Allowable Axial Flaw Sizes for Stainless Steel Pipes Derived From Limit Load Criteria and Failure Assessment Diagram Procedure

2003 ◽  
Author(s):  
Kunio Hasegawa ◽  
Katsumasa Miyazaki ◽  
Gery M. Wilkowski ◽  
Douglas A. Scarth
Keyword(s):  
Stainless Steel ◽  
Limit Load ◽  
High Fracture Toughness ◽  
High Fracture ◽  
Steel Pipes ◽  
Failure Assessment Diagram ◽  
Axial Part ◽  
Wide Range ◽  
Failure Assessment ◽  
Asme Code

Piping containing flaws that exceed the Acceptance Standards of Section XI of the ASME Code is evaluated using analytical procedures described in Section XI to determine plant operability for the evaluated time period. Subarticle IWB-3640 of Section XI provides allowable axial and circumferential part-through-wall flaws determined from limit load criteria. ASME Section XI Code Case N-494-3 also provides evaluation procedures based on use of a failure assessment diagram to determine allowable flaw sizes. To understand the allowable flaw sizes determined by the limit load criteria and the failure assessment diagram procedure, anstenitic stainless steel pipes with axial part-through-wall flaws with a wide range of pipe diameters were analyzed. The allowable flaw depth based on limit load from Code Case N-494-3 was determined to be very close to that determined from IWB-3640 of Section XI, when the predicted failure mode is elastic-plastic fracture. It was found that the allowable flaw depths derived from the failure assessment diagram procedure of Code Case N-494-3, are lower, but are not significantly different, from those determined from the limit load criteria of IWB-3640. This is due to the relatively high fracture toughness that was used for the austenitic stainless steel.

Evaluation of a Weld Overlay Design for a Bimetallic Weld Using the Failure Assessment Diagram

2014 ◽  
Author(s):  
Jens Heldt ◽  
Christopher Lohse ◽  
Nathaniel G. Cofie ◽  
Michael Lashley
Keyword(s):  
Brittle Fracture ◽  
Failure Modes ◽  
Limit Load ◽  
Resistance Curve ◽  
Weld Overlay ◽  
Ductile Tearing ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Asme Code ◽  
Overlay Design

During routine inspection of an N5 feedwater nozzle dissimilar metal weld (DMW) of a BWR, an axial flaw was detected in the weld. The flaw was mitigated by applying a full structural weld overlay (WOL) repair consisting of Alloy 52M weld metal and using the gas tungsten arc welding process (GTAW). Because of the ductile nature and very high toughness of the Alloy 52M material, the limit load approach of ASME Code, Section XI, Appendix C was used for the sizing of the overlay. The use of limit load for the design of weld overlays for Alloy 52M material is supported by several studies documented in the industry [1]. In order to address other fracture failure modes such as failure by ductile tearing and brittle fracture, a failure assessment diagram (FAD) approach was used to evaluate the acceptability of the weld overlay design. FADs have been used for evaluating flaws in piping components, but not for acceptance of flaws in WOLs. The FAD evaluation was performed in accordance with the ASME Code, Section XI, Appendix H requirements which address brittle fracture, elastic-plastic fracture mechanics (ductile tearing), and limit load failure modes. The applicable stress combinations were used in combination with the materials JR resistance curve to determine flaw acceptability at the end of the evaluation period. The evaluation considered the presence of both a circumferential flaw (360° around the circumference and 100% through the original pipe wall; the design basis for the full structural weld overlay) and an axial flaw. For both circumferential and axial flaws, several assessment points corresponding to the JR resistance curve were determined and plotted on the FAD curve for austenitic steels in ASME Section XI, Appendix H. The FAD curve in Appendix H was derived based on strength properties of stainless steel and is considered conservative in application to Alloy 52M since Alloy 52M has higher strength. All the assessment points were found to be below the FAD curve thus indicating the acceptability of the weld overlay with consideration to all the three possible fracture regimes.

Failure Stresses for Pipes With Multiple Circumferential Flaws

2004 ◽  
Author(s):  
Kunio Hasegawa ◽  
Hideo Kobayashi
Keyword(s):  
Stainless Steel ◽  
Limit Load ◽  
Combination Rules ◽  
Steel Pipes ◽  
Ductile Materials ◽  
Asme Code ◽  
As Stress ◽  
Simple Equations ◽  
Service Inspection ◽  
Single Flaw

Flaw evaluation for fully-plastic fracture uses the limit load criterion. As stainless steels are high toughness ductile materials, limit load criterion is applicable to stainless steel pipes. When a single circumferential flaw is detected in a stainless steel pipe during in-service inspection, the single flaw is evaluated in accordance with Article EB-4000 in the JSME Code or Appendix C in the ASME Code, Section XI. However, multiple flaws such as stress corrosion cracking are sometimes detected in the same circumferential cress-section in a pipe. If the distance between adjacent flaws is short, the multiple flaws are considered as a single flaw in compliance with combination rules. Failure stress is easily calculated by the equations given by Article EB-4000 or Appendix C. If the two flaws are separated by a large distance, it is not required to combine the two flaws. Each flaw is treated as independent. However, there are no equations for evaluating collapse stress for a pipe containing multiple independent flaws in Article EB-4000 and Appendix C. The present paper focus on a proposal of simple equations for evaluating collapse stresses for pipes containing multiple circumferential part-through wall flaws.

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.

Introduction of CASS Pipe Flaw Evaluation of JSME Rules on Fitness for Service

2019 ◽  
Author(s):  
Kiminobu Hojo
Keyword(s):  
Stainless Steel ◽  
Evaluation Method ◽  
Limit Load ◽  
Evaluation Procedure ◽  
Screening Criteria ◽  
Steel Pipes ◽  
Evaluation Procedures ◽  
Degradation Models ◽  
Fracture Tests ◽  
Cast Stainless Steel

Abstract This paper summarizes the revised flaw evaluation procedures for cast austenitic stainless steel (CASS) pipe of the Japan Society of Mechanical Engineers (JSME) rules on fitness for service (FFS) in 2018 addenda. The revision includes the introduction of thermal aging degradation models for stressstrain curve and fracture resistance (J-R) curve, application of a screening criteria for the fracture evaluation procedure of cast stainless steel pipes, and introduction of a new critical stress parameter for the limit load evaluation method of a shallow flaw with a flaw depth to thickness ratio of less than or equal to 0.5. These revisions are based on a large database of specimen tests and several fracture tests of flat plate and large pipe models using thermally aged material, which have already been published.

An Improvement in the Code Evaluation of Flawed Pipes

2007 ◽  
Author(s):  
Amy J. Smith ◽  
Keshab K. Dwivedy
Keyword(s):  
Stainless Steel ◽  
Fracture Mechanics ◽  
Base Material ◽  
Limit Load ◽  
Evaluation Methodology ◽  
Linear Elastic ◽  
Weld Material ◽  
Steel Base ◽  
Asme Code ◽  
Elastic Fracture

ASME Code Section XI Nonmandatory Appendix C [1] formalized evaluation of flaws in piping for justification of continued service of piping components with an identified crack-like flaw. The revision of this appendix in 2004 was a significant improvement in the evaluation methodology for both flawed austenitic stainless steel and ferritic steel pipe depending upon the failure mode governed by limit load (fully plastic), elastic-plastic fracture mechanics, or linear elastic fracture mechanics. The appendix also provides a screening procedure to determine failure mechanism and a procedure for flaw modeling based on the estimated flaw size at the end of a specified evaluation period. The purpose of this paper is to propose an improvement to the limit load method applicable to screened-in carbon steel, wrought stainless steel base material, stainless steel weld material with nonflux weld, and cast products in which the ferrite content is less than twenty percent. In addition, changes in the formulation are proposed to extend the methodology to non-crack-like flaws. Both crack-like and non-crack-like circumferential flaws in the piping are analyzed to simplify formulation for flaw evaluation. The paper concludes that the proposed formulation improves efficiency of the application of Appendix C methodology for crack-like flaw and non-crack-like flaw evaluations.

Evaluation of Alignment Rules Using Stainless Steel Pipes With Non-Aligned Flaws

2009 ◽  
Author(s):  
Kunio Hasegawa ◽  
Katsumasa Miyazaki ◽  
Koichi Saito ◽  
Bostjan Bezensek
Keyword(s):  
Stainless Steel ◽  
Limit Load ◽  
Plastic Collapse ◽  
Paper Briefly ◽  
Limit Loads ◽  
Bending Tests ◽  
Steel Pipes ◽  
Four Point Bending ◽  
Close Proximity ◽  
As Stress

Multiple flaws such as stress corrosion cracks are frequently detected in the same welded lines in pipes. If multiple discrete flaws are in close proximity to one another, alignment rules are used to determine whether the flaws should be treated as non-aligned or as coplanar. Alignment rules are provided in fitness-for-service codes, such as ASME, JSME, API 579, BS 7910, etc. However, the criteria of the alignment rules are different among these codes. This paper briefly introduces these flaw alignment rules, and four-point bending tests performed on stainless steel pipes with two non-aligned flaws. The experimental plastic collapse stresses are determined from the collapse loads and compared with collapse stresses calculated from the limit load criteria. The limit loads are obtained for single non-aligned or aligned coplanar flaws in accordance with the alignment rules. On this basis, the conservatism of the alignment rules in the above codes is assessed.

scholarly journals Failure assessment diagram analysis of creep crack initiation in 316H stainless steel

2003 ◽  
Vol 80 (7-8) ◽  
pp. 541-551 ◽  
Author(s):  
C.M. Davies ◽  
N.P. O'Dowd ◽  
D.W. Dean ◽  
K.M. Nikbin ◽  
R.A. Ainsworth
Keyword(s):  
Stainless Steel ◽  
Crack Initiation ◽  
Failure Assessment Diagram ◽  
Creep Crack ◽  
Failure Assessment ◽  
Diagram Analysis

Technical Basis for the Extension of ASME Code Case N-494 for Assessment of Austenitic Piping

1996 ◽  
Vol 118 (4) ◽  
pp. 513-516 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Lower Bound ◽  
Pressure Vessel ◽  
Strain Curve ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Failure Assessment Diagram ◽  
Strain Behavior ◽  
Failure Assessment ◽  
Asme Code ◽  
Constraint Effects

In 1990, the ASME Boiler and Pressure Vessel Code for Nuclear Components approved Code Case N-494 as an alternative procedure for evaluating flaws in light water reactor (LWR) ferritic piping. The approach is an alternate to Appendix H of the ASME Code and allows the user to remove some unnecessary conservatism in the existing procedure by allowing the use of pipe specific material properties. The Code case is an implementation of the methodology of the deformation plasticity failure assessment diagram (DPFAD). The key ingredient in the application of DPFAD is that the material stress-strain curve must be in the format of a simple power law hardening stress-strain curve such as the Ramberg-Osgood (R-O) model. Ferritic materials can be accurately fit by the R-O model and, therefore, it was natural to use the DPFAD methodology for the assessment of LWR ferritic piping. An extension of Code Case N-494 to austenitic piping required a modification of the existing DPFAD methodology. Such an extension was made and presented at the ASME Pressure Vessel and Piping (PVP) Conference in Minneapolis (1994). The modified DPFAD approach, coined piecewise failure assessment diagram (PWFAD), extended an approximate engineering approach proposed by Ainsworth in order to consider materials whose stress-strain behavior cannot be fit to the R-O model. The Code Case N-494 approach was revised using the PWFAD procedure in the same manner as in the development of the original N-494 approach for ferritic materials. A lower-bound stress-strain curve (with yield stress comparable to ASME Code specified minimum) was used to generate a PWFAD curve for the geometry of a part-through wall circumferential flaw in a cylinder under tension and bending. Earlier work demonstrated that a cylinder under axial tension with a 50-percent flaw depth, 90 deg in circumference, and radius to thickness of 10, produced a lower-bound FAD curve. Validation of the new proposed Code case procedure for austenitic piping was performed using actual pipe test data. Using the lower-bound PWFAD curve, pipe test results were conservatively predicted (failure stresses were predicted to be 31.5 percent lower than actual on the average). The conservative predictions were attributed to constraint effects where the toughness values used in the predictions were obtained from highly constrained compact test specimens. The resultant development of the PWFAD curve for austenitic piping led to a revision of Code Case N-494 to include a procedure for assessment of flaws in austenitic piping.

Microstructure and Performance of the Hot-Pressed Silicon Nitride Ceramics with Lu2O3 Additives

2010 ◽  
Vol 434-435 ◽  
pp. 37-41
Author(s):  
Jian Feng Tong ◽  
Da Ming Cheng ◽  
Bao Wei Li ◽  
Huang Hao Ling ◽  
Wang Ling
Keyword(s):  
Fracture Toughness ◽  
Bimodal Distribution ◽  
Crack Size ◽  
High Fracture Toughness ◽  
High Fracture ◽  
Β Phase ◽  
Wide Range ◽  
Nitride Ceramics ◽  
And Performance ◽  
Si3n4 Ceramics

The influence of Lu2O3 on phase transformation and seeds morphology was investigated. The result showed that the β-Si3N4 seeds with up to 95% β phase content could be obtained with 2wt% Lu2O3 as the additive content under 1750°C for two hours. The microstructure and mechanical properties of hot-pressed Si3N4 ceramics, using 9wt.% of Lu2O3• additives were investigated by the means of MTS measurements and Vickers indentation crack size measurements, as well as XRD and SEM. It was known that the high fracture toughness of Si3N4 ceramics was attributed to the rodlike morphology of β-Si3N4 grains. And the reinforcement effect and mechanism of β-Si3N4 seed were studied. It was found that the grain size and its distribution influence the property and microstructure of Si3N4 ceramics, namely, the relative narrow distribution of grain diameter in some extent and relative wide range of bimodal distribution of grain aspect ratio could improve the property of Si3N4 ceramics. The improvement in the fracture toughness with the amount of additive was mainly attributed to elongated grain growth during the sintering process.The high temperature properties of self-reinforced Si3N4 with different additives were studied. By this method, self-reinforced Si3N4 ceramics with an increment of 10~20 percent of fracture toughness was successfully fabricated.

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