Questions about elbows
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Our company has recently been installing a large number of pressure pipelines (including those for compressed air, oxygen, gas, and steam). The pressure in these pipelines is generally around a few MPa, with the highest value reaching only 1.2 MPa. I noticed that other companies use cold bending techniques for installing small pipes, while our company relies heavily on elbows. This not only results in more material being used, but it also raises doubts regarding the efficiency of the construction process as well as the reliability of the welds. I raised this issue at a meeting, but was almost laughed at (with comments such as it not conforming to certain GB standards). However, after researching the national standards, I couldn’t find any such regulations; the GB standards only specify requirements regarding the radius of bends. Am I wrong? What exactly are the regulations outlined in the national standards, and which ones? I hope the experts here will kindly share their insights! I’m new to this field and there’s so much I don’t understand
Elbow pipes are mainly used in high-pressure pipelines in the chemical industry. It’s not high-pressure and non-corrosive; why use this then? Its cost is higher compared to elbows, and it’s also prone to becoming defective during bending.
I disagree with what was said above; using a hydraulic pipe bender for installing pipes results in much higher efficiency and better construction quality compared to using elbows, especially for pipes with small diameters. Here, we use pipe benders to bend the smaller steam pipes, but as far as I know, hydraulic pipe benders can only bend pipes with a diameter of up to 76.
For pipes smaller than DN25, cold bending can be considered; however, special tools are required for cold bending in order to ensure aesthetics and quality, and space constraints may also exist in some areas at the construction site when performing cold bending. For large pipes, bending can also be used as a method of connection, but it is difficult to carry out this approach at the construction site, especially for pipes larger than DN50; in such cases, the bends must be prefabricated by the manufacturer. The cost of such bends is higher than that of elbows, and they are also less attractive aesthetically as well as from a spatial layout perspective. Therefore, considering factors such as pressure rating, cost, aesthetics, and installation site, for medium and low-pressure pipelines, small pipes are suitable for bending (less than DN25), while larger pipes are better suited for elbows (equal to or greater than DN25).
The bending radius of curved pipes is large; for hot bending, it is generally 4–6D, while for cold bending it should be 18–30D. These pipes are mainly used in buried pipelines. I’ve never heard of using elbows for overhead pipelines, considering the site layout requirements
I agree with zhanghao0127: \"The curvature radius of bent pipes should be large; for hot bending, it is generally 4–6D, while for cold bending it needs to be 18–30D. Such pipes are mostly used in buried pipelines.\" For overhead pipelines, I’ve never heard of the use of elbows considering the requirements of the installation site; in terms of aesthetics and ease of construction, elbows are superior to bent sections. Additionally: I would like to ask that bent pipes are generally smaller than DN25 – are there any requirements regarding the wall thickness of such pipes? Can thin-walled stainless steel pipes be bent nowadays?
Generally, for D-fluid pipelines with a diameter of DN25 or less and a working pressure of up to 1 MPA, on-site bending is quite commonly used, such as in heat tracing pipelines and compressed air drainage pipelines. So it can’t be generalized; each case needs to be analyzed on its own.
For our high and medium pressure pipes with a diameter of 76 MM or less, we use elbows; we rarely use tees
Here, we usually bend small-diameter pipes by hand, but sometimes elbows can be used for speed. The pipeline pressure in your factory is not high, and it’s not corrosive, so everything is fine.
The bending radius of curved pipes is large; for hot bending, it is generally 4–6D, while for cold bending it should be 18–30D. These pipes are mainly used in buried pipelines. I’ve never heard of using elbows for overhead pipelines, considering the site layout requirements
I agree with the original poster’s opinion. Our factory was established in 1958; back then, elbow fittings were used everywhere. Now that elbow fittings are available, we no longer use bends, as it’s too troublesome. I’ve only seen regulations prohibiting the use of mechanical elbows, but not those prohibiting bends. I think the reasons are as follows: (1) Bends have a larger radius, which is more suitable for fluid flow conditions, but they’re difficult to manufacture and inefficient to use, so no one wants to handle them. Process systems prefer bends, while equipment systems prefer elbows. (2) In this era of economic development and a harmonious society, there are increasingly more companies that produce elbows. If we don’t support this industry, how will these companies survive?
Based on my understanding of national standards: many of them are becoming increasingly restrictive. National standards should be adapted to the requirements of a market economy, and many of them are proposed and primarily developed by industry stakeholders. The elbow manufacturing industry really wants the first clause of such standards to stipulate the mandatory use of formed elbows; however, the standards that are ultimately established tend to take a middle ground approach, aiming to promote progress across the entire industry.
It’s been very inspiring to see everyone’s discussions. Thank you all
In principle, carbon steel pipes with a diameter of 40 mm or less can all use elbows that are bent on site; however, in actual projects, many construction companies are reluctant to do this. Firstly, the elbows formed in this way do not have an attractive appearance, and secondly, it increases the workload. They prefer to use socket-welded elbows instead.
I found the discussions of everyone very inspiring.
Generally, prefabricated elbows can be used for pipe elbows; for DN50 and below, bending the pipe manually is also acceptable. This depends on the practices of the construction contractor, provided that a bending radius of 5 to 10D is ensured. Obviously, if aesthetic appearance is required for the layout, it is better to use standard elbows.
It’s truly enlightening to see all of you back; thank you so much to everyone! I really want to give everyone extra points, but there aren’t enough points available; I’m keeping some back as evidence. So please don’t call me hypocritical, and definitely don’t vote against me!
The curvature radius of bent pipes should be large; for hot bending, it is generally 4–6D, while for cold bending it needs to be 18–30D. Generally speaking, for fluid pipelines with a diameter of DN25 or less and a working pressure of up to 1 MPA, bending is the method more often used. However, nothing is absolute – each case must be analyzed on its own.
It depends on the diameter of your pipe. If the pipe diameter is less than 40 mm, at your operating pressure, it’s entirely possible to bend it on site. However, note that the radius of the bend, as well as the change in diameter at the curved part of the pipe, should not exceed 5%
Cold bending is not recommended; using elbows is a safer option. . . . . . The level of bending done by some construction teams these days is really disappointing. . .
Elbows can be used in situations where high requirements are not imposed, but generally, this is not allowed in project construction