A Simplified Evaluation of Stress Intensity Factors for a Small Diameter Pipe Penetrating a Thick Plate

2003 ◽  
Author(s):  
John M. Emery ◽  
Katsumasa Miyazaki ◽  
Anthony R. Ingraffea
Keyword(s):  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Complex Geometry ◽  
Three Dimensional ◽  
Small Diameter ◽  
Boiling Water Reactors ◽  
Intensity Factors ◽  
Pressurized Water ◽  
Diameter Pipe ◽  
Water Reactors

Recent trouble with stress corrosion cracking in the internal parts of boiling water reactors and similar issues found in pressurized water reactors has prompted interest in developing simplified methods to determine stress intensity factors for such cracks. Currently, there are many practical and accurate simplified methods to calculate stress intensity factors for a surface crack in plates and pipes. However, there are none that deal with the complex geometry that can arise within the reactors. The complex geometry found within the vessels often entails reentrant comers, welds, holes, and other stress amplifiers. This paper sets forth a means by which some commonly known and accepted simplified solutions to cracks in pipes and plates can be modified to improve the accuracy of stress intensity factors when applied to this complex geometry. The effort to do so included axisymmetric and fully three-dimensional numerical modeling of both the cracked and uncracked body with a variety of assumed surface flaws. It was confirmed that the simplified methods lead to exceedingly conservative estimates for the stress intensity factors of the complex geometry. Finally, a correction factor based on the axisymmetric analyses was applied to the three-dimensional results to improve the accuracy of the simplified solutions.

Demonstrate ASME Section XI Appendix G Margins for Pressurized Water Reactor Inlet and Outlet Nozzle Corner Regions

2018 ◽  
Author(s):  
Anees Udyawar ◽  
J. Brian Hall ◽  
Justin Webb ◽  
Alexandria Carolan
Keyword(s):  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Temperature Limit ◽  
Flaw Size ◽  
Pressurized Water Reactor ◽  
Intensity Factors ◽  
Outlet Nozzle ◽  
Element Analysis ◽  
Pressurized Water ◽  
Water Reactors

Since the implementation of pressure-temperature (P-T) limit curves in the 1960s for light water reactors, the P-T limit curves have been based on the limiting locations in the reactor coolant system, which are typically the irradiated reactor pressure vessel (RPV) region adjacent to the core (beltline) and the closure head flange. Recently, it has been questioned as to whether the reactor vessel inlet or outlet nozzle corners could be more limiting due to the stress concentration at these locations. The discussion presented in this paper provides technical justification that the RPV nozzle corner P-T limit curves are bounded by the traditional P-T limit curves for the pressurized water reactors (PWRs). The current approach in evaluating the Pressurized Water Reactor Inlet and Outlet nozzle corner regions with respect to plant heatup and cooldown Pressure Temperature Limit Curves contains a number of conservatisms. These conservatisms include postulation of a large 1/4T flaw at the nozzle corner region, use of RTNDT (reference nil-ductility temperature), and fracture toughness prediction based on plane strain fracture toughness. The paper herein discusses several factors that can be considered to improve the pressure temperature limit curves for nozzle corners and increase the operating window for nuclear power plant operations. Prior to the 2013 edition, the ASME Section XI Appendix G did not require the use of a 1/4T flaw for the nozzle corners; furthermore, a smaller postulated flaw size is permissible. Based on inspection capability and experience, a smaller flaw size can easily be justified. The use of a smaller flaw size reduces the stress intensity factors and allows for the benefit of being able to take advantage of increased material toughness due to the loss of constraint at the nozzle corner geometry. The analysis herein considers the calculation of stress intensity factors for small postulated nozzle corner flaws based on a 3D finite element analysis for Westinghouse PWR inlet and outlet nozzle corner regions. The Finite Element Analysis (FEA) stress intensity factors along the crack front are used in the determination of allowable pressures for the cooldown transient Pressure-Temperature limit curves.

A Coupled SBFEM-FEM Approach for Evaluating Stress Intensity Factors

2013 ◽  
Vol 353-356 ◽  
pp. 3369-3377 ◽  
Author(s):  
Ming Guang Shi ◽  
Chong Ming Song ◽  
Hong Zhong ◽  
Yan Jie Xu ◽  
Chu Han Zhang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Complex Geometry ◽  
Stress Singularity ◽  
Intensity Factors ◽  
Finite Element Software ◽  
Scaled Boundary Finite Element ◽  
Element Method

A coupled method between the Scaled Boundary Finite Element Method (SBFEM) and Finite Element Method (FEM) for evaluating the Stress Intensity Factors (SIFs) is presented and achieved on the platform of the commercial finite element software ABAQUS by using Python as the programming language. Automatic transformation of the finite elements around a singular point to a scaled boundary finite element subdomain is realized. This method combines the high accuracy of the SBFEM in computing the SIFs with the ability to handle material nonlinearity as well as powerful mesh generation and post processing ability of commercial FEM software. The validity and accuracy of the method is verified by analysis of several benchmark problems. The coupled algorithm shows a good converging performance, and with minimum additional treatment can be able to handle more problems that cannot be solved by either SBFEM or FEM itself. For fracture problems, it proposes an efficient way to represent stress singularity for problems with complex geometry, loading condition or certain nonlinearity.

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