GB/T 13465.11-2025 "Test Methods for Impermeable Graphite Materials - Part 11: Permeability Coefficient" is a standard for impermeable graphite, a critical material in chemical equipment. It specifically outlines a unified test method for measuring the permeability coefficient of materials using the vacuum decay method. This method is applicable for determining the permeability coefficient of impermeable graphite materials within a specified range under natural environmental conditions, using air as the test gas. To conduct the test, the core testing instruments mentioned in the standard include a specialized test device that forms a sealed container, as well as high-precision pressure sensors or vacuum gauges used for accurately measuring changes in vacuum pressure within the container. This standard provides essential technical guidance for accurately assessing the sealing safety and material quality of impermeable graphite equipment.