Technical Basis for Proposed Revisions to Code Case N-806, Evaluation of Metal Loss in Class 2 and 3 Metallic Piping Buried in a Back-Filled Trench

2014 ◽  
Author(s):  
Robert O. McGill ◽  
Mark A. Moenssens ◽  
George A. Antaki ◽  
Douglas A. Scarth
Keyword(s):  
Soil Properties ◽  
Structural Integrity ◽  
Ease Of Use ◽  
Nuclear Industry ◽  
Task Group ◽  
Metal Loss ◽  
Buried Pipe ◽  
Acceptance Criteria ◽  
Evaluation Procedures ◽  
Technical Basis

ASME Section XI Code Case N-806, for evaluation of metal loss in Class 2 and 3 metallic piping buried in a back-filled trench, was published in 2012. This Code Case has been prepared by the ASME Section XI Task Group on Evaluation Procedures for Degraded Buried Pipe. The Code Case addresses the nuclear industry need for evaluation procedures and acceptance criteria for the disposition of metal loss that is discovered during the inspection of metallic piping buried in a back-filled trench. A number of improvements have been proposed for Code Case N-806. These include improvements to the analytical procedures for structural integrity evaluation under soil and surcharge loads. In addition, tables of soil properties and other parameters needed in the evaluation are proposed to be provided to improve ease of use. This paper presents the technical basis for the proposed revision to Code Case N-806.

Further Improvements to ASME Section XI Code Case N-806 for Evaluation of Metal Loss in Class 2 and 3 Metallic Piping Buried in a Back-Filled Trench

2015 ◽  
Author(s):  
Robert O. McGill ◽  
Mark A. Moenssens ◽  
George A. Antaki ◽  
Douglas A. Scarth
Keyword(s):  
Corrosion Rate ◽  
Ease Of Use ◽  
Nuclear Industry ◽  
Task Group ◽  
Metal Loss ◽  
Buried Pipe ◽  
Acceptance Criteria ◽  
Evaluation Procedures ◽  
Technical Basis

ASME Section XI Code Case N-806, for evaluation of metal loss in Class 2 and 3 metallic piping buried in a back-filled trench, was first published in 2012. This Code Case has been prepared by the ASME Section XI Task Group on Evaluation Procedures for Degraded Buried Pipe. The Code Case addresses the nuclear industry need for evaluation procedures and acceptance criteria for the disposition of metal loss that is discovered during the inspection of metallic piping buried in a back-filled trench. A number of additional improvements have been proposed for Code Case N-806. These include expanded guidance for the determination and validation of a corrosion rate and other clarifications to improve ease of use. This paper presents an update of details of the proposed revisions to Code Case N-806 and their technical basis.

Technical Basis for Code Case N-806, Evaluation of Metal Loss in Class 2 and 3 Metallic Piping Buried in a Back-Filled Trench

2012 ◽  
Author(s):  
Robert O. McGill ◽  
Mark A. Moenssens ◽  
George A. Antaki ◽  
Douglas A. Scarth
Keyword(s):  
Ease Of Use ◽  
Nuclear Industry ◽  
Task Group ◽  
Metal Loss ◽  
Buried Pipe ◽  
Acceptance Criteria ◽  
Case Methods ◽  
Evaluation Procedures ◽  
Division 1 ◽  
Technical Basis

This paper presents the technical basis for Code Case N-806, Evaluation of Metal Loss in Class 2 and 3 Metallic Piping Buried in a Back-filled Trench – Section XI, Division 1. This Code Case has been prepared in the ASME Section XI Task Group on Evaluation Procedures for Degraded Buried Pipe. It addresses the nuclear industry need for evaluation procedures and acceptance criteria for the disposition of metal loss that may be discovered during the inspection of piping buried in a back-filled trench. This paper provides background discussion, scope of the Code Case, key definitions and a summary of Code Case methods followed by the basis explanation where necessary. It is organized to follow the same structure as the Code Case for ease of use.

Further Improvements to ASME Section XI Code Case N-806 in a Proposed Second Revision

2019 ◽  
Author(s):  
Robert O. McGill ◽  
George A. Antaki ◽  
Mark A. Moenssens ◽  
Douglas A. Scarth
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Nuclear Industry ◽  
Metal Loss ◽  
Soil Reaction ◽  
Buried Pipe ◽  
Element Analysis ◽  
Design Factor ◽  
Evaluation Procedures ◽  
Need To Evaluate

Abstract ASME Section XI Code Case N-806, for evaluation of metal loss in Class 2 and 3 metallic piping buried in a backfilled trench, was first published in 2012. This Code Case has been prepared by the ASME Section XI Task Group on Evaluation Procedures for Degraded Buried Pipe. The Code Case addresses the nuclear industry need for evaluation procedures and acceptance criteria for the disposition of metal loss that is discovered during the inspection of metallic piping buried in a back-filled trench. In a second revision of the Code Case, several changes are proposed. First, guidance is provided for analytical evaluation of greater detail including finite element analysis methods. A new nonmandatory appendix is included to provide procedures for the evaluation of soil and surcharge loads using finite element analysis. Next, a second new nonmandatory appendix is provided giving detailed guidance on the evaluation of seismic loads. Finally, the need to evaluate the fatigue life of buried piping subjected to cyclic surface loading is now included and a design factor applied to the modulus of soil reaction is introduced. This paper presents details of the proposed changes to Code Case N-806-1 and their technical basis where applicable.

Supplementary Technical Basis for ASME Section XI Code Case N-597

2005 ◽  
Author(s):  
Doug Scarth
Keyword(s):  
Wall Thickness ◽  
Structural Integrity ◽  
Computer Code ◽  
Nuclear Regulatory Commission ◽  
Original Design ◽  
Acceptance Criteria ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Technical Basis ◽  
Flow Accelerated Corrosion

Efforts to develop clear and conservative methods to measure and evaluate wall thinning in nuclear piping have been underway since the late 1980’s. The Electric Power Research Institute (EPRI) carried out a successful campaign to address programmatic issues, such as locating and predicting flow-accelerated corrosion (FAC) degradation. This included developing a computer code (CHECWORKS), a users group (CHUG), and a comprehensive program guideline document for the effective prediction, identification and trending of flow-accelerated corrosion degradation. U.S. Nuclear Regulatory Commission (NRC) guidelines are provided in the NRC Inspection Manual Inspection Procedure 49001. At the same time, committees under Section XI of the ASME Boiler and Pressure Vessel Code have addressed evaluation of structural integrity of piping subjected to wall thinning. Code Case N-480 of Section XI provided acceptance criteria that focused on primary piping stresses, with evaluation based on a uniform wall thinning assumption for evaluating the minimum wall thickness of the piping. However, when applying this methodology to low pressure piping systems, Code Case N-480 was very conservative. Code Case N-597 was first published in 1998, and supercedes Code Case N-480. The current version is N-597-2. Code Case N-597-2 provides acceptance criteria and evaluation procedures for piping items, including fittings, subjected to a wall thinning mechanism, such as flow-accelerated corrosion. Code Case N-597-2 is a significant improvement over N-480, containing distinct elements to be satisfied in allowing the licensee to operate with piping degraded by wall thinning. The Code Case considers separately wall thickness requirements and piping stresses, and maintains original design intent margins. The Code Case does not provide requirements for locations of inspection, inspection frequency or method of prediction of rate of wall thinning. As described in the original technical basis document published at the 1999 ASME PVP Conference, the piping stress evaluation follows very closely the Construction Codes for piping. Five conditions related to industry use of Code Case N-597-1 have been published by the NRC in Regulatory Guide 1.147, Revision 13. A number of these issues are related to a need for additional explanation of the technical basis for the Code Case, such as the procedures for evaluation of wall thickness less than the ASME Code Design Pressure-based minimum allowable wall thickness. This presentation addresses these NRC conditions by providing additional description of the technical basis for the Code Case.

Cycle-Wise Process-Zone Model for Prediction of Delayed Hydride Cracking Initiation Under Flaw-Tip Hydride Ratcheting Conditions

2018 ◽  
Author(s):  
Steven X. Xu ◽  
Jun Cui ◽  
Douglas A. Scarth ◽  
David Cho
Keyword(s):  
Structural Integrity ◽  
Process Zone ◽  
Operating Conditions ◽  
Zone Model ◽  
Evaluation Procedures ◽  
Fuel Bundle ◽  
Pressure Tubes ◽  
Delayed Hydride Cracking ◽  
Technical Basis ◽  
Hydride Cracking

Flaws found during in-service inspection of Zr-2.5Nb pressure tubes in CANDU(1) reactors include fuel bundle scratches, debris fretting flaws, fuel bundle bearing pad fretting flaws and crevice corrosion flaws. These flaws are volumetric and blunt in nature. A key structural integrity concern with in-service blunt flaws is their susceptibility to delayed hydride cracking (DHC) initiation, particularly for debris fretting flaws under flaw-tip hydride ratcheting conditions. Hydride ratcheting conditions refer to situations when flaw-tip hydrides do not completely dissolve at normal operating temperature, and accumulation of flaw-tip hydrides occurs with each reactor heat-up/cool-down cycle. A significant number of in-service flaws are expected to be under hydride ratcheting conditions at late life of pressure tubes. DHC initiation evaluation procedures based on process-zone methodology for flaws under hydride ratcheting conditions are provided in CSA (Canadian Standards Association) N285.8-15. The process-zone model in CSA N285.8-15 predicts whether DHC initiation occurs or not for given flaw geometry and operating conditions, regardless of the number of reactor heat-up and cool-down cycles. There has been recent new development. Specifically, a cycle-wise process-zone model has been developed as an extension to the process-zone model in CSA N285.8-15. The cycle-wise process-zone model is able to predict whether DHC initiation occurs or not during a specific reactor heat-up and cool-down cycle under applied load. The development of the cycle-wise process-zone model was driven by the need to include flaw-tip stress relaxation due to creep in evaluation of DHC initiation. The technical basis for the development of the cycle-wise process-zone model for prediction of DHC initiation under flaw-tip hydride ratcheting conditions is described in this paper.

Flaw Evaluation Procedures and Acceptance Criteria for Nuclear Components in ASME Code Section XI

2003 ◽  
Author(s):  
Russell C. Cipolla ◽  
Guy H. DeBoo ◽  
Warren H. Bamford ◽  
Kenneth K. Yoon ◽  
Kunio K. Hasegawa
Keyword(s):  
Nuclear Power ◽  
Structural Integrity ◽  
Primary Objective ◽  
Surveillance Program ◽  
Acceptance Criteria ◽  
Evaluation Procedures ◽  
Asme Code ◽  
Nuclear Component ◽  
American Society ◽  
Plant Components

The primary objective of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section XI is to provide the rules and requirements for maintaining pressure boundary integrity of components, piping, and equipment during the life of a nuclear power plant. Pressure boundary integrity in terms of assuring resistance to sudden and catastrophic failure has been an essential objective of the ASME Code since its inception in 1914. These objectives are especially important in ASME Section XI since maintaining pressure boundary integrity of components has a crucial role in ensuring safe and reliable operation in nuclear operating plants. The purpose of this paper is to describe the evaluation procedures, methods, and acceptance criteria for flaws detected in plant components during implementation of in-service inspection surveillance program. For nuclear plant components, pressure boundary integrity includes both leak integrity (no leakage from the reactor coolant system) and structural integrity (no rupture or burst of the pressure boundary). The evaluation requirements in ASME Section XI provide specific rules for assessing the acceptance limits for flaw indications that may be detected during the service life of a nuclear component. In addition to describing current flaw evaluation procedures, details of recent Code developments and improvements are discussed.

Proposed ASME Section III Code Case: Reduction of NDE Weld Repairs

2011 ◽  
Author(s):  
Steven L. McCracken ◽  
Steven M. Swilley ◽  
Yoshihisa Sekinuma ◽  
Owen Hedden ◽  
Dave Cowfer ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Structural Integrity ◽  
Acceptance Criteria ◽  
Lack Of Fusion ◽  
Radiographic Testing ◽  
Structural Impact ◽  
Qualification Testing ◽  
The Cost ◽  
Technical Basis ◽  
Structural Significance

Section III of the ASME Boiler and Pressure Vessel Code requires radiographic testing (RT) of pressure boundary welds. RT is performed to detect flaws that might be created in welds as they are fabricated. Current Section III acceptance standards require rejection and repair of flaw indications characterized as cracks, lack of fusion, or incomplete penetration regardless of the size of the indication or the structural significance of such indications on fitness for service (FFS). The current Section III requirements have been effective in meeting the design objective of preventing pressure boundary failures. However, the rules are sufficiently conservative that not only are structurally significant flaws excluded, but they also exclude more benign indications that have no impact on structural integrity. This approach has resulted in repairs for even minor flaws that have no FFS impact. In addition to the cost of performing these unnecessary repairs, the repairs may have contributed to service induced cracking because of the higher residual stresses from the repair. Clearly, there is a need to revisit the Section III inspection and repair rules so as to distinguish between structurally unacceptable flaws and benign flaws that have no FFS impact. This paper describes the technical basis for the proposed Section III Code Case that uses the FFS approach to eliminate the need for weld repairs for minor flaws that have been shown to have no structural impact. Specifically, the Code Case will provide the option to use qualified volumetric inspection to size the flaw indications accurately and define acceptance criteria to determine flaw sizes that are judged to have little structural significance. In addition to describing the requirements of the proposed Code Case, this paper also describes the technical basis for the flaw acceptance criteria and the results of ultrasonic (UT) qualification testing to demonstrate the capability to detect and characterize fabrication flaw indications.

Technical Basis for Revisions to ASME Section XI Code Case N-597-2 on Requirements for Analytical Evaluation of Pipe Wall Thinning

2015 ◽  
Author(s):  
Douglas A. Scarth ◽  
Michael Davis ◽  
Phil Rush ◽  
Steven X. Xu
Keyword(s):  
Nuclear Regulatory Commission ◽  
Pressure Vessels ◽  
Acceptance Criteria ◽  
Accelerated Corrosion ◽  
Evaluation Procedures ◽  
Technical Requirements ◽  
Wall Thinning ◽  
Regulatory Commission ◽  
Technical Basis ◽  
Flow Accelerated Corrosion

Code Case N-597-2 provides procedures and acceptance criteria for the evaluation of piping items subjected to wall thinning mechanisms such as flow-accelerated corrosion (FAC). The acceptance criteria ensure that margins equivalent to those of the ASME B&PV Code are maintained. Subsequent to the publication of Code Case N-597-2, the U.S. Nuclear Regulatory Commission (NRC) found the Code Case conditionally acceptable. A number of task items have been undertaken by the ASME Section XI Working Group on Pipe Flaw Evaluation (WGPFE) to address the NRC conditions. A 2006 ASME Pressure Vessels and Piping (PVP) Division conference paper was published to provide an expanded explanation of the technical basis for Code Case N-597-2. A 2009 PVP paper was published to provide results of validation of evaluation procedures and acceptance criteria in Code Case N-597-2 against experimental and historic wall thinning events. More recently, revisions to Code Case N-597-2 have been made and were proposed as N-597-3. Significant changes have been made in the proposed revised Code Case to clarify the technical requirements and address the NRC concerns over N-597-2. The technical basis for revising Code Case N-597-2 is provided in this paper.

Structural Integrity for Nuclear Power Plant Against Excessive Load on Design Extension Condition

2013 ◽  
Author(s):  
Daigo Watanabe ◽  
Kiminobu Hojo
Keyword(s):  
Nuclear Power ◽  
Structural Integrity ◽  
Safety Factors ◽  
Design Code ◽  
Acceptance Criteria ◽  
Integrity Assessment ◽  
Current Design ◽  
Factor Design ◽  
Excessive Load ◽  
Load And Resistance Factor

This paper introduces an example of structural integrity evaluation for Light Water Reactor (LWR) against excessive loads on the Design Extension Condition (DEC). In order to assess the design acceptance level of DEC, three acceptance criteria which are the stress basis limit of the current design code, the strain basis limit of the current design code and the strain basis limit by using Load and Resistance Factor Design (LRFD) method were applied. As a result the allowable stress was increased by changing the acceptance criteria from the stress basis limit to the strain basis limit. It is shown that the practical margin of the LWR’s components still keeps even on DEC by introducing an appropriate criterion for integrity assessment and safety factors.

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.

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