bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of Fracture Toughness Behavior of SA508 Steel Considering Biaxial Loading Condition
Authors: Kim Jong-Min , Lee Ki-Hyoung , Lee Ho-Jin , Lee Bong-Sang 
Published: August 2013

The crack-tip stress field and fracture mechanics assessment parameters, such as the elastic stress intensity factor and the elastic-plastic J-integral, for a surface crack can be significantly affected by the loading condition and crack geometry. Current guidance considers that the ductile-to-brittle transition is defined using uniaxially loaded specimens with a deep crack even when the reactor pressure vessel is under biaxial loading and the existence of deep crack is not probable through periodic in-service-inspection. Thus, such a constraint effect caused by differences between standard specimens and a real structure can overestimate the fracture toughness and affects the results of the structural integrity assessment.
The present paper investigates the constraint effect by evaluating the Mater Curve T0 reference temperature of PCVN (Pre-cracked Charpy V-Notch) and small scale cruciform specimens of SA508 Gr. 3 low alloy steel through the fracture toughness tests of theses specimens and 3-dimensional elastic-plastic finite element analyses. Based on the finite element results, the fracture toughness values of a small-scale cruciform specimen were estimated, and the geometry-dependent factors of the cruciform specimen considered in the present study were determined and then the transferability of the test results of these specimens were discussed.
Prediction of Creep Void Growth in Heat-Affected Zone of High Chromium Steel Weldments Considering Multiaxial Stress State
Authors: Murakami Eiji , Hashimoto Masamitsu , Kikuhara Seiji 
Published: August 2013

This paper deals with a method for predicting creep void growth in heat-affected zone (HAZ) of high chromium steel weldments. The method has been proposed by authors based on the relationship between creep void density increasing rate and multiaxial stress state.
In this study, internal pressure creep tests of ASME grade 91 (9Cr-1Mo-Nb-V) tubes with longitudinal weldments subjected to several internal pressures have been conducted to reveal creep void growth behavior in HAZ. In addition, finite element creep analyses of the specimens at different creep strain rates in base metal, weld metal and HAZ have been carried out to investigate distribution of stresses and stress triaxiality factor in HAZ. A comparison between stress distributions and void distributions revealed that stress triaxiality factor predominantly affects growth behavior of creep voids. From the result, the relationship between creep void density increasing rate and the parameter as a function of principal stress and triaxiality factor was established. It was found that there is a proportional relationship between creep void density increasing rate and the parameter to represent stress multiaxiality on the logarithmic graph.
To verify proposed prediction method, the method was applied to the internal pressure creep test specimens at different experimental conditions. As a result, the predicted void distribution and void density increasing rates were in good agreement with experimental results.
The Residual Bolt Force and the Sealing Performance of Flanged Connections With Expanded PTFE Gaskets (Based on Test Results for One Year)
Authors: Kobayashi Takashi , Hagiri Taiki , Nishiura Kengou , Hiratsuka Masaaki , Itoi Katsutoyo 
Published: August 2013

It is known that bolt forces reduce significantly after tightening bolted flanged connections in which expanded PTFE gaskets are used. Bolts are often post-tightened in practice after initial tightening to compensate for the reduction of bolt forces. The viscoelastic characteristic of expanded PTFE gaskets is thought to be the main cause for the phenomenon. Some gasket users are not confident whether the bolt forces remain above a minimum required gasket load until next maintenance. However, the long term characteristics of the residual bolt forces and the sealing performance of flanged connections have not been clarified yet.
In this study, using flanged connections with expanded PTFE gaskets, the reduction of bolt forces and the change in the sealing performance were measured at room temperature for one year. Based on the test results, the residual bolt force and the sealing performance were studied.
It was clarified that bolt forces converges to a certain level at early stage within almost 1000 hours. After that, the bolt forces were significantly affected by the ambient temperature change. This is because the thermal expansion of PTFE material is high and also the thermal characteristic of PTFE material has a temperature dependency. It was confirmed that although the bolt force reduced significantly at early stage, it is maintained in long-term. The sealing performance was improved due to the increased compression of gasket.
Brittle Fracture Analysis of Dissimilar Metal Weld Joints
Authors: Blouin A. , Chapuliot S. , Marie S. , Bergheau J. M. 
Published: August 2013

Demonstration of large components integrity is based on the demonstration that they could never undergo brittle fracture. In parallel, considering a conventional defect somewhere in the component, failure must prevent ductile crack propagation.
Connections between a ferritic component and an austenitic one have to respect these rules. The considered case is a Ni base alloy weld joint between a ferritic pipe and an austenitic one. For brittle fracture exclusion, the aim of the present study is to show that in the same loading conditions, the weld joint is less sensitive to the brittle fracture than the surrounding ferritic part of the component. That is to say that the demonstration should be focused on the ferritic base metal which is the weakest material.
For that purpose, Chapuliot developed a stress-based criterion model, using a threshold stress (σth) below which the cleavage cannot occur. It can be used to define the brittle crack occurrence probability, which means that it is possible to determine the highest loading conditions without any brittle fracture risk.
For the experimental part of this demonstration, two different mock-ups with DMW are used. The first one is composed of a 16MND5 (A508 cl. 3) steel pipe welded to a 316L stainless steel pipe with Ni base alloy 82. As for the second one, the materials are the 18MND5 (A533) steel, the 316L stainless steel and the Ni base alloy 52. Conventional defects have been considered in the ferritic part, close to the weld joint in the heat affected zone, and far away from the weld joint in the ferritic part. Two hundred specimens have been taken from the mock-ups: special tensile specimens, compact tensile specimens, single edge notch tension specimens, notched tensile specimens, smooth tensile specimens. All the materials have been characterized at −125°C/−130°C and −170°C/−175°C, even the heat affected zones. Finite element calculations have been done to complete the experimental investigations. The first results show that, due to the mismatch of the materials, the brittle fracture risk is much lower in the HAZ. Thus, DMW HAZ could not be a weak part concerning brittle fracture. This paper presents the criterion, the experimental work and the analyses made to evaluate the conservatism of the homogeneous ferritic case compared to the DMW.
The Proposal of Wall Thickness Management Criteria of T-Pipes
Authors: Tsunokawa Kiyoharu , Ohira Taku , Miura Naoki , Kitajima Yasumi , Yoshimura Daisuke 
Published: August 2013

Although the reinforcement for openings is checked in accordance with design / construction standard when thinning was observed in T-pipes, this evaluation becomes too conservative or requires much time and effort.
This paper describes additional parametric study results and proposes a guideline for thickness management of wall thinning T-pipes. On the other papers related to this project, the experiment and numerical simulation results are reported. This paper referred these results and performed further investigation.
Magnitude and Distribution of Retained Residual Stresses in Laboratory Fracture Mechanics Specimens Extracted From Welded Components
Authors: Hurlston R. G. , Sharples J. K. , Sherry A. H. 
Published: August 2013

Quantifying material fracture toughness properties is an important step in ensuring structural integrity of industrial components. Welding of structural components can cause large magnitudes of residual stress to be generated, which can be defined as a stress that exists in a material when it is under no primary loading. These stresses can be retained in laboratory fracture mechanics testing specimens removed from non-stress relieved welds, making the quantification of valid material fracture toughness difficult.
The aim of this paper is to investigate, analytically, the levels and distributions of residual stresses retained in fracture mechanics specimens taken from welded components. This was achieved using parametric finite element analyses. Furthermore, in order to ensure the validity of fracture toughness measurements derived from components that contain residual stress, a robust method for the design of stress-free fracture mechanics specimens is proposed.
Significant weld residual stresses have been shown to be retained in certain laboratory specimens post extraction from non stress-relieved welds. The magnitude and distribution of retained residual stress has been shown to be dependant on material properties, specimen size, specimen type and removal location. In addition, the stress partitioning method has been shown to provide a useful approach for estimating the levels and distributions of residual stresses retained in fracture mechanics specimens extracted in certain orientations.
Crack Propagation Under High Thermal Amplitude Cycles in a Ductile Material
Authors: Vallet Christophe , Chau The Hiep , Stéphan Jean-Michel 
Published: August 2013

An experimental setup was built in order to study the fatigue crack propagation in high stressed structure with plastified zone.
This paper deals with results obtained in a first stage of the experiment program. Thermal cycles are applied on a simplified mock-up including four short pre-cracking defects. Local measurements (thermocouples, strain gages) and crack lengths are provided.
A numerical interpretation of the test was then performed and the results were compared to the experiment.
Hot Isostatic Pressing of Hardfacing and Stainless Steel Powders for PWR Components: Materials and Manufacturing Benefits
Authors: Burdett W. Barry 
Published: August 2013

Hot Isostatic Pressing (HIP) has been used for many years to consolidate porosity in cast metal shapes to improve mechanical properties. When applied to fine metal powders, it is possible to produce Near Net Shape (NNS) items and more complex geometry components that are fully dense and offer an attractive set of properties at reduced cost.
NNS items from powder deliver cost savings by reducing initial material usage and subsequent machining costs. Powder production and HIP processing are automated methods, which provide protection against forging route obsolescence. Setup costs are lower and batch sizes smaller, particularly well suited to small numbers of high integrity components.
HIPped powder microstructures are isotropic and equiaxed, with uniformly fine grain sizes not normally achieved in heavy section components, which facilitates ultrasonic NDE examination. Improved features to facilitate NDE are readily incorporated into the HIP assembly. Inclusion contents are lower and of more benign geometry, easing fracture assessment.
Use of the technology has grown, particularly in the off-shore oil industry where it is already established in high integrity applications, particularly in place of welded joints. Take-up in the more conservative nuclear industry has been slow. The quality of HIPped powder items can provide through life cost savings since there is greater assurance of structural integrity compared to welded or wrought components.
This paper presents a materials perspective on the way in which Rolls-Royce has gained experience with HIPped powders since the 1990s, initially with hardfacing materials to minimise welding defects and provide a robust manufacturing route. Building on this database, we have now established that HIPped powder 316L/304L components, in items up to several tons in weight, have equivalent or slightly better strength, toughness and corrosion resistance to their forged or cast counterparts. This data is now part of a submission to ASME for inclusion in the Pressure Vessel Code.
Rolls-Royce now has a robust methodology in place to develop safety cases and is extending the number of applications in pressure boundary components on current and future classes of equipment. A strength-in-depth argument has been endorsed by external approval organisations and is supporting current submarine build programmes. Other applications in the growing civil nuclear market are now under consideration.
Influence of PWR Primary Water on LCF Behavior of Type 304L Austenitic Stainless Steel at 300°C: Comparison With Results Obtained in Vacuum or in Air
Authors: De Baglion Laurent , Mendez José , Le Duff Jean-Alain , Lefrancois André 
Published: August 2013

Nowadays, it is well known that the low cycle fatigue (LCF) life of austenitic stainless steels can be affected in specific conditions of temperature, strain rate, strain amplitude or dissolved oxygen concentration by the effect of Pressurized Water Reactor (PWR) primary coolant environment. Nevertheless, questions remain about the best methodology that must be used to consider environmental effects for nuclear power plant licensing and for operating lifetime extensions.
These environmental effects are most commonly evaluated from a mean fatigue curve based on tests conducted in air at room temperature. However, it is well established that air is not a neutral environment for metallic alloys and its effect can be highly dependent on the temperature level.
Thus, in order to evaluate the intrinsic fatigue resistance of a 304L austenitic stainless steel at 300°C and the importance of complex fatigue – environment interactions in air or in PWR water, LCF tests were performed in both environments and specifically designed ones were conducted in secondary vacuum. Tests were performed on 304L cylindrical specimens at 20 or 300°C in vacuum or in air and only at 300°C in PWR water, under total axial strain control using a triangular waveform at strain amplitudes of ±0.3 or ±0.6% and strain rates of 4 × 10−3, 1 × 10−4 or 1 × 10−5 s−1.
It was found that compared with vacuum, air is responsible for a strong decrease in fatigue lifetime in this steel, especially at 300°C and low strain amplitude. The PWR water coolant environment is still more active than air and leads mainly to increased damage kinetics, with slight effects on initiation sites or propagation modes. More precisely, the decreased fatigue life in PWR water is essentially attributed to an enhancement of both crack initiation and “short crack” micropropagation stages. Furthermore, a detrimental influence of low strain rates on the fatigue lifetime at 300°C was observed in PWR water environment or in air, but also in vacuum without environmental effects, and was in the last case exclusively attributed to the occurrence of the dynamic strain aging (DSA) phenomenon.
So, the use of data obtained in a neutral environment as a reference allows the evaluation of the intrinsic effect of each environmental or loading condition. Moreover, in an active environment such as air or PWR primary water, damage evolutions as well as fatigue lives cannot be predicted by a simple multiplication of each parameter effect taken separately because they are the result of numerous interactions.
The last conclusion is supported by complementary results showing that the PWR water environment effect as well as the ground surface finish effect can be attenuated when LCF tests are performed with a more representative loading signal shape.
Advanced Assessment of the Integrity of Ductile Components
Authors: Daly Michael , Sherry Andrew H. , Sharples John K. 
Published: August 2013

Nuclear Reactor Pressure Vessels (RPV) are manufactured from medium strength low alloy ferritic steel, specifically selected for its high toughness and good weldability. The ability of the pressure vessel to resist crack growth is crucial given that it is one of the fundamental containment safety systems of the reactor. For most of their lifetime, the pressure vessel operates at sufficiently elevated temperatures to ensure the material is ductile. However, the development of ductile damage, in the form of voids, and the ability to predict the ductile crack growth in RPV materials requires further work.
The Gurson-Tvergaard-Needleman (GTN) model of void nucleation, growth and coalescence provides one tool for predicting ductile damage development. The model is normally calibrated against fracture toughness test data. However, recent work [1] has demonstrated the benefit of refining calibrations against measured void volume fractions generated from notched and pre-cracked specimen tests.
This paper described the measurement of void distributions below the fracture surface of a range of notched and pre-cracked specimens. The void distribution below the fracture surface is shown to be dependent upon the local stress triaxiality and plastic strain distribution. As a result, pre-cracked specimens show a greater concentration of voids close to the fracture surface, whilst notched tensile specimens show a lower volume fraction of voids close to the crack surface. In both specimen types, voids are observed to extend between 2.5 and 3.5 mm below the fracture surface.
Managing Check Valve Flange Leaks: Technical Solutions and Challenges to Overcome
Authors: Ezekoye L. Ike , Densmore William E. , Turkowski William M. , Becse Robert E. 
Published: August 2013

Check valves are the simplest valves in power plants. Their simplicity and passive nature, combined with their relatively low maintenance requirements, often mask their relative importance in piping systems. Compared to power operated valves (POVs), such as motor operated valves or air operated valves, check valves have very few parts. The more parts a valve has, the more likely failures will occur. As such, power operated valves tend to have more stringent requirements that cover periodic verification of operability, in-service testing (IST), and scheduled preventive maintenance to assure functionality. Check valves, on the other hand, do not require nearly the same amount of rigor to assure operability.
The passive nature of check valves often leads the user not to expect failures. Consequently, lacking of attention often results to inadvertent failures. One failure that has received significant attention from both the industry and the regulator is check valve body-to-bonnet joint leakage. In nuclear power plants this leakage can contaminate the general area where the valve is located, can lead to a plant shutdown, and pose personnel hazards.
In this paper, the technical solutions that can be used to manage check valve body-to-bonnet joint leakage will be presented. The merits of each technical solution and the associated challenges will be discussed. Also, as some of the leakage containment solutions are appurtenances to the valve, the paper will address the interface between the appurtenances and the valve.
Proposal of a Guideline for Thickness Management of Wall Thinning T-Joints
Authors: Ochi Mayumi , Yamakami Katsuhiko , Hamaguchi Yoshinobu , Miyazaki Katsumasa , Naito Keita , Toyota Kiyoo , Teshima Kaina 
Published: August 2013

Although the required minimum thickness (tsr) of T-joints (tees) of class 2, 3 and lower classes of nuclear power plants in Japan is calculated from the design pressure and temperature for design, there are neither any rules nor standards for thickness management of wall thinning T-joints for facilities maintenance.
This paper describes additional parametric study results and proposes a guideline for thickness management of wall thinning T-joints. In other papers related to this project, the experiment and numerical simulation results are reported. This paper refers to these results and performs further investigation under the consideration of JSME (The Japan Society of Mechanical Engineers) design, construction and maintenance codes and standards.
Effect of Undermatched Weld on Deformation and Brittle Fracture Behaviors in High-Tensile Strength Steel Plate Welded Joint
Authors: Mochizuki Masahito , Kawabata Tomoya 
Published: August 2013

High tensile strength steel such as 950 MPa class is used in hydropower plant components due to its lower cost and higher reliability. This steel is already used for penstocks in the Kanna-gawa and Omaru-gawa hydropower plants in Japan. Proper welding is one of the most critical factors to ensure integrity of the plant components against brittle fracture from weld defects. For example, preheat- and interpass-temperature controls are essential to avoid weld defects and to ensure strength, since the weld process induces residual stress and possible weld deformations such as angular distortion or unevenness. Undermatching (lower strength in weld metal than in the base plate) makes high strength steel plate become easier to use for welding because restrictions in the welding process can be reduced by using softer welding consumables. Tensile strength in welded joints increases near the base plate when the undermatched zone is not much wider than the thickness. When the appropriate welding conditions for assuring strength and preventing brittle fracture are clarified, it becomes clear to be possible to use undermatched joints for penstock.
In this paper, numerical simulation of stress-strain behavior during the weld process is performed by considering the microstructural effect due to phase transformation. Phase transformation data is obtained from measured dilatometric curves in continuous cooling transformation (CCT) diagrams. Phase transformation data involves many parameters, including not only the maximum temperature, cooling rate and heat input, but also the superposition of multi heat cycles. Then, the characteristics of deformation and strength in a welded joint of 950 MPa class steel plate for penstock with undermatched region, which is equivalent to using weld material with lower strength level, are discussed to expand the allowable welding conditions in penstock fabrication. Finally, brittle fracture behaviors are discussed by using standard crack-tip opening displacement (CTOD) tests and wide plate tests with through-thickness notch by the welded joint.