To put it bluntly, the most underestimated component in the pipeline system is the metal expansion joint. Two days ago, I met a customer and chose a DN200 universal corrugated expansion joint. As a result, less than three months after installation, the corrugated pipe cracked. After removing it, the pressure level doesn't match. The actual working condition is 1.6MPa, and he bought PN0.6-who will roll over if this doesn't roll over? Metal expansion joint standard specification size this thing, really can't be placed with a glance at the caliber.
How much does it cost to choose the wrong size?
Excessive pipeline stress, damaged equipment, and even safety incidents – these are not alarmist. If the size of the expansion joint is wrong, the bellows can't absorb the heat displacement normally, and the thrust of the pipe is directly held on the bracket, which can lead to leakage or burst. To put it bluntly, metal expansion joints are not something that can be used just by finding any size. Nominal diameter, pressure grade, compensation amount, these parameters must be in perfect accordance with the actual pipeline system, almost not.
How to dismantle the core parameters? Come one by one
Let's talk about nominal diameter (DN) first. This thing determines whether the interface can align with the pipe. DN50, DN100, DN200... Don't just look at the numbers, you have to confirm whether the flange standard is PN or Class, and whether the sealing surface is RF or MFM. Then the pressure level-from PN0.25 to PN6.4, or even higher, if you choose a small bellows, it will collapse directly, and if you choose a large one, it will be wasted money.
Let's talk about the compensation amount. The number of bellows layers and the wave number are directly related to how much displacement it can absorb. Similarly, the general-purpose corrugated expansion joint of DN200 may only have a single-wave compensation of 10mm, while the three-wave structure can reach more than 30mm. But it wasn't over — the allowable stress of austenitic stainless steel dropped as soon as the temperature was high. 304 can still stand at 100℃, and at 400℃, the wall thickness has to double. 316L is better. If you really want to go above 600℃, you have to Inconel. Different materials, the corresponding wall thickness and wave height are completely different. Looking at the same data on the selection table, the actual difference is more than ten kilograms.
The working condition determines the structure, and the structure determines the size
Axial displacement Simple, upper universal corrugated expansion joint orExternal pressure single axial expansion joint。 Lateral displacement can never be carried with the axial type-that is not its job, it has to be usedCompound hinge transverse expansion joint。 Vacuum pipeline is more particular, ordinary expansion joint into the vacuum degree cannot be kept, must useSpecial hose for vacuumOrDouble hinge expansion joint for air-cooled island vacuum pipeline。
The size calculation logic is different for each structure. Such asStraight pipe pressure balanced expansion jointIt has to be equipped with an extra balance ring, which takes up tens of millimeters of axial space. You reserve the installation position according to the general size, and it won't fit in at all. Is that the truth?
Pits installed on site, each deeper than the last
Some people use the expansion joint as a pipe support, and the tie rod nut is tightly screwed. As a result, the bellows can't move at all, and the compensation amount is zero. Then what is it for? How to adjust the nut of the expansion joint tie rod-I have to make this question clear: the tie rod is used for transportation protection, and it must be loosened before installation. The screw should be removed when it should be removed, and never screw it to death. Another common rollover: without looking at the installation direction arrow, the deflector tube is installed backwards. The medium flushes directly against the bellows and perforates in a few months. The specific function of the expansion joint guide tube is to guide the flow direction of the medium and protect the bellows from erosion-the reverse direction is equal to white installation.
How to use the standard system and size chart?
Domestic metal expansion joints mainly follow GB/T 12777-2019. The allowable axial compensation, lateral compensation, angular compensation and fatigue life corresponding to the nominal diameter are usually listed on the enterprise sample. But pay attention-the same DN200, the compensation amount of multi-wave structure is more than three times that of single wave, and the error in the weight meter can be more than ten kilograms different. Therefore, when selecting the type, don't just look at the caliber, but all the wave number, layer number and pressure level must be matched. Really not sure, flip through this siteUniversal corrugated expansion jointProduct page with a detailed size comparison table.
There is no universal size, only reasonable selection for matching working conditions
There is no universal standard size, only reasonable selection for matching working conditions. After getting the project parameters, honestly calculate the thermal displacement, check the pressure level and the interface size. If you are really unsure, find the manufacturer to come up with a plan-the calculation book in their hands is much more reliable than the comparison table circulating on the Internet. The standard specifications and dimensions of metal expansion joints are wrong one step at a time. I would rather spend two more days accounting than two months reworking after rolling over.