How to check the integrity of the coating film in tinplate cans with easy-open lids?

The tinned (chromium) steel plate and the bottom cover of the tank use an internal coating film integrity tester with a reading ≤0.1mA and a working voltage of 6.3V (DC). The tank is connected to the anode, and 20g/L sodium sulfate solution is added to the tank. The surface is 3mm away from the tank mouth, insert a stainless steel rod to connect to the negative electrode, and the reading takes the 4S inner coating defect current value. The aluminum alloy sheet is easy to open the lid and the bottom lid, and then use 10g/L sodium chloride solution for testing.