LBB Nozzle Transition Parameter Variation and Plasticity Influence

2014 ◽  
Author(s):  
Peter Baas ◽  
Frederic Blom
Keyword(s):  
Stress Intensity Factor ◽  
Crack Opening ◽  
Longitudinal Force ◽  
Suppressive Effect ◽  
Parameter Variation ◽  
Development Programme ◽  
Transition Parameter ◽  
Stress Relieving ◽  
The Individual ◽  
Leak Before Break

In the framework of the R6 development programme on leak before break NRG investigated a circumferential through wall crack in a pipe with nozzle. A range of crack angles (3–180°), radius over wall thickness ratios (Ri/t = 5, 10, 20, 50 and 100) and nozzle divergence angles (0, 5, 10, 20, 30 and 40°) have been investigated in order to investigate parameter sensitivity. The stress intensity factor (KI) and the Crack Opening Area (COA) are compared for the nozzle and pipe models. The nozzle investigation is performed using a longitudinal force (100 MPa). It can be concluded that with larger nozzle divergence angles, the resulting maximum KI nozzle factors are higher. The larger nozzle divergence angles have a suppressive effect on the crack opening resulting in a lowered COA nozzle factor. The influence of plasticity has been investigated by a number of analyses including plastic behaviour. The geometry variations are five Ri/t ratios (5, 10, 20, 50 and 100) and eight different crack angles (3, 10, 30, 50, 75, 100, 140 and 180°). A 30° nozzle angle was selected for plastic analyses. The plasticity investigation is performed using longitudinal force (100 MPa). In general the results for KI are higher with the inclusion of plasticity. However, since the inclusion of plasticity has a stress relieving effect on the pipe/nozzle transition, the resulting maximum KI nozzle factor is lowered. The COA results for the individual analyses are overall higher due to the inclusion of plasticity. The COA nozzle factor is lowered, because the relative influence of plasticity is lower on the stiffer nozzle.

scholarly journals Comparison of BS 7910 and API 579-1/ASME FFS-1 Solutions With Regards to Leak-Before-Break

2016 ◽  
Author(s):  
Renaud Bourga ◽  
Bin Wang ◽  
Philippa Moore ◽  
Yin Jin Janin
Keyword(s):  
Experimental Data ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Material Properties ◽  
Crack Opening ◽  
Surface Cracks ◽  
Not Given ◽  
Reference Stress ◽  
The Common ◽  
Leak Before Break

One of the ways to aid the decision whether or not to live with defects in pressurised components is through the demonstration of Leak-Before-Break (LBB). In this paper, three of the main solutions to carry out the LBB assessment, namely Stress Intensity Factor (SIF), Reference Stress (RS) and Crack Opening Area (COA) have been evaluated and compared for both BS 7910 and API 579/ASME FFS-1 standards. Differences with respect to the choice of solutions and boundary conditions are illustrated and discussed. The same applied loads and material properties have been used when applying each procedure. Different geometries for potential pressurised components which are of interest with regards to LBB have been considered for each solution. Focus is made on cylinders where axially and circumferentially oriented through-wall and surface cracks were analysed. While SIF solutions produce similar results for both standards, reference stress solutions show greater differences in the results. However, in LBB assessments it is the reference stress solution which is more relevant, since most LBB assessments pre-suppose the material to be ductile. In terms of COA, solutions are not given exactly equivalent, however they seem to agree well within the common range of applicability. Differences in the assessment route between the standards is also discussed. Experimental data from literature has also been compared to the different standard predictions, to illustrate the accuracy of the solutions for axially oriented surface cracks. The ability of solutions to predict the boundary between leak and break is discussed, in relation to how this shows the level of conservatism.

Influence of Nozzle Transition on Leak Before Break Parameters

2012 ◽  
Author(s):  
Peter Baas ◽  
Frederic Blom
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Stress Concentration ◽  
Finite Elements ◽  
Intensity Factor ◽  
Wall Thickness ◽  
Crack Opening ◽  
Negative Influence ◽  
Inner Radius ◽  
Leak Before Break

In the framework of leak before break a circumferential through-wall crack in a pipe with nozzle is investigated by means of finite elements and compared to a pipe only geometry. A range of crack angles (3–180°) and inner radius to wall thickness ratios (Ri/t = 5, 10, 20, 50 and 100) have been analysed in order to investigate parameter sensitivity. The nozzle and pipe models are compared for the leak before break parameters stress intensity factor (KI) and Crack Opening Area (COA). The results of the comparisons are presented as KI nozzle factor (KI nozzle / KI pipe) and COA nozzle factor (COAnozzle / COApipe). At small crack angles the KI nozzle factor is larger than unity, caused by the stress concentration at the nozzle to pipe intersection. At larger crack angles the KI nozzle factor decreases below unity, caused by the so-called bulging effect, which is apparent in the pipe only model. The COA nozzle factor is smaller than unity for all crack angles, caused by the increased stiffness of the nozzle. As the ratio Ri/t increases, both the KI and COA nozzle factors decrease since the nozzle stiffness relative to the pipe increases. For demonstration of leak before break the nozzle has a negative influence regarding the COA as smaller leaks are more difficult to detect. However, since the KI nozzle factor decreases at larger cracks the influence of nozzles regarding leak before break is not so straight forward.

Crack Opening Areas Under Combined Primary and Secondary Loading

2020 ◽  
Author(s):  
W. J. Brayshaw ◽  
P. James ◽  
J. Sharples ◽  
C. Aird
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Plastic Material ◽  
Crack Opening ◽  
Combined Loading ◽  
Element Analysis ◽  
Elastic Plastic ◽  
Leak Before Break

Abstract Leak-before-break is a methodology to assess whether a leak through a defect in a pressurised component can be detected prior to the defect attaining a critical size. Developing leak-before-break arguments in non-stress relieved piping components can be challenging, in part due to the lack of solutions available, including in R6, to predict the crack opening area (required to evaluate leak rate) for combined primary and secondary stresses under elastic-plastic conditions. This is because the nature of the secondary stresses is to relax with plasticity, which can be captured in the calculation of the crack driving force (elastic-plastic stress intensity factor), but methods to account for the additional crack-tip strain this induces and its influence on crack opening are not available. Here primary stresses are those resulting from an applied force, such as pressure, and secondary stresses are those which result from an internal mismatch and do not contribute to plastic collapse, such as thermal or residual stresses. There is, of course, potential for a higher accuracy of crack opening area evaluations from finite element analysis modelling approaches, which include elastic-plastic material properties, in the presence of combined loading scenarios. In this study, a series of finite element analyses have been conducted whereby crack opening area and stress intensity factor have been calculated from circumferential through-wall defects, under the influence of combined primary and secondary stresses, where the magnitude and order of the combined stress has also been varied. The crack opening areas have been compared to current elastic ‘handbook’ solutions, which are conservative for primary stresses, to better understand the effect of plasticity on crack opening area and to help inform assessments when accounting for the inclusion of plasticity with secondary stresses.

The Effect of Crack Shape Idealisation on Leak-Before-Break Assessment

2016 ◽  
Author(s):  
Renaud Bourga ◽  
Bin Wang ◽  
Philippa Moore ◽  
Yin Jin Janin
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Crack Front ◽  
Structural Integrity ◽  
Crack Opening ◽  
Integrity Assessment ◽  
Crack Shape ◽  
Leak Before Break

Based on detailed 3D finite element (FE) analyses, idealized and non-idealized axial through-wall flaws were evaluated in a cylinder under internal pressure. The key parameters (Stress Intensity Factor, Reference stress, and Crack Opening Area) from widely accepted structural integrity assessment procedures (BS 7910 and API 579-1/ASME FFS-1) were explored and compared between idealized (perpendicular straight-sided flaw) and non-idealized geometry. The effect of crack shape on the evolution of stress intensity factors and crack opening areas along the crack front were also investigated. Non-idealized crack shapes have been modelled assuming a straight crack front with different internal and external crack lengths. The influence of crack shape has been evaluated by varying the crack front location and lengths ratios. The current findings highlight the significance of assessing a more realistic crack shape and should be considered in a leak-before-break (LBB) analysis. A non-idealized crack has a significantly smaller crack opening area than the equivalent idealized through-wall crack. Therefore the leakage rate at this stage of crack growth will be lower than predicted by standard solutions. Stress intensity factor solutions should also take the crack shape variation into account with regards to fatigue crack growth as a surface flaw propagates through-thickness.

Prediction of Durability of Concrete in Monuments using Fracture Mechanics / Vorhersage der Dauerhaftigkeit von Beton in Baudenkmalen durch Anwendung der Bruchmechanik

1999 ◽  
Vol 5 (6) ◽  
pp. 619-626
Author(s):  
S.N. Leonovich
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Structural Model ◽  
Critical Stress Intensity Factor ◽  
Hardened Cement ◽  
Global Response ◽  
Coarse Aggregates ◽  
The Individual ◽  
Durability Of Concrete

Abstract The extension of cracks and pores are considered to be a theoretical basis for the prediction of durability of concrete of monuments. For this purpose a two-level structural model has been introduced: (I) matrix of hardened cement paste with fine and coarse aggregates, (2) voids and cracks created by external actions. The main parameter of this approach is the critical stress intensity factor: [xxx] The stress intensity factor of the material in the vicinity of the crack tip governs the crack growth. If all micro- and macro-defects are taken into consideration on the different levels of the hierarchic structural system, it is possible to formulate the global response. Each pore or crack creates a characteristic stress field around its­ elf in the material. If these pores are classified into periodic volume elements, the individual stress fields can be superimposed. This results in the complex state of stress under an imposed deformation.

A Simplified Method for Calculating Crack Opening Area

2002 ◽  
Author(s):  
E. Smith
Keyword(s):  
Plastic Deformation ◽  
Stress Distribution ◽  
Crack Opening ◽  
Two Dimensional ◽  
Simple Method ◽  
Tensile Stresses ◽  
Normal Operating ◽  
General Stress ◽  
Simplified Method ◽  
Leak Before Break

In the context of the formulation of a leak-before-break case for a component in a pressurized system, this paper is concerned with the quantification of the crack opening area associated with a two-dimensional crack that is subjected to tensile stresses. We present a simple method, based on the strip yield representation of plastic deformation, for calculating the area. The method is validated against the known result for the ease of an isolated crack in a uniformly stressed infinite solid. It is then used for a general stress distribution, as might arise from a combination of pressure induced and weld residual tensile stresses, with the considerations being focussed on the case where plastic deformation is limited, as is usually appropriate for normal operating situations; application of the method is then especially simple.

scholarly journals Engineering Leak-Before-Break Analyses of Pressurized Piping: Part I- Crack Opening Displacement

2004 ◽  
Vol 47 (4) ◽  
pp. 591-599 ◽  
Author(s):  
Yun-Jae KIM ◽  
Nam-Su HUH ◽  
Young-Jin KIM ◽  
Jun-Seok YANG
Keyword(s):  
Crack Opening Displacement ◽  
Crack Opening ◽  
Opening Displacement ◽  
Leak Before Break
Sign in / Sign up

Export Citation Format

Share Document