If a standard is already validated (for example ASTM F2096 Standard Test Method for Detecting Gross Leaks in Medical Packaging by Internal Pressurization), what else are we supposed to do in house to validate the procedure? (other than validating the equipment)
You should verify with your test method and equipment that you can detect to the same sensitivity as the standard. This can be done by creating a hole or channel the size designated in the test method and testing accordingly. The point of test method validation is to ensure that you understand the anticipated variation in your testing.