The problem of brittleness of 304L heat exchange tubes
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My unit has a heat exchanger with an inlet temperature of 180°C, a pressure of 2.3MPa, and an exhaust temperature of 85°C. It separates the moisture in the gas. After using it for a month, the 304L tube bundle at the steam inlet end became brittle. There was no problem with the tube sheet welding, but there were cracks in the circumferential seams at the expansion joints, and the outermost tube bundle became brittle. As shown in the picture
It is recommended to check the Cl ion content inside the heat exchange medium. Austenitic stainless steel has strict requirements for the Cl ion content in the medium. Please refer to the following parameters for details.：
Intergranular corrosion has occurred. See the second floor for the reason.
Low-carbon stainless steel has relatively strong resistance to intergranular corrosion. It seems that the cracks mainly appear at the expansion joint deformation position. It may be stress corrosion. It should be because chloride ions are not controlled.
The chloride ion content in this gas is 15PPM/standard cubic meter. At 2.3MPa, the actual chloride ion per cubic meter is about 250. I think it is also during the expansion welding that the stress is not completely eliminated. At this temperature and under the corrosion of chloride ions, stress corrosion occurs.
This is obviously stress corrosion. The chloride ion content exceeds the limit. We have encountered similar working conditions and the owner has the same situation.
What is the concentration of chloride ions? 15ppm or 250ppm?
You can add a short section of stainless steel pipe (10-15cm flanged casing) to each pipe head, and the casing is one nominal diameter level smaller. See if it has any effect
It was very clear to everyone that the stress at the expansion joint was too great. If stainless steel heat exchange tubes need to be expanded or expanded, the expansion must be controlled. It is best to use hydraulic expansion and try not to expand manually.
Apparently, your factory uses plugs to force the joints in and complete the expansion joint, right? The picture below shows the plug, and 2 shows the mark left after the pipe was damaged after knocking. If this kind of mark appears on new equipment, it can be judged as failed. In a word, the things on the equipment still require technical work.