Seeking help on how to detect leaks in heat exchangers
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This post was last edited by foam_ZPTK on 2018-7-12 at 23:15. The conversion low-pressure steam superheater (horizontal U-tube heat exchanger) is leaking; the gas flowing inside the tubes is at a pressure of 6.1 Mpa, while the steam flowing outside the tubes is at a pressure of 1.1 Mpa, and the mixture is heated to 250 degrees before being sent out. It has now been found that there is CO in the steam; the shell side pressure was reduced to 2.0 Mpa, but no leaks were detected, and leakage continued even after operation resumed. What are good ways to find gaps? Replaced last year
There are two possible scenarios: 1. Leakage in the tube itself; 2. Leakage at the joint where the tube sheet meets the tube. You didn’t specify whether it’s a fusion joint or a welded joint. If the pressure applied to the shell side reaches 2 MPA without any leakage, try increasing the pressure further – it’s best to use water pressure for this purpose. Disconnect one end of the tube and check for any leakage
1. For holes in the tubes, airtightness tests can be conducted one by one. 2. In the case of leaks at the tube sheet, a PT test can be performed. 3. If it is an internal floating roof design, pressure should first be applied to the tube side to check for leaks at the flanges. The above suggestions are provided for reference
Vacuum method: it’s relatively fast, but minor leaks cannot be sealed off by the vacuum
Disassembly reduces pressure on the pipe train. Find the drawing and increase the pressure in stages to the test pressure as specified in the drawing (do not reach the pressure all at once). It will be troublesome if it can’t be disassembled; conduct pressure retention tests on each pipe individually. A pressure leak of 6.1 MPa is a real hassle just to think about it.
When testing a heat exchanger for pressure, the first step is to determine the pressure on the high-pressure side; thereafter, multiplying this value by 1.25 gives the reference pressure for applying water pressure. Only in this way can problems in that part of the heat exchanger be identified more comprehensively.
This post was last edited by foam_ZPTK on 2018-8-6 08:44. You’d better take a look at the drawings; it’s similar to the steam generators I’ve repaired before. To check for leaks in the tube side, it’s necessary to apply pressure from the shell side. If the thickness of the shell side isn’t sufficient to withstand such high pressure, then ammonia leak testing or helium leak testing must be carried out. Feel free to ask me if you have any questions
Ammonia permeation: first fill with 15% pure ammonia, the remainder being nitrogen