Rules for Flaw Interaction for Subsurface Flaws in Operating Pressurized Vessels: Technical Basis of Code Case N-877

2018 ◽  
Author(s):  
Valéry Lacroix ◽  
Pierre Dulieu ◽  
Sebastien Blasset ◽  
Ralf Tiete ◽  
Yinsheng Li ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Pressure Vessels ◽  
Sensitivity Analyses ◽  
Operating Pressure ◽  
Combination Process ◽  
Asme Code ◽  
Technical Basis ◽  
Single Flaw

When multiple flaws are detected in pressure retaining components during inspection, the first step of evaluation consists of determining whether the flaws shall be combined into a single flaw or evaluated separately. This combination process is carried out in compliance with proximity rules given in the Fitness-for-Service (FFS) Codes. However, the specific criteria for the rules on combining multiple flaws into a single flaw are different among the FFS Codes. In this context, revised and improved criteria have been developed, to more accurately characterize the interaction between multiple subsurface flaws in operating pressure vessels. This improved approach removes some of the conservatism in the existing ASME Code approach, which was developed in the 1970s based on two flaws interacting with each other. This paper explains in detail the methodology used to derive improved flaw proximity rules through three-dimensional FEM and XFEM analyses. After the presentation of the calculations results and the improved criteria, the paper also highlights the multiple conservatisms of the methodology using several sensitivity analyses.

The Sensitivity of Pressurized Thermal Shock Analysis Results to Alternative Models for Weld Flaw Distributions

2003 ◽  
Author(s):  
T. L. Dickson ◽  
F. A. Simonen
Keyword(s):  
Thermal Shock ◽  
Nuclear Regulatory Commission ◽  
Evaluation Study ◽  
The United States ◽  
Metal Plate ◽  
Pressure Vessels ◽  
Sensitivity Analyses ◽  
Pressurized Thermal Shock ◽  
Technical Basis ◽  
The Impact

The United States Nuclear Regulatory Commission (USNRC) initiated a comprehensive project in 1999 to determine if improved technologies can provide a technical basis to reduce the conservatism in the current regulations for pressurized thermal shock (PTS) while continuing to provide reasonable assurance of adequate protection to public health and safety. A relaxation of PTS regulations could have profound implications for plant license renewal considerations. During the PTS re-evaluation study, an improved risk-informed computational methodology was developed that provides a more realistic characterization of PTS risk. This updated methodology was recently applied to three commercial PWRs. The results of this study provide encouragement that a technical basis can be established to support a relaxation of current PTS regulations. One significant model improvement applied in the PTS re-evaluation study was the development of flaw databases derived from the non-destructive and destructive examinations of material from cancelled reactor pressure vessels (RPV). Empirically-based statistical distributions derived from these databases and expert illicitation were used to postulate the number, size, and location of flaws in welded and base metal (plate and forging) regions of an RPV during probabilistic fracture mechanics (PFM) analyses of RPVs subjected to transient loading conditions such as PTS. However, limitations in the available flaw data have required assumptions to be made to complete the risk-based flaw models. Sensitivity analyses were performed to evaluate the impact of four flaw-related assumptions. Analyses addressed: 1) truncations of distributions to exclude flaws of extreme depth dimensions, 2) vessel-to-vessel differences in flaw data, 3) large flaws observed in weld repair regions, and 4) the basis for estimating the number of surface breaking flaws. None of the four alternate weld flaw models significantly impacted calculated vessel failure frequencies or invalidated the tentative conclusions derived from the USNRC PTS re-evaluation study.

Weight-Saving Plastic Design of Pressure Vessels

1997 ◽  
Vol 119 (2) ◽  
pp. 161-166
Author(s):  
J. S. Porowski ◽  
W. J. O’Donnell ◽  
R. H. Reid
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Pressure Vessels ◽  
Engineering Practice ◽  
Finite Element Analyses ◽  
Equilibrium Models ◽  
Plastic Design ◽  
Primary Stress ◽  
Asme Code ◽  
Analytical Approaches

Within the last two decades, the use of elastic finite element analyses to demonstrate design compliance with the rules of the ASME Code has become a generally accepted engineering practice. Linearized stresses from these analyses are commonly used to evaluate primary stresses. For redundant structures or complex structural details, the use of such analyses, instead of simple equilibrium models, often results in significant overconservatism. Direct use of finite element results is often preferred because equilibrium solutions are not unique and effective equilibrium models are not easily constructed for complex three-dimensional structures. However, finite element analyses include secondary stresses, even for pressure, mechanical, and shock loading. For primary stress evaluation, the ASME Code allows the use of inelastic methods based on lower-bound solutions and plastic analysis. For primary stresses, the Code requires equilibrium to be satisfied without violating the yield strength of the material. The use of finite element inelastic analysis to partition mechanically induced stresses into the primary and secondary categories was introduced by Porowski et al. (1993). The latter provides a detailed discussion of the technical approach and the results for the axisymmetric junction between the plate and shell in a pressure vessel. This example was selected by the Session Organizer as a benchmark case to compare the efficiency of various analytical approaches presented at the Session. The authors have since used this approach to design more efficient structures. The practical application of this method to reduce the weight of complex redundant structures designed to meet primary stress limits is described herein for a more complex three-dimensional case. Plastic design utilizes the ability of actual materials to find the most efficient load distribution. A heat exchanger subjected to pressure, accelerations, and nozzle external loads is evaluated as a practical example. The results of elastic analyses are compared with those obtained by inelastic analyses. It is shown that inelastic analyses can be used effectively to reduce the weight of structures using only modern PCs for the engineering computations, as illustrated in this paper.

Fatigue Consideration of Layered Vessels

2020 ◽  
Author(s):  
Kang Xu ◽  
Mahendra Rana ◽  
Maan Jawad
Keyword(s):  
Fatigue Life ◽  
Structural Integrity ◽  
Cost Effective ◽  
Pressure Vessels ◽  
Asme Code ◽  
Section Viii ◽  
Cyclic Service ◽  
Gap Height ◽  
Technical Basis ◽  
Division 2

Abstract Layered pressure vessels provide a cost-effective solution for high pressure gas storage. Several types of designs and constructions of layered pressure vessels are included in ASME BPV Section VIII Division 1, Division 2 and Division 3. Compared with conventional pressure vessels, there are two unique features in layered construction that may affect the structural integrity of the layered vessels especially in cyclic service: (1) Gaps may exist between the layers due to fabrication tolerances and an excessive gap height introduces additional stresses in the shell that need to be considered in design. The ASME Codes provide rules on the maximum permissible number and size of these gaps. The fatigue life of the vessel may be governed by the gap height due to the additional bending stress. The rules on gap height requirements have been updated recently in Section VIII Division 2. (2) ASME code rules require vent holes in the layers to detect leaks from inner shell and to prevent pressure buildup between the layers. The fatigue life may be limited by the presence of stress concentration at vent holes. This paper reviews the background of the recent code update and presents the technical basis of the fatigue design and maximum permissible gap height calculations. Discussions are made in design and fabrication to improve the fatigue life of layered pressure vessels in cyclic service.

New Common Design Rules for U-Tube Heat Exchangers in ASME, CODAP and UPV Codes

2002 ◽  
Author(s):  
F. Osweiller
Keyword(s):  
Heat Exchangers ◽  
Pressure Vessels ◽  
Design Rule ◽  
Technical Approach ◽  
Design Rules ◽  
Asme Code ◽  
European Code ◽  
Section Viii ◽  
Technical Basis ◽  
Year 2000

In year 2000, ASME Code (Section VIII – Div. 1), CODAP (French Code) and UPV (European Code for Unfired Pressure Vessels) have adopted the same rules for the design of U-tube tubesheet heat exchangers. Three different rules are proposed, based on different technical basis, to cover: • Tubesheet gasketed with shell and channel. • Tubesheet integral with shell and channel. • Tubesheet integral with shell and gasketed with channel or the reverse. At the initiative of the author, a more refined technical approach has been developed, to cover all tubesheet configurations. The paper explains the rationale for this new design rule which is being incorporated in ASME, CODAP and UPV in 2002. This is substantiated with comparisons to TEMA Standards and a benchmark of numerical comparisons.

U-Tube Heat-Exchangers: New Common Design Rules for ASME, CODAP, and EN 13445 CODES

2005 ◽  
Vol 128 (1) ◽  
pp. 95-102
Author(s):  
F. Osweiller
Keyword(s):  
Heat Exchangers ◽  
Design Method ◽  
Pressure Vessels ◽  
European Standard ◽  
Technical Approach ◽  
Design Rules ◽  
Asme Code ◽  
Section Viii ◽  
Technical Basis ◽  
Year 2000

In the year 2000, ASME Code Section VIII—Div. 1, CODAP (French Code) and EN 13445 (European Standard for Unfired Pressure Vessels) have adopted the same rules for the design of U-tube tubesheet heat exchangers. Three different rules were proposed, based on a different technical basis, to cover: —Tubesheet gasketed with shell and channel; —Tubesheet integral with shell and channel; —Tubesheet integral with shell and gasketed with channel or the reverse. At the initiative of the author, a more refined and uniform technical approach has been developed, to cover all tubesheet configurations. The paper explains the rationale for this new design method which has been incorporated recently in ASME, CODAP, and EN 13445. This is substantiated with comparisons to TEMA Standards and a benchmark of numerical comparisons

Generic Proximity Rules for Multiple Radially Oriented Planar Flaws: Technical Basis of Code Case N-877 Revision 1

2019 ◽  
Author(s):  
Pierre Dulieu ◽  
Valéry Lacroix ◽  
Kunio Hasegawa
Keyword(s):  
Aspect Ratio ◽  
Relative Position ◽  
Three Dimensional ◽  
Wide Range ◽  
Surface Flaws ◽  
Close Proximity ◽  
Actual Interaction ◽  
Technical Basis ◽  
Flaw Characterization ◽  
Single Flaw

Abstract In the case of planar flaws detected in pressure components, flaw characterization plays a major role in the flaw acceptability assessment. When the detected flaws are in close proximity, proximity rules given in the Fitness-for-Service (FFS) Codes require to combine the interacting flaws into a single flaw. However, the specific combination criteria of planar flaws vary across the FFS Codes. These criteria are often based on flaw depth and distance between flaws only. However, the level of interaction depends on more parameters such as the relative position of flaws, the flaw sizes and their aspect ratio. In this context, revised and improved proximity criteria have been developed to more precisely reflect the actual interaction between planar flaws. Thanks to numerous three-dimensional XFEM analyses, a wide range of configurations has been covered, including interaction between two surface flaws, interaction between two subsurface flaws and interaction between a surface flaw and a subsurface flaw. This paper explains in detail the steps followed to derive such generic proximity rules for radially oriented planar flaws.

Risk-Based Fracture Evaluation of Reactor Vessels Subjected to Cool-Down Transients Associated With Shutdown: An Examination of the Effects of Different Modeling Approaches on Estimated Failure Probabilities

2006 ◽  
Author(s):  
T. L. Dickson ◽  
M. T. EricksonKirk
Keyword(s):  
Nuclear Reactor ◽  
Structural Integrity ◽  
Nuclear Regulatory Commission ◽  
The United States ◽  
Pressure Vessels ◽  
Asme Code ◽  
Computational Methodology ◽  
Regulatory Commission ◽  
Technical Basis ◽  
Evaluation Project

The current regulations, as set forth by the United States Nuclear Regulatory Commission (USNRC), to insure that light-water nuclear reactor pressure vessels (RPVs) maintain their structural integrity when subjected to planned startup (heat-up) and shutdown (cool-down) transients are specified in Appendix G to 10 CFR Part 50, which incorporates by reference Appendix G to Section XI of the ASME Code. In 1999, the USNRC initiated the interdisciplinary Pressurized Thermal Shock (PTS) Re-evaluation Project to determine if a technical basis could be established to support a relaxation in the current PTS regulations. The PTS re-evaluation project included the development and application of an updated risk-based computational methodology that incorporates several advancements applicable to modeling the physics of vessel fracture due to thermal hydraulic transients imposed on the RPV inner surface. The results of the PTS re-evaluation project demonstrated that there is a sound technical basis to support a relaxation of the current PTS regulations. The results of the PTS re-evaluation are currently under review by the USNRC. Based on the promising results of the PTS re-evaluation, the USNRC has recently applied the updated computational methodology to fracture evaluations of RPVs subjected to planned cool-down transients, associated with reactor shutdown, derived in accordance with ASME Section XI – Appendix G. The objective of these analyses is to determine if a sound technical basis can be established to provide a relaxation to the current regulations for the derivation of bounding cool-down transients as specified in Appendix G to Section XI of the ASME Code. This paper provides a brief overview of these analyses, results, and the implications of the results.

Inspection Optimization Justification for PWR Main Steam and Feedwater Nozzles Using Probabilistic Fracture Mechanics

2019 ◽  
Author(s):  
C. Lohse ◽  
D. J. Shim ◽  
D. Somasundaram ◽  
R. Grizzi ◽  
G. L. Stevens ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Nuclear Regulatory Commission ◽  
Pressure Vessels ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Asme Code ◽  
Sensitivity Studies ◽  
Main Steam ◽  
Regulatory Commission ◽  
Technical Basis

Abstract Pressurized water reactor (PWR) steam generator (SG) main steam and feedwater nozzles are classified as ASME Code, Section XI, Class 2, Category C-B, pressure retaining welds in pressure vessels. Current ASME Code requirements specify that the nozzle-to-shell welds (Item No. C2.21 & C2.32) and nozzle inner radius sections (Item C2.22) are to be examined very 10 years. An evaluation was performed to establish a technical basis for optimized inspection frequencies for these items. The work included a review of inspection history and results, a survey of components in the PWR fleet (which included both U.S. and overseas plants), selection of representative main steam and feedwater nozzle configurations and operating transients for stress analysis, evaluation of potential degradation mechanisms, and flaw tolerance evaluations consisting of probabilistic and deterministic fracture mechanics analyses. The results of multiple inspection scenarios and sensitivity studies were compared to the U.S. Nuclear Regulatory Commission (NRC) safety goal of 10−6 failures per year.

Thermomechanical Analysis of Pressure Vessels

2012 ◽  
Author(s):  
Michael Benson ◽  
David Rudland ◽  
Mark Kirk
Keyword(s):  
Thermal Stresses ◽  
Thermomechanical Analysis ◽  
Pressure Vessels ◽  
Pressurized Water ◽  
Asme Code ◽  
Water Reactors ◽  
Inner Vessel ◽  
American Society ◽  
The One ◽  
Technical Basis

Regulatory Guide (RG) 1.161 and American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section XI, Nonmandatory Appendix K contain stress intensity factor (SIF) equations for both the internal pressure and thermal gradient loading cases. However, the technical basis behind these equations was developed only for Ri/t = 10, were Ri is the inner vessel radius and t is the vessel thickness. While this geometry is appropriate for most pressurized water reactors (PWR), most boiling water reactor (BWR) vessels have Ri/t = 20. This paper explores the validity of applying these SIF equations to BWRs. This confirmatory work includes calculating SIF by independent methods. The one-dimensional heat equation is solved to provide a physical basis for the thermal stresses.

Sign in / Sign up

Export Citation Format

Share Document