1 Scope
This part of ISO 4126 specifies the sizing of safety valves for gas/liquid two-phase flow in pressurized systems such as reactors, storage tanks, columns, heat exchangers, piping systems or transportation
tanks/containers. The possible fluid states at the safety valve inlet that can result
in two-phase flow are given in Table 1.
NOTE The expression “safety valve” is a synonym for valves as described in ISO 4126‑1, ISO 4126‑4 and ISO 4126‑5.
Table 1
—
Possible fluid state at the inlet of the safety valve that can result in two-phase
flow
| Fluid state at valve inlet | Cases | Examples |
|---|---|---|
| liquid | subcooled (possibly flashing in the safety valve)
saturated
with dissolved gas
|
cold water
boiling water
CO2/water
|
| gas/vapour | near saturated vapour (possibly condensing in the safety valve) | steam |
| gas/liquid | vapour/liquid
non-evaporating liquid and non-condensable gas (constant quality)
gas/liquid mixture, when gas is desorbed or produced
|
steam/water
air/water
|