Heat exchanger airtightness issue

Airtightness testing can be carried out at the design pressure, as well as ammonia permeation and helium mass spectrometry leak testing.

Our company generally conducts hydrostatic tests on the tube side and shell side, using the design pressure, with the pressure maintained for 30 minutes.

We also conduct hydrostatic tests.

If the equipment manufacturer is reputable, the pressure test is definitely carried out before the equipment leaves the factory; here, only a gas-tightness test is generally performed, without a pressure test. During pressure testing, it is important to test both the tube and the shell simultaneously, as if the design pressure difference between the two sides is small, the tubes may be thin, and testing only one side could lead to rupture.

Our company’s cold boxes feature on-site piping installation and 100% flaw detection. Then conduct a airtightness test, holding the pressure for 24 hours.

For ordinary heat exchange equipment, air-tightness or hydrostatic pressure testing is usually sufficient; for heat exchange equipment with higher requirements, ammonia leak testing can be employed. This testing method is rather complicated, especially regarding the handling of ammonia gas after the leak test.

We generally use airtightness testing for heat exchange equipment, and occasionally conduct hydraulic pressure testing along with the pipelines; however, for heat exchange equipment with higher requirements, ammonia leak testing can be carried out. As mentioned above, this testing method is rather cumbersome.

The tube side generates pressure; during the pressure retention phase, it is checked whether there is any leakage at the flanges of the test tube box, as well as the sealing condition of the shell side, to determine if pressure is being built up

Hydraulic tests are conducted separately on the tube side and shell side, using the design pressure; the pressure is maintained for 30 minutes to check for any leaks.

Pneumatic testing 7.3.1 Pneumatic testing must be carried out in accordance with safety technical measures approved by the technical supervisor of the construction unit, and safety supervision must be provided throughout the testing process. 7.3.2 The testing medium to be used for the pneumatic pressure test of heat exchange equipment shall be dry and clean air, nitrogen, or other inert gases. 7.3.3 The pneumatic test pressure for heat exchange equipment shall be calculated using Equation (3). The pneumatic pressure test for the vacuum side of vacuum heat exchange equipment shall be conducted at the test pressure of the non-vacuum side, and calculated using formula (4). PT = 1.15P …………………………………………………… (3) PT = 1.15P …………………………………………………………… (4) In the above equations: PT – test pressure at the test temperature, in MPa ； P — Design pressure of the heat exchange equipment, MPa ； ——Allowable stress of the material at the test temperature, MPa ； t — allowable stress of the material at the design temperature, MPa. 7.3.4 During the pneumatic testing of heat exchange equipment, the gas temperature shall meet the following requirements: a) For heat exchange equipment made of carbon steel and low-alloy steel, the gas temperature must not be lower than 15 ℃ ； b) For heat exchange equipment made of other materials, the gas temperature shall comply with the specifications in the design documents. 7.3.5 During the pressure test, the pressure should be increased gradually to 10% of the test pressure, with an increase rate not exceeding 0.05 MPa. After holding this pressure for 5 minutes, a preliminary leak check should be conducted on all welds and connection points; if any leaks are detected, the pressure should be reduced before attempting to increase it again. After passing the initial inspection, the pressure is gradually increased to 50% of the test pressure; thereafter, it is raised in steps of 10% of the test pressure until the test pressure is reached. After holding this pressure for 10 minutes, it is reduced to the design pressure, and this condition is maintained for at least 30 minutes. All welds and connection points are then inspected. No air leakage and no visible abnormal deformation indicate compliance. In the event of a leak, handle it after depressurization, and then conduct the test again in accordance with the above regulations. 7.4 Airtightness test 7.4.1 The airtightness test can be carried out only after the hydraulic test of the heat exchange equipment has been successful; the test pressure shall be the design pressure. During the test, the pressure should be increased gradually; once the test pressure is reached, it should be maintained for a sufficient length of time to conduct a leak check on all welds and joints. No leaks indicate that the test is successful. In the event of a leak, pressure should be relieved before taking action, and a leak test should be conducted again after the treatment. 7.4.2 For heat exchange equipment that has passed the pressure test, no airtightness test is required further if there are no specifications in the design documents.

The manufacturing plant passed the hydrostatic test, and production is complete. After on-site installation is complete, a leak test is carried out. At this stage, air is injected at the design pressures for both the tube side and the shell side to maintain pressure, in order to inspect all welds and sealing surfaces ； Alternatively, the 1% ammonia leakage method can be used to inspect the tube-side and shell-side welds as well as the sealing surfaces separately.