Heat exchanger manufacturing process: the issue of welding first then expanding versus expanding first then welding
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The company has recently launched a project in Inner Mongolia, and together with staff from the procurement department, inspected several pressure vessel manufacturing plants in the area. During the inspection, discussions were held with the container manufacturer regarding the manufacturing process of heat exchangers, and specifically the issue of expanding first and then welding, or welding first and then expanding, when joining the heat exchange tubes to the tube sheet. It is understood that the process of expanding first and then welding is commonly used these days; please share your opinions.
This post was last edited by ztr1118 on 2012-3-19 at 12:23. Generally, welding is done first and then expansion follows. If expansion is carried out before welding, the oil present during expansion can expand due to heat or turn into gas or create high pressure, which affects the quality of welding. Therefore, it is generally preferred to weld first and then expand. However, expanding after welding can also impact the welding process and damage the weld seam; hence, standards specify a starting point for expansion, with further analysis required in special cases
It’s an old issue; generally it works fine, with welding done first and expansion following in most cases
Weld first and then expand – that’s the right approach, just as mentioned on the second floor. After the first expansion, the pipes are covered in a lot of oil and dirt, making it quite difficult to clean them. The air between the expansion points and the weld points expands when heated, and since there’s no place for this air to escape, pores can form. The stress generated during thermal processing is much greater than that during cold processing; heating the pipe ends after expansion can affect both the quality of the expansion process and the quality of the welds
“Generally, welding is done first followed by expansion. If expansion is carried out first and then welding, the oil present during expansion expands when heated or turns into a gas or creates high pressure, which affects the quality of welding; therefore, it is generally preferred to carry out welding first after expansion. That’s wrong!
You can explain the view you think is correct. The information I have come across is as follows; please feel free to correct me
He meant that you typed the four characters \"first expand then weld\" incorrectly; according to your wording, it should be \"first weld then expand\", so I marked it in red for you
This post was last edited by ztr1118 on 2012-3-19 at 12:50. In actual production, welding first and then expanding is the more common approach. There are two reasons: ——Mechanical expansion jointing requires lubrication, and the oil generated is difficult to remove, which affects the welding quality. ——After expansion joining, the air in the unexpanded areas at the ends expands due to heat during welding and has nowhere to escape, resulting in pores easily forming in the weld. Therefore, the method of expanding first and then welding definitely has its drawbacks. Hydraulic expansion joining is now widely used. Hydraulic expansion jointing avoids the problem of pipe ends being contaminated. However, welding first and then expanding introduces new problems: the working clearance between the hydraulic expansion head and the pipe is only around 0.3–0.4, and the contraction of the weld after welding the pipe end makes it difficult to insert and remove the hydraulic expansion head. Therefore, when hydraulic expansion joining is used, in practice it is common to first weld a joint at one end of the pipe, then perform the expansion joining, and finally weld another joint. Practice has shown that this is a method that ensures quality while being easy to operate.
Yes, that’s exactly what I mean. Thank you all for your active participation in the comments!
We weld first and then expand. The reasons are explained very clearly on the second floor a few days ago: victory: