This study focuses on the application of expansion technology to rupture disc safety relief devices for high‑pressure hydrogen storage vessels，using ultra‑high purity （UHP） AISI 316L austenitic stainless steel.Internal inclusions act as hydrogen traps and corrosion initiation sites，directly influencing the material's susceptibility to hydrogen embrittlement as well as the triggering accuracy and reliability of the rupture disc.Currently，the industry lacks a systematic evaluation and comparison of cleanliness and inclusion control for such materials.In this study，a systematic quality assessment was carried out by comparing materials produced by different manufacturers using vacuum induction melting combined with vacuum arc remelting （Material A），as well as the argon‑oxygen decarburization process followed by VAR （Material B）.Innovatively，this study employed a combination of microscopic characterization techniques including metallographic microscopy，scanning electron microscopy，and energy‑dispersive X‑ray spectroscopy，coupled with thermodynamic calculations to simulate the evolution of inclusions during cooling.This approach revealed the characteristics and distribution patterns of inclusions resulting from different processes and sources.The results indicate that among the evaluated samples，Material B produced by China Factory A exhibited the best cleanliness，with both inclusion density and area fraction significantly lower than those of the other samples.This finding is in strong agreement with the thermodynamic simulation predictions，confirming the reliability of the adopted methodology.The results provide important guidance for the selection and process optimization of ultra‑high purity 316L stainless steel used in critical hydrogen‑containing rupture disc safety components，and also offer a reference framework for the quality assessment and control of similar high‑cleanliness materials.