Effect of the Yield to Tensile Ratio on Structural Integrity of Line Pipes Subjected to Bending Loads

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Hugo A. Ernst ◽  
Richard E. Bravo
Keyword(s):  
Structural Integrity ◽  
Defect Tolerance ◽  
Deformation Control ◽  
Critical Defect ◽  
Bending Loads ◽  
Critical Defect Size ◽  
Circumferential Defects ◽  
T Values ◽  
Lower Limits ◽  
Leak Before Break

This work studies the effect of the yield (Y) to tensile (T) ratio, Y∕T, on the structural integrity of line pipes with part through the thickness (PTT) circumferential defects subject to bend loading. A model based on elastic-plastic fracture mechanics and plasticity theory was developed for that purpose. The analysis handles situation with load or deformation control conditions. The results are shown in terms of curves of critical defect size versus the controlling variable, i.e., load or deformation. For each one of the different materials studied, cases with different Y∕T values were considered. Even for the lower limits of experimental data, i.e., larger Y∕T, the materials have adequate defect tolerance. A leak before break analysis of a PTT circumferential defect growing into a through the thickness defect growing circumferentially was performed.

Effect of the Yield to Tensile Ratio, Y/T, on Structural Reliability of Linepipes Subject to Bend Loading

2004 ◽  
Author(s):  
Hugo A. Ernst ◽  
Richard E. Bravo ◽  
Jose´ A. Villasante ◽  
Alfonso Izquierdo
Keyword(s):  
Structural Reliability ◽  
Defect Tolerance ◽  
Deformation Control ◽  
Critical Defect ◽  
Control Situations ◽  
Critical Defect Size ◽  
Circumferential Defects ◽  
T Values ◽  
Lower Limits ◽  
Leak Before Break

A model based on elastic-plastic fracture mechanics (EPFM) and plasticity theory, was developed to study the effect of the Yield (Y) to Tensile (T) ratio, Y/T, on the structural reliability of linepipes with part through the thickness (PTT) circumferential defects subject to bend loading. The analysis allows for load or deformation control situations. The results are shown in terms of curves of critical defect size vs. the controlling variable, i.e. load or deformation. For each one of the materials studied, different cases with different Y/T values were considered. Even for the lower limits of experimental data, i.e. larger Y/T, the materials have adequate defect tolerance. A Leak Before Break Analysis was also conducted.

Effect of the Yield to Tensile Ratio on Structural Integrity of Linepipes Subjected to Internal Pressure

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Hugo A. Ernst ◽  
Richard E. Bravo ◽  
José A. Villasante ◽  
Alfonso Izquierdo
Keyword(s):  
Internal Pressure ◽  
Structural Integrity ◽  
Defect Size ◽  
Defect Tolerance ◽  
Deformation Control ◽  
Critical Defect ◽  
Control Situations ◽  
Critical Defect Size ◽  
T Values ◽  
Lower Limits

The effect of the yield (Y) to tensile (T) ratio Y∕T on the structural integrity of linepipes with part through the thickness longitudinal defects subject to internal pressure was studied in this work. A model based on elastic-plastic fracture mechanics and plasticity theory was developed for that purpose. The analysis allows for load or deformation control situations. The results are shown in terms of curves of critical defect size versus the controlling variable, i.e., load or deformation. For each one of the several materials studied, different cases with different Y∕T values were considered. Even for the lower limits of experimental data, i.e., larger Y∕T, the materials have adequate defect tolerance.

Effect of the Yield to Tensile Ratio, Y/T, on Structural Reliability of Linepipes

2003 ◽  
Author(s):  
Hugo A. Ernst ◽  
Jose´ A. Villasante ◽  
Alfonso Izquierdo
Keyword(s):  
Structural Reliability ◽  
Plasticity Theory ◽  
Defect Size ◽  
Defect Tolerance ◽  
Deformation Control ◽  
Critical Defect ◽  
Control Situations ◽  
Critical Defect Size ◽  
T Values ◽  
Lower Limits

The effect of the Yield (Y) to Tensile (T) ratio, Y/T, on the structural reliability of linepipes with longitudinal defects was studied in this work. A model based on elastic-plastic fracture mechanics (EPFM) and plasticity theory, was developed for that purpose. The analysis allows for load or deformation control situations. The results are shown in terms of curves of critical defect size vs. the controlling variable, i.e. load or deformation. For each one of the several materials studied, different cases with different Y/T values were considered. Even for the lower limits of experimental data, i.e. larger Y/T, the materials have adequate defect tolerance.

Use of Nuclear Mechanical Design Codes and Fracture Mechanics Procedures for the UK EPR™ at Hinkley Point C

2013 ◽  
Author(s):  
Martin Gallegillo ◽  
Andrew Goodfellow ◽  
Christophe Philipp ◽  
Lol Miles ◽  
Anthony Williams
Keyword(s):  
Fracture Mechanics ◽  
Structural Integrity ◽  
Mechanical Design ◽  
Defect Size ◽  
Critical Defect ◽  
Safety Case ◽  
Asme Code ◽  
Critical Defect Size ◽  
The Uk

Structures, systems and components that are important to nuclear safety are designed, manufactured, constructed, installed, commissioned, quality assured, maintained, tested and inspected to the appropriate standards. The codes and standards need to be evaluated to determine their applicability, adequacy and sufficiency. The consideration of a conservative design is one important element of the Safety Case. This is generally used together with high manufacturing quality, the use of proven materials, inspection, functional testing and defect tolerability. In a UK Safety Case, the assessment of fracture risk of those mechanical components whose likelihood of gross failure is so low that can be discounted requires the determination of the actual critical defect size in order to compare it with the detectable defect size used for inspections. For the UK EPR™ the 2007 Edition of the RCC-M Code including Addenda 2008, 2009 and 2010 will be the design code of reference and the RSE-M Code version 2010 Appendix 5 will form the basis of the methodology used for standard fracture mechanics assessments of the UK EPR™. Previously, the UK nuclear structural integrity community has used the ASME Code Section III for the UK previous PWR and the R6 procedure for fracture mechanics assessments. This paper explains the choice of these two codes for the UK EPR™ and the work carried out to date by EDF Energy to demonstrate its compliance with the UK expectations for components critical to safety.

Features Testing of Stud Material Under Low Constraint Ductile Tearing

2017 ◽  
Author(s):  
P. James ◽  
M. Jackson ◽  
P. Birkett ◽  
C. Madew
Keyword(s):  
Structural Integrity ◽  
High Stress ◽  
Crack Tip ◽  
Pressure Vessels ◽  
Materials Testing ◽  
Screw Thread ◽  
Surface Point ◽  
Defect Tolerance ◽  
Material Response ◽  
Crack Tip Constraint

Defect tolerance assessments are carried out to support the demonstration of structural integrity for high integrity components such as nuclear reactor pressure vessels. These assessments often consider surface-breaking defects and assess Stress Intensity Factors (SIFs) at both the surface and deepest points. This can be problematic when there is a high stress at the surface, for example due to the stress concentration at the root of a screw thread. In the past this has led to the development of complex and costly 3D finite element analyses to calculate more accurate SIFs, and still resulting in small apparent limiting defect sizes based on initiation at the surface point. Analysis has been carried out along with supporting materials testing, to demonstrate that the increased SIF at the surface point is offset by a reduction in crack-tip constraint, such that the material exhibits a higher apparent fracture toughness. This enables a more simplistic assessment which reduces the effective SIF at the surface such that only the SIF at the deepest point needs to be considered. This then leads to larger calculated limiting defect sizes. This in turn leads to a more robust demonstration of structural integrity, as the limiting defect sizes are consistent with the capability of non-destructive examination techniques. The high SIF at the surface location, and the concomitant reduction in crack-tip constraint, meant that it was not possible to demonstrate the material response with conventional tests, such as those using shallow-notched bend specimens. Instead it was necessary to develop modified specimens in which semielliptical defects were introduced into a geometry which replicated the notch acuity at the root of a screw thread. These feature tests were used to demonstrate the principle, prior to testing with more conventional specimens to fit more accurately the parameters required to represent the material response in a defect tolerance assessment. Margins in defect tolerance assessments are usually measured against the initiation of tearing, even though the final failure for the material may occur at a higher load following stable crack extension. This work measured and assessed the benefit of reduced crack-tip constraint on both the point of initiation and on the development of the tearing resistance curve. This demonstrated that the effect of constraint was valid with tearing for this material and that there was additional margin available beyond the onset of tearing. The feature test geometry also provided evidence of the tearing behaviour at the surface and deepest points of a surrogate component under representative loading. This paper provides an overview of the range of tests performed and the post-test interpretation performed in order to provide the R6 α and k constraint parameters.

Leak-before-break analysis of a pipe containing circumferential defects

2015 ◽  
Vol 58 ◽  
pp. 369-379 ◽  
Author(s):  
X.B. Ren ◽  
B. Nyhus ◽  
H.L. Lange ◽  
M. Hauge
Keyword(s):  
Circumferential Defects ◽  
Leak Before Break

Probabilistic Leak Before Break

2018 ◽  
Author(s):  
L. Stefanini ◽  
F. J. Blom
Keyword(s):  
Fracture Toughness ◽  
Yield Stress ◽  
Master Curve ◽  
Structural Integrity ◽  
Probabilistic Approach ◽  
Leakage Rate ◽  
Critical Crack ◽  
Critical Crack Length ◽  
Integrity Assessment ◽  
Leak Before Break

In this study a probabilistic Leak-Before-Break (LBB) analysis was carried out based on the R6 FAD Option 1 assessment method. The method uses the material fracture toughness and yield stress in order to determine, deterministically, a Critical Crack Length (CCL) and a Leakage Rate (LR) through a crack. In order to define the fracture toughness of the material, the Master Curve approach was used accordingly to BS7910:2013 Annex J. Initially, deterministic analyses were carried out and the fracture toughness and yield stress were set to 190 MPa√m and 158 MPa, respectively. In order to implement a probabilistic approach, the yield stress and fracture toughness were introduced as stochastic parameter. The Fracture toughness was generated using a Weibull distribution to match the Master Curve. The distribution was built such that 190 MPa√m represents the 5% probability fracture toughness. The Yield stress (0.2% proof strength) was generated using a normal distribution with standard deviation 10.35 MPa such that the average value was 175 MPa and the lower bound (5% of probability of occurrence) was 158 MPa. The choice of building the distribution as above mentioned was justified by the fact that in structural integrity assessment the lower 5% is generally used for material parameters. Thus, once a Detectable Leakage Rate (DLR) was determined, it was possible to assign an implicit probability of failure to the deterministic case. The calculations were then extended by using several LR formulas. The calculations were carried out making use of the probabilistic software RAP++ coupled to MATLAB. The probabilities of failure were calculated with regard to a postulated DLR and a DLRSF corrected with a safety factor of 10. The probabilities of failure for the DLRSF were proved to be 9 to 15 times higher than for the postulated DLR case, which leads to the opportunity of conservatism reduction.

Investigation of the Improvements on Mechanical Properties and Thermal Performance of MgO-MgAl2O4 Composite Refractories by Additions of ZnO-Al2O3 to MgO

2012 ◽  
Vol 445 ◽  
pp. 530-535 ◽  
Author(s):  
Cemail Aksel
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Thermal Performance ◽  
Industrial Applications ◽  
Sem Analysis ◽  
Defect Size ◽  
Structural Variations ◽  
Factors Affecting ◽  
Critical Defect ◽  
Critical Defect Size

The variations and developments with the reasons on the mechanical properties of MgO-MgAl2O4 and MgO-ZnO-Al2O3 composite refractories were examined and thermal parameters affecting the durability of composites at high temperatures were investigated. The density, porosity, strength, modulus of elasticity, fracture toughness, fracture surface energy, critical defect size and mean MgO grain size values of composites were measured/calculated and evaluated. In addition, microstructural changes using XRD measurements and SEM analysis were examined. Thermal stress/shock parameters R and Rst that are used for determining high temperature performance of composites were calculated. The relationships between mechanical properties and structural variations for different compositions and the factors affecting this connection were investigated. With the additions of various amounts of ZnO-Al2O3 to MgO, significant improvements were achieved on both mechanical properties and R-Rst parameters of in-situ formed M-S-ZnAl2O4 composite refractories, compared to MgO-MgAl2O4 materials containing preformed spinel, by factors of up to 3.6 and 2.0, respectively. The important parameters increasing mechanical properties and thermal performance of M-S-ZnAl2O4 composites were determined as follows: i) formation of ZnAl2O4 phase leading to a high resistance to crack initiation and propagation, ii) propagation of microcracks formed in the structure for a short distance by interlinking to each other, iii) arresting or deviation of microcracks when reaching pores or ZnAl2O4 particles, and additionally iv) co-presence of both intergranular and transgranular types of cracks on fracture surfaces, and with the incorporations of ZnO-Al2O3, v) increase in density, vi) rise in critical defect size, and vii) a significant reduction in MgO grain size. The optimisation of M-S-ZnAl2O4 composite refractories that could be used for obtaining longer service life in industrial applications was performed.

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