Prior to the hydrostatic test of the container, all titanium cladding welds must undergo color inspection, strip cover plate or connecting pipe liner leak detection nozzle inflation for reverse airtightness test, and helium gas filling into the container for helium leak detection test. Due to the large diameter of some container equipment, the pressure for airtightness testing and helium leak testing is low, resulting in some minor defects or quality hazards on titanium clad fillet welds that cannot be detected under low-pressure leak testing. After high-pressure water pressure testing, leaks can only be discovered in titanium clad fillet welds.
Liquid leakage test
After a water pressure test of 11.3 MPa, it was found that there was water in the leak detection nozzle of the connecting pipe liner. This indicates that there is water in the narrow gap between the liner and the connecting pipe. If airtightness, ammonia leakage, helium leak detection and other tests are directly conducted through the leak detection nozzle, it will seriously affect the sensitivity of the test. At this time, all titanium welds on the connecting pipe liner and the adjacent laminated base material within a range of 100mm (including the entire inner surface of the titanium liner flange) should be wiped to keep them clean and dry. Spray white developer (or lime) on it, wait for it to dry, and then fill 0.3 MPa nitrogen gas into the leak detection nozzle of the connecting pipe. After holding the pressure for 30 minutes, carefully observe whether there is water leakage from the weld seam of the titanium lining tube and the base material of the connecting pipe. After inspection, no leakage points were found, indicating that this detection method cannot detect micro leakage defects in the welding seam of the titanium lining tube in this state.
Air tightness test
In the case where the liquid infiltration method cannot detect the leakage point of the titanium lining tube, it is necessary to ensure that the inner surface of the titanium lining tube, all titanium welds, and the adjacent laminated base material within a range of 100 mm, as well as the narrow space between the dry connection tube and the titanium lining tube, are kept clean. Inject 0.3 MPa nitrogen gas from the leak detection nozzle,
After holding pressure for 30 minutes, apply soapy water to the inner surface of the titanium lining cylinder, titanium welds, and the adjacent 100mm range of the laminated base material, and observe for soap bubbles. If there are no soap bubbles, it means that no leakage points have been found, which means that this detection method cannot detect micro leakage defects in the welding seam of the titanium lining tube in this state.
Ammonia leakage test
In the case where the reverse airtightness test cannot detect the leakage point of the titanium lining cylinder of the connecting pipe, ammonia leakage is carried out in the narrow cavity between the connecting pipe and the titanium lining cylinder
Experiment, as shown in Figure 2. Vacuum the narrow cavity between the connecting pipe and the titanium lining cylinder through a leak detection nozzle (with a vacuum degree of 93.7 kPa), fill it with ammonia gas for testing and raise the pressure to 0.3 MPa. Wet apply the ammonia leakage test paper with phenolphthalein solution on the inner surface of the titanium lining cylinder, all titanium welds, and adjacent composite base materials within 100 mm range. Keep the pressure moist for 3-4 hours and observe whether there is any discoloration on the test paper. There is no discoloration on the test paper, indicating that the reverse ammonia leakage test cannot detect micro leakage defects in the weld seam of the titanium lining tube in this state.
Schematic diagram of ammonia leakage
Helium leak test
In the case where the ammonia leakage test cannot detect the leakage point of the titanium lining cylinder of the connecting pipe, a helium leak test is conducted on the narrow cavity between the connecting pipe and the titanium lining cylinder
Verify, as shown in Figure 3. Seal the inner surface of the titanium lining cylinder, titanium welds in different areas, and the adjacent laminated base material within a range of 100mm with adhesive tape to form if
Dry sealed small space, fill 100% pure helium gas from the leak detection nozzle, increase the pressure to 0.3 MPa, and maintain the pressure for 2 hours. Use helium mass spectrometry suction gun cumulative leak detection method to detect several sealed spaces of titanium lining cylinder and laminated base material. After inspection with a suction gun, it was found that there is an area of the titanium lining tube flange and the container cladding fillet weld
The helium leakage rate reached 3.1 × 10-7 Pa · m3/s, and the helium leak detector triggered an alarm, but the specific location of the micro leak point cannot be determined.
Schematic diagram of helium leak detection
Penetration testing
The fluorescence permeation method should be selected to search for micro leakage defects, and the fluorescence permeation method should be used for the alarm area of the helium leak detector according to NB/T 47013.5-
2015 Level I requires testing and evaluation to identify micro leakage defects; At the same time, the fluorescent penetration method is also used for other corner welds of the titanium lining tube flange, and the inspection and evaluation are carried out according to the requirements of Level I. After identifying suspected points, they are processed together according to the repair plan.
Re weld
When liquid leakage test, airtightness test, ammonia leakage test, helium leak test, and penetration test cannot find the location of micro leakage defects, all cladding fillet welds in the tested area can only be removed and re welded.
