USED FOR:
(multi-part) Safety devices for protection against excessive pressure
Design, sizing, and testing of pressure relief valves and rupture discs.
RELATED STANDARDS:
- API 520 (Part I and II) “Sizing, Selection, and Installation of Pressure-relieving Devices”
- API 521 “Pressure-relieving and Depressuring Systems”
- API 526 “Flanged Steel Pressure-relief Valves”
- ASME BPVC Section VIII “Rules for Construction of Pressure Vessels”
DIMENSIONAL RANGE:
ISO 4126 doesn’t fix a standard set of orifice designations or inlet/outlet sizes the way API 526 does with its D-through-T letter series; the effective discharge area comes out of the sizing calculation itself, based on set pressure, relieving capacity, and fluid state, rather than off a table in the standard. The connection sizes and pressure-temperature envelope of the valve body instead follow whatever flange standard the project has adopted, typically ASME B16.5 or EN 1092, so we always check ISO 4126 against the piping class it’s being fitted into rather than expecting it to declare a DN or Class range on its own. The real numeric boundary we track here is the set-pressure and back-pressure envelope the device is qualified for, not a nominal size range.
DESCRIPTION:
Covers spring-loaded safety valves, controlled safety pressure relief systems, and bursting-disc safety devices, including sizing methodology for gas, liquid, and two-phase discharge. It’s the reference we check against whenever a relief valve datasheet needs independent verification of set pressure, capacity, and back-pressure correction.
IMPORTANT NOTES:
Relief system design (the header/flare network sizing) is governed separately by process/piping codes, ISO 4126 covers the device itself, not the downstream disposal on the system.
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