Air to Liquid Correlation
Often a process or product has an ISO or similar standard for leak testing. The following describes how a customer took the ISO 10555 leak test and correlated it to a pressure decay leak test using an Isaac HD pressure decay test.
The ISO 10555 process states that a product can leak no more than one falling drop of water in less than 30 seconds when pressurized to 3 ATM of liquid pressure. The following describes the tests that were performed to correlate this to a nondestructive pressure decay test.
A group of parts were gathered that had been determined to be leak free. Some of the parts were sent out to a company to have holes drilled through them in varying diameters. The part was a catheter and the hole was drilled through the catheter hub directly into the eventual fluid path of the catheter. The holes varied in size from 1 to 20 micron in diameter. The parts were then taken and tested with air. The customer wanted to use 15 PSI of air pressure as their test medium. The laser drilled catheters were first put on a flow meter to determine the amount of flow through the hole. Once a flow had been recorded the parts were put on an Isaac HD pressure decay tester to measure the amount of decay that they generated. The pressure decay test was repeated four times with a one minute interval between tests. Once this data had been recorded the parts were tested with water. The parts were pressurized with water to 3 ATM and monitored for water drops forming. Each part was timed and the timer stopped once the drop formed and fell off of the part. The following chart shows the air flow, diameter and time for the drop to fall. The study determined that for a drop to fall the hole size had to be 10 micron and the air flow at 15 PSI was greater than 2 SCCM. A leak standard of 2 SCCM at 15 PSI was then created to be used for test development.