Under what circumstances is the bending radius of elbows larger?
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I saw that a 5D radius elbow was used in one of the process packages. The medium flowing through the pipes was regenerated medium-pressure steam, and the nominal diameter of the pipes was 600; therefore, an elbow with a radius of 3000 was required. It seemed a bit strange to me – I wasn’t sure why that was the case. As I understand it, ultra-long-radius elbows can be considered to reduce pressure drop during turning; are there any other situations?
The pipe diameter of DN600, as mentioned by the original poster, has a bending radius of 5D; this is because for such a large diameter, it is necessary to have a certain bending radius during actual production processes
That’s not right; 1.5D elbows for DN600 pipes are commonly used in the chemical industry
There are also those suitable for blocking pipelines. I’ve never seen 5D used for steam pipelines; it’s probably for pressure reduction.
The selection of the elbow radius generally takes several factors into account: 1. Pipeline resistance； 2. Flexibility of the pipeline ； 3. On-site layout of pipelines ； 4. Difficulty of processing and production.
It is mainly for the sake of pipeline safety; if the bending radius of a DN600 pipe is 1.5R, then the pressure resistance of the pipe, that is, its allowable stress, will be significantly reduced, which is very dangerous. Therefore, the bending radius is usually set to be large. Of course, as long as safety is ensured and production requirements are met, the smaller the bending radius, the better!
Generally, the curvature radius of elbows is 1 time D or 1.5 times D; in cases of high temperature and pressure, or when dealing with particulate materials, it should be 2 times D or more
For the transportation of Texaco water-coal slurry, 5D elbows are required.
Most of the issues mentioned above relate to pipeline resistance and the flexibility of the pipes
I’ve really never seen an elbow of this size used for medium-pressure steam; I guess large power plants might have them. The elbow uses a large bending radius, which is the result of pipeline stress calculations.
I have not encountered the situation mentioned by the poster yet; when working on oil pipelines, it is necessary to use pigging devices, with the diameter of the elbows being 3 times that of D.
The first things to consider are material resistance and the degree of compression. Secondly, the bending radius can be determined based on the site conditions; welding or bending techniques, or a larger bending radius, can be used to reduce bending stress. Additionally, the available space at the site and the construction procedures must also be taken into account
To transport dry and wet mixtures, I have seen 6D ones
The bending radius for standard pipe elbows is 1.5D. Such a large radius is used in very special cases, I guess. Could it be that there’s an error in the process package?
It is quite common when transporting powdery materials. As for steam pipelines, I think the possible reasons could be: 1) stress considerations; 2) considerations related to equipment layout; 3) the high flow rate in the steam pipeline, which reduces the pressure drop; 4) the steam in that area is intended for downstream users, and there is a risk of condensation, leading to increased impact from gas-liquid mixtures :$ :$
SH3501-2002 stipulates that for pipelines transporting gas-solid and liquid-solid two-phase flow materials, elbows with a large radius of curvature should be used.
The bending radius of elbows on pipelines for solid materials should not be less than six times the nominal diameter of the pipeline.
The selection of the elbow radius generally takes several factors into account: 1. Pipeline resistance； 2. Flexibility of the pipeline ； 3. On-site layout of pipelines ； 4. Difficulty of processing and production.
Yesterday I saw the outdoor steam pipes in the suburbs, which used large-radius elbows; however, the projects we are working on at present basically do not require such elbows. Which specifications address this aspect? It seems that the R/D ratio should be greater than 3
The diameter of this pipe is too large. Medium-pressure steam isn’t particularly special, nor are DN600 pipes; however, DN600 pipes used for medium-pressure steam are a bit special. Think about how great the force on the blind flange at the elbow will be during operation or when there are pressure fluctuations. Using elbows with a larger radius can provide significant protection for the pipe； Moreover, the thermal stress in large-diameter thermal pipelines is astonishing; from the perspective of pipeline stress, it is also necessary to use elbows with large radii.