Withstand voltage test
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One of our company’s heat exchangers has a diameter of Ф600; its heat exchange tubes have a diameter of Ф25 and are made of material 20. The shell side was subjected to a hydrostatic test at a pressure of 4.0 MPa, with the pressure held for 1 hour – no leaks were detected after inspection； During the piping pressure test, when the pressure reached 4.0 MPa, water was detected in the shell side, flowing out from the connection on the shell side. No defects such as tubes or fillet welds were found upon inspection; what could be the reason? I have a question.
What kind of heat exchanger? Fixed tube sheet?
Yes, it’s a fixed tube sheet type, with the water in the tube side flowing into the shell side.
If it is a floating-head heat exchanger, the flanges at the floating-head connection may leak
Are you sure all the water has been drained after the shell side hydrostatic test?
Sorry, I’m not very good at using quick replies; I meant to press Enter to start a new line, but the message was sent right away. Please have the moderator delete my two previous replies. Let me ask first: is the original poster the manufacturer of the equipment or the owner? Is this heat exchanger new, or is it undergoing a hydrostatic test during maintenance? I think there are essentially two problems with leakage in fixed-tube-sheet heat exchangers: one is leakage at the tube joints, and the other is leakage within the tubes themselves. Please have the original poster confirm the following points: 1. First of all, are you sure that all the water was completely drained after the shell-side hydrostatic test? 2. If it has indeed been completely drained, then perform magnetic particle or penetrant testing on the pipe fittings on both sides to confirm that there are no issues with their welding ； 3. If there is no problem with the pipe fittings as well, it can be basically determined that the pipe has leaked. Please carefully check the quality of the pipe itself. Is the pipe fitting expansion-welded? If so, please review the expansion welding process to check for the possibility of expansion cracking.
Was the joint between the heat exchange tubes and the tube sheet damaged during the shell-side pressure testing? For the pressure testing of these two pressure chambers, when testing the shell side, some pressure must also be applied to the tube side, unless it is confirmed to be fine after verification.
What is the maximum design positive pressure for the pipe train, and what is the negative pressure?