Correlating Gas Leakage Rates to Fluid Ingress in Sensor Seals
Correlating gas leakage rates to liquid ingress requires deriving equivalent pore radius to confirm capillary entry pressure exceeds target hydrostatic head.
Micro Pore Leakage
Defect Type
Gas or liquid migration through microscopic voids in a material structure identifies a compromise in the hermetic seal of a component. This micro pore leakage typically occurs in cast metals, welded joints, extruded plastics and thin membranes where the material is not perfectly solid. It represents a flow rate that is too small for visual detection but large enough to cause long-term failure.
Physical Mechanism
Flow through these tiny channels follows different physical rules depending on the size of the opening and the pressure of the fluid. In very small pores, gas molecules collide with the walls more often than with each other, leading to molecular flow. If the pore is larger, the gas behaves like a continuous fluid governed by viscous flow equations.
Helium Tracing
Detection often requires a vacuum chamber and a mass spectrometer to find the minute quantities of tracer gas escaping the part. Helium is the preferred choice because of its small atomic size and low natural presence in the atmosphere. The part is pressurized with helium while the outside environment is evacuated to draw the gas through any existing pores.
Surface Interference
Moisture and oils can temporarily plug these voids and hide the defect during a test. This clogging effect leads to inconsistent results where a part passes the initial check but fails after the contaminants evaporate or move. Rigorous cleaning and drying are necessary to ensure the pores remain open for the tracer gas to pass through.