Treatment of Stresses Exceeding Material Yield Strength in ASME Code Section XI Appendix G Fracture Toughness Evaluations

2014 ◽  
Author(s):  
Hardayal S. Mehta ◽  
Gary L. Stevens ◽  
Daniel V. Sommerville ◽  
Michael Benson ◽  
Mark Kirk ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Yield Strength ◽  
Yield Stress ◽  
Linear Elastic ◽  
Primary Stress ◽  
Current State ◽  
Asme Code ◽  
Operating Stress ◽  
Technical Basis ◽  
Operating Plant

A previous PVP paper [1] identified suggested improvements to be made to ASME Code, Section XI, Nonmandatory Appendix G, “Fracture Toughness Criteria for Protection Against Failure” [2]. That paper also identified that the current version of Appendix G does not have any provisions for when the calculated operating stress (pseudo stress) exceeds the material yield strength. The treatment of stresses exceeding yield was included in earlier versions of Appendix G, but it was removed via Code Action ISI-94-40 in 1995. The specific reasons for removal of these provisions were not documented. In some Appendix G postulated flaw evaluations for pressure-temperature (P-T) limits, the calculated total linear-elastic (or pseudo) stress (i.e., including the primary stress due to pressure loading and thermal stress) may exceed the material yield stress. The ASME Section XI Working Group on Operating Plant Criteria (WGOPC) decided that this provision needed to be more fully considered, with appropriate benchmarking and possible adjustments to Appendix G made consistent with the current state of knowledge in elastic-plastic fracture mechanics (EPFM) methods. This is appropriate since the state of knowledge in EPFM has significantly advanced since the time the technical basis for Appendix G was established, as documented in Welding Research Council (WRC) Bulletin No. WRC-175, which was published in 1972. Furthermore, EPFM provides an improved method for evaluating the effects of high stresses. This paper describes the results of preliminary investigations of stresses exceeding the material yield stress in fracture toughness assessments associated with Appendix G. Also included in the technical evaluations presented are the temperature conditions for which upper shelf conditions are present and where EPFM methods are applicable.

The Non-Effect of Yield Strength on RTT0 and on the Master Curve

2019 ◽  
Author(s):  
Mark Kirk ◽  
Marjorie Erickson
Keyword(s):  
Fracture Toughness ◽  
Yield Strength ◽  
Cleavage Fracture ◽  
Working Group ◽  
Master Curve ◽  
Room Temperature ◽  
Code Change ◽  
Underlying Mechanisms ◽  
Operating Plant

Abstract During the August 2018 ASME Committee Week, a Code Change Inquiry was presented to the Working Group on Operating Plant Criteria (WGOPC): Question 1: Is it the intent of G-2110 to limit RTT0 use to ferritic materials with specified minimum room temperature yield strengths 50 ksi or less? Question 2: If the reply to Question 1 is “No”, is it the intent of G-2110 that G-2110(b) requirement must be met before RTT0 may be used for ferritic materials above 50 ksi but not exceeding 90 ksi? During that meeting the WGOPC replied “no” to both questions. This paper provides an evaluation of available fracture toughness data augmented by an understanding of the underlying mechanisms of cleavage fracture to demonstrate the veracity of the WGOPC’s answer with regards to RTT0 and, more generally, with respect to the Master Curve.

Direct Use of Fracture Toughness for Flaw Evaluations of Pressure Boundary Materials in Section XI, Division 1, Class 1 Ferritic Steel Components

2017 ◽  
Author(s):  
Marjorie Erickson ◽  
Mark Kirk
Keyword(s):  
Fracture Toughness ◽  
Crack Initiation ◽  
Crack Growth ◽  
Pressure Vessel ◽  
Round Robin ◽  
Statistical Characterization ◽  
Best Estimate ◽  
Asme Code ◽  
Technical Basis

The ASME Boiler and Pressure Vessel Code; Section XI provides Rules for inspection and fracture safety assessment of nuclear plant pressure boundary components. This Code provides methods for assessing the stresses and moments contributing to the forces available to drive crack growth in a component as described by stress intensity factors as well as the measures of material resistance to crack extension, measured by fracture toughness. Much of the current Code is based on linear elastic fracture mechanics methodologies developed 40 years ago [1], or more, at a time when drop weight tear tests [2] and Charpy V-notch impact tests [3] were the accepted standards used for characterizing a material’s resistance to brittle fracture. Ensuing research produced experimental methods to directly measure a material’s resistance to both brittle and ductile fracture. Data from such experiments provided the evidence supporting a suite of best estimate models describing fracture toughness behavior across a range of temperatures and strain rates. These models include cleavage crack initiation and crack arrest fracture toughness (KJc and KIa behavior, respectively) on the lower shelf and through transition, and also ductile crack initiation and crack growth resistance (JIc, J0.1, and J–R behavior) on the upper shelf. Best-estimate models provide a more accurate means of assessing a material’s expected behavior under all loading and temperature conditions; they also enable an explicit characterization of uncertainties. For these reasons, there is a growing advocacy within ASME Code groups for incorporating these best estimate toughness models into Sections III and XI of the Boiler and Pressure Vessel Code. The first direct implementation of the KJc best-estimate model in the ASME Code was in Code Case (CC) N-830, which was adopted by the ASME Code in 2014. N-830 states that the 5th percentile lower bound of the KJc Master Curve [4], indexed by T0, can be used as an alternative to the ASME RTNDT-indexed KIc curve in a flaw evaluation performed using Non-Mandatory Appendix A to Section XI. Since that time, work has progressed within the Working Group on Flaw Evaluation (WGFE) to further improve the CC. The proposed Revision 1 of CC N-830 incorporates a complete and self-consistent suite of models that completely describe the temperature dependence, scatter, and interdependencies (such as those resulting from irradiation or other hardening mechanisms) between all fracture toughness metrics (i.e., KJc, KIa, JIc, J0.1, and J–R) from the lower shelf through the upper shelf. By incorporating both a statistical characterization of fracture toughness as well as the ability to estimate a bounding curve at any percentile, the revised CC provides a consistent basis for the conduct of both conventional deterministic flaw evaluations as well as probabilistic evaluations that may be pursued in certain circumstances. Additionally, for the first time within ASME Section XI, both transition and upper shelf toughness properties are provided in a consistent manner in the same document, which provides the analyst an easy means to determine what fracture behavior (i.e., transition or upper shelf) can be expected for a particular set of conditions. The WGFE conducted round-robin assessments of the proposed CC N-830-R1 equations and their use in flaw evaluations, and is supporting documentation of the technical basis supporting the development and implementation of N-830-R1. This paper summarizes that technical basis report. A companion paper presented at this meeting describes the round-robin assessments.

Application of the ASME Code SEC III Pressure Design Requirements on Locally Thinned Tight Radius Pipe Bends

2010 ◽  
Author(s):  
Usama Abdelsalam
Keyword(s):  
Wall Thickness ◽  
Thickness Distribution ◽  
Element Model ◽  
Thickness Variation ◽  
Pipe Bend ◽  
Linear Elastic ◽  
Primary Stress ◽  
Asme Code ◽  
Wall Thickness Variation ◽  
Code Compliance

This paper addresses the primary stress requirements for the pressure loading of tight radius pipe bends according to the ASME Code SEC III NB-3200 (Design by Analysis). Solid FEA models are constructed to represent a tight radius pipe bend with general and local internal wall thinning. The wall thickness variation is considered using uniform and non-uniform axial and circumferential profiles. It is demonstrated that for a tight radius bend with wall thickness equal to the pressure based thickness of the corresponding straight pipe, the linear elastic criteria of NB-3221 are significantly exceeded. Results are presented to show the minimum acceptable wall thickness using uniform thickness distributions. The allowable wall thickness criterion of the ASME Code SEC XI Code Case N-597-2 is examined using a finite element model implementing the recommended thickness distribution along the circumferential direction. It is demonstrated that this distribution achieves a uniform stress intensity over the entire bend (uniform strength). A local thin area (LTA) centered at the intrados of the bend is super-imposed on a general thinned area and the axial and circumferential extents are varied. FEA results are presented to demonstrate Code compliance and its dependency on the axial and circumferential extents of the LTA and the thickness of the surrounding material.

Solution of a Sample Problem Related to Revision 1 of Code Case N-830

2017 ◽  
Author(s):  
Mark Kirk ◽  
Steven Xu ◽  
Cheng Lui ◽  
Marjorie Erickson ◽  
Yil Kim ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Temperature Dependence ◽  
Master Curve ◽  
Nuclear Reactor ◽  
Sample Problem ◽  
Asme Code ◽  
American Society ◽  
Technical Basis ◽  
Direct Use ◽  
Current Code

Within the American Society of Mechanical Engineers (ASME) the Section XI Working Group on Flaw Evaluation (WGFE) is currently working to develop a revision to Code Case (CC) N-830. CC N-830 permits the direct use of fracture toughness in flaw evaluations as an alternative to the indirect/correlative approaches (RTNDT-based) traditionally used in the ASME Code. The current version of N-830 estimates allowable fracture toughness values in the transition regime as the 5th percentile Master Curve (MC) indexed to the transition temperature T0. The proposed CC N-830 revision expands on this capability by incorporating a complete and self-consistent suite of models that describe completely the temperature dependence, scatter, and interdependencies between all fracture metrics (i.e., KJc, KIa, JIc, J0.1, and J–R) used currently, or useful in, a flaw evaluation for conditions ranging from the lower shelf through the upper shelf. Papers presented in previous ASME Pressure Vessel and Piping (PVP) Conferences since 2014 provide the technical basis for these various toughness models. This paper contributes to this overall CC N-830 documentation suite by presenting the results of a sample problem run to assess the proposed revision of the CC. The objective of the sample problem was (1) to determine if the revised CC was written with adequate clarity to permit different engineers to accurately and consistently calculate the various allowable toughness values described by the equations in the CC, (2) to assess how these allowable toughness values would be used to calculate allowable flaw depths using standard ASME SC-XI approaches, and (3) to compare allowable flaw depths calculated using established Code practices (RTNDT-based) to those calculated using proposed CC practices (T0-based). The sample problem demonstrated that (1) the CC was written with sufficient clarity to allow different engineers to arrive at the same estimated value of allowable toughness, (2) the latitude associated with the provisions of the ASME Code pertinent to estimation of allowable flaw depth are responsible for some differences in the allowable flaw depth values reported by different participants, and (3) current Code estimates of allowable flaw depth are far more conservative (that is: smaller) than values estimated by the candidate CC methods based on the MC, this mostly due to the generally-conservative bias of the Code’s RTNDT & KIc approach. The candidate CC methods provide much more consistent conservatism than current Code approaches for all conditions in the operating nuclear reactor fleet via their use of an index temperature (T0) defined by actual fracture toughness data and a temperature dependence defined by those data. The WGFE is continuing to evaluate candidate approaches to estimate allowable toughness values for CC N-830 using a T0-indexed Master Curve. Associated work is addressed by two companion papers presented at this conference.

Technical Basis for Expansion of ASME BPVC Section XI, KIC Curve Applicability

2019 ◽  
Author(s):  
Hongqing Xu ◽  
Nathan Palm ◽  
Anees Udyawar
Keyword(s):  
Fracture Toughness ◽  
Lower Bound ◽  
Fracture Mechanics ◽  
Yield Strength ◽  
Room Temperature ◽  
Ferritic Steels ◽  
Initiation Toughness ◽  
Room Temperature Yield Strength ◽  
Class 1 ◽  
Technical Basis

Abstract When the Appendix G methodology, fracture toughness criteria for protection against failure, was first adopted by ASME Section III in 1972, it included a lower-bound Kir curve for ferritic steels with specified minimum room-temperature yield strength up to 50 ksi. In 1977, Section III Appendix G added a requirement to obtain fracture-toughness data for at least three heats (base metal, weld metal, and heat-affected zone) if the KIR curve is used for ferritic steels with specified minimum room-temperature yield strength between 50 and 90 ksi. The three-heat data requirement has not changed when the lower bound curve was adopted by Section XI, or when the lower-bound crack initiation toughness curve was changed from the dynamic Kir curve to the static KIc curve during the 2000s. Based on the accumulation of fracture-mechanics data of ferritic steels with specified minimum yield strength between 50 ksi and 90 ksi and their use for Class 1 pressure vessel production, Section XI recently expanded the applicability of the KIc curve to SA-508 Grade 2 Class 2, SA-508 Grade 3 Class 2, SA-533 Type A Class 2, and SA-533 Type B Class 2 whose specified minimum room-temperature yield strength is 65 ksi or 70 ksi. This paper describes the technical basis including the fracture-mechanics data to support the expansion of the applicability of the KIc curve by ASME Section XI.

Direct Use of the Fracture Toughness Master Curve in ASME Code, Section XI, Applications

2013 ◽  
Author(s):  
William Server ◽  
Russ Cipolla
Keyword(s):  
Fracture Toughness ◽  
Master Curve ◽  
Potential Problem ◽  
Standard Test ◽  
Test Method ◽  
Alternative Approach ◽  
Alternative Index ◽  
Asme Code ◽  
Technical Basis ◽  
Direct Use

The ASME Code, Section XI, has adopted the indirect use of the fracture toughness Master Curve to define an alternative index (RTT0) rather than RTNDT for using the Code KIC and KIa curves in Appendices A and G. RTT0 is defined as T0 + 19.7°C (T0 + 35°F), where T0 is the Master Curve reference temperature as defined in ASTM Standard Test Method E 1921. This alternative approach was first approved in ASME Code Case N-629 for Section XI and Code Case N-631 for Section III. Most recently this approach has been integrated directly into the Code, Section XI, and will be published in the 2013 Edition. When this alternative indexing approach was developed, it was recognized that the direct use of the Master Curve itself also could be used as an alternative to the Code KIC curve. A Code Case for the direct use of the fracture toughness Master Curve has been developed and has been presented to Section XI for approval. This paper provides the technical basis for using the fracture toughness Master Curve as an alternative to the Section XI KIC curve. An adjustment to the Master Curve at very low temperatures is included which alleviates a potential problem for low temperature overpressure (LTOP) protection setpoints as would be determined using the existing Code KIC curve.

VALLOUREC VM 85 13Cr

Alloy Digest ◽  
2016 ◽  
Vol 65 (4) ◽  
Keyword(s):  
Fracture Toughness ◽  
Corrosion Resistance ◽  
Carbon Steel ◽  
Yield Strength ◽  
Physical Properties ◽  
Tensile Properties ◽  
Alloy Carbon ◽  
Sour Service ◽  
Minimum Yield

Abstract Vallourec VM 85 13Cr (minimum yield strength 85 ksi, or 586 MPa) is a low alloy carbon steel for use in oil country tubular goods as a material suitable for sour service. This datasheet provides information on composition, physical properties, hardness, and tensile properties as well as fracture toughness. It also includes information on corrosion resistance as well as forming. Filing Code: CS-198. Producer or source: Vallourec USA Corporation.

VALLOUREC VM 90 13CR

Alloy Digest ◽  
2016 ◽  
Vol 65 (3) ◽  
Keyword(s):  
Fracture Toughness ◽  
Corrosion Resistance ◽  
Carbon Steel ◽  
Yield Strength ◽  
Physical Properties ◽  
Tensile Properties ◽  
Alloy Carbon ◽  
Sour Service ◽  
Minimum Yield

Abstract Vallourec VM 90 13CR (minimum yield strength 90 ksi, or 620 MPa) is a low alloy carbon steel for use in oil country tubular goods as a material suitable for sour service. This datasheet provides information on composition, physical properties, hardness, and tensile properties as well as fracture toughness. It also includes information on corrosion resistance as well as forming. Filing Code: CS-197. Producer or source: Vallourec USA Corporation.

N-A-XTRA M800

Alloy Digest ◽  
2016 ◽  
Vol 65 (11) ◽  
Keyword(s):  
Fracture Toughness ◽  
Yield Strength ◽  
Structural Steel ◽  
Tensile Properties ◽  
Impact Energy ◽  
Heat Treating ◽  
Service Temperature ◽  
Minimum Yield ◽  
Minimum Impact

Abstract N-A-XTRA M800 is a quenched and tempered structural steel produced as heavy plates. N-A-XTRA steel can be supplied in six different grades with a minimum yield strength of 550, 620, 700 and 800 MPa (79.8, 89.9, 101.5 and 116.0 ksi). Some grades are delivered with different toughness properties. This last quality is for low service temperature with minimum impact energy at -40 deg C (-40 deg F) for grade N-A-XTRA M in a thickness range from 3 to 120 mm (0.118 to 4.724 in.). This datasheet provides information on composition and tensile properties as well as fracture toughness. It also includes information on forming, heat treating, and joining. Filing Code: SA-771. Producer or source: ThyssenKrupp Steel Europe AG.

RUUKKI RAEX 300

Alloy Digest ◽  
2012 ◽  
Vol 61 (2) ◽  
Keyword(s):  
Fracture Toughness ◽  
Wear Resistance ◽  
Shear Strength ◽  
Impact Toughness ◽  
Yield Strength ◽  
Physical Properties ◽  
Tensile Properties ◽  
High Strength ◽  
Structural Components ◽  
Wear Resistant

Abstract RUUKKI RAEX 300 (typical yield strength 900 MPa) is part of the Raex family of high-strength and wear-resistant steels with favorable hardness and impact toughness to extend life and decrease wear in structural components. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and shear strength as well as fracture toughness. It also includes information on wear resistance as well as forming, machining, and joining. Filing Code: SA-643. Producer or source: Rautaruukki Corporation.

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