bluuebunny/crossref_metadata_2025 huggingface dataset:
Crack Growth Analysis of High-Pressure Equipment for Hydrogen Storage
Authors: Li Z. Y. , Zhou C. L. , Zhao Y. Z. , Hua Z. L. , Zhang L. , Wen M. , Xu P.
Published: January 2014

Crack growth analysis (CGA) was applied to estimate the cycle life of the high-pressure hydrogen equipment constructed by the practical materials of 4340 (two heats), 4137, 4130X, A286, type 316 (solution-annealed (SA) and cold-worked (CW)), and type 304 (SA and CW) in 45, 85 and 105 MPa hydrogen and air. The wall thickness was calculated following five regulations of the High Pressure Gas Safety Institute of Japan (KHK) designated equipment rule, KHKS 0220, TSG R0002, JB4732, and ASME Sec. VIII, Div. 3. We also applied CGA for four typical model materials to discuss the effect of ultimate tensile strength (UTS), pressure and hydrogen sensitivity on the cycle life of the high-pressure hydrogen equipment. Leak before burst (LBB) was confirmed in all practical materials in hydrogen and air. The minimum KIC required for LBB of the model material with UTS of even 1500 MPa was 170 MPa·m0.5 in 105 MPa. Cycle life qualified 103 cycles for all practical materials in air. In 105 MPa hydrogen, the cycle life by KIH was much shorter than that in air for two heats of 4340 and 4137 sensitive to hydrogen gas embrittlement (HGE). The cycle life of type 304 (SA) sensitive to HGE was almost above 104 cycles in hydrogen, while the cycle life of type 316 (SA and CW) was not affected by hydrogen and that of A286 in hydrogen was near to that in air. It was discussed that the cycle life increased with decreasing pressure or UTS in hydrogen. This behavior was due to that KIH increased or fatigue crack growth (FCG) decreased with decreasing pressure or UTS. The cycle life data of the model materials under the conditions of the pressure, UTS, KIH, FCG and regulations in both hydrogen and air were proposed quantitatively for materials selection for high-pressure hydrogen storage.
Measurement and Simulation of Water Hammer in Piping Systems Including Junction Coupling
Authors: Riedelmeier Stefan , Becker Stefan , Schlücker Eberhard
Published: January 2014

For the analysis of the effects of fluid-structure interaction (FSI) during water hammer in piping systems, a complex test facility was constructed. Resonance experiments with movable bends in two system configurations were carried out. The pressure and the displacement of the bend were recorded. The aim was to reproduce the results with two coupled codes: a one-dimensional solver based on the method of characteristics (MOC) for the hydraulic system and a three-dimensional solver based on the finite element method (FEM) working with one-dimensional beam elements for the structural system. The calculation included junction and friction coupling. The models were fine-tuned separately. For this purpose, special measurements were carried out. These included the determination of the structural damping, the friction factor, the influence of the bending of the anchorage, etc. After the validation of the models, the results of the coupled calculations were compared against the measurements, the performance of the coupled codes was evaluated and the most important physical effects were analyzed and are discussed.
High Frequency Statistical Energy Analysis Applied to Fluid Filled Pipe Systems
Authors: van Beek Pieter J. G. , Smeulers Jan P. M.
Published: January 2014

In pipe systems, carrying gas with high velocities, broadband turbulent pulsations can be generated causing strong vibrations and fatigue failure, called Acoustic Fatigue. This occurs at valves with high pressure differences (i.e. chokes), relief valves and obstructions in the flow, such as sharp bends and T-branches. Characteristic for the turbulent sources is the strong and broadband excitation caused by turbulent flow, complex acoustic response and vibrations. The traditional approach to calculate the response per resonance frequency. This brute force method is too (computational) time consuming and perhaps even not feasible. As an alternative probabilistic methods can be used. The Statistical Energy Analysis (SEA) is such a method, which only assumes statistical knowledge. The method is particularly suited for modeling multi-modal structural-acoustic systems, excited at frequencies well above their fundamental natural frequencies. To validate the SEA approach for fluid filled pipe systems, in this paper first a well-defined laboratory setup is presented: SEA results, structural-acoustic coupled FEM results and experimental results are compared. After that the SEA approach is used to assess the mechanic integrity of a complex subsea installation, from which also a very elaborate structural-acoustic FE model is available.
A Conservative Damage Accumulation Method for the Prediction of Crack Nucleation Under Variable Amplitude Loading for Austenitic Stainless Steel
Authors: Taheri Said , Vincent Ludovic , Leroux Jean C.
Published: January 2014

The application of Miner’s rule using a loading issued from a mock-up of a RHR (removal heat system) of PWR plant, made of 304 steel gives a very important non-conservative fatigue lifetime in strain control when strain fatigue curve is used. A large number of test in strain and stress control are performed in different laboratories. Two modeling of literature Smith-Watson-Topper (SWT) and Fatemi-Socie (FS) have been used to simulate these tests. Much better responses than Miner’s rule are obtained. However these models need an elastic-plastic constitutive law which is difficult to propose in the presence of high cycle secondary hardening observed in austenitic stainless steels. So a conservative model for fatigue damage accumulation under variable amplitude loading is proposed for austenitic stainless steels (AISI 304, 316) in strain control, which does not need a constitutive law. Linear damage accumulation is used, while, sequence effect is taken into account using the elastic-plastic memory effect through cyclic strain stress curves with pre-hardening. This modeling is based on the fact that for stainless steels, pre-hardening is detrimental for fatigue life in strain control while it is beneficial in stress control. In the case of materials that do not demonstrate load sequence memory the modeling is identical to Miner rule. In the presence of low mean stress, the modeling is approved based on a large number of tests. Moreover the modeling permits to explain the larger detrimental effect of a tension mean stress in strain control tests than in stress control tests. To extend the modeling to higher values of mean stress it is proposed to divide mean stress effect into maximal and “real” mean stress effects. Extending this work to the case of significant mean stress is ongoing.
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.
Simplified Thermo-Elasto-Plastic Analysis Models for Determination of Global and Local Stresses in Coke Drums
Authors: Zhang Yanxiang , Xia Zihui
Published: January 2014

Coke drums are major pressure vessels used in petroleum refineries. In this paper, two simplified analytical models based on thermo-elasto-plastic constitutive theory have been developed to evaluate global and local stresses in coke drums during their operation cycles. The first model considers the temperature and internal pressure cycle experienced by a drum shell element consisting of clad and base steels. The second model is an axisymmetric circular cladding plate model experiencing a non-uniform temperature distribution history. The latter model considers the effects of severe local non-uniform temperature distributions produced by the hot/cold spots appearing randomly in coke drums during the water quenching stage. The predicted results by the simplified models are in agreement with the results obtained from much complicated and time-consuming finite element analysis (FEA) models for the coke drums. Corresponding software packages for application of the two simplified analysis models (SAM) have also been developed. The developed SAM and software could be a more convenient analysis tool for coke drum designers and engineers in comparison to the use of FEA software package.
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.
Approximation of Fluid Pressure on the Cylindrical Tanks in Rock With the Crescent-Like Uplift Part in the Bottom Plate by Radially Sliced Tank Model
Authors: Taniguchi Tomoyo , Shirasaki Takumi
Published: January 2014

Flat-bottom cylindrical shell tanks may rock and have a crescent-like uplift part in the bottom plate at the event of a severe earthquake. Effects of the deformed tank bottom plate on the fluid pressure on the cylindrical tank have not been, however, quantified yet. Since the crescent-like uplift part appears eccentrically on the periphery of the tank bottom plate, its mathematical treatment would be troublesome. Regarding a cylindrical tank as a set of pieces of a thin rectangular tank with a deformed bottom plate that correspond radially sliced parts of the cylindrical tank with the crescent-like uplift part in the bottom plate, this paper defines the fluid pressure on the cylindrical tank by calculating that on the rectangular tank. For designer’s convenience, the fluid pressure computed are normalized and depicted in accordance with the aspect of the cylindrical tank and the uplift ratio of the tank bottom plate.
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.
The Application of Ultrasonic Guided Waves in the Furnace Tube Inspection
Authors: Xia Li , Ye Yufeng , Wang Xianggang
Published: January 2014

According to the problem of the conventional thickness measurement method used to measure the furnace wall thinning in petrochemical industry, proposed a new NDT named guided wave to detect the presence of the wall thickness. Use of the technique for detection of dangerous parts of the refinery furnace tube, take the coker furnace and the furnace of crude oil distillation unit guided wave inspection application for Example, and through analysis of test data and field-proven and found many security risks, and guide the user to process. It concluded that the ultrasonic guided wave technology can effective realization radiation section of the furnace tube wall thickness detection.
Buckling of Cylinders With Imperfect Length
Authors: Błachut J.
Published: January 2014

Eighteen mild steel cylinders with the length-to-radius ratio, L/R ≈ 2.4 and with the radius-to-wall thickness ratio, R/t ≈ 185 were collapsed by axial compression. Cylinders had variable length at one end of sinusoidal profile. The magnitude-to-wall thickness ratio, 2A/t, was varied between 0.05 and 1.0. Experimental results show that buckling strength strongly depends on the axial amplitude of imperfection. On average imperfect cylinders, with 2A/t = 1.0, are able to support 49 % of experimental buckling load obtained for geometrically perfect model. The largest sensitivity of buckling strength was associated with small amplitudes of axial length. For example, for axial length imperfection amounting to 25 % of wall thickness the buckling strength was reduced by 40 %. It appears that the number of sinusoidal waves in the imperfection profile plays a secondary role, i.e., its role in reducing the buckling strength is not a dominant factor. The paper provides experimental details and comparisons with numerical results.
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.
Sulfur Effects on High-Temperature Creep and Fracture Behavior of 25Cr35Ni-Nb Alloys
Authors: Chen Tao , Chen Xuedong , Ye Juan , Hao Xiyun
Published: January 2014

Centrifugal cast 25Cr35Ni-Nb alloy furnace tubes with different contents of S are selected to investigate effects of S addition on creep and fracture behavior. Rupture tests in air at 1100 °C and 17 MPa and slow rate tensile tests at 850 °C showed that the presence of S decreased the creep rupture life and elevated temperature ductility of 25Cr35Ni-Nb alloy obviously. Scanning electron micrographs (SEM) of the fracture and energy dispersive X-ray spectroscopy (EDS) analysis results indicated that S was the important element to control creep rupture life and elevated temperature ductility. S segregated to grain boundaries at elevated temperatures, blocky fine sulfide particles with smooth surface distribute on the grain boundaries. The presence of sulfides became effective nucleation sites for intergranular creep cavities. Micro cracks occurred by linking up cavities at elevated temperatures due to local stress concentration. Eventually, early failure happened.
Finite Element Simulation of Laser Welding in a P91 Steel Plate
Authors: Venkata Kiranmayi Abburi , Truman Christopher E.
Published: January 2014

New methods for joining materials used in advanced nuclear power plants are of interest to increase the efficiency and productivity. Optimised joints require narrow heat affected zones, low residual stress, strain and distortion. This requires research into a large range of aspects including the nature of the joining processes, characterisation of the joint materials and the integrity of joints in manufacture and service. Of particular interest is the laser welding of the P91 steel used extensively in the power plants. The objective of this paper is to fully characterise the laser welding process using numerical modelling techniques and compare the measured residual stresses for P91 steel welds induced by the welding process with the predicted residual stresses by numerical simulation. The FE simulation consists of thermal analysis and a sequentially coupled structural analysis. Solid state phase transformation is included in the analysis to account for the volumetric changes due to martensitic transformation during cooling. The neutron diffraction technique is used to measure the residual stresses in the welded plate. The measurements are compared with the simulation results and the characteristics of the residual stress distribution and the influence of phase transformations are discussed.
A Novel Procedure for Measuring the Dynamic Fracture Toughness Using Direct Tension Hopkinson Bar
Authors: Testa Gabriel , Ruggiero Andrew , Bonora Nicola
Published: January 2014

In this paper a technique for determining the dynamic fracture toughness is presented. The proposed experimental method is based on the use of the direct tension Hopkinson bar allowing accurate control of the generated tensile stress pulse and avoiding limitations showed by other similar configurations. The sample geometry investigated here is the circumferentially cracked bar in tension (CCB(T)). This geometry does not require special fixtures to be hold between the bars and does not suffer loss of contact during dynamic loading. Numerical simulation showed that, at least for high toughness materials, the relative displacement of the bars can be used to have a direct measure of the CTOD that can be used to derive the corresponding J-integral value.
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.
Damping of Acoustic Waves in Pipelines due to End Conditions
Authors: Goyder Hugh
Published: January 2014

Acoustic waves in pipelines are of concern because they can cause failure due to structural vibration and fatigue. The maximum wave amplitude that can be generated is limited by damping; a good understanding of damping is therefore vital. The damping considered here is due to the loss of energy from a resonant mode at a reflecting boundary. This type of damping is straightforward to analysis and consequently simple equations for damping are developed. A further aspect of damping is that it considerably modifies the description of acoustic resonance. The use of damped acoustic modes is shown to be problematic because they are complex and do not satisfy orthogonally conditions. A further and more significant observation is that damping prevents modes from being uncoupled and considered as independent. An uncoupled configuration is always found in undamped modes and is useful in forming simplified models however such uncoupling does not, in general, extend to damped modes. A condition for determining if modes can be uncoupled is derived. If a damped mode, which is not uncoupled, is used in an acoustic model it can generate energy as well as absorb energy. This non-physical behaviour greatly complicates the analysis of acoustic systems with damping.
Resistance of Ferritic Steels to Stress Corrosion Cracking in High Temperature Water
Authors: Rebak Raul B.
Published: January 2014

Austenitic stainless steels such as type 304 and 316 are susceptible to stress corrosion cracking in high temperature water environments typical of boiling water reactors (BWR) and pressurized water reactors (PWR). The accumulation over time of irradiation dose on the austenitic materials increases further their susceptibility to environmental cracking. Ferritic steels containing chromium are less susceptible to irradiation damage such as void swelling. Ferritic steels also offer desirable higher thermal conductivity and lower thermal expansion coefficient. Little is known however about the stress corrosion cracking behavior of ferritic steels in high temperature water. Crack propagation rate studies were conducted using four types of wrought and welded ferritic steels (5 to 17% Cr) in high purity water at 288°C containing dissolved oxygen or dissolved hydrogen. Results show that the ferritic steels are notably more resistant to environmental assisted cracking than the austenitic materials.
Hydrogen-Assisted Twin Boundary Fracture of Type 304 Austenitic Stainless Steel at Low Temperature Investigated by Scanning Probe Microscopy
Authors: An Bai , Itouga Hisatake , Iijima Takashi , San Marchi Chris , Somerday Brian
Published: January 2014

Scanning tunneling microscopy (STM), atomic force microscopy (AFM) and magnetic force microscopy (MFM) are used to characterize the morphology and strain-induced α′ martensite distribution on the twin fracture surfaces of hydrogen-precharged type 304 austenitic stainless steel tensile tested at 200–218 K. The STM images of the twin fracture surfaces show that the topographies of two conjugate fracture surfaces match well with each other at the micron scale but not at the nanoscale. Three sets of shallow grooves, intersecting each other at an angle of 120°, are formed on the twin fracture surfaces and the parallel nanoplate-like features are formed between the shallow grooves, resulting from the intersection of hydrogen-enhanced deformation bands with the twin boundary. The α′ martensite distribution observed by MFM from two conjugate fracture surfaces and longitudinal section of microcracks indicate that the fracture occurs along the phase boundary between the austenite and strain-induced α′ martensite near the twin boundary. The hydrogen-assisted twin boundary fracture processes are discussed in the theoretical framework of hydrogen-enhanced localized plasticity (HELP).
Applicability of FFS Assessment Using Partial Safety Factors Evaluated by Infinite Plate
Authors: Qu Qiang , Izumi Satoshi , Sakai Shinsuke
Published: January 2014

This paper investigates the applicability of a Fitness-For-Service (FFS) assessment of crack-like flaws using the Partial Safety Factors (PSFs) calculated from the infinite plate model. Procedures of FFS assessment using PSFs are provided in API579-1, and several PSFs calculated from an infinite plate are given to evaluate structures approximately for simplification. However, the applicability of these PSFs is not clear, and the safety margin cannot be evaluated precisely. To clarify the applicable region of these infinite plate PSFs in this paper, we calculate PSFs of various structures, crack geometries and load types and compare with those of the infinite plate. We also examine whether the target reliability is satisfied when infinite plate PSFs are applied to the concrete structures. In addition, we used sensitivity analysis to show the dependence of probabilistic properties on the safety margin. Both the limit state function method and the Monte Carlo simulation method are used for the analysis, and the limit state is defined by the Failure Assessment Diagram (FAD) curve. Finally, the relation between infinite plate PSFs’ applicability and probabilistic properties of structure, and crack geometries are discussed.
The Further Development of National Safety Assessment Standard for In-Service Pressure Equipment Containing Defects
Authors: Shao Shanshan , Jia Guodong , Sun Liang , Wang Hui
Published: January 2014

The fitness-for-service assessment is widely used to demonstrate whether identified defects or in-service deterioration threaten the structure integrity of the pressure equipment. This article introduces the development of the Chinese national safety assessment standard. The assessment procedure and assessment techniques of current Chinese national safety assessment standard GB/T 19624-2004 are demonstrated, and the improvement is proposed. In order to maintain availability of aging equipment and enhance the long-term economic performance of in service pressure equipment, a new Chinese national safety assessment standard system is methodology proposed based on the analysis of some international structure integrity procedures or standards. A new national standard fitness-for-service which focuses on the evaluation of in-service damage and degeneration will be established while GB/T 19624 is applicable for general defects.
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.
Dynamic Experimental Investigation on the Self-Vibration Characteristics of Liquid Storage Tanks Under Seismic Excitations
Authors: Fang Zhou , Chen Zhiping , Jia Guodong , Wang Hui , Li Xiang
Published: January 2014

A large-scale earthquake simulation experiment about the unanchored cylindrical steel liquid storage model tanks has been completed. The self-vibration characteristics of the model tanks with liquid inside were investigated based on the experimental data of the acceleration dynamic response. The seismic table test, the analysis methods are designed and conducted, and experimental results of the model tanks were carefully measured. Furthermore, ANSYS finite element software was used to simulate and calculate the low order natural frequency and fundamental frequency of the model tank systems according to the national design standard. The reasons for the existence of consistency and differences among the results obtained from experiments, numerical simulation and national design standard were discussed.
Stability of a Flexible Wall Separating Two Inviscid Channel Flows
Authors: Burke Meagan A. , Lucey Anthony D. , Elliott Novak S. J. , Howell Richard M.
Published: January 2014

The stability of a finite flexible wall occupying part of a rigid wall that separates two inviscid channel flows is investigated. The two-dimensional system is solved using a boundary-element method coupled with a finite-difference method. The motion of the wall is driven by the transmural pressure while the no-flux condition at the wall provides the kinematic boundary condition for each of the flows. Flows and structure are fully coupled to yield a system equation that is then transformed into state-space form so that its eigenvalues can be analysed. The flow velocities at which divergence and modal-coalescence flutter of the flexible wall occur are then determined as are mode shapes. We show that decreasing the channel heights and increasing the fluid density causes instabilities to occur at lower flow velocities. When the channels flow in opposite directions it is possible to suppress modal-coalescence of the first two modes.
Synthesis of the NESC VII European Project: Demonstration of Warm Pre-Stressing Effect in Biaxial Loading Conditions
Authors: Jacquemoud C. , Marie S. , Yuritzinn T. , Moinereau D. , Nédélec M. , Chapuliot S.
Published: January 2014

In the framework of the NESC VII European project, a large experimental program has been dedicated to characterizing the Warm Pre-Stressing (WPS) effect in different testing configurations. One of the CEA (France) contributions to this project is the realization of five point bending tests on large cruciform specimens considering different WPS loading cycles. The five cruciform specimens, sponsored by EDF (France) and IRSN (France), are made of 18MND5 steel. Two of them have been tested on a same LCF (Load-Cool-Fracture) loading cycle and three others on a LCTF (Load-Cool-Transient-Fracture) loading cycle. The experimental results presented in this paper give a successful demonstration of the WPS effect in biaxial loading conditions either on a LCF or on a LCTF cycle. During the test interpretations, different models have then been tested and compared in order to evaluate their ability to predict the cleavage fracture in the case of different WPS loading cycles. They all provide very conservative predictions whatever loading cycle is concerned.
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.
Development of Equipment Integrity Management System Based on Predictive Maintenance
Authors: Jia Guodong , Wang Hui , Li Xiang , Zhong Jiandong , Xie Guoshan , Wang Weihua
Published: January 2014

Equipment integrity management technology is to take a combination of technical improvement measures and standardizing the equipment management, to ensure the operating status integrity for critical equipments in the entire device. It is a device risk management philosophy. Equipment integrity management technology is playing a more and more important role in raising the standard of business management, reducing the cost of production, ensuring the long period safe operation of plants. In this paper, firstly, the concept of equipment integrity management was provided. Secondly, the content and implementation of equipment integrity management system was given. Furthermore, an Equipment Integrity Management System Based on Predictive Maintenance built by China Special Equipment Inspection & Research Institute (CSEI) is introduced. The scheme and the thoughts of the system are introduced in details. And the characteristics and functions of the proposed system have been demonstrated.
Manufacture, Residual Stress Measurement and Analysis of a VVER-440 Nozzle Mockup
Authors: Tatár Levente , Török Gyula , Smith David J. , Do Son , Ohms Carsten , Kovács László
Published: January 2014

As part of the STYLE EU FP7 project a modified 1:5 scale replica of a VVER-440 type reactor pressure vessel inlet nozzle was manufactured. The nozzle included a dissimilar metal weld of the type found in full-scale nozzles. This scale model was developed to permit accurate measurements to be made and detailed finite element (FE) models to be developed without recourse to using a full scale mock-up. It was also found that a full-scale mock-up would not permit the application of certain residual stress measurement methods. Temperatures and displacements were recorded during welding of the dissimilar metals, with measurements used to guide simulation of the welding process using finite element models. Through thickness residual stress profiles were measured using a comprehensive range of different techniques, such as deep hole drilling, neutron diffraction, magnetic Barkhausen noise. Usage of contour method had been planned too, but it but could not be accomplished in due time. The measured residual stresses obtained by the different methods are presented and compared. Measured residual stresses, temperatures and displacements were then used to validate the results derived from the FE model.
Fatigue Behavior of Nuclear Materials Under Air and Environmental Conditions
Authors: Herter Karl-Heinz , Schuler Xaver , Weissenberg Thomas
Published: January 2014

The assessment of fatigue and cyclic crack growth behavior of safety relevant components is of importance for ageing management with regard to safety and reliability. For cyclic stress evaluation different codes and standards provide fatigue analysis procedures to be performed considering the various mechanical and thermal loading histories and geometric complexities of the components. For the fatigue design curves used as limiting criteria the influence of different factors like e.g. environment, surface finish and temperature must be taken into consideration in an appropriate way.

Fatigue tests were performed in the low cycle fatigue and high cycle fatigue regime with low-alloy steels as well as with Nb- and Ti-stabilized German austenitic stainless steels in an air and high temperature BWR environment to extend the state of knowledge of environmentally assisted fatigue as it can occur in BWR plants.

Using the RPV steel 22NiMoCr3-7 experimental data was developed to verify the influence of BWR coolant environment (high purity water as well as water containing sulphate with 90 ppb SO4 and water containing chloride with 50 ppb Cl at a test temperature of 240 °C and an oxygen content of 400 ppb) on the fatigue life and to extend the basis for a reliable estimation of the remaining service life of reactor components. Corresponding experiments in air were performed to establish reference data to determine the environmental correction factor Fen.

The experimental results are compared with available international mean data curves, the new design curves and on the basis of the environmental factor Fen.
Long Term Fatigue Evaluation in Primary Circuit Components Within Nuclear Power Plants Operated by E.ON
Authors: Reese Sven H. , Klucke Dietmar
Published: January 2014

Temperature-measuring thermocouples have been applied to various positions on primary circuit piping where most significant thermal loads were expected. Measuring positions were monitored and evaluated, leading to comprehensive information of existing thermal loadings like stratification and thermo shock events.

During design of NPP (nuclear power plant) predicted cumulative fatigue usage factors (CUF) were defined based on specified transients. Conservative assumptions are part of this predicted end of life CUF. In comparison to detailed analysis based on real measured values, these predictions based on specified loads are leading to more conservative results in general. Evaluations underline the conservatism of design predictions in general and result in substantial progress in component integrity assessment knowledge. The range of methods to calculate component specific fatigue usage factors goes from conservative approaches based on the evaluation of the stress range of the specific events up to numerical Finite Element simulations. Based on the level of detail the conservatism decreases while the complexity of the model increases.

An overview of monitoring measures of passive piping components in terms of thermal fatigue assessment is being applied in NPPs operated by E.ON Kernkraft GmbH. Evaluation methods will be discussed in detail and differences between these methods will be presented.
Consideration of Environmentally Assisted Fatigue in Austenitic Stainless Steel — Applicability and Comparison of Existing Numerical Procedures
Authors: Reese Sven H. , Seichter Johannes , Klucke Dietmar
Published: January 2014

Consideration of environmentally assisted fatigue (EAF) is in discussion internationally. In German KTA Rules the effect is taken into account by means of so called attention thresholds. While the laboratory phenomena themselves are being accepted widely, numerical calculation procedures are revised continuously and transition from laboratory to real plant components is not clarified yet.

Since NUREG/CR-6909, formulas for calculating the Fen factors have been modified several times. For example in ANL-LWRS47-2011 a new set of formulas was published and slightly revised by ANL in 2012. Various calculation procedures like the strain-integrated method and simplified approach have been published while each approach yields to different results.

Beyond this, additional topics like weld factors or plasticity correction factors have to be taken into account. Calculation procedures depending on the level of detail and in the description of loads are yielding to significant variations in the results. Respecting these topics in context of different levels of detail in computational simulations, numerical cumulative usage factor (CUF) evaluation results are likely to differ, depending on the assumptions made.

On the basis of a practical example, methods and approaches will be discussed and recommendations in terms of avoiding over-conservatism and misinterpretation will be presented.
Reliability of Water Jet Peening as Residual Stress Improvement
Authors: Kono Yusuke , Okimura Koji , Toth Rebecca , Sato Tomonobu , Tajima Masakazu , Jardin Cecile , Le-Bec Philippe
Published: January 2014

As a countermeasure against high residual stress, we have developed some residual stress improvement methods; Water Jet Peening (WJP) [1] [2] for components installed in water, Shot Peening by Ultrasonic-wave vibration (USP) for components installed in air, and outer surface irradiated Laser Stress Improvement Process (L-SIP)[3] for components that can only be accessed from the outer surface.

WJP is applied to Reactor Vessel (RV) outlet/inlet nozzle safe-end joints (Alloy600 weld metal), RV Bottom Mounted Instrument (BMI) inner surface and J-weld. Especially, it is difficult to apply the technology to BMI because BMI inner surface is a very narrow space (inner diameter; approximately 10–15mm) and BMI J-weld configuration is a complicated 3-dimensional form.

On the occasion of actual application, we carry out the verification tests and check that a stress improvement was effective as one of PWSCC mitigations. And the compressive stress induced by the WJP was verified to continue to exist under actual plant operation conditions.

Thus, in addition to replacing the material with Alloy 690, converting the residual stress to compressive one can prevent the occurrence of PWSCC.
Experimental Study of Two-Phase Flow Induced by Cavitation Through a Safety Relief Valve
Authors: Pinho Jorge , Rambaud Patrick , Chabane Saïd
Published: January 2014

The goal of this study is to understand the behavior of a safety relief valve in presence of a two-phase flow induced by cavitation, in which the mass flux tends to be reduced. Two distinct safety relief valves are tested: an API 2J3 type and a transparent model based on an API 1 1/2G3 type. Instead of using a spring, the design of both valves allows the adjustment of the disk at any desired lift. Tests are conducted with water at ambient temperature. Results show a similar influence of cavitation on the flow characteristics of both valves. The liquid pressure recovery factor FL, which is normally used to identify a choked flow condition in a control valve, is experimentally determined in a safety relief valve. The existence of a local minimum located at a height position L/D = 0.14 indicates in this position, a change on the flow characteristics of both valves. It is verified that the existence of a local minimum in the liquid recovery factor is related to the minimum cross section of the flow, which does not remain constant for every lift positions. Furthermore, it is remarked that in the case of the 2J3 safety valve, the blow down ring adjustment has significant influence on the location of the minimum cross sections of the flow.