Wall thickness issues for elbows, tees, and reducers

The wall thickness of the elbow mentioned here refers to the wall thickness at the end where the pipes are connected; it is not the same as the wall thickness of the elbow itself. There are specifications regarding the wall thickness of the curved part of the elbow, and these specifications are followed during manufacturing. For butt-welded elbows, the wall thickness is generally considered to be uniform

1. A complete description is required for elbows in order to determine their wall thickness and dimensions; for example: 20# GB/T8163 LR BW SH3408 SCH40. 2. SCH40 indicates the wall thickness of the elbow; the wall thickness of an DN200 SCH40 elbow is 8.0 mm

1. In accordance with the principle of equal strength design, the pressure-bearing capacity of fittings such as elbows, tees, and reducers should not be lower than that of straight pipes with the same wall thickness. Therefore, the wall thickness of the ports of welded pipe fittings should be greater than or equal to that of straight pipes. Under normal circumstances, the wall thicknesses of the two are the same. 2. During plastic deformation of pipe fittings, the deformation is uneven throughout, resulting in uneven wall thickness as well. Taking a elbow as an example, its outer wall thins under tensile stress, while its inner wall thickens under compressive stress. The same is true for tees; the intersection point where the main branch and the branch connect is a weak spot. 3. For design purposes, it is required that the pressure-bearing capacity of the fittings be no less than that of the straight pipe sections; therefore, it is sufficient to specify the wall thickness of the straight pipes at the butt-welded ends to the manufacturer. It is the responsibility of the manufacturer to consider the effects of thinning certain areas and to produce fittings that meet the required standards. 4. Fittings are required to undergo type testing, with the standards specifying stress analysis and burst testing. Force analysis is generally carried out using the finite element method, while pressure testing involves applying a certain pressure until failure occurs, or it is considered successful if no failure takes place within a specified time. 5. The wall thickness at the intersection of the standard tee is 1.5 times that of the main pipe wall thickness (see GB50316, etc.), but few domestic manufacturers are capable of achieving this. The blasting test also has problems, as there is a process from plastic deformation of the pipe fittings to their rupture, which can be seen from the stress-strain curve. In fact, we prefer that deformation occur only within the range of elastic deformation. It can only be said that the technology of domestic manufacturers still needs improvement.

Thank you to the friends above for their helpful explanations :)

Thank you so much! I have another question: when selecting the material for pipe fittings, for a elbow of SCH40, DN200, does SCH40 refer to the wall thickness of the straight section at the butt-welded ends? Is it still necessary to specify the design pressure when cutting the material?

Generally, it is sufficient to specify the wall thickness corresponding to the dimensions of the steel pipe. In some special cases, additional notes are required; for example, if an X-ray inspection is needed, the end portion must match the end of the steel pipe so that the inspection can be successful. For high-pressure applications, the wall thickness at the thinnest part of the elbow is usually specified, and in such cases the material needs to be made thicker during production. For tees, reducers, elbows, etc., different materials must be used, depending on the manufacturing process. Stainless steel is typically processed through cold bending and cold drawing, while ultra-thick-walled alloy steels are generally manufactured using hot pressing and hot drawing methods. Carbon steel is usually processed through hot pushing, cold drawing, hot pressing, etc. Different products require different manufacturing processes – it’s not something that can be accomplished with just one single processing method for pipes

Thank you! I’ll call you if I need to! :)

If the specification of the elbow is indicated as DN200 SCH40. So the nominal thickness of this elbow is 8.18 mm. . . So the inspection is carried out based on this nominal thickness. . The general standards specify that the thinning amount should not exceed 12.5%. Individual technical requirements with higher demands are calculated separately. As for what thickness of material you use for processing, it is up to the manufacturer to decide. Meeting the requirement for the thickness reduction is sufficient.