. Assuming that DN250 pipeline is 30m long and the temperature difference is 200℃, the thermal elongation is 0.012×30×200=72mm. Then the axial compensation amount of the expansion joint you choose should be at least greater than 72mm, leaving 20% safety margin, that is, about 90mm.
But it is not enough to look at the axial direction-if the line has elbows that cause lateral displacement, then considerCompound hinge transverse expansion jointOrUniversal hinge type。 We have products on our site that deal with this combined displacement. In addition, don't forget the internal pressure thrust: DN250 has a blind plate force of about 49kN at 1.0MPa. If you don't use the pressure balance type, the fixed bracket has to hold this force, otherwise the pipe will fly out. Last year, there was a case in a power plant. They chose the ordinary axial type to install it in the position of a large-diameter thick-walled expansion joint, but the bracket collapsed during pressure test-a painful lesson.
Don't make mistakes about the pits that are easy to step on during installation, the guide tube and the tie rod
Let's startguide tubeIt is on the inner wall of the bellows, and its function is to guide the high-speed fluid away to avoid the bellows from being washed and worn. weFAQThe role of the guide tube is talked about in detail. Don't underestimate the thin plate-without it, the expansion joint of DN250 is used in the dusty flue gas pipe, and it will be worn out in half a year. Againtie rod nut adjustmentMany construction teams do not disassemble the transportation fixings after installation, or screw the tie rod nut to death, resulting in the expansion joint losing its compensation function. On expansion jointArrow DirectionIt is the flow direction of the medium, and the guide tube will not play a role if it is installed backwards. We still have clients who putDouble-sealed single-axis circular baffle doorIt's used as an expansion joint. Laughing to death. That thing is used for truncation, not compensation. Therefore, be sure to check the product nameplate before installation to confirm whether it is a general-purpose type or a high-temperature axial type, and do not mix it.
In addition,Do you need to remove the screw of the expansion joint？ The transportation fixing parts must be disassembled, but the adjusting nut on the pull rod should not be disordered-how to adjust it specifically,FAQThere are also instructions in. In short, installation is not by brute force, but by looking at nameplates and drawings.
Summary: Don't just look at parameters in type selection, working conditions are the fundamental
The diameter of DN250 can be expanded from 30mm to 300mm. The key is that you should give the working pressure, temperature, medium, pipe direction and fixed bracket position. Instead of guessing blindly on the parameter table, it is better to directly find the manufacturer to produce a calculation book. All expansion joint products on our station-includingUniversal corrugated expansion joint、High temperature axial expansion joint、Straight pipe pressure balanced expansion joint、Large diameter thick wall expansion joint、Compound hinge transverse expansion jointAnd so on-all support customization according to GB/T 12777 standard. You provide the working conditions, and we will calculate them for you. The data speaks for itself, and it is not false.
How much expansion and contraction of the metal expansion joint DN250 does not depend on the model, but what exactly your pipe wants it to carry. Wrong choice, no matter how beautiful the parameters are, they are still scrap iron.