Origin and understanding of the requirements for elbow straight pipe sections
Thread Content
When designing piping systems, elbows (ASME long elbows or short elbows) require a straight section of pipe; the minimum length of this straight section must be at least equal to the outer diameter of the pipe, and it must also be no less than 100 mm. The reason for this is, I believe, mainly to provide sufficient space for welding operations, as well as to address the issues related to stress concentration at the two welds and their mutual influence. However, I’m not sure what experts consider in this regard, and where these regulations originate from Hope for in-depth discussion.
SH/T 3501-2002 Code for Construction and Acceptance of Pipelines for Toxic and Flammable Media in Petrochemical Industries 7.2.1 a) Except for prefabricated elbows without straight sections, the distance between the center of the pipe weld and the starting point of the bend should not be less than the outer diameter of the pipe, nor less than 100 mm
GB 50235-97 Code for Construction and Acceptance of Industrial Metal Piping: 5.0.2.2 The distance from the weld to the starting point of the bend (excluding press-bent, hot-push, or medium-frequency bent pipes) must be no less than 100 mm, and it must also be no less than the outer diameter of the pipe. In both cases, what is referred to is a bend, not an elbow. Please verify the source and check this issue
I think this regulation is related to the manufacturing of curved pipes; if they are too short, the curvature will be too large, which may result in the area at the 90° elbow becoming too thin due to bending. The intense fluid friction in such areas is not conducive to the stable operation of the pipeline
Maybe it’s not actually aimed at elbows; in one of our company’s products, the starting point of the 90-degree elbow is only about fifty to sixty millimeters away from the weld seam