Issues with piercing and fitting tubes in tube bundles
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In our company, the following problem often occurs: 1. When installing the U-shaped tube bundles, it is found that after installation, the tubes on the innermost ring are much longer than those on the outermost ring. Of course, the dimensions specified in the drawings are correct, but considering that there will inevitably be some deviation when the tubes are bent, a margin needs to be left; therefore, the lengths of the tubes on the innermost and outermost rings should differ. I was wondering if any experienced technicians could provide some guidance regarding appropriate values for this margin 2. When installing the U-tube bundle in the conical cylinder, it was found that the support plates of the bundle were often blocked by welds, or the cylinder’s roundness was not sufficient to allow access; moreover, the required dimensions for those support plates were 6 mm smaller than the diameter of the 600-series tubes. I’m not sure if this request is appropriate Is it the tolerance that is too small, or is the machining precision insufficient? I wonder if anyone has encountered this problem. Additionally, our cone-shaped cylinders are all pressed using hydraulic presses, making it difficult to ensure roundness. Are there any more advanced methods for manufacturing them? Please give me some advice, thank you.
First of all, I should clarify that I am not an experienced technician; I only solve problems theoretically. Problem 1: Solution 1: The amount of expansion can be calculated based on the heat bending temperature, the material of the tube, and the length of the heat exchange tube, and this amount of expansion should be the margin you need to leave. Solution 2: Cold bending can be used; although it may cause damage to the heat exchange tubes, it remains an option. Question 2: According to GB151, the diameter of the heat exchanger is 600, while the diameter of its support plate is 591, resulting in a deviation of -0.8. The diameter of the heat exchanger support plate you have used, which is 588 (taking the negative deviation into account), can be said to meet the requirements. So the problem lies not in the support plate, but rather in the weld between the cone and the cylinder. According to standard heat exchanger design principles, this weld should be smoothed and polished. It seems like your heat exchanger isn’t working as it should.
The Ministry of Machinery must have relevant standards; following those for tube threading and assembly should be fine, right?
Thank you to the two people above. But how can the problem of the conical cylinder not being circular be solved? We use cold bending; if the tubes are inserted according to the theoretical dimensions, the length of the last few turns will not exceed that of the exposed tube sheet. What we do is to reserve a margin of 100, and that will suffice, but it will require many more pipes, which is a waste.