Problems with heat exchanger pressure testing?
Thread Content
The design pressure for the tube side of the heat exchanger is 1.6 MPa, while that for the shell side is 6.4 MPa. During maintenance, it is difficult to apply pressure to the shell side due to its connection to the steam drum. What pressure is appropriate to apply to the tube side?
Clearly, pipe threading cannot detect the quality of heat exchange tube joints.
Check the heat exchange tube joints in the shell side by applying the test pressure of the shell side!
For this type of heat exchanger, our factory’s practice is as follows: in the case of a shell-and-tube heat exchanger (with plain tubes, where gas flows on the tube side and water flows on the shell side), hydraulic pressure is applied to both the tube side and the shell side at 1.25 times the design pressure respectively. In addition, a separate ammonia testing is carried out on the core assembly, in accordance with the requirements of HG20584. After the overall assembly is completed, hydraulic pressure at 1.25 times the design pressure is applied again to the shell side. Moreover, penetrant testing is required for CD-type welds on both the tube side and the shell side； For shell-and-tube air coolers of the cartridge type, the tube side and shell side are each pressurized with water at 1.25 times the design pressure. In addition, an ammonia test or a helium test is conducted separately on the core assembly; the ammonia test is carried out in accordance with HG20584 standards, while helium testing is done using a helium mass spectrometer for leak detection. The required leakage rate is 10 to the power of -4 under wet-air conditions and 10 to the power of -6 under dry-air conditions. After the overall assembly, a leak tightness test is performed on the shell side at 1 time the design pressure. For shell-side CD-type welds where the design pressure exceeds 4 MPa, penetrant testing is required ； Foreign manufacturers employ another approach for shell-and-tube air coolers of the cartridge type (we produce them according to their designs). Pressure testing is carried out during the final assembly: first, water is filled on the tube side, and the pressure is maintained at 1.25 times the design pressure for 30 minutes; then water is filled on the shell side, with the pressure again maintained at 1.25 times the design pressure for 30 minutes. After that, the water from the tube side is drained, and the pressure is held for another 30 minutes – only if all tests pass is the unit considered acceptable. Overall, only welds of type AB are required to undergo radiographic inspection, while the remaining welds are inspected by penetrant testing, with only a few specific areas requiring such testing as per ASME standards
In shell-and-tube heat exchangers, when the pressure on the tube side is higher than that on the shell side, and if the difference is not significant and the strength permits it, the test pressure on the shell side can be increased to make the test pressures on both sides equal； If the difference is significant, each side can be pressurized to its respective required pressure for the hydrostatic test, after which an airtightness test shall be conducted on the shell side, using the design pressure of that side as the test pressure
Our factory also applies pressure at 1.25 times the standard value!
The test pressure for the tube side = 1.6 MPa × 1.25 × temperature correction factor; a 1% ammonia leak test is conducted on the pipe joints on the shell side, while magnetic particle testing is used to inspect the remaining C and D welds.