Rupture Disc Sizing & Kr Flow Resistance Calculator
Calculate certified velocity head loss Kr, equivalent piping length, burst tolerance, maximum recommended operating pressure, and relieving flow capacity per ASME Section VIII Div 1 UG-127.
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Flow Geometry & Certified Kr Factor
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Frequently Asked Questions
What is the certified Kr factor in rupture disc sizing?
The Kr factor is a dimensionless velocity head loss coefficient certified per ASME Section VIII Div 1 and ISO 4126-2. Because a burst rupture disc leaves petals protruding into the flow stream, it creates frictional resistance equivalent to Kr velocity heads (deltaP = Kr * rho * V^2 / 2), which is converted to equivalent piping length in relief system hydraulic networks.
Why do reverse-buckling discs permit much higher operating ratios (90-95%) than forward-acting discs (70%)?
Forward-acting discs operate in pure tension; sustained pressure causes continuous microscopic metal creep and thinning at the crown dome, leading to premature fatigue failure if operating pressure exceeds 70% of burst. Reverse-buckling discs operate in compression, where dome geometry resists fatigue until instantaneous Euler buckling occurs at the scored shear lines.
What is the ASME default combination capacity factor (0.90) for disc + PRV installations?
When a rupture disc is installed upstream of a pressure relief valve to prevent toxic fugitive emissions or protect the valve from corrosive slurry, ASME Section VIII Div 1 UG-127 requires applying a mandatory 0.90 de-rating multiplier to the rated capacity of the PRV unless the specific disc-valve combination has undergone certified ASME flow testing.