Issues regarding the connection between heat exchange tubes and tube sheets
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This post was last edited by sunhe0310 on 2015-10-12 08:49. Recently, while studying the provisions in *GB151-2014 regarding the connection between heat exchange tubes and tube sheets, I had two questions: 1. The applicable range of strength expansion is for design pressures less than or equal to 4.0 MPa； Design temperature is less than or equal to 300 degrees ； There is no vibration during operation, no excessive temperature fluctuations, and no significant tendency for stress corrosion. May I ask: Do the design pressure and design temperature mentioned here refer to those of the tube side, the shell side, or are both required? 2. In the combination of strength welding + fillet welding, are there any specific requirements regarding the length of the fillet weld (such as a minimum and maximum length)? The standards only specify the length for which no fillet welding is required.
1. It should refer to the shell side. 2. Sealed welding should be used; the welding dimensions can follow those for strength welding, and the size of the weld corner l should be no less than the thickness of the heat exchange tube. Strength expansion + seal welding is generally used less often; strength welding + bonding expansion is more commonly employed
Thank you for your advice. I would like to clarify the second question: what I actually want to ask is about the method of using strength welding combined with expansion fitting when connecting the heat exchange tubes to the tube sheet. GB151 does not specify the length of expansion fitting in such cases. I would like to know what the minimum possible length for this expansion fitting is, and whether there is any limit on the maximum length
I’ve modified Question 2; I made a mistake while writing it by accident. I’m sorry
As specified in GB/T151-2014, the non-expansion length is approximately 15+3 mm; the remaining expansion length is the thickness of the tube sheet minus this non-expansion length.
Thank you, I understand. But if the thickness of the tube sheet calculated is relatively thin (in one of our projects, the tube sheet of the heat exchanger had a thickness of only 28 mm), and if we then subtract the 15+3 mm amount corresponding to the non-expansion length, wouldn’t that result in an expansion length that is too short? Would it still be possible to carry out expansion jointing? I’m quite confused about this issue
Let it expand if it can, because expansion jointing is used to eliminate the gap between the heat exchange tubes and the tube sheet; I assume it’s done to prevent gap corrosion.
If the requirements for combined expansion and welding are not met, it is not necessary to use expansion bonding; strength welding can be employed instead.
If the tube sheet is too thin, grooved expansion or strength welding can be used as solutions depending on the situation. Additionally, in the case of using both expansion welding and welding, 15 mm as the non-expansion zone doesn’t seem to be an absolute requirement; as long as the length of this zone is sufficient to ensure that expansion welding does not pull on the weld, it is possible to reduce this value accordingly
Okay, thanks for the advice. . . . .
Crevice corrosion is more likely to occur after expansion bonding