Some rough thoughts on butt-welded and socket-welded pipe fittings
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Recently, while studying the tables of pipe material grades, I noticed that for fittings with a diameter of DN40 and below, socket welding is generally used, while butt welding is employed for those with larger diameters. But I generally prefer to use butt welding in all cases – butt-welded pipe fittings cannot be used in some situations, whereas there are no such restrictions for butt welding. 2. Some people use socket welding because the wall thickness of pipes with small diameters is relatively thin, making it easy to cause penetration during welding; but I think that since welded joints with small dimensions are an option, it’s definitely possible to carry out the welding process – it’s just a matter of cost, right? 3. Which is more expensive: socket weld pipe fittings + installation costs, or butt weld pipe fittings + installation costs? I’m not quite sure about this. Is it really okay to use simple and brute-force full butt-welded pipe fittings everywhere? Is there still any reason to use socket welding for small-sized pipe fittings today?
It is used in places with modest requirements.
Here, we usually use socket welding for low-pressure applications, while butt welding is used for high-pressure ones
Don’t generalize; consider the operating conditions and the owner’s preferences.
For small-diameter applications, socket welding or threaded connections are methods that have been developed through years of practical experience in engineering projects. The approach suggested by the original poster, of adopting a one-size-fits-all solution, is not recommended. Small-diameter pipes with thin walls can indeed be welded together, but this is done solely from the perspective of simplifying the design. Engineering decisions take into account not only design aspects but also factors such as construction, procurement, manufacturing, and investment. The specific features of conventional designs reflect, to some extent, the attitude and competence of the designers; therefore, it’s important not to oversimplify things. Only by setting high standards for oneself can one achieve greater improvements.
That being said, what exactly are the advantages of socket welding?
The disadvantages of socket welding include stress concentration at the weld toe and root, root notches (affecting fatigue and toughness), as well as limitations in radiographic and ultrasonic inspection. These defects are more significant for large-diameter pipes, but can be ignored for small-diameter pipes. The advantage of socket welding lies in its simplicity of construction: once the parts are inserted, they can be welded right away. For butt welding, bevels need to be prepared, and if TIG welding is used as a pre-welding step, the welding speed for butt welding is roughly 2-4 times that of socket welding
Hello, may I ask what voltage level serves as the boundary for your high-voltage category? Also, for high-pressure small-diameter butt-welded pipe fittings, is forged material used, or is the material standard the same as that of steel pipes?
The two points mentioned by the original poster above should be enough to answer the question. Additionally, welding small-diameter pipes using direct welding requires high skill from the welder; however, it facilitates construction and helps ensure quality, which is indeed an advantage