Fracture Assessment of Austenitic Stainless Steel Piping With Multiple Flaws in Heat-Affected Zone

2010 ◽  
Author(s):  
Chihiro Narazaki ◽  
Toshiyuki Saito ◽  
Masao Itatani ◽  
Takuya Ogawa ◽  
Takao Sasayama
Keyword(s):  
Stainless Steel ◽  
Heat Affected Zone ◽  
Nuclear Power ◽  
Power Plants ◽  
Estimation Method ◽  
Limit Load ◽  
Low Carbon ◽  
Fracture Assessment ◽  
Steel Piping ◽  
Weld Heat

Stress corrosion cracking (SCC) has been observed as circumferential multiple flaws in the weld heat-affected zone of primary loop recirculation system piping and core shrouds made of low carbon stainless steel. In the Japan Society of Mechanical Engineers code, Rules on Fitness-for-Service for Nuclear Power Plants, there is no fracture assessment of piping with multiple flaws which are not subject to flaw combination rule criteria. Through fracture testing of piping with two circumferential flaws in the weld heat-affected zone, the limit load estimation method was used for fracture assessment of stainless steel piping.

Prediction of Collapse Stress for Pipes With Arbitrary Multiple Circumferential Surface Flaws

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Yinsheng Li ◽  
Kunio Hasegawa ◽  
Kunio Onizawa ◽  
Nathaniel G. Cofie
Keyword(s):  
Stainless Steel ◽  
Nuclear Power ◽  
Numerical Solutions ◽  
Estimation Method ◽  
Limit Load ◽  
Arbitrary Distribution ◽  
Piping System ◽  
Load Estimation ◽  
As Stress ◽  
Steel Piping

When a flaw is detected in a stainless steel piping system of a nuclear power plant during in-service inspection, the limit load estimation method provided in codes such as ASME Section XI or JSME S NA-1-2008 can be applied to evaluate the integrity of the pipe. However, in the current editions of these codes, a limit load estimation method is only provided for pipes containing a single flaw. Independent multiple flaws, such as stress corrosion cracks, have actually been detected in the same plane of stainless steel piping systems. In this paper, a failure estimation method by formula is proposed for any number and arbitrary distribution of multiple independent circumferential flaws in the same plane of a pipe. Using the proposed method, numerical solutions are compared with experimental results to validate the model, and several numerical examples are provided to show its effectiveness.

Experimental Investigation on the Failure Estimation Method of Cracked Cylinders Subjected to Multi-Axial Loads

2011 ◽  
Author(s):  
Yinsheng Li ◽  
Kunio Hasegawa ◽  
Naoki Miura ◽  
Katsuaki Hoshino
Keyword(s):  
Stainless Steel ◽  
Nuclear Power ◽  
Power Plants ◽  
Estimation Method ◽  
Bending Moment ◽  
Limit Load ◽  
Analytical Investigation ◽  
Failure Behavior ◽  
Axial Loads ◽  
Torsion Moment

When a crack is detected in a stainless steel pipe during in-service inspections, the failure estimation method given in the codes such as ASME Boiler and Pressure Vessel Code Section XI or JSME Rules on Fitness-for-Service for Nuclear Power Plants can be applied to evaluate the integrity of the cracked pipe. In the current codes, the failure estimation method considers the bending moment and axial force due to pressure. The torsion moment is assumed to be relatively small and is not considered in the method. Recently, an analytical investigation has been carried out by several of our authors on the limit load considering multi-axial loads including torsion, and a failure estimation method for combined bending moment, torsion moment and internal pressure is proposed. In this study, to investigate the failure behavior of cracked pipes subjected to multi-axial loads, including the torsion, and to provide experimental support for the failure estimation method, experiments were carried out on small sized stainless steel cylinders containing a circumferential surface and a through-wall crack, taking into consideration the combined tensile and torsion loads. Based on the experimental results, the proposed failure estimation method is verified for cracked pipes subjected to multi-axial loads.

Experimental Investigation on the Limit Load Estimation Method for Pipes Containing a Circumferential Surface Flaw With Complicated Shape

2011 ◽  
Author(s):  
Yinsheng Li ◽  
Kunio Hasegawa ◽  
Naoki Miura ◽  
Katsuaki Hoshino
Keyword(s):  
Stainless Steel ◽  
Nuclear Power ◽  
Power Plants ◽  
Estimation Method ◽  
Limit Load ◽  
Surface Flaw ◽  
Experimental Results ◽  
Load Estimation ◽  
Bending Moments ◽  
Steel Pipes

When a flaw is detected in the stainless steel pipes at nuclear power plants during in-service inspections, the limit load estimation method provided in the codes such as JSME Rules on Fitness-for-Service for Nuclear Power Plants or ASME Boiler and Pressure Vessel Code Section XI can be applied to evaluate the integrity of the flawed pipe. However, in these current codes, the limit load estimation method is only derived for pipes containing a flaw with uniform depth, although many flaws with complicated shapes, such as stress corrosion cracks, have actually been detected in pipes. In order to evaluate the integrity of the flawed pipes in a more rational way, a limit load estimation method has been proposed by authors considering the complicated circumferential surface flaw in its shape. In this study, failure bending experiments are performed for stainless steel pipes containing a circumferential surface flaw with a complicated asymmetrical shape. The proposed method is verified by comparing with experimental results of failure bending moments obtained in this study and in previous experiments. It is observed that the predicted failure bending moments by the proposed method are consistent with the experimental results, and the proposed method is applicable to estimate the realistic load-carrying capacity of flawed pipes.

Load Factor for Evaluating Non-Planar Flaws in Carbon Steel Piping Using Limit Load Methodology

2016 ◽  
Author(s):  
Phuong H. Hoang
Keyword(s):  
Carbon Steel ◽  
Nuclear Power ◽  
Power Plants ◽  
Pipe Wall ◽  
Local Strain ◽  
Limit Load ◽  
Evaluation Methodology ◽  
Load Factor ◽  
Wall Thinning ◽  
Steel Piping

Non-planar flaw such as local wall thinning flaw is a major piping degradation in nuclear power plants. Hundreds of piping components are inspected and evaluated for pipe wall loss due to flow accelerated corrosion and microbiological corrosion during a typical scheduled refueling outage. The evaluation is typically based on the original code rules for design and construction, and so often that uniformly thin pipe cross section is conservatively assumed. Code Case N-597-2 of ASME B&PV, Section XI Code provides a simplified methodology for local pipe wall thinning evaluation to meet the construction Code requirements for pressure and moment loading. However, it is desirable to develop a methodology for evaluating non-planar flaws that consistent with the Section XI flaw evaluation methodology for operating plants. From the results of recent studies and experimental data, it is reasonable to suggest that the Section XI, Appendix C net section collapse load approach can be used for non-planar flaws in carbon steel piping with an appropriate load multiplier factor. Local strain at non-planar flaws in carbon steel piping may reach a strain instability prior to net section collapse. As load increase, necking starting at onset strain instability leads to crack initiation, coalescence and fracture. Thus, by limiting local strain to material onset strain instability, a load multiplier factor can be developed for evaluating non-planar flaws in carbon steel piping using limit load methodology. In this paper, onset strain instability, which is material strain at the ultimate stress from available tensile test data, is correlated with the material minimum specified elongation for developing a load factor of non-planar flaws in various carbon steel piping subjected to multiaxial loading.

Probabilistic Models of Reliability of Cast Austenitic Stainless Steel Piping

2011 ◽  
Author(s):  
Haiyang Qian ◽  
David Harris ◽  
Timothy J. Griesbach
Keyword(s):  
Fracture Toughness ◽  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Tensile Properties ◽  
Nuclear Power ◽  
Power Plants ◽  
Probabilistic Models ◽  
Probabilistic Approach ◽  
Delta Ferrite ◽  
Steel Piping

Thermal embrittlement of cast austenitic stainless steel piping is of growing concern as nuclear power plants age. The difficulty of inspecting these components adds to the concerns regarding their reliability, and an added concern is the presence of known defects introduced during the casting fabrication process. The possible presence of defects and difficulty of inspection complicate the development of programs to manage the risk contributed by these embrittled components. Much work has been done in the past to characterize changes in tensile properties and fracture toughness as functions of time, temperature, composition, and delta ferrite content, but this work has shown a great deal of scatter in relationships between the important variables. The scatter in material correlations, difficulty of inspection and presence of initial defects calls for a probabilistic approach to the problem. The purpose of this study is to describe a probabilistic fracture mechanics analysis of the maximum allowable flaw sizes in cast austenitic stainless steel piping in commercial power reactors. Attention is focused on fully embrittled CF8M material, and the probability of failure for a given crack size, load and composition is predicted considering scatter in tensile properties and fracture toughness (fracture toughness is expressed as a crack growth resistance relation in terms of J-Δa). Random loads can also be included in the analysis, with results generated by Monte Carlo simulation. This paper presents preliminary results for CF8M to demonstrate the sensitivity of key input variables. The outcome of this study is the flaw sizes (length and depth) that will fail with a given probability when a given load is applied.

Experimental Investigation on Failure Estimation Method for Circumferentially Cracked Pipes Subjected to Combined Bending and Torsion Loads

2013 ◽  
Author(s):  
Yinsheng Li ◽  
Kunio Hasegawa ◽  
Michiya Sakai ◽  
Shinichi Matsuura ◽  
Naoki Miura
Keyword(s):  
Experimental Investigation ◽  
Pressure Vessel ◽  
Nuclear Power ◽  
Power Plants ◽  
Structural Integrity ◽  
Estimation Method ◽  
Bending Moment ◽  
Limit Load ◽  
Piping System ◽  
Torsion Moment

When a crack is detected in a nuclear piping system during in-service inspections, the failure estimation method provided in codes such as the ASME Boiler and Pressure Vessel Code Section XI or JSME Rules on Fitness-for-Service for Nuclear Power Plants can be applied to evaluate the structural integrity of the cracked pipe. In the current codes, the failure estimation method for circumferentially cracked pipes includes bending moment and axial force due to pressure. Torsion moment is not considered. The Working Group on Pipe Flaw Evaluation for the ASME Boiler and Pressure Vessel Code Section XI is developing guidance for combining torsion load within the existing solutions provided in Appendix C for bending and pressure loadings on a pipe. A failure estimation method for circumferentially cracked pipes subjected to general loading conditions including bending moment, internal pressure and torsion moment with general magnitude has been proposed based on analytical investigations on the limit load for cracked pipes. In this study, experimental investigation was conducted to confirm the applicability of the proposed failure estimation method. Experiments were carried out on 8-inch diameter Schedule 80 stainless steel pipes containing a circumferential surface crack. Based on the experimental results, the proposed failure estimation method was confirmed to be applicable to cracked pipes subjected to combined bending and torsion moments.

Experimental Investigation of Failure Estimation Method for Cylinders With a Circumferential Crack Subjected to Combined Tensile and Torsion Loads

2012 ◽  
Author(s):  
Yinsheng Li ◽  
Kunio Hasegawa ◽  
Naoki Miura ◽  
Katsuaki Hoshino
Keyword(s):  
Stainless Steel ◽  
Nuclear Power ◽  
Power Plants ◽  
Structural Integrity ◽  
Estimation Method ◽  
Bending Moment ◽  
Failure Behavior ◽  
Axial Loads ◽  
Circumferential Crack ◽  
Torsion Moment

When a crack is detected in a stainless steel pipe during in-service inspections, the failure estimation method given in codes such as the ASME Boiler and Pressure Vessel Code Section XI or JSME Rules on Fitness-for-Service for Nuclear Power Plants can be applied to evaluate the structural integrity of the cracked pipe. In the current codes, the failure estimation method includes the bending moment and axial force due to pressure. The torsion moment is assumed to be relatively small and is not considered. Recently, analytical investigations considering multi-axial loads including torsion were conducted in several previous studies by examining the limit load for pipes with a circumferential crack. A failure estimation method for the combined bending moment, torsion moment and internal pressure was proposed. In this study, the failure behavior of pipes with a circumferential crack subjected to multi-axial loads including the torsion is investigated to provide experimental support for the failure estimation method. Experiments were carried out on small size stainless steel cylinders containing a circumferential surface or through-wall crack, subjected to the combined tensile and torsion loads. Based on the experimental results, the proposed failure estimation method was confirmed to be applicable to cracked pipes subjected to combined tensile and torsion loads.

Fracture Assessment of Austenitic Stainless Steel Piping With Twin Flaws in TIG Weld

2009 ◽  
Author(s):  
Masao Itatani ◽  
Chihiro Narazaki ◽  
Takahiro Hayashi ◽  
Toshiyuki Saito ◽  
Takuya Ogawa
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Limit Load ◽  
Outer Diameter ◽  
Bending Tests ◽  
Four Point Bending ◽  
Electro Discharge Machining ◽  
Fracture Assessment ◽  
Type 316L Stainless Steel ◽  
Steel Piping

Fracture behavior of austenitic stainless steel piping for boiling water reactor (BWR) internals with circumferential through wall twin flaws at the weld was investigated. A 150A Sch.40 piping of type 316L stainless steel which has an outer diameter of 165.2 mm and a thickness of 7.1 mm was butt welded by tungsten inert gas (TIG) weld and single or twin through wall slits were introduced by an electro discharge machining (EDM) on the weld bead. Four point bending tests were conducted and failure stress was evaluated by currently proposed limit load equation for a piping with multiple flaws. The fracture loads obtained by the test were higher than the limit load based on the recently proposed equation for pipe with multiple flaws using 2.7Sm. It was concluded that the limit load criterion is able to be applied to the fracture assessment of austenitic stainless steel piping with twin flaws in the TIG weld. Through the pipe fracture test, it was found that the crack tends to grow in base metal rather than weld metal.

Development of Load Multipliers (Z-Factors) in Elastic-Plastic Fracture Mechanics Evaluation in Rules on Fitness-for-Service for Nuclear Power Plants

2012 ◽  
Author(s):  
Seiji Asada ◽  
Masao Itatani ◽  
Naoki Miura ◽  
Hideo Machida
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Fracture Mechanics ◽  
Ferritic Steel ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Elastic Plastic ◽  
Surface Flaws ◽  
Steel Piping

Not only nonmandatory Appendix C, “Evaluation of Flaws in Piping,” in ASME Boiler & Pressure Vessel Code Section XI but also Appendix E-9, “Elastic-Plastic Fracture Mechanics Evaluation,” in the JSME Rules on Fitness-for-Service for Nuclear Power Plants use the load multiplier Z-factor that is applied to elastic-plastic fracture mechanics evaluation for a circumferential flaw of austenitic stainless steel piping and ferritic steel piping. The Z-factor is defined as the ratio of the limit load to the load at fracture load. Basically, the Z-factor equations were conservatively formulated by using the Z-factors for circumferential through-wall flaws. However, the Codes require flaw evaluation for circumferential surface flaws. Accordingly, Z-factors for circumferential surface flaws should be developed to have the consistency. Therefore Z-factor equations of austenitic stainless steel piping and ferritic steel piping have been developed for circumferential surface flaws.

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