The question arises: Why is the installation distance of the expansion joint not a fixed number?
"How far apart are the expansion joints?" To be honest, this question is a bit like asking "how long to drive to refuel"-it depends on how big the fuel tank is and how the road is like. The installation spacing of metal corrugated expansion joints is directly determined by the amount of thermal expansion of the pipe system. The pipe elongates as soon as it heats up, and the longer the single straight pipe section, the greater the elongation. And guess what? A DN200 steam pipe, 200 meters long, can expand to about 70 cm when the temperature rises by 300℃. If you slap your head and install one every 5 meters, you're not installing a compensator, you're opening a grocery store. On the other hand, if the interval is too large, the expansion joint can't absorb the displacement, and the pipeline will be directly damaged or leaked. Therefore, the spacing is not shot, it is calculated.
First understand who is "eating" displacement-the layout of fixed bracket and guide bracket
The installation spacing of the expansion joints is essentially determined by the arrangement of the fixed brackets. The pipe section between the two fixed brackets is the section that the expansion joint needs to serve. Usually, the designer will control the spacing of fixed brackets to 30 to 60 meters according to the direction of the pipe, the medium temperature and the diameter of the pipe. Corresponding to the expansion joint, if it is a general-purpose corrugated expansion joint (axial type), an expansion joint can generally absorb an axial displacement of 30 to 50 mm. If the spacing of the fixed brackets is 40 meters, the temperature rise is 250℃, and the carbon steel pipe expands about 0.012 mm/℃ per meter (refer to the linear expansion coefficient), and the total expansion is 40×250×0.012=120 mm, then 2 to 3 axial types have to be installed. But don't forget, if you install an extra expansion joint, you have to be equipped with a set of tie rods or guide tubes, and the cost will rise. Therefore, in actual combat, designers will give priority to double hinge transverse expansion joints or straight pipe pressure balance expansion joints, one top two.
How big is the difference in spacing under different working conditions?
Take the power station industry and the cement industry as examples. The steam pipeline of power station has high temperature and high pressure, and the distance between fixed brackets is often controlled at 20 to 40 meters, which is matched with external pressure single axial expansion joint or high temperature axial expansion joint. However, the hot air ducts in the cement industry have dusty media and large temperature fluctuations, and the spacing may be relaxed to more than 50 meters. At this time, the compound three-way expansion joint or the general type with guide tube will appear. Let's talk about another common pit: some people used universal expansion joints for directly buried pipelines, and as a result, the spacing was set at 60 meters, which was directly cracked in winter-the friction resistance of the soil of directly buried pipelines was large, and the actual displacement was much smaller than that in the free state, so there was no need for such a long compensation distance at all. To put it bluntly, there is no universal formula for spacing, pipeline laying method and media characteristics.
Too dense or too thin, the consequences are very "stimulating"
On the steam pipeline, they installed a general-purpose corrugated expansion joint according to the head-slapping experience of "one every 6 meters". As a result, after two months of operation, the bellows became unstable-because the spacing was too small, each expansion joint only absorbed less than 5mm of displacement, but became a "weak point" on the pipeline with frequent air leakage. The restoration cost 300,000. Conversely, what about too much spacing? The pipeline will be transversely displaced where there is no guide bracket, from smashing the insulation layer to breaking the expansion joint. What's more troublesome is that the guide tube will be damaged by washing under some working conditions. Therefore, the spacing is not a pat on the head, but a linkage decision involving the selection of expansion joints, bracket design and media parameters.
Then how do you set the spacing? Give you a reliable idea
Determine the maximum temperature difference and the coefficient of linear expansion of the pipe material. Step 2: Calculate the total expansion based on the length of the line. Step 3: See what type of expansion joint to choose-for example, the single compensation amount of the general axial type is 60% of the rated value (leaving a safety margin), and the transverse type of compound hinge can take transverse displacement, but the angular displacement needs to be calculated. Step 4: Match the fixed bracket spacing to ensure that the displacement shared by each expansion joint does not exceed 80% of the rated value. Final step: Refer to the simplified calculation diagram of pipe system in Appendix D of national standard GB/T 12777, or directly use the selection software provided by the manufacturer. Each kind of expansion joint in our station has detailed technical parameters, such as large-diameter thick-walled expansion joint and vacuum special hose. When selecting the type, we must provide the actual working condition parameters, and don't just look at the diameter of the pipe.
To summarize: stop asking "how long distance", ask "what working conditions" first
The installation spacing of metal corrugated expansion joints is essentially a balance of thermal expansion, bracket layout and expansion joint capacity. There is no standard answer, but there is a standard process. Next time you encounter this problem, first take out the working condition parameters, and then find the corresponding product type-metal corrugated expansion joint for cement industry, corrugated expansion joint for power station industry, don't mix it. If you are really unsure, go directly to the case library of our website, or let the technicians help you do the math.