The flow resistance factor Kr quantifies the pressure drop that a rupture disc introduces after activation, expressed as a fraction of the static pressure. The lower the Kr (<0.2 in HPX discs), the greater the discharge capacity and the lower the back pressure on the equipment. The value is used in sizing vent lines according to API 520/521 and EN ISO 4126-6. Choosing discs with a low Kr allows smaller piping and cost savings.
Complete guide: Rupture disc glossary: technical terms explained