Background and Technical Basis for the Evaluation of Flaws in PWR Reactor Vessel Head Penetration Regions

2004 ◽  
Author(s):  
Warren Bamford ◽  
Guy De Boo
Keyword(s):  
Reactor Vessel ◽  
Flaw Size ◽  
Acceptance Criteria ◽  
Head Penetration ◽  
Industry Group ◽  
Surface Flaws ◽  
Critical Flaw ◽  
Technical Basis ◽  
Outside Diameter

Acceptance criteria have been developed for indications found during inspection of reactor vessel in upper head penetrations. These criteria were originally developed for inside surface flaws, as part of an industry program coordinated by NUMARC (now NEI) in 1992. These criteria were not inserted into Section XI at the time, because inspections were not required for these regions. In developing the enclosed acceptance criteria, the approach used by the industry group was similar to that used in other portions of Section XI, in that an industry consensus was reached using input from the operating utility technical staff, each of the three PWR vendors, and representatives of the NRC staff. The criteria developed are applicable to all PWR plant designs. The discovery of leaks at Oconee, ANO-1, and several other plants, have led to the imposition of inspection requirements for head penetration regions, and therefore the need to develop criteria for indications in all portions of the tubes. This would include indications on the inside diameter of the tube, as well as on the outside diameter of the tube below the attachment weld, and flaws in the attachment weld itself. The criteria presented herein are limits on flaw sizes which are acceptable. The criteria are to be applied to inspection results. It should be noted that determination of the period of future service during which the criteria are satisfied is plant-specific and dependent on flaw geometry and loading conditions. It has been previously demonstrated by each of the owners groups that the penetrations are very tolerant of flaws. It was concluded that complete fracture of the penetration would not occur unless very large through-wall flaws were present; therefore, protection against leakage during service is the priority. The approach used here is more conservative than that used in Section XI applications where the acceptable flaw size is calculated by putting a margin on the critical flaw size. In this case, the critical flaw size is far too large to allow a practical application of this approach, so protection against leakage is the key element used to define the acceptance criteria. Also, the use of flaw acceptance standards tables is not allowed for this region, for penetrations which are susceptible to stress corrosion cracking. The acceptance criteria apply to all flaw types regardless of orientation and shape. The same approach is used by Section XI, where flaws are characterized according to established rules and their future predicted size is then compared with the acceptance criteria.

Sensitivity of Stress-Strain Parameters in Leak-Before-Break Evaluations

2007 ◽  
Author(s):  
Nathaniel G. Cofie ◽  
Robert O. McGill ◽  
G. Angah Miessi ◽  
Jim Wu
Keyword(s):  
Fracture Mechanics ◽  
Strain Curve ◽  
Flaw Size ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Approximate Methods ◽  
Critical Flaw ◽  
Leak Before Break ◽  
Actual Stress

Leak-before-break (LBB) evaluations involve the use of deterministic fracture mechanics to establish the margin between critical and leakage flaw sizes in order to assure that leaks can be detected by the plant leak detection system before a through-wall flaw reaches critical flaw size. When the material is semi-ductile, the fracture mechanics evaluations involve the use of elastic-plastic fracture mechanics (EPFM) consisting of the J-integral and tearing modulus (J/T) analyses. An important input into the J/T analyses is the Ramberg-Osgood (R-O) material stress strain parameters which describe the stress-strain curve of the material of interest. These are also key inputs in the determination of leakage associated with through-wall flaws. If the stress-strain curve of the material of interest is available, the R-O parameters can be determined from power law curve fit. However, in most cases, archival material of existing plant piping is not readily available to determine the actual stress-strain curve. In the absence of the actual stress-strain curve, several approximate methods for determining the R-O parameters from basic mechanical properties have been proposed in the literature. These approximate methods however produce different sets of R-O parameters. In this paper, the effect of using different sets of R-O parameters from three R-O formulations on LBB analyses results is investigated. EPFM analyses are performed to determine the critical through-wall flaw lengths with the various sets of the R-O parameters for various materials and various pipe sizes. The same sets of parameters are then used to determine the leakage associated with through-wall flaws. The results of the evaluation indicate that different sets of R-O parameters can yield different critical flaw sizes as well as leakage flaw sizes, thus resulting in different margins in LBB evaluations. Considering the margins involved in LBB evaluations (factor of two on critical flaw size and factor of 10 on leakage), it is believed that these differences are small enough that any of the three correlations presented in this paper for determination of the R-O parameters can be adequately used in LBB evaluations employing EPFM analyses.

Technical Basis for Acceptance/Rejection Criteria for Flaws in High Pressure Gas Cylinder

2009 ◽  
Author(s):  
Mahendra D. Rana ◽  
John H. Smith ◽  
Henry Holroyd
Keyword(s):  
High Pressure ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Experimental Tests ◽  
Operating Conditions ◽  
Flaw Size ◽  
Critical Flaw ◽  
Test Pressure ◽  
Technical Basis

The objective of this paper is to present the technical basis used for developing acceptance/rejection limits for seamless, high pressure gas cylinders that can be used at the time of retesting the cylinders. The development of acceptance/rejection limits for cylinders is done in three steps. First, the “critical flaw sizes” (e.g. depth and length or area) for selected types of flaws are established by an analysis procedure that has been verified by experimental tests. Next the “allowable flaw sizes” are calculated by modifying (reducing) the size of the “critical flaw sizes” for each cylinder by adjusting for fatigue crack growth that may occur during the use of the cylinder. Finally the “acceptance/rejection criteria” is established to take into account other factors such as all the expected operating conditions that the cylinders may see in service and the reliability and detectability of the specific inspection equipment to be and to adjust the “allowable flaw sizes” to provide an additional margin of safety. This acceptance/rejection limits have been incorporated in recently published ISO Technical Report TR 22694: 2008 [1]. In this work, the API 579 “Recommended Practice for Fitness-for-Service” [2] was used to calculate the “critical flaw sizes” for a range of cylinder sizes and strength levels. For this study the “critical flaw size” is defined as the size of the flaw that will cause the cylinders to fail at the test pressure of the cylinder. The results of flawed-cylinder burst tests were used to experimentally verify the calculated “critical flaw sizes”. The “allowable flaw sizes” were then calculated by using well established fatigue crack growth rate data for steel and aluminum alloys to allow for the expected amount of fatigue crack growth that may occur during the specified retesting intervals. A limited number of tests were conducted to verify the “allowable flaw size” calculations. Further adjustments are made to the “allowable flaw sizes” to define the “acceptance/rejection criteria” to be used during cylinder retesting.

Section XI: Responding to Inservice Inspection Findings

2003 ◽  
Author(s):  
Warren Bamford
Keyword(s):  
Stress Corrosion ◽  
Design Process ◽  
Stress Corrosion Cracking ◽  
Reactor Vessel ◽  
Corrosion Cracking ◽  
Low Energy ◽  
Evaluation Methodology ◽  
Acceptance Criteria ◽  
Head Penetration ◽  
Class 1

As plants continue to age, modes of degradation are found that had not been anticipated as part of the design process. One of the most important modes of degradation found recently has been stress corrosion cracking. This presentation will deal with three examples of such cracking for which acceptance criteria and evaluation methodology are being developed for Section XI. These three include: • Class 1 piping; • Reactor Vessel Head Penetration Cracking (PWR only); • Low Energy Piping, Vessels and Tanks.

Technical Basis for Acceptance/Rejection Criteria for Flaws in High Pressure Gas Cylinder

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Mahendra D. Rana ◽  
John H. Smith ◽  
Henry Holroyd
Keyword(s):  
High Pressure ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Operating Conditions ◽  
Flaw Size ◽  
Technical Report ◽  
Critical Flaw ◽  
Technical Basis ◽  
Gas Cylinders

The objective of this paper is to present the technical basis used for developing acceptance/rejection limits for seamless, high pressure gas cylinders that can be used at the time of retesting the cylinders. The development of acceptance/rejection limits for cylinders is done in three steps. First, the “critical flaw sizes” (e.g., depth and length or area) for selected types of flaws are established by an analysis procedure that has been verified by experimental tests. Next the “allowable flaw sizes” are calculated by modifying (reducing) the size of the critical flaw sizes for each cylinder by adjusting for fatigue crack growth that may occur during the use of the cylinder. Finally, the “acceptance/rejection criteria” is established to take into account other factors, such as all the expected operating conditions that the cylinders may see in service, and the reliability and detectability of the specific inspection equipment to be used and to adjust the allowable flaw sizes to provide an additional margin of safety. This acceptance/rejection limits have been incorporated in a recently published ISO Technical Report No. TR 22694:2008 (2007, “Gas Cylinders—Methods for Establishing Acceptance/Rejection Criteria for Flaws in Seamless Steel and Aluminum Alloy Cylinders at Time of Periodic Inspection and Requalification,” The International Standards Organization, Geneva, Switzerland, Technical Report No. 22694). In this work, the API 579 “Recommended Practice for Fitness-for-Service” (2000, API 579: Recommended Practice for Fitness-for-Service, 1st ed., American Petroleum Institute, Washington, DC) was used to calculate the critical flaw sizes for a range of cylinder sizes and strength levels. For this study, the critical flaw size is defined as the size of the flaw that will cause the cylinders to fail at the test pressure of the cylinder. The results of flawed-cylinder burst tests were used to experimentally verify the calculated critical flaw sizes. The allowable flaw sizes were then calculated by using well established fatigue crack growth rate data for steel and aluminum alloys to allow for the expected amount of fatigue crack growth that may occur during the specified retesting intervals. A limited number of tests was conducted to verify the allowable flaw size calculations. Further adjustments are made to the allowable flaw sizes to define the acceptance/rejection criteria to be used during cylinder retesting.

Determination of Critical Flaw Size in Gun Launch 40-mm GRENADE

2010 ◽  
Author(s):  
N. Payne ◽  
J. Jablonksi ◽  
J. Cordes
Keyword(s):  
Flaw Size ◽  
Critical Flaw

A Tiered Approach to Girth Weld Defect Acceptance Criteria for Stress-Based Design of Pipelines

2006 ◽  
Author(s):  
Yong-Yi Wang ◽  
Ming Liu ◽  
David Horsley ◽  
Gery Bauman
Keyword(s):  
Test Data ◽  
Plastic Collapse ◽  
Department Of Transportation ◽  
Acceptance Criteria ◽  
Weld Defect ◽  
The Us ◽  
Welding Procedure ◽  
Assessment Procedures ◽  
Technical Basis ◽  
New Procedures

Alternative girth weld defect acceptance criteria implemented in major international codes and standards vary significantly. The requirements for welding procedure qualification and the allowable defect size are often very different among the codes and standards. The assessment procedures in some of the codes and standards are more adaptive to modern micro-alloyed TMCP steels, while others are much less so as they are empirical correlations of test data available at the time of the standards creation. A major effort funded jointly by the US Department of Transportation and PRCI has produced a comprehensive update to the girth weld defect acceptance criteria. The newly proposed procedures have two options. Option 1 is given in an easy-to-use graphical format. The determination of allowable flaw size is extremely simple. Option 2 provides more flexibility and generally allows larger flaws than Option 1, at the expense of more complex computations. Option 1 also has higher fracture toughness requirements than Option 2, as it is built on the concept of plastic collapse. In comparison to some existing codes and standards, the new procedures (1) provide more consistent level of conservatism, (2) include both plastic collapse and fracture criteria, and (3) give necessary considerations to the most frequently occurring defects in modern pipeline constructions. This paper provides an overview of the technical basis of the new procedures and validation against experimental test data.

Analysis of Stress Concentrations in Thick Cylinders With Sideholes and Crossholes

1972 ◽  
Vol 94 (3) ◽  
pp. 815-824 ◽  
Author(s):  
J. C. Gerdeen
Keyword(s):  
Stress Concentration ◽  
Stress Concentrations ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Experimental Values ◽  
Pressure Stress ◽  
Shrink Fit ◽  
Outside Diameter ◽  
Theoretical Results

An approximate theoretical analysis is presented for the determination of stress concentration factors in thick walled cylinders with sideholes and crossholes. The cylinders are subjected to both internal pressure and external shrink-fit pressure. Stress concentration factors are plotted as functions of the geometrical ratios of outside diameter-to-bore diameter, and bore diameter-to-sidehole diameter. Theoretical results are compared to experimental values available in the literature and results of experiments described in a separate paper.

Technical Basis of Proposed New Acceptance Standards for Class 1, 2 and 3 Piping

2007 ◽  
Author(s):  
Katsumasa Miyazaki ◽  
Kunio Hasegawa ◽  
Naoki Miura ◽  
Koichi Kashima ◽  
Douglas A. Scarth
Keyword(s):  
Fracture Mechanics ◽  
Ultrasonic Inspection ◽  
Limit Load ◽  
Flaw Size ◽  
High Fracture Toughness ◽  
Evaluation Procedure ◽  
High Fracture ◽  
Development Methodology ◽  
Class 1 ◽  
Technical Basis

Acceptance Standards in Section XI of the ASME Boiler and Pressure Vessel Code have an important role as the first step in the flaw evaluation procedure. When a flaw size is within the allowable flaw size in the Acceptance Standard, the flaw is acceptable and analytical evaluation is not required. Although ASME Section XI has Acceptance Standards for Class 1 piping in IWB-3500, there are no Acceptance Standards for Class 2 and 3 piping. Furthermore, the development of the current Acceptance Standards for Class 1 piping was based on flaw detectability by ultrasonic inspection and consideration of fracture mechanics. In this paper, the development of proposed new Acceptance Standards for Class 2 and 3 piping, as well as for Class 1 piping, is described. The development methodology is based on a fracture mechanics approach. For Class 1 piping with high fracture toughness, the allowable flaw sizes were determined by limit load solution. For Class 1 piping, the intent was to maintain overall consistency with the current Acceptance Standards. Proposed Acceptance Standards for Class 2 and 3 austenitic piping were also developed by the methodology used to develop the proposed new Acceptance Standards for Class 1 piping. Allowable flaw sizes for both surface flaws and subsurface flaws for preservice and inservice examinations were developed.

Experimental Determination of Side Boundary Effects on Stress Intensity Factors in Surface Flaws

1975 ◽  
Vol 97 (1) ◽  
pp. 45-51 ◽  
Author(s):  
M. Jolles ◽  
J. J. McGowan ◽  
C. W. Smith
Keyword(s):  
Stress Intensity ◽  
Crack Length ◽  
Taylor Series ◽  
Stress Intensity Factors ◽  
Taylor Series Expansion ◽  
Correction Method ◽  
Intensity Factors ◽  
Surface Flaws ◽  
Plate Width

A technique consisting of stress-freezing photoelasticity coupled with a Taylor Series Expansion of the maximum local in-plane shearing stress known as the Taylor Series Correction Method (TSCM) is applied to the determination of stress intensity factors (SIF’s) in flat bottomed surface flaws of flaw depth/length ratios of approximately 0.033. Flaw depth/thickness ratios of approximately 0.20 and 0.40 were studied as were plate width/crack length ratios of approximately 2.33 and 1.25, the former of which corresponded to a nearly infinite width. Agreement to well within 10 percent was found with the Rice-Levy and Newman theories using a depth-modified secant correction and equivalent flaw depth/length ratios. The Shah-Kobayashi Theory, when compared on the same basis, was lower than the experimental results. Using a modified net section stress correction suggested by Shah, agreement with the Shah-Kobayashi Theory was greatly improved but agreement with the other theories was poorer. On the basis of the experiments alone, it was found that the SIF was intensified by about 10 percent by decreasing the plate width/crack length from 2.33 to 1.25.

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