How to check for leaks in sealed paint cans?

First, look:
Invert or place horizontally for 30 seconds and observe for paint or oil seepage around the can opening, welds, and pressure relief valve. If any, it indicates a leak.

Second, listen:
Put your ear close to the can lid and gently shake it. If you hear a hissing sound or a noticeably louder sloshing sound, the seal has failed.

Third, press (hand pressure/vacuum gun):
• Hand pressure: Press the center of the can lid with both hands. If the lid doesn't immediately rebound after release or a "clicking" sound is heard, it indicates a negative pressure leak.
• Vacuum gun: Use a portable vacuum gun (-0.06 MPa) to hold the can lid in place. If the vacuum gauge doesn't drop within 15 seconds, it's considered acceptable.

Fourth, bubble (soapy water):
Apply soapy water to the can lid weld, pressure relief valve, and bottom bead. Observe for 30 seconds. If bubbles appear, it indicates a leak and requires resealing or replacing the lid. Five Instruments (Helium Mass Spectrometer or Differential Pressure Meter)
For batch inspections: Products can be released if the sensitivity of the helium mass spectrometer leak detector is <1×10⁻⁶ Pa·m³/s, or the pressure drop of the differential pressure meter is <100 Pa over 30 seconds.