Question regarding the size of holes in the tube sheet
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For example, the current specification for the dimensions is 19.25+0.15; I propose using drill bits with a size of 19.4 or 19.5 to drill the holes in the tube sheet. The manager said that such a large size isn’t allowed. I was wondering if it’s possible to use those sizes after all Is there any evidence? The tube sheet thickness is 38 mm. I’m a beginner; please feel free to give me some advice. Thank you
Use drills with a diameter of 19.4 or 19.5 to drill the holes in the tube sheet; I estimate that none of your drilled holes will meet the requirements specified in the drawings. Your supervisor is right – it’s necessary to meet the standard of 19.25 + 0.15. It’s difficult to ensure this standard just by drilling once; it’s better to start by using a smaller drill bit to make the holes and then expand them. For applications with higher requirements, reaming is also necessary.
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The requirement of 19.25+0.15 on the drawings is correct; if drills with a diameter of 19.4 or 19.5 are used, with such a large gap between the pipe and the hole, how can the welding quality between them be ensured?
It seems that you’re using a first-level control approach here. If you use drills with a diameter of 19.4 or 19.5 to drill holes in the tube sheet, the resulting holes will be at least between 19.5 and 19.6. You should use a drill with a diameter of 19.2. Nowadays, heat exchange tubes have a negative deviation; the outer diameter of tubes with a diameter of 19 is basically around 18.9. As a result, the gap between the tubes and the holes is too large, which not only makes it difficult to ensure welding quality and leads to excessive waste of welding wire, but also makes tube expansion difficult
One more thing to note: when equipment equipped with tubes is in operation, over time the tubes vibrate significantly, which results in higher noise levels from the equipment! It is advisable to follow the instructions of the supervisor, as that is more reasonable. Heat exchange tubes are generally manufactured in accordance with standards, but regarding their outer diameter, manufacturers usually allow tolerances within the range specified by the standards. This makes it easier and faster to insert the tubes, and it also helps to reduce the costs for the purchasing party.
The size and tolerance of the tube holes are determined based on the material of the heat exchange tubes; this is specified on page P25 of GB151
No, the drawing specifies an outer diameter of 19.25 with a tolerance of +0.15 mm. If you use a drill bit with a diameter of 19.4 or 19.5 mm, the holes that will be created will be larger than what is specified in the drawing, meaning they do not meet the design requirements.
Using a 19.4 drill bit definitely won’t work. The hole drilled by a 19.4 drill bit, including the associated deviations, exceeds the upper limit specified in the drawings, which is 19.4 (19.25 + 0.15); this is not in line with the design requirements.
The primary tube bundle you are using requires a tube hole diameter of 19.25+0.15, meaning a maximum of 19.4; using a drill bit with a diameter of 19.4 or 19.5 will definitely result in deviations from this specification