Safety devices for protection against excessive pressure - Part 3: Safety valves and bursting disc safety devices in combination (ISO 4126-3:2020)

This document establishes technical specifications for the design, construction, and testing of combination safety valve and rupture disc devices used to protect pressurized equipment from exceeding their maximum allowable pressure. It defines performance criteria for such assemblies, ensuring they function reliably under various operating conditions. The standard outlines requirements for selection, installation, and maintenance to maintain system integrity. It addresses specific configurations where a safety valve is combined with a rupture disc, including the interaction between the two components and the assessment of their combined discharge capacity. Guidance is provided on material compatibility, pressure ratings, and the impact of back pressure on device performance. The provisions cover both liquid and gas service applications, detailing how to verify that the combination meets the required relief requirements. Compliance with these specifications helps ensure the safety of industrial plants and processing systems by providing a reliable method to prevent overpressure incidents through the coordinated action of safety valves and rupture discs.