Cracking in the bent section of the U-tube
Thread Content
A U-tube heat exchanger, with a working pressure of 6 kilograms in both the tube side and the shell side; the fluid on the tube side is liquid nitrogen at a temperature of around -190 degrees. The heat exchange tube material is 304. After one week of operation since leaving the factory, the medium in the shell side flowed out through the openings in the tube side; upon inspection, it was found that the bent sections of 3 U-tubes had burst. They are all bent pipe sections; let’s discuss what could be the reason
Apart from this reason, is it possible that there is a problem with the quality of the heat exchange tubes?
Your device isn’t actually under much pressure, as long as the material is fine. Due to the low temperature, that material should be subjected to low-temperature impact testing to see if such testing has been carried out. Additionally, for such low-temperature materials, if the pipe bends are formed by cold bending, it is necessary to first calculate their degree of deformation; if the degree of deformation is too high, heat treatment aimed at restoring the material’s properties is required, that is, solution treatment. The high likelihood of tube rupture is likely due to a cold bending issue.
I guess the part of your tube where it burst is the one with the smaller radius of curvature near the middle, right?
Is it there? I’m waiting urgently; I want to test my theoretical knowledge. :lol
304 material, cooled by liquid nitrogen; normal medium, no issues. What is the bending radius for a low U-bend at a pressure of 6 kilograms? Under general deformation, deformed martensite forms in austenitic stainless steels; to eliminate it, solution treatment is required. .
Whether the manufacturer has similar supply experience is a key factor in assessing its capability to ensure product quality.
Standard austenitic stainless steels do not require impact testing at temperatures above -196 degrees； I found some relevant information online; it seems that martensite was formed during the cold bending process, which altered the microstructure, and no solution treatment was carried out.
Two are in the middle, out of sight, but can be felt by hand; one is on the periphery and visible to the naked eye.