Expansion joint protrusion length from the tube sheet
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In Section 6.6 of GB/T151-2014, regarding the connection between the heat exchange tubes and the tube sheet, if mechanical expansion joining is used, there is a requirement regarding the length by which the joint extends beyond the tube sheet (Page P27, Table 6-19). Is this extension length determined based on the mechanical expansion joining process, or is there some other reason for it? What are the protrusion lengths for other crimping methods? Are there any standards or information available on this topic?
Generally, there is a requirement for some degree of extension, as mechanical expansion jointing relies on rotational expansion which causes the tube to stretch; hydraulic expansion jointing, on the other hand, uses liquids such as water for expansion, and the extent of stretching is not as great as in mechanical expansion jointing. If the tube is forced not to stretch, it may have a slight impact on the quality of the expansion joint. However, in practice, some customers require that the tube ends be flush with the tube sheet. Different customers have different requirements, and the medium being used also plays a role; some mediums require that there be no protrusions, while others require that the tubes be recessed into the tube sheet
There should also be requirements regarding a corrosion allowance, right? In the actual manufacturing process, due to manufacturing tolerances, it is not possible to ensure that the pipe ends protrude exactly from the tube sheet; there are many cases where their lengths vary, and they move flexibly
The explanation can be found on page 474 of the older version of the \"Training Manual for Pressure Vessel Design Engineers\": the requirement regarding the protrusion length is there to protect the tube sheet and the starting point of the heat exchange tubes from erosion.
How should this be understood? Thank you.
In production, reinforcement welding by adhesive expansion is generally used. We generally don’t extend it; high pressure can cause vibrations, and extending it can lead to problems.