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research-article

PREDICTING LEAK RATE THROUGH VALVE STEM PACKING IN NUCLEAR APPLICATIONS

[+] Author and Article Information
Ali Salah Omar Aweimer

PhD student, Ecole de Technologie Superieure, 1100 Notre-Dame Ouest, Montreal (Quebec) CANADA H3C 1K3
ali-salah-omar.aweimer.1@etsmtl.ca

Hakim A. Bouzid

Professor, ASME Fellow, Ecole de Technologie Superieure, 1100 Notre-Dame Ouest, Montreal (Quebec) CANADA H3C 1K3
hakim.bouzid@etsmtl.ca

Mehdi Kazeminia

Graduated phd student, Ecole de Technologie Superieure, 1100 Notre-Dame Ouest, Montreal (Quebec) CANADA H3C 1K3
mehdi.kazeminia.1@ens.etsmtl.ca

1Corresponding author.

ASME doi:10.1115/1.4040493 History: Received September 08, 2017; Revised May 30, 2018

Abstract

Leaking valves has forced shutdown in many nuclear power plants. The myth of zero leakage or adequate sealing must give way to more realistic maximum leak rate criterion in design of nuclear flange joints and valve stem packing. It is well established that the predicting leakage in these pressure vessel components boxes is a major engineering challenge to designers and end users. This is particularly true in nuclear valve due to the different working conditions and material variations. The prediction of the leak rate through packing rings is not a straightforward task to predict. This work presents a study on the ability of micro channel flow models to predict leak rates through packing rings made of soft materials such as flexible graphite. A methodology based on the experimental characterization of the porosity parameters is developed to predict leak rates at different compression stress levels. Three different models are compared to predicate the leakage, where the diffusive and second order flow models are derived from Naiver-Stokes equations and incorporate the boundary conditions of an intermediate flow regime to cover the wide range of leak rate levels. The lattice model is based on porous media of packing rings as packing bed. The flow porosity parameters of the micro channels assumed to simulate the leak paths present in the packing are obtained experimentally. The predicted leak rates from different gasses are compared to those measured experimentally, in which the set of packing rings is mainly subjected to different gland stresses and pressures.

Copyright (c) 2018 by ASME
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