Leak Before Break: Studies in Support of New R6 Guidance on Leak Rate Evaluation

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
J. P. Taggart ◽  
P. J. Budden
Keyword(s):  
Gas Flow ◽  
Flow Direction ◽  
Nuclear Industry ◽  
Leak Rate ◽  
Effective Roughness ◽  
Crack Morphology ◽  
Morphology Model ◽  
Flow Through ◽  
Rate Evaluation ◽  
Leak Before Break

The concept of leak-before-break (LBB) is often used in safety cases for pressure systems, particularly, in the nuclear industry. An important factor in making a LBB case is in the prediction of the leak rate of fluid through a crack. This paper presents a summary of a program of work, which had the aim of improving guidance on leak rate evaluation for the LBB procedures in the R6 defect assessment methodology. Methods of calculating leak rates have been reviewed, and this has led to a crack morphology model being proposed, which represents single-phase isothermal compressible flow through a crack. In the crack morphology model, the flow is assumed by default to be fully rough turbulent, and the effective roughness to vary between a local roughness value for narrow cracks and a global value (i.e., the overall crack contours) for wide cracks. The effect of pressure drops due to changes in the flow direction at crack turns has also been included. Calculations using the model show that the friction factor relation due to Spence et al. (1991, “Leakage Flow Through Small Cracks—Report of Second Stage of Experimental Work,” unpublished) gives better agreement with measured flow rates than that due to Button et al. (1978, “Gas Flow Through Cracks,” ASME J. Fluids Eng., 100, pp. 453–458), which tends to overestimate the flow rate for the examples studied. The inclusion of an inertial pressure term arising from changes in overall flow direction appears to be justified.

Leak Before Break: Studies in Support of New R6 Guidance on Leak Rate Evaluation

2005 ◽  
Author(s):  
J. P. Taggart ◽  
P. J. Budden
Keyword(s):  
Flow Direction ◽  
Nuclear Industry ◽  
Leak Rate ◽  
Pressure Drops ◽  
Effective Roughness ◽  
Crack Morphology ◽  
Morphology Model ◽  
Safety Cases ◽  
Rate Evaluation ◽  
Leak Before Break

The concept of leak-before-break (LBB) is often used in safety cases for pressure systems, particularly in the nuclear industry. An important factor in making a LBB case is in the prediction of the leak rate of fluid through a crack. This paper presents a summary of a programme of work, which had the aim of improving guidance on leak rate evaluation for the LBB procedures in the R6 defect assessment methodology. Methods of calculating leak rates have been reviewed, and this has led to a crack morphology model being proposed, which represents single-phase isothermal compressible flow through a crack. In the crack morphology model, the flow is assumed by default to be fully rough turbulent, and the effective roughness to vary between a local roughness value for narrow cracks, to a global value (i.e. the overall crack contours) for wide cracks. The effect of pressure drops due to changes in the flow direction at crack turns has also been included. Calculations using the model show that the friction factor relation due to Spence et al. gives better agreement with measured flow rates than that due to Button et al., which tends to overestimate the flow rate for the examples studied. The inclusion of an inertial pressure term arising from changes in overall flow direction appears to be justified.

Modeling of Cracked Pipe System: Effect of Boundary Conditions on Displacement-Controlled and Load-Controlled Leak-Before-Break

2019 ◽  
Author(s):  
M. Uddin ◽  
G. Wilkowski ◽  
E. Kurth ◽  
L. Hill ◽  
K. Bagnoli
Keyword(s):  
Boundary Conditions ◽  
Nuclear Industry ◽  
Refining Industry ◽  
Leak Rate ◽  
Design Stage ◽  
Piping System ◽  
Dynamic Rupture ◽  
System Effect ◽  
Pipe System ◽  
Leak Before Break

Abstract In recent years, there has been a growing interest of using Leak-Before-Break (LBB) concept in the refining industry. LBB methodology has been applied in the nuclear industry for decades, but generally for elimination of hardware for dynamic rupture control at the design stage. However, in the refining industry the purpose of the LBB application could be quite different than for the nuclear industry. In the refining industry the purpose of LBB is to show in-service leakage can be detected well ahead the potential for rupture allowing for ample time for safe replacement of piping. This paper explores conditions in which LBB can be applied to refinery piping. Initially, the analysis was conducted using a finite element model of a typical pipe system with its design boundary conditions under operating loadings, i.e., gravity, pressure, thermal and hanger loadings. The results with various circumferential crack sizes show a displacement-controlled manner (LBB is easy to satisfy) for the pipe system mainly due to higher secondary stresses, i.e., thermal loadings. However, the pipe system behaved in a load-controlled manner (LBB is harder to satisfy) when some of the boundary conditions were changed simulating a possible support failure and/or hanger failure. This paper investigates how boundary conditions can change a displacement-controlled LBB behavior to load-controlled LBB for a representative pipe system and the implications regarding leak rate detection capability. The effect of material’s toughness reduction due to high-temperature hydrogen-attack (HTHA) damage was also included in these analyses. The procedure outlined here can be applied to a piping system to identify piping supports that are critical for inspection to demonstrate LBB, and the anticipated leak rate before reaching critical flaw size.

scholarly journals Experimental Assessment of Porous Material Anisotropy and its Effect on Gas Permeability

2018 ◽  
Vol 4 (4) ◽  
pp. 906 ◽  
Author(s):  
Grzegorz Wałowski
Keyword(s):  
Porous Material ◽  
Gas Flow ◽  
Gas Permeability ◽  
Flow Direction ◽  
Clean Energy ◽  
Gas Production ◽  
Material Anisotropy ◽  
Internal Structures ◽  
Flow Through ◽  
New Generation

The results of experimental research upon the assessment of porous material anisotropy and its effect on gas permeability of porous materials with respect to the gas flow. The conducted research applied to natural materials with an anisotropic gap-porous structure and - for comparative purposes - to model materials such as coke, pumice and polyamide agglomerates. The research was conducted with the use of a special test stand that enables measuring the gas permeability with respect to three flow orientations compared with symmetric cubic-shaped samples. The research results show an explicit impact of the flow direction on the permeability of materials porous, which results from their anisotropic internal structures. The anisotropy coefficient and permeability effective coefficient of such materials was determined and an experimental evaluation of the value of this coefficient was conducted with respect to the gas stream and the total pressure drop across the porous deposit. The process of gas permeability was considered in the category of hydrodynamics of gas flow through porous deposits. It is important to broaden the knowledge of gas hydrodynamics assessment in porous media so far unrecognised for the development of a new generation of clean energy sources, especially in the context of biogas or raw gas production.

A Special Finite Element for Leak-Before-Break Analysis

2012 ◽  
Author(s):  
Peter J. Gill ◽  
John Sharples ◽  
Keith Davey
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Crack Opening ◽  
Nuclear Industry ◽  
Leak Rate ◽  
Assessment Procedure ◽  
Factors Affecting ◽  
First Results ◽  
Crack Faces ◽  
Leak Before Break

Leak-before-Break is increasingly being used as part of safety justifications, particularly within the nuclear industry. In order to make a Leak-before-Break case for a pressurised component, it is necessary to determine leak rates through cracks under the operating load conditions. The R6 assessment procedure provides equations to calculate leak rates from a known crack opening area. Leak rates evaluated from this calculational route, however, can be subject to safety factors being applied due to various uncertainties. As such there is a strong motivation to better understand the factors affecting leak rates through cracks in pipes, so that there is less conservatism in the leak rate estimation. To perform the investigations into these factors, a special finite element has been developed. This element uses the extended finite element method to model cracks with boundary conditions on the faces due to the leaking fluid. Previous work has shown that leak rates through a crack are affected by closure of the crack, which is due to convective heat transfer from the leaking fluid to the crack faces. Therefore the new 2-D element is used to investigate this and it shows the effect of heat transfer and pressure acting on the crack faces. The first results of leak rate evaluations, using this new element, are presented in the paper.

Comparison of Leak Rates From Alloy 82/182 Butt Weld Cracks for Leak-Before-Break Applications

2006 ◽  
Author(s):  
A. D. Nana ◽  
K. K. Yoon
Keyword(s):  
Fatigue Crack ◽  
Leak Rate ◽  
Alloy 600 ◽  
Base Metals ◽  
Butt Weld ◽  
System Pressure ◽  
Crack Morphology ◽  
Piping Systems ◽  
The Impact ◽  
Leak Before Break

The discovery of leaking cracks in Alloy 82/182 bimetal welds at the V.C. Summer Nuclear Station has lead the industry to reassess the Leak-Before-Break (LBB) analysis of the reactor coolant system pressure boundary piping components involving Alloy 600 base metals and Alloy 82/182 welds. The leaking cracks were attributed to primary-water-stress-corrosion-cracking (PWSCC). To-date, LBB analysis submittals to the NRC have not considered PWSCC cracks in bimetal welds or Alloy 600 base metals and the leak rate calculations have only considered the conventional fatigue crack morphology. There are limited observed in-service leakage cracks of Alloy 82/182 pipe butt welds with plant measured leak rate data. Effects of PWSCC induced crack morphology involving these welds is investigated through various modeling techniques. The differences in leakage prediction when evaluating as a fatigue crack versus assessing as a PWSCC crack is addressed for various PWR LBB piping systems. The impact of this finding to the overall LBB assessment is discussed. Additionally, the LBB results are compared against the results from another paper.

EFFECT OF GAS FLOW DIRECTION ON PASSIVE SUBSEA COOLER EFFECTIVENESS

2019 ◽  
Vol 11 (1-2) ◽  
pp. 1-16 ◽  
Author(s):  
Nikolay Ivanov ◽  
Vladimir V. Ris ◽  
Nikolay A. Tschur ◽  
Marina Zasimova
Keyword(s):  
Gas Flow ◽  
Flow Direction

INVESTIGATION OF THE TIME OF GAS FLOW THROUGH A HOLE IN LONG PIPELINES UNDER HIGH PRESSURE

2020 ◽  
Vol 58 (1) ◽  
pp. 30-43
Author(s):  
N.D. Yakimov ◽  
◽  
A.I. Khafizova ◽  
N.D. Chichirova ◽  
O.S. Dmitrieva ◽  
...  
Keyword(s):  
High Pressure ◽  
Gas Flow ◽  
Flow Through

Free area for gas flow through sieve plates with a bubbled bed

1975 ◽  
Vol 40 (11) ◽  
pp. 3315-3318 ◽  
Author(s):  
M. Rylek ◽  
F. Kaštánek ◽  
L. Nývlt ◽  
J. Kratochvíl
Keyword(s):  
Gas Flow ◽  
Flow Through ◽  
Sieve Plates ◽  
Free Area

scholarly journals A Study on Liquid Leak Rates in Packing Seals

2021 ◽  
Vol 11 (4) ◽  
pp. 1936
Author(s):  
Abdel-Hakim Bouzid
Keyword(s):  
Environmental Protection ◽  
Liquid Flow ◽  
Environmental Protection Agency ◽  
Gas Flow ◽  
Outer Boundary ◽  
Health And Safety ◽  
Toxic Substances ◽  
Packing Materials ◽  
Thickness Change ◽  
Flow Through

The accurate prediction of liquid leak rates in packing seals is an important step in the design of stuffing boxes, in order to comply with environmental protection laws and health and safety regulations regarding the release of toxic substances or fugitive emissions, such as those implemented by the Environmental Protection Agency (EPA) and the Technische Anleitung zur Reinhaltung der Luft (TA Luft). Most recent studies conducted on seals have concentrated on the prediction of gas flow, with little to no effort put toward predicting liquid flow. As a result, there is a need to simulate liquid flow through sealing materials in order to predict leakage into the outer boundary. Modelling of liquid flow through porous packing materials was addressed in this work. Characterization of their porous structure was determined to be a key parameter in the prediction of liquid flow through packing materials; the relationship between gland stress and leak rate was also acknowledged. The proposed methodology started by conducting experimental leak measurements with helium gas to characterize the number and size of capillaries. Liquid leak tests with water and kerosene were then conducted in order to validate the predictions. This study showed that liquid leak rates in packed stuffing boxes could be predicted with reasonable accuracy for low gland stresses. It was found that internal pressure and compression stress had an effect on leakage, as did the thickness change and the type of fluid. The measured leak rates were in the range of 0.062 to 5.7 mg/s for gases and 0.0013 and 5.5 mg/s for liquids.

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