bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ductile Tearing Prediction in Welds Considering Hydrogen Embrittlement
Authors: Robin Vincent , Gilles Philippe , Mourgue Philippe , Tchoukien David 
Published: January 2014

Some flaws may appear in metal components, in the weld region, and more especially in the case of electron beam girth weld in the slope area of the process (start and stop of the welding operation). These initial flaws can growth with delay even without any external loads. Indeed close to the junction, the material undergoes the combination of high tensile residual stresses due to welding operation and the presence of hydrogen brought by manufacturing process. Hydrogen assisted cracking is then suspected to explain the origin of crack growth through hydrogen embrittlement of the base metal.
To understand by numerical modeling, at least qualitatively, the scenario of appearance of such cracks and their evolution, without any external load or under pressure load, the proposed approach consists first in simulating the welding process and its consequences on residual stress distribution and hydrogen concentrations [1]. The hydrogen diffusion computation is pursued after the welding operation simulation in order to highlight the most critical moment at which macroscopic defects may appear. Then, a macroscopic defect is created in the so determined critical zone, the stability of which is studied by estimating the energy release rate at the crack front and by comparing these values with experimental data such as the critical energy release rate at initiation and the tearing resistance curves which may depend on the hydrogen content. So, it is numerically possible to propagate the defect in the time, considering hydrogen diffusion and residual stress rebalancing, by successive crack front definition performed as the crack tip region exceeds the critical energy release rate [14]. Finally, the evolution of the defect is estimated in the same way under pressure test loading conditions. Results and discussions are presented to propose an engineering approach for the design assessment of such specific weld junctions with a low and hydrogen dependant toughness.
Investigations on Crack Propagation Under Cyclical Isothermal and Thermo-Mechanical Loadings for a Type 304-L Stainless Steel Used for Pressurized Water Reactor
Authors: Gourdin C. , Rossillon F. , Le Delliou P. , Perez G. , Fissolo A. 
Published: January 2014

The integrity of structures exhibiting flaws in Pressurized Water Reactor (PWR) has to be assessed to meet safety criteria. This paper deals with crack-propagation under cyclic thermo-mechanical loadings, as encountered in class I austenitic pipes of PWR’s. To have a conservative and reliable assessment of the crack propagation due to the in-service loading, various codes and standards use simplified method. For example, RSE-M introduces a plastic correction depending on the proportion of the mechanical loading. An improvement of the current method requires additional investigations. Moreover, components loaded with transient or thermal fluctuations are not really in strength-controlled conditions.
To this end, a new device called “PROFATH” was designed. The specimen is a pre-cracked thick-walled tube undergoing a set of thermal cycles and loaded with a static mechanical force. During the first part of the cycle, a high frequency induction coil heats the external wall. Then, the heating system stops and the specimen is cooled down by running water inside the tube. Finite element calculations show that only a region half-way along the tube should be heated to ensure adequate structural effect. In the heated zone, the machining of a sharp circumferential groove ensures the propagation of a unique crack. An electro-mechanical jack controls the level of the mechanical static load.
To obtain a very precise thermal mapping, a specific specimen with dedicated instrumentation is used: 20 thermocouples are appropriately located on the outer surface and along the wall thickness. During the test, the crack-propagation is estimated through crack-opening measurements (compliance method). To improve actual measurements, installation of a laser extensometer sensor is now in progress.
Validation of Plastic Collapse Assessments Using BS 7910:2013 and R6 Procedures
Authors: Eren Şefika Elvin , London Tyler , Yang Yang , Hadley Isabel 
Published: January 2014

The British Standard, BS 7910 Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures is currently under revision [1]. Major changes have been undertaken, especially in the fracture assessment routes, and this paper specifically addresses the assessment of proximity to plastic collapse, usually expressed as the parameter Lr via either a reference stress or limit load approach.
In the new edition of BS 7910, the reference stress approach has been retained for the assessment of many geometries, mainly for reasons of continuity. However, new limit load solutions (originating in the R6 procedure) are given for use in the assessments of strength mismatched structures or clad plates.
In general, a reference stress solution and a limit load solution for the same geometry should deliver the same value of Lr. However, recent comparative studies have shown differences in the assessment of plastic collapse depending on whether the reference stress solutions in BS 7910:2013 or the limit load solutions in R6 are used for the calculation of Lr.
In this paper, the extent of the difference in the assessment results with respect to the choice of solutions and boundary conditions are discussed. The results of the assessments in accordance with BS 7910 and R6 are compared with the results of numerical assessments obtained via Finite Element Analysis (FEA).
The collapse loads observed in various wide plate tests conducted in the last 20 years are also compared with the collapse loads predicted by BS 910:2013, R6 and FEA.
Finally, observations regarding the accuracy of different Codes and FEA are discussed.
PLiM Lessons After Fukushima
Authors: Rothenhöfer Horst 
Published: January 2014

After each severe nuclear incident new safety requirements arise. So the desirable action list gets longer and more specific every time. On the other hand way too many plants have not yet implemented lessons learned from past incidents. The challenge is to prioritize required and desirable measures and implement them incrementally in the sense of continuous improvements.
In parallel, there is the plant life management process (PLiM) that gives the framework for single measures. Each remarkable event has to be assessed with PLiM criteria. Could the event have been prevented by implementing the state of the scientific and technical knowledge or has something happened that requires an update of this knowledge?
Some details of the Fukushima event are discussed in the paper. These examples demonstrate that safety can be improved just by the application of proven practices which some operators have applied many years before the Fukushima incident. More examples, not only from the Fukushima incident are given in the paper.
The conclusion of all these details is that it is necessary to share and implement best practices in a continuous PLiM process rather than defining new safety requirements after single severe incidents. Nuclear safety primarily does not require new knowledge but to take responsibility and implement measures according to available knowledge. This insight links PLiM to the need for an appropriate safety culture, both of which are prerequisite for nuclear safety.
The motivation for operators to implement these practices is not only to improve safety but to maximize uptime of a plant and deciding for relevant measures which pays back the money invested in the long run.
IAEA Activities on Concrete Ageing in Containment and Other Structures in Nuclear Power Plants
Authors: Kang Ki-Sig , Moore John H. 
Published: January 2014

Significant industry developments over the past decade have placed concrete ageing at the forefront of life extension decisions related to nuclear power plants. Recent issues encountered include alkali–silica reactivity in concrete, delamination events, larger than anticipated loss of pre-stressing force, spent fuel pool leakage, corrosion of steel reinforcement in water intakes, and others.
Concrete structures at nuclear power plants are being asked to perform for longer periods than originally design life. Utilities around the world are investigating plant service life extensions (with 60 years or more total being a quoted target), and for some projects delayed construction schedules, and/or decommissioning strategies that involve the use of containment as a “safe store” for periods of up to 100 years, mean that containment buildings and other concrete structures often have to perform their functions for a time period significantly greater than their initial design life. Newer plants are designed with design lives of 60 years or more.
Concrete is a durable material and its performance as part of the containment function in NPPs has been good. However, experience shows that ageing degradation of concrete structures, often caused or accelerated by factors such as faulty design, use of unsuitable or poor quality materials, improper construction, exposure to aggressive environments, excessive structural loads, and accident conditions, can impair its safety functions and increase risks to public health and safety. Effective ageing management of concrete containment buildings and other concrete structures is therefore required to ensure their fitness-for-service throughout the plant service life and during decommissioning.
The paper presented will present current International Atomic Energy Agency activities in the area of concrete structures and ageing management, and point to where guidelines and best practises related to concrete structure ageing management, relevant operating experience, and applicable codes and standards may be located.
A New Experimental Approach for Measuring Friction Coefficients of Threaded Fasteners Focusing on the Repetition of Tightening Operation and Surface Roughness
Authors: Fukuoka Toshimichi , Nomura Masataka , Kawabayashi Hiromu 
Published: January 2014

Torque method is widely used when tightening threaded fasteners. Although it has a great advantage of easy operation, the scatter of bolt preloads inevitably occurs due to the scatter of friction coefficients. Friction coefficients on the contact surfaces are affected by various factors such as joint materials, surface roughness, tightening speed, etc. To evaluate the effects of those factors with high accuracy, experimental errors must be suppressed as low as possible.
In this study, a new simple test equipment for measuring the friction coefficients is designed, in which the strain gages are attached to the equipment to eliminate the experimental errors caused by the gages being attached to each test specimen. Using the equipment, friction coefficients on the thread surface and nut loaded surface are measured separately. Experimental results show that the surface roughness has a smaller effect when using threaded fasteners made of stainless steel than the case of carbon steel fasteners. As for the repetition of tightening operations, it is found that the removal of metal power, which is generated by the galling between the mating surfaces, is effective for reducing the scatter of friction coefficients.
Analysis of Multi-Axial Fatigue Test Data Using a Path-Dependent Effective Stress/Strain Definition
Authors: Wei Zhigang , Dong Pingsha , Batra Romesh C. , Nikbin Kamran 
Published: January 2014

Multi-axial fatigue life assessment is important in power generation, aerospace, automotive, and many other industries. The newly developed path-dependent multi-axial cycle counting and fatigue life assessment method has been shown effective for some applications. For instance, when stress range is used as the only driving force for fatigue failure, the method correlates high cycle fatigue test data well. The method consists of two parts: (1) maximum-range (or maximum distance) based cycle counting method, so that the method can be applied to 2-D and 3-D stress or strain space, as compared to the conventional rainflow counting method, which is based on the peak-valley concept, therefore, can be applied only to uniaxial (1-D) loadings; and (2) a path-length based stress range is used as the fatigue damage parameter replacing the traditional concept of stress or strain range, which is the difference between the peak value and the valley value of a cycle. This method has been justified using the classical fracture mechanics in multidimensional stress space.
In this paper, we apply the method to analyze two additional classes of multi-axial fatigue test data reported in the literature: (1) low-cycle strain based tests, which has an important implications in high-temperature applications, such as piping/vessels in power industry, turbine, and automotive exhaust systems; (2) a series of test data that require an introduction of two parameters in either fatigue crack growth model or S-N curve based approach. For the latter, an incremental crack growth model reported earlier by the authors is recast to incorporate one additional stress based parameter to account either mean stress or maximum principle stress effects in multi-axial fatigue damage process, dependent upon material characteristics under consideration. The results show that strain-based low-cycle multi-axial fatigue data can be effectively correlated in the form of a single S-N curve using a path-dependent effective strain range definition. Furthermore, a two parameter based interpretation of the crack propagation model is capable of capturing effects of the maximum principle and mean stresses on multi-axial fatigue damage process associated with some of the test data. Finally, the physical basis of the method in these extended applications is discussed.
Design Curve Construction Based on Monte Carlo Simulation
Authors: Wei Zhigang , Luo Limin , Lin Burt , Konson Dmitri , Nikbin Kamran 
Published: January 2014

Good durability/reliability performance of products can be achieved by properly constructing and implementing design curves, which are usually obtained by analyzing test data, such as fatigue S-N data. A good design curve construction approach should consider sample size, failure probability and confidence level, and these features are especially critical when test sample size is small. The authors have developed a design S-N curve construction method based on the tolerance limit concept. However, recent studies have shown that the analytical solutions based on the tolerance limit approach may not be accurate for very small sample size because of the assumptions and approximations introduced to the analytical approach.
In this paper a Monte Carlo simulation approach is used to construct design curves for test data with an assumed underlining normal (or lognormal) distribution. The difference of factor K, which measures the confidence level of the test data, between the analytical solution and the Monte Carlo simulation solutions is compared. Finally, the design curves constructed based on these methods are demonstrated and compared using fatigue S-N data with small sample size.
Evaluation for Nondestructive Crack Sizing Capability on Cracked Surface Treated by Water Jet Peening
Authors: Kimura Ryuji , Yoshikubo Fujio , Ehara Kazuya , Murakami Nobuo , Kanno Akihiro 
Published: January 2014

Water Jet Peening (WJP) is an approved mechanical mitigation technique that has been widely applied in Japanese nuclear power plants since 1999. WJP suppresses stress corrosion cracking (SCC) initiation in SCC susceptible materials which have been widely used in the fabrication of reactor internals [1].
Laboratory data shows that WJP is effective at mitigating or suppressing shallow crack propagation if the post application compression depth layer is deeper than the original crack depth and that WJP has no adverse effect on pre-existing cracks, such as crack propagation or acceleration of the crack propagation during and after WJP [2]. In addition, it has also been reported that WJP has no adverse effect on Ultrasonic testing (UT) sizing capability for pre-existing cracks in 304S.S. and Alloy 182 [3].
Based on these evaluation test results, Hitachi-GE Nuclear Energy, Ltd (HGNE) successfully applied WJP on the cracked surfaces of reactor internals in an operating Japanese nuclear power plant in 2011 [4].
Recently, to evaluate the applicability of this process in a PWR power plant, HGNE has performed an evaluation of Ultrasonic testing (UT) and Eddy Current Testing (ECT) sizing capabilities for surface cracks on a dissimilar metal weld coupon that had been mitigated utilizing the WJP process. No significant differences in their sizing capabilities were observed between the before and after WJP treatment test coupons. During this evaluation, it was also confirmed that surface residual stress on the coupon was improved from tensile to compressive (from max approximately 800MPa to min approximately −600MPa).
As a result of this evaluation, it was determined that WJP has no adverse effect on UT and ECT sizing capabilities. In addition, HGNE has taken this knowledge and applied it to the development of a WJP tool for PWR Bottom Mounted Instrumentation (BMI) nozzles, which accommodates all the parameters used for this testing and enables HGNE to reduce the total application time as a result of the inclusion of advanced technological improvements.
Effect of Hammer Peening Processing on Fatigue Property of Welded Joints After Overload
Authors: Morikage Yasushi , Igi Satoshi , Oi Kenji 
Published: January 2014

One general method for improving the fatigue strength of welded joints is introduction of compressive residual stress by peening. However, there is concern that the fatigue strength of the welded joint may decrease if excessive preloading is applied after peening.
It has been found that fatigue strength decreased after applying compressive preloading to a welded joint due to cancellation of the compressive stress at the weld toe.
In the present research, the influence of excessive preloading on the fatigue strength of welded joints with compressive residual stress at the weld toe was clarified by experiments using hammer peening with an improved pin.
When hammer peening was applied to welded joints, increasing the radius of the weld toe reduced the decrease of compressive residual stress due to excessive preloading. As a result, the decrease of the fatigue strength of the welded joint was also reduced.
Efficient Probabilistic Calculation of a Thermal Transient on a 3D FE Model With Variable Heat Exchange Coefficient
Authors: Demol Thibault , Izard Jean-Pierre , Tartare Nicolas 
Published: January 2014

Probabilistic calculations are often used to evaluate reliability in nuclear industry. One of their main difficulties is that failure probabilities are, in this domain, very low and therefore their computations are very long. The speed of the calculations depends on the probabilistic algorithm and the complexity of the physical problem (usually modeled by a finite element analysis). The optimization of the probabilistic algorithms benefits from a wealth of literature but the physical problem is often very simplified by a lot of approximations. This paper develops a methodology to avoid some approximations. The geometry of the problem is often brought back to a 1D or 2D problem. Here, large 3D mesh can still be used thanks to transfer functions. This requires the linearity of the problem and especially a constant heat transfer coefficient for a thermo-elastic analysis. This limitation has been removed.
This article’s focus is on methodology but qualitative results of a probabilistic brittle fracture application of a reactor pressure vessel (RPV) in ferritic steel are given. Other kinds of analysis can benefit from similar methodology.
Experimental Determination of the Static Equivalent Pressures of Gas Phase Detonations in Pipes and Comparison With Numerical Models
Authors: Schildberg Hans-Peter , Smeulers Jan P. M. , Pape Gersom 
Published: January 2014

In order to determine the effective load of gas phase detonations on pipe walls (“static equivalent pressure”), comprehensive experiments have been conducted in 48.3×2.6 and 114.3×3.6 pipes (outer diameter [mm] × wall thickness [mm]), in which deflagrative explosions of stoichiometric C2H4/O2/N2-mixtures at 20 °C underwent the transition to detonation. Initial pressures were chosen high enough to produce detonation pressures that caused significant bulging of the pipe walls.
All 8 different pressure scenarios that can be distinguished for gas phase detonations in pipes were addressed by the experiments, even the extremely rare case of having the deflagration to detonation transition occurring within about 1 pipe diameter a head of blind flange which yields the largest static equivalent pressure of all scenarios.
By these tests it was possible to (1) validate the predictions of recently developed numerical models for predicting the structural response of the pipe wall and to (2) determine the static equivalent pressure of gas phase detonations in pipes even for those detonative pressure scenarios for which a reliable pressure/space/time profile required as input for the numerical models is at present not yet available. Once the static equivalent pressure is known, the well-established pressure vessel design guidelines, which can only cope with static loads, can be applied for detonation pressure proof pipe design in all those cases where the detonation speed is not close to the propagation speed of the flexural waves in the pipe.
Furthermore, preliminary information was obtained about which of the 8 detonative pressure scenarios only depends on the Chapman-Jouguet pressure ratio of the involved mixture and which scenarios will also depend on other characteristic parameters of the involved mixture (difference between initial temperature and auto ignition temperature, ignition delay time).
System Identification and Reduction of Vibrations of Piping in Different Conditions
Authors: Hinz Gereon , Kerkhof Klaus 
Published: January 2014

Safe operation, availability and lifetime assessment of piping are of utmost concern for plant operators. The knowledge on how failures in piping and its support construction are reflected in changes of the dynamic behavior (eigen-frequencies, -modes and damping) is a useful basis for System Identification and Structural Health Monitoring (SHM). Modal analysis of complex piping, the identification of system changes and the use of vibration dampers in piping still constitute challenges. In this study three different piping systems are investigated:
1. In the first piping system at a chemical plant, which is supported by a tall steel structure fixed at the base, piping-elbow forces at the top of the building cause large vibration amplitudes. Tuned mass dampers (TMD) for minimizing vibration amplitudes were first tested in the laboratory of MPA Stuttgart and then designed for the piping system in the plant for preventing failures.
2. Another piping system is reported that is excited at resonance frequency to cause failure due to in-plane bending in an elbow with local wall thinning.
3. Finally, a large piping system at a lignite power plant is investigated under ambient vibration to detect changes in boundary conditions.
Experimental Output Only Modal Analysis (OOMA) and Operational Modal Analysis (OMA), FE-model studies and model-updating are performed. Changes in the natural frequencies and corresponding mode shapes due to through-wall cracks or changing boundary conditions were observed.