bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stress Intensification Factors for Fabricated Lateral Piping Connections
Authors: Mair David 
Published: January 2014

Stress intensification factors (SIFs) are published in the piping codes for tees; branch connections where the branch intersects the header pipe at 90 degrees. These factors when multiplied by the nominal stress provide a measure of the increased local stresses at the junction of the two pipes. However, in cases where the branch pipe meets the header at an angle of other than 90 degrees, the main piping codes do not provide a method of calculating the SIFs. This presents a difficulty for the pipe stress engineer who must determine appropriate SIFs, usually in a conservative way and then manually enter these into the pipe stressing program.
This paper summarizes some of the published methods of calculating SIFs for a limited range of lateral branch connections and makes recommendations based on comparisons with FEA studies. It also includes recommendations on how such FEA studies should be applied in order to provide suitable SIF values.
A Parametric Study Into the Competing Effects of Stress and Strain Rate in Environmental Fatigue Usage Calculations
Authors: Emslie Julian , Watson Chris 
Published: January 2014

Data have emerged that indicate a Pressurised Water Reactor (PWR) environment can have a significant detrimental effect on the fatigue life of plant materials. Proposed methods for accounting for the PWR environment in an ASME III fatigue assessment are presented in ASME Code Case N-792 and NUREG/CR-6909, both of which use a fatigue penalty factor (Fen) approach that directly multiplies the Partial Usage Factor (PUF). Formulae are provided for the Fen factor which are dependent on strain rate, temperature and the dissolved oxygen content of the water. A slower strain rate provides for increased Fen values and therefore increased PUFs.
In stress analysis, defining the ramp of a thermal transient as a step change is pessimistic for thermal stress calculations. The dependence of the Fen factor on strain rate means that this approach may not be conservative when the stresses are carried through to a PWR environment enhanced ASME III fatigue calculation. An increased ramp time gives a lower stress, however this also provides for a slower strain rate, and therefore a larger Fen factor.
By a series of parametric studies using simple austenitic stainless steel 2D axisymmetric cylinder FE models, this paper examines the competing effects of reduced stress and increased Fen that an increased transient ramp time has upon a PWR environment enhanced ASME III calculated fatigue usage factor for stainless steel components.
It was found for thin walled sections that the assumption of a step to define the thermal transient is still pessimistic despite the competing effects. For thicker sections the results showed that this is not always the case, but the potential increase in PUF was found to be minimal.
Improvement of Jet Pump Inlet Mixer in Boiling Water Reactor for Mitigating Flow-Induced Vibration and Fouling
Authors: Watanabe Masanobu , Sayano Akio , Kinugasa Kunihiko , Mori Hajime , Hagiwara Tsuyoshi 
Published: January 2014

Jet pumps in Boiling Water Reactor (BWR) have risk of damages by Flow-Induced Vibration (FIV) for when increasing the core flow rate for power uprating. Especially, the vibration by leakage flow at the slip joint between an inlet mixer and a diffuser can cause serious damage on jet pumps. It is one of the obstructive factors for power uprating. Another problem is crud deposition on the inside surface of the inlet mixer and nozzle. Thus fouling causes performance degradation of jet pumps.
To reduce the risk of an FIV problem, the gap flow passage of the slip joint was modified based on the leakage-flow-induced vibration theory. The effect and characteristic of vibration suppression for the improved design was confirmed by fundamental tests that simulated the slip joint configuration. To mitigate crud deposition, a sol-gel ceramic coating process using ZrTiO4, which generates electrostatic repulsion force to crud, was developed. The effect of the coating was confirmed by experiments using test pieces. These techniques for mitigating damage due to FIV and fouling were applied to inlet mixers of jet pumps for replacement in the actual BWR plant.
Automatic Fatigue Monitoring Based on Real Loads and Consideration of EAF: Live Demonstration
Authors: Bergholz Steffen , Jouan Benoit , Rudolph Jürgen , Heinz Benedikt 
Published: January 2014

The fatigue assessment of power plant components based on local fatigue monitoring approaches is an essential part of the integrity concept and modern lifetime management. An integral approach like the AREVA Fatigue Concept (AFC) basically consists of two essential modules: realistic determination of occurring operational thermal loads by means of a high end fatigue monitoring system and related highly qualified fatigue assessment methods and tools. The fatigue monitoring system delivers continuously realistic load data at the fatigue relevant locations. Consequently, realistic operational load sequences are available as input data for all ensuing fatigue analyses. This way, realistic load data are available and qualified fatigue usage factors can be determined.
The mode of operation of the fatigue monitoring system will be explained in the framework of a live demonstration by means of the FAMOSi (i = integrated) demonstration wall. The workflow starts with the continuous online measurement of outer wall temperatures transients on a pipe. Visualization is implemented within the FAMOSi viewer software. In a second step, inner wall temperatures are directly calculated. In a third step, the resulting linearly elastic stress history will be calculated as the basis for subsequent code conforming fatigue assessment.
Subsequently, the related advanced fatigue assessment methods of the three staged AFC-approach are addressed.
Analysis of Corrosion Areas in Pipelines Using Guided Wave Propagation: Numerical Simulations and Experimental Tests
Authors: Turcu Florin , Bertoncini Francesco , Giunta Giuseppe , Raugi Marco 
Published: January 2014

Guided Waves (GW) have become widely used for the inspection of unpiggable and inaccessible pipelines because of the presence of coating, because of their position or because they are buried.
Among the possible anomalies, corrosion is the main integrity issue affecting pipelines. The effect that corrosion has on guided wave propagation is attenuation and increased coherent noise when it is generalized or reflection when corrosion is localized.
In this paper, the possibility to characterize corrosion areas affecting pipelines through long range guided wave inspection or monitoring is investigated. With this purpose field testing was performed and the results were used for the validation of numerical methods able to simulate the phenomenon.
Crack Growth Behavior and Preventive Maintenance for Reactor Internals With Cracks in Tokai-2 Nuclear Power Plant
Authors: Fujino Takushi , Terakado Takeshi , Dozaki Koji , Ito Nobuo , Hasegawa Kunihiro 
Published: January 2014

Three cracks assumed to be caused by Stress Corrosion Cracking (SCC) were detected on shroud support of Tokai Daini Nuclear Power Plant (Tokai-2) in 2005. Additional inspections were performed in 2009 and 2011, and additional initiation and propagation of cracks were observed on core shroud and shroud support. Flaw evaluation was performed at each time. The results showed that these structures were allowed to use without repair.
There has been a few inspection experiences in Japan, of successive SCC behavior in operating plants. In this paper, the change of crack shape and crack growth rate (CGR) was investigated. The result showed that cracks tend to change its shape as they grow and crack growth rate in an operating plant was below the crack growth disposition line of Japan Society of Mechanical Engineers (JSME) Code.
Water Jet Peening for core shroud with cracks was performed in 2011 and Noble Metal Chemical Addition is planned in next cycle to mitigate crack initiation and growth. These preventive maintenances are effective also in cracked surface. It is important to confirm that crack behavior and effect of preventive maintenances in successive inspections.
Sophisticated Procedures for Fatigue Evaluation in the Framework of German KTA Codes
Authors: Seichter Johannes , Reese Sven H. , Klucke Dietmar 
Published: January 2014

German KTA consider the intensively discussed topic of environmentally assisted fatigue (EAF) by introducing so called attention thresholds for the cumulative fatigue usage factors (CUF). Threshold values for both austenitic steels and ferritic steels are defined. If the threshold value is exceeded, further measures like NDT, in-service inspections or detailed assessment procedures have to be performed. One way to handle those measures is to apply sophisticated procedures and to show that the numerically calculated CUF is below the defined attention thresholds. The article presents some examples to reduce calculated CUFs.
Fatigue analyses performed during design phase of NPP are based on specified loads consisting of conservatively determined reference transients, covering the whole lifetime including events with significantly fewer cycles than assumed during design phase as well as events with very low probability of occurrence at all. But there might be also operational loads which are not included in the load specifications. In general, there is a lot of potential to reduce computed CUFs in terms of considering realistic loading scenarios.
In German NPPs various temperature measurement planes are applied at fatigue relevant positions among others to calculate actual CUFs based on real loads. Detailed finite element (FE) calculations considering these loads can reduce computed CUFs considerably. Therefore detailed evaluation of temperature measurements in combination with FE calculations is carried out, reducing calculated CUFs below the threshold values given in German KTA.
Response Analysis of a Seismic Isolated Structure Considering the Nonlinearity of the Rubber Bearings
Authors: Borsoi Alexandre , Fujita Satoshi , Minagawa Keisuke 
Published: January 2014

In Japan, the application of seismic isolation systems using rubber bearings to industrial structure and new generation Nuclear Power Plants have been considered in order to enhance seismic safety. However, the isolation performance will decline in case of huge earthquakes, because of the nonlinearity of both horizontal and vertical restoring characteristics of the rubber bearings. The horizontal restoring force has a hardening characteristic and the vertical restoring force has a softening characteristic. In addition, the horizontal nonlinearity depends on vertical load, so the interaction between the horizontal and vertical response is important. Consequently, in this paper, the analysis of the nonlinearity of the rubber bearings and the coupling between those two directions will be carried out. Then, after comparing these two approaches, the utility of considering this dependency will be estimated.
To do so, a simulation program, based on the Runge-Kutta-Gill’s method has been developed in order to evaluate the seismic response of the isolated structure composed of rubber bearings and oil dampers. The nonlinearity of the rubber bearings is considered, and the coupling of the vertical load and the horizontal hardening has been implemented.
Influence of a Variable in Time Heat Transfer Coefficient on Stresses in Model of Power Plant Components
Authors: Okrajni Jerzy , Twardawa Mariusz 
Published: January 2014

The paper discusses the issue of modelling of strains and stresses resulting from heating and cooling processes of components in power plants. The main purpose of the work is to determine the mechanical behaviour of power plant components operating under mechanical and thermal loading. Finite element method (FEM) has been used to evaluate the temperature and stresses changes in components as a function of time.
Temperature fields in the components of power plants are dependent, among parameters, on variable heat-transfer conditions between components and the fluid medium, which may change its condition, flowing inside them. For this reason, evaluation of the temperature field and the consequent stress fields requires the use of heat-transfer coefficients as time-dependent variables and techniques for determining appropriate values for these coefficients should be used. The methodology of combining computer modelling of the temperature fields with its measurements performed at selected points of the pipelines may be used in this case. The graphs of stress changes as a function of time have been determined for the chosen plant components. The influence of the heat transfer conditions on the temperature fields and mechanical behaviour of components have been discussed.
Impact of Non-Uniform Temperature on Flange Leak Tightness
Authors: Jung Gong H. , Kim Minsu , Gage Eric 
Published: January 2014

It is critical to maintain uniformity of gasket stress in control against leakage in piping and heat exchangers. Many innovative bolting tools have been developed, but their benefit could be downgraded if there were sources disrupting initially achieved uniformity of gasket stress, especially temperature differences in mating flanges and non-axisymmetric temperature. It is thus necessary to understand behaviors of flanges and gaskets with non-uniform temperature distribution.
The impact of temperature differences in mating flanges with various types of gaskets on leak tightness was evaluated by lab tests. Based on test results, 250°F was proposed as a tentative allowable skin temperature difference of mating flanges in heat exchangers.
The characteristics of gasket stress behaviors with non-axisymmetric temperature distribution were studied using analytical solution and finite element analysis. It was found that change of gasket stress is independent of the magnitude of initial bolt stress, and initial bolt stress of 50 ksi is sufficient to protect all evaluated flanges against leakage under evaluated non-axisymmetric temperature distributions.
Reliability Analysis of Spring Operated Pressure Relief Valve
Authors: Bao Shiyi , Li Zhibin , Luo Lijia , Gao Zengliang 
Published: January 2014

Pressure relief valve (PRV) is an important automatic overpressure protection system in the process industry. Because of the operating characteristics, the performance of PRV is supposed to be proved by the proof test. However, it’s difficult to determine the proof test intervals and the availability of the PRV between two proof tests. Based on stochastic Petri nets (SPN), the reliability modeling and analysis procedure of spring operated full lift pressure relief valve which is the most widely used PRV is depicted in this paper.
Firstly, the FMECA method is used to analyze the causes and effects of the typical six failure modes of the PRV, such as vibration, leakage, frequency hopping, unable to open, open before the settings and the low back seat pressure. Second, the corresponding fault tree (FT) models of the PRV are built through the multi-component failure analysis. Third, the SPN models of the PRV are established by employing the logical relations in the FT models. Based on the collected failure data of the PRVs, the steady state and transient reliability index are calculated by Monte Carlo simulation based on the SPN software SPN@. Last, the idea about PRV reliability data collection in domestic process industries is proposed.
The result of the reliability analysis can provide the basis for determination the proof test intervals of the PRV, and the proposed procedure also bears significance in its application in the reliability analysis of general system in process industry.
Design and Performance of Valves for Compressors in LDPE Plants
Authors: Giacomelli Enzo , Schiavone Massimo , Manfrone Fabio , Raggi Andrea 
Published: January 2014

For the production of LDPE the reaction pressures are reached by Hyper-compressors, while Booster and Primary help to attain the recycle circuit pressure. These are complex machines, because of the need of wide operating ranges, due to the different products and conditions often required by the process.
Developments on electro-mechanical actuators give further opportunities on capacity control, being able to reach extended efficient and safe running conditions.
The cylinder valves, as critical parts, need a careful design and technology selection that will be important for adequate operation, with targets of Performance, Reliability, but considering safety as a priority.
High valve efficiency is obtained by the use of methodologies able to optimize the geometry and fluid-dynamic aspects, positively affecting the life and energy consumption.
The operating results (energy consumption and mechanical behavior) are achieved by proper simulation using advanced mathematical models optimizing the performance and ensuring reliable operation.
Valve type selection, (ring, plate, poppet etc), can influence performance significantly depending on final pressure, oil characteristics, quantity etc. Metallic poppet valves represent for the Hypers the most reliable solution.
In order to have theoretical results closer and closer to real conditions, a combination of CFD and 3D dynamic shutter analysis including valve pocket features, increases the simulation accuracy.
In addition to that, the manufacturing valve part quality process is decisive for a long operating life, supported by adequate reconditioning procedure during the maintenance.
Creep Deformation Parameters and Creep Life of Gr.91
Authors: Abe Fujio 
Published: January 2014

The correlation between the creep deformation parameters and creep life has been investigated for Gr.91 by analyzing creep strain data at 450 to 725 °C, 40 to 450 MPa and tr = 11.4 to 68,755 h in the NIMS Creep Data Sheet. The creep life tr is correlated with the time to minimum creep rate tm as
t r = 3.7 t m .
Taking the stress dependence of tm / tr into account, the creep life could be predicted more reliably. The minimum creep rate ε̇min depends on both the tm and the strain to minimum creep rate εm as
ε . min = 0.54 ε m / t m .
The εm is evaluated to be 0.02 to 0.03 at high stresses at each temperature but it decreases with decreasing stress at temperatures above 550 °C, suggesting that the creep deformation in the transient region becomes more inhomogeneous with decreasing stress probably due to localized creep deformation within 1 μm in the vicinity of prior austenite grain boundaries. The downward deviation takes place in the the tr versus ε̇min curves (Monkman-Grant plot). At the same ε̇min, both the εm and tm change upon the condition of tm ∝ εm as can be seen from the above equation. The decrease in εm with decreasing stress, corresponding to decreasing ε̇min, causes a decrease in tm, indicating the downward deviation of the tr versus ε̇min curves.
Comparison of PTS Guides for Reactor Pressure Vessel Integrity Assessment
Authors: Brumovsky Milan 
Published: January 2014

Integrity of reactor pressure vessels (RPV) are of the most importance for safety of the whole NPP. From all potential regimes, Pressurized Thermal Shock (PTS) regimes during emergency cooling conditions are the most severe and most important.
Several nuclear codes are based in similar approaches but their procedures differ and are based on national knowledge and approach to fracture mechanics as well as non-destructive methods of reactor pressure vessel testing.
The paper will compare requirements and procedures for PTS evaluation in accordance with RCC-M code in France [2], KTA in Germany [3], Russian original code PNAEG from 1989 [5] and new procedure from 2004 for WWER vessels [4], as well as VERLIFE procedure and IAEA-NULIFE VERLIFE [6] procedure for WWER RPVs and finally ASME Code requirements [1] including US NRC RG approach.
Detailed comparison of individual parameters in calculations are compared — material properties, degradation of materials, calculated defects size and form, fracture mechanics approach, warm pre-stressing possibility etc.
Crack Growth Behavior of Ferritic Pressure Vessel Steels in Oxygenated High Temperature Water Under Transient Loadings
Authors: Herter Karl-Heinz , Schuler Xaver , Weissenberg Thomas 
Published: January 2014

The assessment of the influence of the LWR coolant environment and postulated chloride transients on the crack growth is of importance for ageing management with regard to safety and reliability. Aim of the investigations was to determine cyclic crack growth rates at LWR conditions and to study possible size effects and the impact of chlorides on environmentally assisted cracking.
Crack growth experiments were performed with fracture mechanics specimens of different size in simulated BWR water of high purity and under the effect of chloride transients with RPV steel 22NiMoCr3-7.
Subsequent to a phase of cyclic loading, the specimens were exposed to static load, interrupted by partial unloadings.
All cyclic crack growth rates da/dN vs. ΔK in high purity water were in good agreement with ASME XI water curves.
No significant influence of specimen size on the crack growth behavior and with regard to SCC could be detected in high purity water environment. Cyclic induced crack propagation immediately stopped when turning to static load. Under static load the chloride transients did not cause crack initiation by SCC.
Load transients in chloride containing environment initiated significant SCC-induced crack growth. A “chloride memory effect” with regard to a preceding chloride transient at static load, leading to SCC-induced crack propagation during subsequent load transients in high purity water environment did not arise.
Loading Conditions Likely to Modify the Benefits of the Warm Pre Stressing Effect
Authors: Jacquemoud C. , Nédélec M. 
Published: January 2014

The benefits of the warm pre-stressing effect have already been demonstrated in some favorable situations such as idealized loading transients: Load-Cool-Fracture (LCF) or Load-Cool-Transient-Fracture (LCTF). This study, sponsored by the IRSN, focuses on the identification of parameters able to reduce significantly or cancel the positive effect of a warm preload on these favourable loading transients LCF, LCTF and LUCF.
Using a finite element analysis together with the Beremin model for fracture probability evaluation, three types of influencing parameters have been identified: the loading history (applying several preloading cycles, including a compression or accumulating different classical cycles (LCF, LCTF or LUCF)), a non-violent thermal shock (corresponding to a low preload) and a preload close to the transition curve illustrating the yield stress variation with irradiation. All these critical loading cycles have been validated by experiments on normalised compact tensile specimens made of 16MND5 steel, confirming globally the phenomena observed on the simulations. Nevertheless, the degradation of the WPS benefits appears less important on experimental results than on the numerical predictions.