GB/T 12137-2025 "Methods for Leak Test of Gas Cylinders" specifies the methods for conducting gas tightness tests on gas cylinders with a nominal working pressure not exceeding 70 MPa. This standard applies to various types of gas cylinders, including steel, aluminum alloy, and composite material cylinders, and elaborates on three core testing methods: the traditional water immersion method, the liquid application method (soap bubble method), and the precise helium mass spectrometry leak detection method. Implementing these methods requires specific instruments and equipment, primarily including working pressure gauges or pressure transmitters with an accuracy class not lower than 1.6, as well as helium mass spectrometry leak detectors, dedicated submersible or gas tightness testing machines, among others. This standard serves as a critical technical basis for the safety inspection of gas cylinders and quality control in production.