bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculation of KJ Under Secondary Loads in Isolation for R6
Authors: James Peter 
Published: November 2015

A range of methods are currently available within R6 to calculate the inelastic secondary stress intensity factor under secondary loads in isolation, KJS. Each of these methods has different levels of associated conservatism depending on assumptions made, the complexity of the approach and the ability to account for different levels of elastic follow-up. Approaches that include an elastic follow-up factor, Z, for treating the interaction of combined primary and secondary stresses have recently been investigated by Ainsworth and James. However, the maturity of this recent work under combined primary and secondary loading means that one of the most significant aspect of the conservatisms in calculating the combined elastic-plastic stress intensity factor, KJ, is now in the calculation of KJS. This work considers existing approaches in R6 to calculate KJS and proposes a further approach allowing the value of Z to be altered.
For comparison this work considers finite element analyses of a circumferentially cracked cylinder with four thermal distributions and two shallow cracks. These conditions were controlled to manipulate the level of Z. The magnitude of the temperature difference in these profiles has been increased over the analysis time to provide a relationship between the elastic and inelastic secondary stress intensity factors, KIS and KJS, with increasing secondary load to demonstrate any enhancement and subsequent redistribution of the secondary stress. These finite element estimates have been compared to existing methods in R6 to calculate KJS/KIS which reinforce the available advice in R6 for each case. The proposed approach also compares favourably with the finite element results through modification of Z. The proposed approach is also seen to be compatible with the other approaches within R6 as it has been shown to reproduce the Option 2 failure assessment curve for cases where the elastic follow-up is significant (i.e. Z ≫ 5) and conforms to the displacement controlled estimate of KJS in Section III.14.5 of R6.
Identification of Failure Modes Under Design Extension Conditions
Authors: Kasahara Naoto , Nakamura Izumi , Machida Hideo , Nakamura Hitoshi , Okamoto Koji 
Published: November 2015

As the important lessons learned from the Fukushima-nuclear power plant accident, mitigation of failure consequences and prevention of catastrophic failure became essential against severe accident and excessive earthquake conditions. To improve mitigation measures and accident management, clarification of failure behaviors with locations is premise under design extension conditions such as severe accidents and earthquakes. Design extension conditions induce some different failure modes from design conditions. Furthermore, best estimation for these failure modes are required for preparing countermeasures and management. Therefore, this study focused on identification of failure modes under design extension conditions. To observe ultimate failure behaviors of structures under extreme loadings, new experimental techniques were adopted with simulation materials such as lead and lead-antimony alloy, which has very small yield stress.
Postulated failure modes of main components under design extension conditions were investigated according three categories of loading modes.
The first loading mode is high temperature and internal pressure. Under this mode, ductile fracture and local failure were investigated. At the structural discontinuities, local failure may become dominant.
The second is high temperature and external pressure loading mode. Buckling and fracture were investigated. Buckling occurs however hardly break without additional loads or constraints.
The last loading is excessive earthquake. Ratchet deformation, collapse, and fatigue were investigated. Among them, low-cycle fatigue is dominant.
Fluid-Elastic Instabilities of Clamped-Clamped Aligned and Inclined Cylinders in Turbulent Axial Flow
Authors: De Ridder Jeroen , Degroote Joris , Doaré Olivier 
Published: November 2015

Fluid-elastic instabilities arise due to the coupling of structural motion and fluid flow. In the specific case of a clamped-clamped cylinder in axial flow, it will buckle at a sufficiently high flow velocity and start to flutter at even higher flow velocities. This dynamic behavior is of importance to nuclear reactor core design, undersea pipe lines and devices for energy harvesting. In this contribution, the fluid forces and the dynamics of a flexible clamped-clamped cylinder in turbulent axial flow are computed numerically. In contrast to present analytical approaches, this numerical model does not require to tune parameters for each specific case or to obtain coefficients from experiments.
To provide insight in the way viscous fluid forces affect the dynamics of a cylinder in axial flow, fluid forces are computed on rigid inclined cylinders, mimicking the damping force experienced by the same cylinder moving perpendicular to the axial flow. The computations showed the existence of two different flow regimes. Each regime gave rise to a different lift force behavior, which will also influence the damping of the coupled system. Furthermore it is shown that the inlet turbulence has a non-negligible effect on these forces and thus on the dynamics of the cylinder.
Next, the dynamics of a flexible cylinder clamped at both ends in axial water flow are computed by means of a methodology developed earlier. The results are successfully compared with dynamics measured in experiments available in literature. Computationally it was found that the cylinders natural frequency decreases with increasing flow velocity, until it loses stability by buckling. The threshold for buckling is in quantitative agreement with experimental results and weakly nonlinear theory. Above this threshold, the amplitude of the steady deformation increases with increasing flow speed. Eventually, a fluttering motion is predicted, in agreement with experimental results. It is also shown that even a small misalignment (1°–2°) between the flow and the structure can have a significant impact on the coupled dynamics.
Semi-Closed-Form Displacement Equations for Calculating J-R Curves From Pipe Fracture Experiments
Authors: Olson Richard , Thornton Ben 
Published: November 2015

The equations to generate a J-R curve from a four-point bend test on circumferentially cracked pipe have been known for many years. Given the experimental pipe load-displacement record and crack growth, the only impediment to routinely calculating pipe J-R curves is the requirement to know the non-cracked pipe elastic and plastic displacements. Traditionally, finite element analyses are used to find these displacements. This paper presents a semi-closed-form solution for the total (elastic plus plastic) non-cracked pipe displacements that eliminates the need to perform finite element analyses to calculate a pipe J-R curve.
Using a Ramberg-Osgood nonlinear representation of the stress-strain curve and the assumption that plane sections remain plane, beam bending equations can be written to find nonlinear beam displacements for pipe bend geometries with a base metal crack. Building on this result, the solution is extended to the dissimilar metal weld (DMW) case with five nonlinear materials.
The non-cracked pipe displacement solutions are presented as well as comparisons using these equations between compact tension specimen J-R toughness curves and J-R curves from pipe experiments.
High Temperature Fatigue of Welded Joints: Experimental Investigation and Local Analysis of Butt Welded Flat and Cruciform Specimens
Authors: Langschwager Kay , Rudolph Jürgen , Scholz Alfred , Oechsner Matthias 
Published: November 2015

Austenitic stainless steel of type X6CrNiNb18-10 exhibits advantageous mechanical and chemical properties and is a common material for numerous applications in the nuclear power plant and chemical industries. Besides the mechanical strain induced by high pressure, the fatigue life in welded pipelines is affected by additional thermomechanical strains due to thermal loading. The welding process mainly determines the geometry and metallurgical constitution of the welded joint. Therefore, the butt welds additionally influence the strain gradient along the component and reduce its lifetime.
While the base and weld material are similar, they show different softening and hardening behavior, especially at ambient temperature. Cyclic hardening occurs in the base material, whereas cyclic softening can be observed in the weld material. The hardness distribution along the welded joint reveals no clear differentiation of base material, the heat affected zone and weld material. The attributes of the individual materials cannot be transferred to the welded joint automatically. Thus, the analysis of the interaction between the materials along the welded joint is a main topic of this research. To this end, digital image correlation is used for different kinds of specimens and load conditions. The position along the testing area at which fatigue failure occurs depends on the specimen type and the load condition but not on the temperature. Further, isothermal and anisothermal fatigue tests on welded cruciform specimens are presented. The common practice of the effective strain is discussed for the analyzed conditions.
Application of the Structural Reliability Methods for Justification of Pressure Reduction of Periodic Hydrostatic Test for Primary Circuit of NPP WWER-1000
Authors: Orynyak Igor , Kozlov Volodymyr , Borodii Mykhaylo , Zarazovskii Maksym 
Published: November 2015

An analysis is formulated to determine how reductions in test pressures change the effectiveness of hydraulic strength tests (HT). The analysis is applied to Series 1000 Water-Water Energetic Reactor (WWER-1000) nuclear power plants (NPP) operating in countries of the former Soviet Union. During periodic HT for these reactors, the applied pressure exceeds the pressure for the normal operation mode (NOM) by a factor of more than 1.5. These HT pressures are among the highest in the nuclear industry. It is desirable to reduce the HT pressure in order to minimize potential damage to equipment due to pressurization during the tests.
To justify a reduction in the HT pressure, a quantitative, risk-informed assessment of HT effectiveness for changes in HT pressures has been performed. This assessment follows the guidelines of INSAG-25 [1]. A deterministic analysis is used to calculate the HT minimum temperature, based on the estimation of the damage caused by HT and the evaluation of the warm prestressing effect. A probabilistic analysis is used to estimate the change in the probability of equipment fracture caused by a reduction in the HT pressure. The probabilistic analysis assumes that HT is performed as a destructive control method for replaceable components, so that HT combined with replacement or repair of defective components increases their reliability.
A simple probabilistic analysis method, based on an exponent distribution law for defect depth and a lognormal law for the defect aspect ratio, taking into account laws for defect growth, has been proposed. The fracture probability is calculated as the proportion of defects that exceed critical sizes for NOM and HT. Limit load models are used for the determination of the critical size of defects. The variation in reliability is calculated as the difference between fracture probability during NOM after HT at routine and reduced pressures. The calculation results make it possible to analyze the effect of HT pressure reduction for WWER-1000 NPPs.
Building the Technical Case for Long-Term Operation
Authors: Tilley Richard , Dyle Robin 
Published: November 2015

United States (US) and International utilities are actively engaged in assessing the economic and societal benefits of operating nuclear plants beyond their initial license periods. Nuclear plant generated electricity is still the largest contributor to non-carbon dioxide emitting generation. In the US, a majority of operating plants has already received approval for an additional 20 years of operation, and soon it is expected that utilities will begin the process to seek a second 20 year renewal. The keys to successful renewal are to maintain safe and reliable operations by building a sound technical case through the following activities:
• Develop comprehensive understanding of aging degradation issues for systems, structures and components (SSCs)
• Implement specific plant aging management programs to address aging degradation
• Confirm behavior of degradation mechanisms for the entire period of operation
This paper will step through the above elements to illustrate how a strong technical case may be created for safe and reliable long-term operation. Examples or case studies will be provided to clearly link the fundamental science of materials degradation to the inspection, testing and evaluation efforts implemented at a plant and to the confirmatory data that is provided by both actual operating experience and the extensive research and development projects pursued by industry, governments, and the academic community.
Push Probe Method for Installing Corrosion Smart Monitoring Test Stations and Collecting Soil Samples on In-Service Pipelines at Depths Up to Forty Feet at Nuclear Power Plants
Authors: Lupia Greg , Darois Matt , Kleinfelder Hank 
Published: November 2015

Innovative Method for Installing Pipe Depth Smart Test Stations at Exelon Nuclear Generation Stations to Quantify Corrosion Rates, Evaluate Cathodic Protection Effectiveness, Quantify Corrosion Potentials and Perform Subsurface Soils Analysis to Support Aging Management Plans and Reasonable Assurance Commitments on In-Service Buried and Underground Pipe and Tanks
For several decades ANSI and NACE direct assessment (DA) standards for monitoring cathodic protection and coating quality (SP0502) have been relied upon by pipeline operators and regulators to accurately monitor the impact of corrosion on transmission pipelines. These same standards have been proven far less useful when deployed in nuclear power plant subsurface environments.
In order to meet regulatory and industry commitments the challenge has been to develop a cost effective method to accurately monitor nuclear plants’ buried pipe. The in-scope pipe is comprised of a dense complex of multiple systems in close proximity at depths sometimes exceeding 30-ft. Most nuclear plants have been in service for over 30 years and rely on original buried pipe systems to perform as designed. These systems are manufactured using various metals, which are bonded together to reduce electrical step and touch potential hazards. Each of these factors reduce the confidence factor of DA, but combined they make the procedure even less effective.
Smart Monitoring Test Stations can be installed without excavation at depths of up to forty feet directly into the subject pipeline local environment. This provides access to critical condition and assessment information that was previously unavailable. Smart test stations have been designed with the following components: two Electrical Resistance Probes (ER), two CP coupons and a stationary reference electrode.
This paper will describe the planning and obstacles encountered during the installation, operation and interpretation of data from recent experiences related to the installation of test stations at Exelon Nuclear Generating Stations. We will describe the process from planning to successful completion including:
• Smart Monitoring Test Station features and function
• Value of precise location insertion of probes
• Digitizing plant buried and underground pipe and tanks
• Smart monitoring test station site location selection
• Push probe method to capture soil samples
• Analyzing and interpreting soil samples
• Evaluating potential impacts from groundwater
• Push probe method of installing smart test stations at or near pipe depth
• Monitoring data from test stations
• Application of information to support AMP and NEI commitments
Study on LTA Measurement for FFS Assessment
Authors: Tahara Takayasu , Kaida Takuyo , Niimura Minoru , Sakai Shinsuke 
Published: November 2015

FFS assessment technologies for pressure equipment have been studied and standardized in recent 15 years in Japan. FFS assessment of local thin area, LTA, is the most frequently used in process industries. However reliability of thickness measurement of LTA and influence to FFS assessment has not been studied much in the past.
Uncertainty of thickness measurements and Remaining Strength Factor, RSF, were investigated on Round Robin Testing using manual UT and additional new technology such as flexi-alley UT and 3D LED system for LTA in pipes, It is recommended to use suitable combination of Manual or mechanized UT and 3D LTA measurement system in case of assessment of critical flaws and decision making for repair and replacement of pressure equipment.
Low-Velocity Impact Analysis of a Stiffened Composite Panel
Authors: Akula Venkata M. K. 
Published: November 2015

The layered architecture of composite material allows for designing light-weight structural components. However, one of the challenges associated with composite structures is design and analysis considering impact damage. Although the damage associated with high-velocity impact events is often readily observed in a structure, by loss of material, for example, low-velocity impact damage is not always visible. However, low-velocity impact damage can undermine the strength capacity of a composite component. To ensure the structural integrity of components, predicting the residual strength after impact damage is critical.
In this paper, a methodology for analysis of low-velocity impact on a curved composite panel is discussed. First, impact analysis of the panel utilizing Abaqus\Explicit is presented. A metallic projectile is utilized to simulate a tool drop event. Thereafter, a simulation technique for predicting the residual strength of the panel is discussed. The residual strength is measured in terms of collapse load when the panel is subjected to axial compression. Finally, parameter sensitivity analysis is performed to understand the influence of the various design parameters on the residual strength of the component after impact. This procedure requires automating the entire simulation workflow. The results of the simulation are presented along with the important observations.
An Analytical Interpretation of Welding Linear Heat Input for 2D Residual Stress Models
Authors: Song Shaopin , Pei Xianjun , Dong Pingsha 
Published: November 2015

Welding residual stress simulation using finite element analysis has become increasingly common in supporting fitness-for-service assessment. Two dimensional (2D) cross-section models, such as using generalized plane strain assumptions for linear welds in plate structures and axisymmetric assumptions for piping and vessel girth welds are typically used due to their computational efficiency and simplicity in data reduction process, especially for performing a large amount of parametric analyses. However, there seem no consistent procedures in place for translating actual weld linear heat input used in practice to a 2D cross-section model in which heat loss in welding travel direction is unaccounted for, often resulting in overheating to a significant degree if actual welding heat input is used.
This paper starts with the introduction of a two-part analytical linear heat input representation for a simplified 2D weld residual stress modeling procedure in which weld metal is deposited at a preset temperature such as melting with a hold time. The first part is based on a simple thermodynamics concept, which describes the heat required for elevating a weld pass from room temperature to deposition temperature. The second part is based on an equivalent transient heat transfer solution that measures the amount of heat needed to sustain deposit temperature during hold time. With this proposed method, linear heat input involved in a 2D residual stress model can be inferred for relating to actual welding conditions, typically specified in terms of current, voltage, and welding speed. By the same token, for a given set of welding parameters, welding heat flow modeling procedure involved in a 2D FE residual stress model can be consistently defined in terms of deposit temperature and hold time. A number of validation case studies are presented and the results have showed that the proposed procedure provides an effective means for inter-relating actual welding linear heat input and heat content associated with 2D residual stress models.
Remaining Fatigue Life Time Assessment of Welded and Braced Side Branches
Authors: Pereboom Hajo , Pijpers Richard , van Beek Pieter , Macdonald Kenneth 
Published: November 2015

High cycle fatigue failure is likely to occur when a rather undamped offshore installation is operated over a long period of time. Especially welded parts are vulnerable to fluctuating stress ranges, if the structural components, such as the small bore side branches, are loaded in resonance. In particular, the welded connections at e.g. tie-in points can be critical. Therefore, it is important to know what the current status of existing welded connections is and how long they can still be operated at any specific operating condition without failure.
This paper describes an advanced fatigue assessment method to determine the cumulative damage in the critical parts of the system. The method is developed for industrial applications where the available information is limited. The method comprises of a mechanical analysis and a fatigue assessment based on a fracture mechanics crack growth model. The method enables determination of inspection intervals and at the same time layout optimization for a long term safe operation. This paper pays special attention to complex, braced small bore side branches. Standard fatigue stress assessment methods can be conservative for the fatigue assessment of high frequent stress ranges with relatively low stress ranges. The current paper shows the effect of the fracture mechanics procedure for an example of a braced side branch connected to the main piping: both a fracture mechanics model and a detailed 3D FE model are made. With these models, the hot spot stress in the welds is evaluated and tailor-made S-N-curves are derived. With information of the operating history, the cumulative damage is determined for the weld detail. This knowledge on the current damage status is crucial for future operations.
Benchmark for the Calculation of Quasi-Laminar Elliptical Cracks Interaction Under Bi-Axial Loading
Authors: Dulieu Pierre , Lacroix Valéry , Shim Do Jun , Brust Frederick (Bud) 
Published: November 2015

In the frame of the Structural Integrity demonstration of the Doel 3 and Tihange 2 RPVs flawed with quasi-laminar cracks, alternative proximity rules based on 3D eXtended Finite Element Method (X-FEM) calculations have been developed by Tractebel Engineering. The calculations have been performed with the X-FEM software Morfeo Crack. This software uses the Level-Sets method allowing a very straightforward cracks modelling.
A large part of the development of these proximity rules for quasi-laminar flaws has been dedicated to the validation of the models and the calculations. This validation has been done through a benchmark with Engineering Mechanics Corporation of Columbus (Emc2). This company uses:
• The Finite Element Alternating Method (FEAM) for calculating stress intensity factors through the FRAC@ALT program. The FEAM is a state-of-the-art method for obtaining stress intensity factors for three-dimensional surface and embedded crack problems.
• The X-FEM functionality as implemented in Abaqus software.
The benchmark consists of the Stress Intensity Factor calculation of interacting quasi-laminar flaws and of the interaction factor assessment as well.