International ISO Standard IS0 4126-10 Second edition Safety devices for protection against 2024-02 excessive pressure - Part 10: Sizing of safety valves and bursting discs for gas/liquid two-phase flow Dispositifs de securite pour protection contre lespressions excessives Partie 10: Dimensionnement des soupapes de sureté et des disques de rupture pour les débits diphasiques gaz/liquide Reference number IS0 4126-10:2024(en) @ ISO 2024 IS0 4126-10:2024(en) COPYRIGHT PROTECTED DOCUMENT @IS02024 All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or Iso's member body in the country ofthe requester. ISO copyright office CP 40i: Ch. de Blandonnet 8 CH-1214 Vernier, Geneva Phone: +41 22 749 01 11 Email: [email protected] Website: www.iso.org Published in Switzerland @IS02024-Allrightsreserved i IS0 4126-10:2024(en) Contents Page Foreword. V Introduction. .vi 1 Scope. .1 2 Normative references .1 3 Terms and definitions 1 3.1 General. 3.2 Pressure. 2 3.3 Flow rate. 4 3.4 Flowarea. .5 3.5 Fluid state. 5 3.6 Temperature 5 4 Symbols and abbreviated terms and figures 6 4.1 Symbols. 6 4.2 Abbreviated terms. 8 4.3 Figures .9 5 Application range of the method 11 5.1 General 11 5.2 Limitations of the method for calculating the two-phase mass flux in safety devices 11 5.2.1 Flashing flow 11 5.2.2 Condensing flow. 12 5.2.3 Flashing flow for multi-component liquids 12 5.2.4 Dissolved gases. 12 5.2.5 Compressibility coefficient w. 13 5.3 Limitations of the method for calculating the mass flow rate required to be discharged 13 5.3.1 Rate of temperature and pressure increase. 13 5.3.2 Immiscibleliguids 13 6 Sizing steps 13 6.1 General outline of sizing steps. 13 6.2 Step 1 Identification of the sizing case .14 6.3 Step 2 - -Flow regime at the inlet of the vent line system 15 6.3.1 General 15 6.3.2 Phenomenon of level swell 15 6.3.3 Influence of liquid viscosity and foaming behaviour on the flow regime 15 6.3.4 Prediction of the flow regime (gas/vapour or two-phase flow) 17 6.4 Step 3 Calculation of the mass flow rate required to be discharged 20 6.4.1 General 20 6.4.2 Pressure increase caused by an excess in-flow 20 6.4.3 Pressure increase due to external heating. 22 6.4.4 Pressure increase due to thermal runaway reactions 25 6.5 Step4 - Calculation of the dischargeable mass flux through and pressure change in the vent line system 29 6.5.1 General 29 6.5.2 .32 6.5.3 Dimensionless mass flow rate, C 33 6.5.4 Compressibility coefficient, w (numerical method) 34 6.5.5 Calculation of the downstream stagnation condition 35 6.5.6 Slip correction for non-flashing two-phase flow. 35 6.5.7 Slip correction for two-phase flow in straight pipes. 36 6.6 Step 5— Ensure proper operation of safety valve vent line systems under plant conditions. .36 6.7 Simultaneous calculation of the dischargeable mass flux and pressure change in the vent line system. 36 6.8 Summary of calculation procedure. .37 @ IS0 2024 - All rights reserved iii IS0 4126-10:2024(en) Annex A (informative) Identification of sizing scenarios 44 Annex B (informative) Example calculation of the mass flow rate to be discharged .46 Annex C (informative) Example of calculation of the dischargeable mass flux and pressure change through connected vent line systems. .50 Annex D (informative) Environmental factor .67 Bibliography. 68 @ IS0 2024 - All rights reserved iv IS0 4126-10:2024(en) Foreword Iso (the International Organization for Standardization) is a worldwide federation of national standards bodies (IsO member bodies). The work of preparing International Standards is normally carried out through Iso technical committees. Each member body interested in a subject for