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Coefficient of Discharge Method

Size or rate a rupture disc for gas, liquid, or steam service, and compare disc options.

API 520 Pt 1 · 5.11.1.2

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Confirm API 520 boundaries

Choose service

Gas, liquid, or steam

Enter conditions

Units, media, pressures

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Disc types that fit your run

Step 1 · API 520 boundaries

The coefficient of discharge method (K_d = 0.62) applies only when all four are true.

Atmospheric discharge

The rupture disc device must discharge directly to atmosphere.

Short inlet run

Installation must be within eight pipe diameters from the vessel nozzle entry.

Short discharge length

Discharge piping length cannot exceed five pipe diameters.

Matched pipe sizes

Nominal inlet and outlet piping must match the device nominal pipe size.

Step 2 · Choose a workflow

For compressible relieving conditions where media properties and back pressure drive the required area.

For incompressible flow cases where density, viscosity, and system losses define the relief path.

For saturated or superheated steam applications that depend on temperature pressure correction data.

Size a disc finds the required flow area from your service conditions. Check capacity rates the flow through a disc you already have.

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