: Equipment connected together by piping of adequate capacity, free from potential blockages, and without isolating valves, can be considered a safety system for the purpose of pressure relief.
ISO 4126-9 PDF: A Comprehensive Guide to Safety Device Installation Iso 4126-9 Pdf
Scope
A key principle is that equipment connected by piping of adequate capacity, with no valves that can isolate any part, can be considered a single safety system for pressure relief purposes. : Equipment connected together by piping of adequate
Safety valves often require periodic testing. The standard provides requirements for lifting devices that allow operational verification without removing the valve from service. free from potential blockages