Representation and Partitioning of Welding Residual Stress Distributions for Use in Structural Integrity Assessments

2007 ◽  
Author(s):  
Adam Toft ◽  
David Beardsmore ◽  
Peter James ◽  
John Sharples ◽  
Michael Martin
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Structural Integrity ◽  
Stress Distributions ◽  
Intensity Factors ◽  
Polynomial Representations ◽  
Stress Profiles

In order to obtain good estimates of stress intensity factors in a structural integrity assessment, the accuracy with which a residual stress distribution is represented should be commensurate with the importance of localised peaks in residual stress, in particular where such peaks lie within the region under assessment. This paper describes work undertaken to investigate the importance of accurately representing residual stress distributions in structural integrity assessments. This has been carried out by comparing regular polynomial representations of residual stress distributions, combined with available weight function stress intensity factor solutions (as provided in the R6 procedures) with alternative polynomial representations of residual stress distributions, which provide a more accurate fit in the region of the crack. Such improvements in representation of residual stress profiles provide an indication as to how stress intensity factor solutions could, in future, be modified in order to result in improved accuracy of calculated stress intensity factors. Representation by partitioning residual stress profiles into membrane, bending and self-balancing components, in terms of providing a more straight-forward route for curve-fitting of residual stress profiles is considered. The investigation considers several transverse, through-thickness residual stress distributions. Stress intensity factors are calculated for a variety of crack sizes. Representation of the residual stress profiles in the stress intensity factor solutions are compared, as are the results of the stress intensity factor calculations. The conclusions arising provide guidance as to how current methods of curve fitting a residual stress distribution may be improved in cases where current methods may not be accurate. Advice is also provided as to the relative merits of representing residual stress distributions as a set of partitioned components or as a single distribution.

Effect of Weld Residual Stress Fitting on Stress Intensity Factor for Circumferential Surface Cracks in Pipe

2012 ◽  
Author(s):  
Do-Jun Shim ◽  
Matthew Kerr ◽  
Steven Xu
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Wall Thickness ◽  
Stress Intensity Factors ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Weld Residual Stress ◽  
Order Polynomial

Recent studies have shown that the crack growth of PWSCC is mainly driven by the weld residual stress (WRS) within the dissimilar metal weld. The existing stress intensity factor (K) solutions for surface cracks in pipe typically require a 4th order polynomial stress distribution through the pipe wall thickness. However, it is not always possible to accurately represent the through thickness WRS with a 4th order polynomial fit and it is necessary to investigate the effect of the WRS fitting on the calculated stress intensity factors. In this paper, two different methods were used to calculate the stress intensity factor for a semi-elliptical circumferential surface crack in a pipe under a given set of simulated WRS. The first method is the Universal Weight Function Method (UWFM) where the through thickness WRS distribution can be represented as a piece-wise cubic fit. In the second method, the through thickness WRS profiles are represented as a 4th order polynomial curve fit (both using the entire wall thickness data and only using data up to the crack-tip). In addition, three-dimensional finite element (FE) analyses (using the simulated weld residual stress) were conducted to serve as a reference solution. The results of this study demonstrate the potential sensitivity of stress intensity factors to 4th order polynomial fitting artifacts. The piece-wise WRS representations used in the UWFM was not sensitive to these fitting artifacts and the UWFM solutions were in good agreement with the FE results.

Stress Intensity Factors for Cracks With Large Aspect Ratio in Cylinder

2013 ◽  
Author(s):  
Yinsheng Li ◽  
Hiroaki Doi ◽  
Kunio Hasegawa ◽  
Kazuya Osakabe ◽  
Hiroshi Okada
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Nuclear Power ◽  
Power Plants ◽  
Structural Integrity ◽  
Surface Cracks ◽  
Large Aspect Ratio ◽  
Intensity Factors

A number of surface cracks with large aspect ratio have been detected in components of nuclear power plants in recent years. The depths of these cracks are even larger than the half-lengths. The solution of the stress intensity factor is very important for the structural integrity assessment of such cracked components. However, in the current codes, such as ASME Boiler and Pressure Vessel Code Section XI and the JSME Rules on Fitness-for-Service for Nuclear Power Plants, solutions of the stress intensity factors are provided for semi-elliptical surface cracks with a limitation of a/l ≤ 0.5, where a is the crack depth and l is the crack length. In order to assess structural integrity in a more rational way, the authors previously developed solutions of the stress intensity factor for semi-elliptical surface cracks in flat plates with a/l = 0.5 to 4 and a/t = 0.0 to 0.8, where t is the wall thickness. In this study, the solutions of the stress intensity factors were calculated for circumferential and axial surface semi-elliptical cracks with large aspect ratios in cylinders. The geometrical dimensions focused on were in the ranges of a/l = 0.5 to 4, a/t = 0.0 to 0.8 and t/Ri = 0 to 1/2, where t is the wall thickness and Ri is the inner radius of the cylinder. Some solutions were compared with the available existing solutions in order to confirm their applicability.

Stress-Intensity Factors for Internal and External Surface Cracks in Cylindrical Vessels

1982 ◽  
Vol 104 (4) ◽  
pp. 293-298 ◽  
Author(s):  
I. S. Raju ◽  
J. C. Newman
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Internal Pressure ◽  
Stress Intensity Factors ◽  
Crack Depth ◽  
Surface Cracks ◽  
Stress Distributions ◽  
Intensity Factors

The purpose of this paper is to present stress-intensity factor influence coefficients for a wide range of semi-elliptical surface cracks on the inside or outside of a cylinder. The crack surfaces were subjected to four stress distributions: uniform, linear, quadratic, and cubic. These four solutions can be superimposed to obtain stress-intensity factor solutions for other stress distributions, such as those caused by internal pressure and by thermal shock. The results for internal pressure are given herein. The ratio of crack depth to crack length from 0.2 to 1; the ratio of crack depth to wall thickness ranged from 0.2 to 0.8; and the ratio of wall thickness to vessel radius was 0.1 or 0.25. The stress-intensity factors were calculated by a three-dimensional finite-element method. The finite-element models employ singularity elements along the crack front and linear-strain elements elsewhere. The models had about 6500 degrees of freedom. The stress-intensity factors were evaluated from a nodal-force method. The present results were also compared to other analyses of surface cracks in cylinders. The results from a boundary-integral equation method agreed well (±2 percent), and those from other finite-element methods agreed fairly well (±10 percent) with the present results.

Computations of Stress Intensity Factors for Deep Cracks in Plates by Using the Tetrahedral Finite Element

2012 ◽  
Author(s):  
Hiroshi Okada ◽  
Hirohito Koya ◽  
Hiroshi Kawai ◽  
Yinsheng Li
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Residual Stresses ◽  
Stress Intensity Factors ◽  
Structural Integrity ◽  
Intensity Factors ◽  
Welded Structures ◽  
Elliptical Cracks

In this paper, stress intensity factor solutions for deep half-elliptical cracks that are applicable to the structural integrity evaluations of welded structures are presented. Welded structures generally have some weld residual stresses resulting in stress corrosion crackings (SCCs). This paper describes a simple way to compute the stress intensity factors under the weld-residual stresses and the mode I stress intensity factor solutions for deep half-elliptical cracks. The residual stresses are set to vary proportional to the constant, the linear, the quadratic and the cubic functions of x which is the distance from the plate surface. Although we use a straightforward finite element method to perform the computations, we can quickly generate the stress intensity factor solutions as we make use of automatic mesh generation program for the tetrahedral finite element. Thus, it is very tractable to generate the finite element models with cracks. Furthermore, present solutions can be compared with those of Li et al. which are also presented in PVP 2012. We conclude that present method is useful for the evaluations of SIFs of cracks under the residual stresses.

Stress Intensity Factors Due to Residual Stresses in T-Plate Welds

2004 ◽  
Vol 126 (4) ◽  
pp. 432-437 ◽  
Author(s):  
Noel P. O’Dowd ◽  
Kamran M. Nikbin ◽  
Hyeong Y. Lee ◽  
Robert C. Wimpory ◽  
Farid R. Biglari
Keyword(s):  
Residual Stress ◽  
Stress Intensity ◽  
Yield Strength ◽  
Stress Intensity Factors ◽  
Structural Integrity ◽  
Diffraction Method ◽  
Local Stress ◽  
Stress Distributions ◽  
Intensity Factors ◽  
Smooth Edge

Residual stress distributions in ferritic steel T-plate weldments have been obtained using the neutron diffraction method. It is shown that the transverse residual stress distribution for two plates of different yield strength are of similar shape and magnitude when normalized appropriately and peak stresses are on the order of the material yield strength. The resultant linear elastic stress intensity factors for these stress distributions have been obtained using the finite element method. It has been shown that the use of the recommended residual stress distributions in UK structural integrity procedures leads to a conservative assessment. The stress intensity factors for the welded T-plate have been shown to be very similar to those obtained using a smooth edge cracked plate subjected to the same local stress field.

Stress Intensity Factors Due to Residual Stresses in T-Plate Welds

2004 ◽  
Author(s):  
Noel P. O’Dowd ◽  
Kamran M. Nikbin ◽  
Hyeong Y. Lee ◽  
Robert C. Wimpory ◽  
Farid R. Biglari
Keyword(s):  
Residual Stress ◽  
Stress Intensity ◽  
Yield Strength ◽  
Stress Intensity Factors ◽  
Structural Integrity ◽  
Diffraction Method ◽  
Local Stress ◽  
Stress Distributions ◽  
Intensity Factors ◽  
Smooth Edge

Residual stress distributions in ferritic steel T-plate weldments have been obtained using the neutron diffraction method. It is shown that the transverse residual stress distribution for two plates of different yield strength are of similar shape and magnitude when normalised appropriately and peak stresses are on the order of the material yield strength. The resultant linear elastic stress intensity factors for these stress distributions have been obtained using the finite element method. It has been shown that the use of the recommended residual stress distributions in UK structural integrity procedures leads to a conservative assessment. The stress intensity factors for the welded T-plate have been shown to be very similar to those obtained using a smooth edge cracked plate subjected to the same local stress field.

Stress Intensity Factors for Circular-Arc Cracks in Plates

2018 ◽  
Author(s):  
D. J. Shim ◽  
S. Tang ◽  
T. J. Kim ◽  
N. S. Huh
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Crack Model ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Element Analysis ◽  
Crack Face ◽  
Circular Arc

Stress intensity factor solutions are readily available for flaws found in pipe to pipe welds or shell to shell welds (i.e., circumferential/axial crack in cylinder). In some situations, flaws can be detected in locations where an appropriate crack model is not readily available. For instance, there are no practical stress intensity factor solutions for circular-arc cracks which can form in circular welds (e.g., nozzle to vessel shell welds and storage cask closure welds). In this paper, stress intensity factors for circular-arc cracks in finite plates were calculated using finite element analysis. As a first step, stress intensity factors for circular-arc through-wall crack under uniform tension and crack face pressure were calculated. These results were compared with the analytical solutions which showed reasonable agreement. Then, stress intensity factors were calculated for circular-arc semi-elliptical surface cracks under the lateral and crack face pressure loading conditions. Lastly, to investigate the applicability of straight crack solutions for circular-arc cracks, stress intensity factors for circular-arc and straight cracks (both through-wall and surface cracks) were compared.

Structural Integrity of Penetration Nozzle of Reactor Pressure Vessel Head of PWR Plant

2008 ◽  
Author(s):  
Kiminobu Hojo ◽  
Naoki Ogawa ◽  
Yoichi Iwamoto ◽  
Kazutoshi Ohoto ◽  
Seiji Asada ◽  
...  
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Field ◽  
Pressure Vessel ◽  
Structural Integrity ◽  
Complex Structure ◽  
Reactor Pressure Vessel ◽  
Reactor Pressure

A reactor pressure vessel (RPV) head of PWR has penetration holes for the CRDM nozzles, which are connected with the vessel head by J-shaped welds. It is well-known that there is high residual stress field in vicinity of the J-shaped weld and this has potentiality of PWSCC degradation. For assuring stress integrity of welding part of the penetration nozzle of the RPV, it is necessary to evaluate precise residual stress and stress intensity factor based on the stress field. To calculate stress intensity factor K, the most acceptable procedure is numerical analysis, but the penetration nozzle is very complex structure and such a direct procedure takes a lot of time. This paper describes applicability of simplified K calculation method from handbooks by comparing with K values from finite element analysis, especially mentioning crack modeling. According to the verified K values in this paper, fatigue crack extension analysis and brittle fracture evaluation by operation load were performed for initial crack due to PWSCC and finally structural integrity of the penetration nozzle of RPV head was confirmed.

Propose of Simplified Stress Intensity Factor Equation for SCC Extension of the Pipe Welds

2008 ◽  
Author(s):  
Mayumi Ochi ◽  
Kiminobu Hojo ◽  
Itaru Muroya ◽  
Kazuo Ogawa
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Crack Extension ◽  
Crack Depth ◽  
Alloy 600 ◽  
Intensity Factors ◽  
Axial Crack ◽  
Extension Analysis

Alloy 600 weld joints have potential for primary water stress corrosion cracks (PWSCC). At the present time it has been understood that PWSCC generates and propagates in the Alloy 600 base metal and the Alloy 600 weld metal and there has been no observation of cracking the stainless and the low alloy steel. For the life time evaluation of the pipes or components the crack extension analysis is required. To perform the axial crack extension analysis the stress intensity database or estimation equation corresponding to the extension crack shape is needed. From the PWSCC extension nature mentioned above, stress intensity factors of the conventional handbooks are not suitable because most of them assume a semi-elliptical crack and the maximum aspect ratio crack depth/crack half length is one (The evaluation in this paper had been performed before API 579-1/ASME FFS was published). Normally, with the advance of crack extension in the thickness direction at the weld joint, the crack aspect ratio exceeds one and the K-value of the conventional handbook can not be applied. Even if those equations are applied, the result would be overestimated. In this paper, considering characteristics of PWSCC’s extension behavior in the welding material, the axial crack was modeled in the FE model as a rectangular shape and the stress intensity factors at the deepest point were calculated with change of crack depth. From the database of the stress intensity factors, the simplified equation of stress intensity factor with parameter of radius/thickness and thickness/weld width was proposed.

Consideration of Reduction in Stiffness due to Cracking and the Impact on Standard Stress Intensity Factor Solutions

2017 ◽  
Author(s):  
Daniel M. Blanks
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Nozzle Geometry ◽  
Intensity Factors ◽  
Factor Solution ◽  
Small Component ◽  
Embedded Crack ◽  
The Impact

An API 579-1/ASME FFS-1 Failure Assessment Diagram based Fitness-for-Service assessment was carried out on an embedded crack-like flaw found in a nozzle to shell weld in a pressure vessel. Stress intensity factors were initially calculated by utilizing stress results from a Finite Element Analysis (FEA) of an uncracked configuration, with the standard embedded crack stress intensity factor solution given in API 579-1/ASME FFS-1. Due to the complex nozzle geometry and flaw size, a second analysis was carried out, incorporating a crack into the FEA model, to calculate the stress intensity factors and evaluate if the standard solution could be applied to this geometry. A large difference in the resulting stress intensity factors was observed, with those calculated by the FEA with the crack incorporated into the model to be twice as high as those calculated by the standard solutions, indicating the standard embedded crack stress intensity factor solution may be non-conservative in this case. An investigation was carried out involving a number of studies to determine the cause of the difference. Beginning with an elliptical shaped embedded crack in a plate, the stress intensity factor calculated with an idealized 3D crack mesh agreed with the API 579-1/ASME FFS-1 solution. Examining other crack locations, and crack shapes, such as a constant depth embedded crack, revealed how the solution began to differ. The greatest difference was found when considering a crack mesh with a small component height (i.e. the distance measured perpendicular from the crack face to the top of the mesh). A close agreement was then found between the stress intensity factors calculated in the nozzle model and an idealized crack mesh with component heights representative of the true geometry. This revealed that reduced structural stiffness is a key factor in the calculation of the stress intensity factors for this geometry, due to the close proximity of the embedded crack to the inner surface of the nozzle. It was found that this reduction is potentially significant even with relatively small crack sizes. This paper details the investigation, and aims to provide the reader with an awareness of situations when the standard stress intensity factor solutions may no longer be valid, and offers general recommendations to consider when calculating stress intensity factors in these situations.

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