Selection and Strengthening Calculation of Thick-Walled Manhole Pipes
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Dear experts, I am new to design work and am not very sure how to choose thick-walled pipes for manholes, as there isn’t much guidance available other than the flange outer diameter. Could you all please check whether my approach is feasible, and if there are any simpler methods? I appreciate your advice! Thank you! ! Basic data of the reflux tank: Nominal shell thickness – 32; design temperature – 120; inner diameter of the cylinder – 2400; length of the cylinder – 6000; corrosion allowance – 3. Data on the manhole: M1, DN600, PN40. Flange standard – HG/T21521 RF. Strengthening measures for the manhole opening: I. According to the minimum wall thickness requirement specified in 20581, Sch40 is selected; minimum wall thickness = 17.5. Outer diameter of the flange – 610; inner diameter – 575. Outer diameter of the connecting pipe; nominal thickness of the connecting pipe: Pass/Fail – 610, 17.5 – 48% (Fail); 639: 1 times the shell thickness = 32 – 12% (Fail); 651.8: 1.2 times the shell thickness = 38.4 + 7% (Pass). Rounded value – 650; 37.5 + 4% (Pass). II. Sch60 is selected; minimum wall thickness = 25. Outer diameter of the flange – 610; inner diameter – 560. Outer diameter of the connecting pipe; nominal thickness of the connecting pipe: Pass/Fail – 610, 25 – 31% (Fail); 624: 1 time the shell thickness = 32 – 11% (Fail); 656: 1.5 times the shell thickness = 38.4 + 42% (Pass); 640: 1.25 times the shell thickness = 40 + 14% (Pass). Rounded value – 645; 1.3 times the shell thickness = 42 + 20% (Pass). Ultimately, it is decided that the strengthening pipe should have an outer diameter of 610 and an inner diameter of 645, with a wall thickness of 25 at the smaller end and 42 at the larger end.
I’m sorry there are no images; my approach was to gradually increase the wall thickness based on the given outer diameter of the flange, through trial calculations. After passing the inspection, 20% is reserved as a reinforcement allowance. For the first table, calculations were started by selecting Sch40 with an inner diameter of 575 and a wall thickness of 17.5; the wall thickness was increased by factors of 0.5 to 2 times the shell thickness, and it was found that when the outer diameter reached 650, the amount of reinforcement required was still very low. Thus, calculations were started using the second table, selecting Sch60 with an inner diameter of 560 and a minimum wall thickness of 25; the thickness was increased by factors of 0.5 to 2 as well, and finally the appropriate dimensions were determined. If there is a better and more reasonable solution, please advise. Thank you
The flange for the manhole is selected in accordance with HG/T20592; it belongs to the B series. It is usually made of steel plates rather than pipes, so there is no need to use pipes of various thicknesses. In your example, the thickness is quite large, so it is sufficient to simply choose forged components for making the pipe support
The nominal thickness of the shell is 32. What thickness of plate do you think is needed for the pipe connection? For a diameter of 600, what kind of machine can be used to roll it out?
First of all, it is necessary to ensure that the wall thickness at the smaller end meets the requirements regarding strength; providing an adequate thickness is sufficient, and there is no need to include any extra margin. Once the thickness at the smaller end is determined, the inner diameter of the manway sleeve is fixed. Next, the thickness of the open section, which corresponds to the larger end, must meet the reinforcement requirements; attention should be paid to the overhang height, as well as to the fact that the ratio of the thickness of the reinforced section to the thickness of the shell should lie between 0.5 and 2. After that, the inner wall end of the short section can be rounded off.
When the manhole has thin walls, it can be rolled (to reach the thickness specified in the standards); it’s not that the value calculated by the original poster is too high. That’s why I recommended using forged parts earlier
This post was last edited by wanlirn on 2022-8-8 at 10:56. Your idea of using thick-walled pipes is fine for a graduation project, but in actual production, many thick-walled pipes are difficult to obtain, or their delivery times can be several months long, which affects production. We all use forged pipes. Sometimes, it may not be economical to determine the inner diameter and then find the corresponding outer diameter; it is also possible to increase the thickness of both the inner and outer sides, and to machine them thinner so that their thickness equals that of the pipe fitting.