Effect of the Physical Properties of Testing Gases on the Leak Test Results of Polyethylene Pipe Assemblies Using the Pressure Decay Method

Current industrial standards for gas pipeline leak testing often assume inert testing gases are universally interchangeable, neglecting specific fluid dynamics. This study quantifies how testing gas properties affect integral pressure decay leak tests. Experimental measurements (5000 Pa initial pressure) were conducted on a PE100RC (polyethylene resistant to crack propagation) pipe assembly with artificial capillary defects (0.13 mm diameter) using five media: nitrogen, air, argon, carbon dioxide, and a propane−butane (PB) mixture. Results demonstrate that in the continuous viscous flow regime, leak rates depend strictly on the gas’s dynamic viscosity. For identical defects, PB (the lowest viscosity gas tested) increased the leak rate by up to 129% compared to standard nitrogen. This relationship is statistically validated by a strong negative Pearson correlation (r = −0.92). To facilitate industrial application, a preliminary mathematical correction procedure is proposed for safely extrapolating these trends to infrastructure intended for pure hydrogen operation. To prevent false-positive tightness certifications during the transition to low-viscosity alternative fuels like pure hydrogen, implementing a dynamic viscosity correction factor is essential.