Cracks at the tube ends of heat exchange tubes
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This post was last edited by zhulvqi123 on 2020-7-28 at 14:57. The chlorobenzene cryogenic heat exchanger operates at a temperature of -20°C; it has been in use for 5 years and now shows small cracks at the pipe ends. At this temperature, there is no significant tendency for stress corrosion cracking, and given the long service time, the possibility of defects in the pipe fittings themselves is also low. Therefore, intergranular corrosion cracking is the phenomenon being analyzed for now; it was also observed that the inner surface of the tubes had become frosted due to corrosion. It is thus speculated that intergranular corrosion may have occurred on the tube surface. The flow rate of chlorobenzene is 0.5 m/s, the inner diameter of the tubes is 20 mm, and the flow is turbulent. It is therefore speculated that under fluid erosion, the surface grains on the metal surface peel off, resulting in a matte surface. Do everyone think this analysis is reasonable? Frosted surface of the tube fins
Why does the issue with the material become less severe after 5 years of service? Time is often like a butcher’s knife.
It’s just a speculation; if the material is not suitable, the problems should appear earlier.
If you insist on understanding it this way, I won’t say anything more:)
I don’t see any cracks. The typical design life of heat exchangers is only ten years, and this design life does not include the weld joints between the heat exchange tubes and the tube sheets; cracks in these joints appear after five years. If the affected area is small rather than large, this is considered normal. The matte surface on the inside doesn’t appear to be corroded based on the images; if it were stress corrosion or intergranular corrosion, problems would arise much sooner. The above are just my personal guesses; they’re for reference only
I didn’t include a picture of the inner surface of the tubes earlier; I removed two tubes back then, so I’ll add photos now.
It’s that tiny crack right at the tip
I’m sorry, I’m not an expert in this area either; it’s better to wait for a professional to answer