Difference between welded smoke pipes and support pipes
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Hello everyone! A problem was encountered during the review of the boiler drawings; the reviewers said that it is not necessary to use support pipes when welding the flue pipes. What is the difference between flue pipes that are welded and those with support pipes? In the calculation of welded smoke pipes with flat gaskets, in addition to performing strength checks and calculating wall thickness based on external pressure, is it also necessary to conduct checks and calculate wall thickness considering the strutting pipes?
Let me share my opinion; I hope experts can give me some feedback: When flat gasket plates are used in shell and tube boilers, strength calculation is very important. To meet the requirements of strength calculations, when support points are necessary and it is not possible to install threaded smoke pipes with a larger diameter, pipes with a smaller diameter are generally used as braces. The coefficient K for the support tube is 0.43, and the coefficient K for the welded smoke duct is 0.45. According to the standards, support pipes should be checked based on their cross-sectional area. When performing calculations, I usually also check the smoke pipes, but in most cases the requirements are met; many people don’t do this though.
In the past, the smoke pipes of industrial boilers were mostly of the expansion-joint type, which required the use of separate support tubes for the tube sheet; nowadays, they are mostly of the fully welded type, which can replace those support tubes. Verification is not required.
In the design of boiler tube sheets, the smoke tubes also serve as strutting tubes, and they must be checked as part of the design process. But it will meet the requirements at the same time.
The tube sheet is calculated based on the diameter of the circle, while the cross-sectional area of the support tubes is determined based on the area that is under tension. Both requirements must be satisfied.
Generally, the smoke pipes surrounding a welded smoke pipe bundle need to be checked as if they were support pipes; this is especially true for boilers with high pressures of 1.6 MPa and 2.5 MPa, as these may not meet the requirements and thus require thick-walled pipes. Generally, there is no need to conduct strength checks on the support members for the smoke tubes in a welded smoke tube bundle.
Experts, support structures are needed when the pull rod is longer than 4 meters. What should be done in cases where the smoke pipe used for pulling serves as a support structure and is also longer than 4 meters?