Comparison of Hydraulic Expansion Tube and Mechanical Expansion Tube Technology

Comparison of Hydraulic Expansion Tube and Mechanical Expansion Tube Technology

1： Mechanical and hydraulic expansion test data

1. Mechanical expansion tube: The mechanical expansion tube is carried out according to the actual process of a 300MW high pressure heater, using two sections of expansion joints before and after. The total length of the expansion joint is about 50r. After the expansion tube is expanded, a pull-out force test and anatomical inspection are carried out.

2. Hydraulic tube expansion: Hydraulic tube expansion is carried out using a hydraulic tube expansion machine imported from Germany. Different tube expansion pressures are selected to expand the full thickness of the tube plate. The length of the expanded tube reaches 350mm. After the tube is expanded, a pull-out force test and anatomical inspection are carried out.

3. According to the theory of pipe expansion, the general strength expansion requires a pipe expansion rate of H=1-3%; The required expansion rate for sticking is H=0.1 to 0.5%. The technical conditions for a 300MIV high pressure heater require that the pipes and tube plate holes be tensioned, and only the gap between the pipes and tube holes should be cleared after expansion. There is no requirement for expansion rate, but the pull-out force after expansion should be greater than 5000N. Based on experience, eliminating the gap between the pipes and tube holes can meet the requirements if the post expansion interference between the pipes and tube holes is greater than 0.05. According to this parameter, the expansion rate H-O.5%.

B. Test steps:

1. Number the tube holes and tubes in their order, with one mechanical expansion tube and one hydraulic expansion tube sample each.

2. Measure the inner diameter of the tube plate hole, the actual dimensions of the inner and outer diameters of the tube, and keep records.

3. Two samples were subjected to mechanical expansion and hydraulic expansion, respectively.

4. Measure the inner diameter of the expanded pipe and calculate the expansion rate.

5. Mill the two expanded specimens into two parts from the middle.

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