bluuebunny/crossref_metadata_2025 huggingface dataset:
Damage Analysis and Fatigue Evaluation of an Aluminium Brazed Plate Fin Heat Exchanger
Authors: Hölzl Reinhold , Hecht Thomas , Freko Pascal
Published: November 2014

During operation of an air separation unit (ASU) a plate fin heat exchanger developed a leak. This apparently simple heat exchanger, exchanging heat between two gaseous streams of air versus nitrogen, was not expected to suffer significant stress levels for producing a damage.

During the analysis of the damage which occurred at the connection welds of three adjacent modules — module construction is widely used in the process industry — an operating situation was discovered leading to high thermal gradients inside the exchanger. It occurred during a stop of the plants nitrogen cycle compressor. The warm flow continued and heated up the exchanger in a very fast way. This led to unacceptably high stresses in the top part of the exchanger. But a more severe situation occurred when the cycle compressor has been restarted. Then cold nitrogen entered the lower end of the exchanger which had been warming up in the meantime.

A finite element analysis based on a modeling technique [4] for brazed plate fin heat exchangers was performed for this dynamic incident showing extreme stress levels at the location of the damage. A fatigue evaluation of the calculated stresses showed that only a few cycles were acceptable for this scenario. As a consequence operational measures have been implemented to protect the exchanger against this severe condition.
Thermal Stress Response to Boundary Oscillation Between Hot and Cold Fluid Temperature
Authors: Soda Kohei , Mizutani Takato , Kasahara Naoto
Published: November 2014

In nuclear power plants, high cycle thermal fatigue induced by temperature fluctuation of the coolant is one of frequent failure modes. To ensure the safety of nuclear power plant systems, it is important to prevent thermal fatigue failure.

Typical causes of high cycle thermal fatigue are thermal striping at Tee-junction and thermal stratification oscillation. In order to evaluate thermal stress caused by thermal striping, a frequency response function has been developed. This function was derived from a heat transfer and thermal elastic theories, and can adequately evaluate thermal stress induced by temperature gradient into wall-thickness direction.

However, this theoretical method cannot adequately evaluate thermal stress by thermal stratification oscillation, because this phenomenon has the fluid temperature distribution gradient along axial direction.

To investigate the mechanism of thermal stress generated by oscillation of thermal stratification, two types of models were studied. In the first type, fluid temperature oscillates with sinusoidal history at the same location, and in the second one, the boundary layer of hot and cold fluid temperature moves with sinusoidal velocity.

Through clarification of the stress generation mechanism, the frequency response function was improved to evaluate stress by the thermal stratification oscillation. Applicability of this function was verified through agreement with finite element simulations.
Effect of Specimen Geometry on the Predicted Mechanical Behavior of Polyethylene Pipe Material
Authors: El-Bagory Tarek M. A. A. , Alkanhal Tawfeeq A. R. , Younan Maher Y. A.
Published: November 2014

The primary objective of the present paper is to depict the mechanical behavior of high density polyethylene, (HDPE), pipes under different loading conditions with different specimen geometries to provide the designer with reliable design data relevant to practical applications. Therefore, it is necessary to study the effect of strain rate, ring configuration, and grip or fixture type on the mechanical behavior of dumb-bell-shaped, (DBS), and ring specimens made from HDPE pipe material. DBS and ring specimens are cut from the pipe in longitudinally, and circumferential (transverse) direction respectively. On the other hand, the ring specimen configuration is classified into two types; full ring, (FR), and notched ring, (NR) (equal double notch from two sides of notched ring specimen) specimens according to ASTM D 2290-12 standard. Tensile tests are conducted on specimens cut out from the pipe with thickness 10 mm at different crosshead speeds (10–1000 mm/min), and ambient temperature, Ta = 20 °C to investigate the mechanical properties of DBS, and ring specimens. In the case of test specimens taken from longitudinal direction from the pipe a necking phenomenon before failure appears at different locations along the gauge section. On the other hand, the fracture of NR specimens occurs at one notched side. The results demonstrated that the NR specimen has higher yield stress than DBS, and FR specimens at all crosshead speeds. The present experimental work reveals that the crosshead speed has a significant effect on the mechanical behavior of both DBS, and ring specimens. The fixture type plays an important role in the mechanical behavior for both FR and NR specimens at all crosshead speeds.
Status of the French Methodology Proposal for Environmentally Assisted Fatigue Assessment
Authors: Métais Thomas , Courtin Stéphan , Genette Pierre , De Baglion Laurent , Gourdin Cédric , Le Roux Jean-Christophe
Published: November 2014

Environmentally Assisted Fatigue is receiving nowadays an increased level of attention for new builds and also for installed bases which are currently having their lives extended to 60 years in various countries. To formally integrate these effects, some international codes have already proposed code cases. More particularly, the ASME code has based itself on the NUREG/CR-6909 [1] to elaborate the Code Case N-792 [2] and suggests a modification of the fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which is to be multiplied by the usual fatigue usage factor.

In France, EDF and AREVA also aim at more explicitly integrating these effects in the RCC-M code. The initiative is technically supported by CEA and bases itself on international methodologies but also on results from French in-house testing campaigns [3] [4]. The approach is globally similar to the one in the ASME code: it will indeed consist in an update of the mean air and design fatigue curves as well as the calculation of an environmental penalty factor. Nevertheless, the methodologies differ in their detailed implementation, as was already hinted in previous papers discussing the French methodology [5] [6]. This paper is the sequel to the proposal already described in [7].
Low-Constraint Toughness Testing of Two SE(T) Methods in a Single Specimen
Authors: Park Dong-Yeob , Gravel Jean-Philippe , Simha C. Hari Manoj , Liang Jie , Duan Da-Ming
Published: November 2014

Single-edge notched tension (SE(T) or SENT) specimens has been increasingly proposed as a low-constraint toughness test to measure toughness of line pipe materials, as the crack tip constraint approximates a circumferential surface flaw in a pipe under loading. The clamped SE(T) single-specimen procedures recently developed by Shen and Tyson [1, 2] and Tang et al. [3] have in common the use of a clamped single-specimen of similar geometry and rely on unloading compliance technique for crack size estimation. In the former case, a single clip gauge is attached to the integral knife edge and the crack-tip opening displacement (CTOD) is estimated by means of a J-integral-to-CTOD conversion, similar to the procedure of ASTM E1820. The latter uses a pair of clip gauges mounted to an attachable raised set of knife edges to estimate CTOD at the original crack tip position by a triangulation rule. Consolidating these two sets of clip gauges in a specimen makes direct comparisons of two SE(T) methods on identical test conditions: material, specimen geometry, equipment, test temperature and operator [4]. In this study, SE(T) testing employing these two SE(T) methods on a single specimen was conducted on BxB shallow-cracked (a/W∼0.35) specimens of two x70 pipeline girth welds. This paper discusses the details of two SE(T) methods and techniques on the same specimen.
Equi-Biaxial Loading Effect on Austenitic Stainless Steel Fatigue Life
Authors: Bradaï S. , Gourdin C. , Courtin S. , Le Roux J. C. , Gardin C.
Published: November 2014

Fatigue lifetime assessment is essential in the design of structures. Under-estimated predictions may result in unnecessary in service inspections. Conversely, over-estimated predictions may have serious consequences on the integrity of structures.

In some nuclear power plant components, the fatigue loading may be equi-biaxial because of thermal fatigue. So the potential impact of multiaxial loading on the fatigue life of components is a major concern. Meanwhile, few experimental data are available on austenitic stainless steels. It is essential to improve the fatigue assessment methodologies to take into account the potential equi-biaxial fatigue damage. Hence this requires obtaining experimental data on the considered material with a strain tensor in equi-biaxial tension.

The aim of this paper is to present the experimental results obtained with a device “FABIME2” developed in the LISN in collaboration with EDF and AREVA. The specimen geometry is optimized by FEM (Cast3M) simulation in order to obtain a stress concentration localized in the central region during the test. This device allows accurate quantification of the effects of both equi-biaxial strain state as well as structure (such as mean stress) on the fatigue life.
Ductile Fracture Analysis Under Large Amplitude Cycles
Authors: Tranchand B. , Chapuliot S. , Aubin V. , Marie S. , Bourgeois M.
Published: November 2014

Demonstration of large components integrity under seismic loading is based up to now on monotonic tearing resistance curves. However, it is well known that cycles decrease the fracture resistance of the material, mainly according to the loading ratio. Most studies use monotonic methods to analyze reversible cyclic loading and the associated increase of crack propagation: Delta J-R curves are largely used. For monotonic loadings, Turner [1] proposed a decomposition of the rate of dissipated fracture energy. This decomposition led on the determination of an energetic criterion for ductile fracture [2]. This intrinsic criterion allows the fracture prediction on large components. This paper aims to propose an analysis of cyclic ductile fracture which should allow the determination of an energetic criterion under large amplitude cycles. For that purpose, compact tension specimens are taken from a carbon steel pipe (Tu42C) used in the secondary circuit of French PWR. A series of cyclic tearing tests are carried out under quasi-static loadings. The effects of loading ratio and incremental plastic displacement are quickly studied. Here, we present an energetic analysis which take into account the crack closure and crack opening. Indeed, displacement fields around the crack tips are measured with digital image correlation and linked with electric potential measurement. That allows an accurate determination of crack closure and crack opening and let a precise calculation of fracture energy possible. The energetic fracture criterion will be confirmed with crack propagation prediction on different geometry like CT specimen and a through-wall-cracked pipe under cyclic reversed loadings.
Flow-Induced Pulsations in Closed Side Branches With Wet Gas
Authors: Sanna F. , Golliard J.
Published: November 2014

In a recent paper it has been shown that the presence of liquid has an influence on Flow Induced Pulsations (FIPs) in closed side branches. Even larger effects of liquid in case of whistling in corrugated pipes were reported.

For this experimental study, the “Tandem configuration” with two closed side branches along a main pipe is considered. It is characterized by the distance between the two closed side branches equal to the double of their acoustic length.

The experiments reported in this paper aim at investigating the effect of the mixture water/gas on FIPs measured at the closed end of the two closed side branches. Different water flow rates are injected in the flow to obtain a mass factor rate in the range 0–10−4 m3/s. Furthermore, the relation between the multiphase flow pattern in the main pipe and the trend in the pulsation amplitude and Strouhal number is discussed, by comparison with the test for dry gas. To understand the effect of the type of flow, tests are performed with the injector far from and close to the upstream side branch.

For the far configuration, at both low and high injection rates, pulsations decrease for increasing injection rates. However, in the intermediate region, an increase of pulsations is observed. These different ranges can be attributed to different (multiphase) flow regimes.

Concerning the close configuration, only a decrease of the pulsations is observed over the full range. Furthermore, a decrease of the Strouhal number corresponding to the maximum pulsation level is observed.
Determination of ASME PCC-1-2010 Appendix-O Gasket Parameters
Authors: Garcia André F. , Dias Camila M. , Pereira Sulivan T.
Published: November 2014

The bolt load calculation method introduced in Appendix-O of ASME PCC-1-2010 – Guidelines for Pressure Boundary Bolted Flange Joint Assembly [1] – has drawn attention from the gasket researching community in the past few years. In this new method, calculation is based on parameters that consider the integrity of each joint component. The parameters related to the gasket are the maximum permissible gasket stress, minimum gasket seating stress and the minimum gasket operating stress. In Appendix-O, those parameters are defined, but no information is provided on how to determine them. The intent of this paper is to determine the values of those parameters for gaskets in different material composition for different thicknesses, and to evaluate the influence of those variables on the parameters.
Automated Synchrotron X-Ray Diffraction of Irradiated Reactor Pressure Vessel Steels
Authors: Sprouster David J. , Ecker Lynne E. , Anderson Thomas , Weidner Randy , Ghose Sanjit , Dooryhee Eric
Published: November 2014

In this work, we outline the development of an automated, high-throughput robotic system designed for the structural characterization of radioactive samples at the X-ray Powder Diffraction beamline of the National Synchrotron Light Source-II (NSLS II).
Simplified Methodology for Analysis of Reflected Detonation and DDT: Part 1 — Elastic Analysis
Authors: Ligon Thomas C. , Gross David J. , Ahnert Stephen D. , Minichiello John C.
Published: November 2014

This paper introduces a simplified approach for analyzing local elastic hoop response of piping to reflected gaseous detonations and deflagration-to-detonation transitions (DDT). A consequence associated with gaseous explosions is the potential for DDT to occur near the end of a closed pipe or gas pocket. As an accelerating deflagration flame approaches a closed end, the unburned fuel ahead of the flame front is compressed to an elevated initial pressure. This process is often referred to as pressure piling or pre-compression, and the combination of detonation reflection with the elevated initial pressure, can produce extremely high peak pressures and large values of impulse. In this paper, the event where DDT occurs immediately ahead of the reflecting surface is referred to as a reflected-DDT (R-DDT).

In addition to gas mixture and initial conditions, the peak pressure and shape of the pressure time-history associated with a reflected detonation or DDT is a function of the detonation propagation distance prior to reflection and the relative distance between the ignition location, the DDT location, and the reflecting surface. An empirical pressure time-history has been developed using pressure data from approximately 190 explosion tests using hydrogen and nitrous oxide mixtures in 2-inch and 4-inch pipe to describe events ranging from fully-developed reflected detonations to R-DDTs. The empirical model of the pressure time-history was validated by comparing measured elastic hoop strains to finite-element model predictions using the pressure time-history model. Part 2 of this paper compares the methodology to plastic response data.
Frequency Distribution Curves for Main Steam Piping Multiaxial Stresses
Authors: Cohn Marvin J. , Faham Fatma G. , Patel Dipak
Published: November 2014

A high energy piping (HEP) asset integrity management program is important for the safety of plant personnel and reliability of the generating unit. HEP weldment failures have resulted in serious injuries, fatalities, extensive damage of components, and significant lost generation. The main steam (MS) piping system is one of the most critical HEP systems. Creep damage assessment in MS piping systems should include the evaluation of multiaxial stresses associated with field conditions and significant anomalies, such as malfunctioning supports and significant displacement interferences.

This paper presents empirical data illustrating that lead-the-fleet girth welds of MS piping systems have creep failures which can be successfully ranked by a multiaxial stress parameter, such as maximum principal stress. Both the as-found elastic (initial) stress and inelastic (redistributed) stress at the piping outside diameter surface are evaluated for the base metal of three MS piping systems. Frequency distribution curves are then developed for the initial and redistributed piping stresses. The frequency distribution curves are subsequently included on a Larson Miller Parameter (LMP) plot for the applicable material, revealing the few critical (lead-the-fleet) girth welds selected for nondestructive examination (NDE).

By including an evaluation of significant field anomalies, multiaxial operating stress on the outside surface, and weldment performance, it is shown that there is a good correlation of calculated creep stress versus the operating time of observed creep damage. This process also reveals the large number of MS piping girth welds that have insufficient applied stress to have substantial creep damage within the expected unit life time (assuming no major fabrication defects).

API 579 recommends an effective stress to compute the creep rupture life using the LMP. This constitutive stress equation includes a combination of the maximum principal, von Mises, and hydrostatic stresses. Considering the stresses in these three MS piping systems, this paper reveals that when the axial and hoop stresses are nearly the same values, the API 579 effective stress may be 10% greater than the maximum principal stress. However, the maximum principal stresses are greater than the API 579 effective stresses at the maximum stress locations in the three MS piping systems, because the axial stresses are significantly greater than the hoop stresses.

This study also provides a comparison of the results of a conventional American Society of Mechanical Engineers (ASME) B31.1 Code as-designed sustained stress analysis versus the redistributed maximum principal stresses for a complete set of MS piping system nodes. A comparison of Code-sustained load versus redistributed maximum principal stress results are illustrated on frequency distribution curves.
Experimental Investigation on Dynamic Fluid Pressure of Liquid Storage Tanks Under Seismic Excitations Based on Rain Flow Counting Method
Authors: Fang Zhou , Chen Zhiping , Liu Deyu , Jia Guodong , Wang Zhe
Published: November 2014

A series of seismic table tests about the large steel cylindrical liquid storage tank models with floating roof were taken in this study. Different direction seismic excitations were input to the experimental structure system under different working conditions to test and analyze the seismic response behavior. The effects of various factors, such as the liquid surface height, the floating roof, the different wave amplitudes and frequencies, as well as their combined effects to the seismic dynamic response were taken into account. Dynamic fluid pressure data was got by the tests, and a new method that rain flow counting method was used in this study, in order to consider mean pressure throughout the vibration process, the pressure amplitude and the effective amplitude of the cumulative number of cycles factors together. Through this method, the strength of the dynamic fluid pressure could be described more reasonably. In addition, the relationship between the test results and the tank uplift responses which were studied in our former work were discussed. A reliable basis could be provided for theoretical analysis, structural design and computer numerical simulation research through this investigation.
Study on Carburizing Inspection of Cracking Furnace Tube Using Acoustic Emission Technique
Authors: Fang Zhou , Jia Guodong , Liu Deyu , Yan He , Wang Zhe
Published: November 2014

Large tube type fuel heating furnaces are important and essential equipments, which have a wide range of applications in the petroleum and chemical industry, and failure modes of the furnace tubes in them are mostly caused by carburizing. It is important to improve effective detection technology for the measure of the tube carburized layer thickness, as well as the research on the comprehensive performance of furnace tubes considering the impacts of different conditions. The specifications of Φ70×6 mm HP40Nb cracking furnace tube was studied by experiment method to evaluate the effectiveness of an acoustic emission (AE) technique, which used to measure the carburized layer thickness. In the experiment, many factors were taking into account, such as different carburizing time, the response of acoustic emission attenuation to the organization changes, the magnetic field changes, and additional stress which caused by carburization are considered. The results show that the short periods strong carburizing has obviously impacts in the changes of the organization and magnetic field of the cracking furnace tube, however, it has little contribution to the acoustic emission signal attenuation.
Benchmark Analysis on Probabilistic Fracture Mechanics Analysis Codes Considering Multiple Cracks and Crack Initiation in Aged Piping of Nuclear Power Plants
Authors: Li Yinsheng , Osakabe Kazuya , Katsumata Genshichiro , Katsuyama Jinya , Onizawa Kunio , Yoshimura Shinobu
Published: November 2014

In recent years, cracks have been detected in piping systems of nuclear power plants. Many of them are multiple cracks in the same welded joints. Therefore, structural integrity evaluation and risk assessment considering multiple cracks and crack initiation in aged piping have become increasingly important. Probabilistic fracture mechanics (PFM) is a rational methodology in structural integrity evaluation and risk assessment of aged piping in nuclear power plants. Two PFM codes, PASCAL-SP and PRAISE-JNES, have been improved or developed in Japan for the structural integrity evaluation and risk assessment considering the age related degradation mechanisms of pipes. Although the purposes to develop these two codes are different, both have almost the same basic functions to obtain the failure probabilities of pipes. In this paper, a benchmark analysis was conducted considering multiple cracks and crack initiation, in order to confirm their reliability and applicability. Based on the numerical investigation in consideration of important influence factors such as crack number, crack location, crack distribution and crack detection probability of in-service inspection, it was concluded that the analysis results of these two codes are in good agreement.
Study on the Deflection of Gaskets and its Effects on Residual Bolt Forces and Tightness of Bolted Flanged Connections
Authors: Kobayashi Takashi
Published: November 2014

The deflections of gaskets after initial tightening largely affect the residual bolt forces and the tightness of bolted flanged connections. The bolt forces decrease significantly due to the deflections of gaskets after initial tightening in the cases where expanded PTFE gaskets are used. The visco-elastic characteristic of the gaskets is the main cause for the phenomenon. It was shown in the paper PVP2012-78694 that the tightness improved even if the bolt forces reduced in the long term. This is because the gasket becomes packed under a high gasket stress. It is important to estimate the thickness change of gaskets to evaluate the tightness of bolted flanged connections.

In this paper, an analytical model of a bolted flanged connection, in which the flanges, the bolts and the gasket are represented by spring constants, is proposed. Experiments were carried out to measure the creep characteristic of the expanded PTFE gasket. The residual bolt forces and the deflection of the gasket were estimated based on the analytical model of the bolted flanged connection and the creep characteristic of the gasket. Thus, the relationship between gasket deflection and the tightness of the bolted flanged connection are clarified.
A Method to Identify the Crack Closure and Opening in Cyclic Tearing Tests on Fracture Mechanics Specimens
Authors: Tranchand B. , Aubin V. , Marie S.
Published: November 2014

To measure crack propagation in compact tension specimen, many methods can be used. The electric drop potential measurement is one of them and allows the detection of crack initiation. In our case, CT specimens, which have been taken from a carbon steel pipe (Tu42C) used in the secondary circuit of French PWR, are employed for cyclic tearing test. The detection of crack closure and crack opening should provide information for energetic analysis. However, the electric signal is unusable due to the cyclic loading. Indeed, because of the clearance between the pin and the specimen, each direction loading change causes a discontinuity in the signal. The roughness of the lips surface or the crack closure during compression loading returns also an unusual signal. Moreover, local measurement is required and there is high strain level around the crack tips, so strain gages are not suitable. Thus, displacement field are measured with digital image correlation and a specific image acquisition is employed. These methods allow a direct measurement of strain fields on the surface of the specimen. Thereby an interpretation of the previous electric signal and the crack opening and closure detection is realizable. Then, F.E. simulation, with non-linear kinematic hardening and node release method, are performed. These simulations allow the check of crack opening and closure detection through the specimen thickness.
Gross Plastic Deformation of Pipe Bends Under Internal Pressure and In- and Out-of-Plane Bending: A Study on the Sensitivity of the Finite Element Models
Authors: Bhattacharya Anindya , Bapat Sachin M.
Published: November 2014

Bends are an integral part of a piping system. Because of the ability to ovalize and warp they offer more flexibility when compared to straight pipes. Piping Code ASME B31.3 [1] provides flexibility factors and stress intensification factors for the pipe bends. Like any other piping component, one of the failure mechanisms of a pipe bend is gross plastic deformation. In this paper, plastic collapse load of pipe bends have been analyzed for various D/t ratios (Where D is pipe outside diameter and t is pipe wall thickness) for internal pressure and in-plane bending moment, internal pressure and out-of-plane bending moment and internal pressure and a combination of in and out-of-plane bending moments under varying ratios. Any real life component will have imperfections and the sensitivity of the models have been investigated by incorporating imperfections as scaled eigenvectors of linear bifurcation buckling analyses. The sensitivity of the models to varying parameters of Riks analysis (an arc length based method) and use of dynamic stabilization using viscous damping forces have also been investigated. Importance of defining plastic collapse load has also been discussed. FE code ABAQUS version 6.9EF-1 has been used for the analyses.
Simplified Limit Load Analysis for Multiple Circumferential Flaws in a Pipe
Authors: Iwamatsu Fuminori , Saito Koichi
Published: November 2014

A simplified method is proposed to evaluate limit load at incipient plastic collapse for a pipe made of ductile materials with multiple circumferential flaws. Fitness-for-service codes such as the ASME Boiler and Pressure Vessel Code Section XI specify limit load analysis for a pipe with a single flaw. Multiple flaws caused by stress corrosion cracking have actually frequently been detected in the same or adjacent weld lines. Therefore, some methods of evaluating limit load for a pipe with multiple flaws have been proposed. Bending stress at limit load i.e., collapse bending stress is evaluated regarding actual flaw depths, angles and locations of multiple flaws with these methods. Computational evaluation is required because of the enormous number of repetitive calculations. Thus, simple evaluation that can be applied to multiple flaws is required to incorporate into the code procedure. A simplified limit load analysis for multiple flaws in a pipe was developed in the present study based on a net-section approach. Multiple flaws were characterized as equivalent symmetric through-wall flaws on the basis of the sizes and locations of the original flaws. The collapse bending stress for the equivalent flaws was evaluated from simple equations on the basis of the net-section approach. The collapse bending stress for original flaws was determined from a lower value between the largest single flaw in the original flaws and equivalent flaws. The collapse bending stresses were evaluated based on previous and present studies. The results from a comparison demonstrated that the simplified limit load analysis could accurately be applied to a pipe with multiple flaws.
Analysis of Stresses and Strains in Packed Stuffing-Boxes
Authors: Kazeminia Mehdi , Bouzid Abdel-Hakim
Published: November 2014

Packed stuffing-boxes are mechanical sealing systems that are extensively used in pressurized valves and pumps. Yet there is no standard design procedure that could be used to verify their mechanical integrity and leak tightness. It is only recently that standard test procedures to qualify the packing material have been suggested for adoption in both North America and Europe. While the packing contact stress with the side walls is predictable using existing models there is no analytical methodology to verify the stresses and strains in the stuffing-box housing.

This paper presents an analytical model that analyzes the stresses and strains of all the stuffing box components including the packing rings. The developed model will be validated both numerically using FEM and experimentally on an instrumented packed stuffing box rig that is specially designed to test the mechanical and leakage performance of different packing materials.
Fatigue Evaluation Under Continuous Strain Rate Changing Condition of Carbon Steel in BWR Environment
Authors: Hirano Akihiko , Mizuta Satoko
Published: November 2014

Fatigue evaluation methods have been proposed based on environmental fatigue test results regarding parameters selected for simulating Boiling Water Reactor (BWR) and Pressurized Water Reactor (PWR) conditions. The effects of strain wave form have been discussed by comparing experimental fatigue life with predicted fatigue life evaluated by modified rate approach (MRA) method. The applicability of the MRA method has been verified extensively by the environmental fatigue tests with strain rate changing conditions consisting of combined constant strain rates. However, different results have been obtained for a sine strain wave in simulated BWR and PWR conditions. More study for evaluating the applicability of MRA method was required by evaluating with continuous strain rate conditions such as a sine wave. For the purpose of verification, two approaches were applied. One is performing the environmental fatigue tests with the sine strain wave in simulated BWR condition. The other is to evaluate the low cycle thermal fatigue test performed in simulated BWR condition because the wave form of this test contains continuous strain rate changing condition. MRA method was indicated to be applicable to predict fatigue lives under these kinds of continuous strain rate changing conditions.

All of the studies including this study verifying the applicability of the MRA method were performed with small specimens having the well polished surfaces in the gage length. These results indicate that the evaluation by the MRA method includes the synergistic effect between the water environment and the transient. However, the synergistic effects with the surface roughness and the component size are not known. Design margin derived by the multiplication of the sub-factors of environment, surface roughness and component size may be conservative. The evaluation of the conservatism is considered to be beneficial.
The Quantitative Estimation of the Sensitivity of Corrosion and Hydrogen Environment on Fatigue Crack Growth Rate for Steels
Authors: Ishikawa Mikihito , Yokobori A. Toshimitsu , Kawashima Yusuke , Ohmi Toshihito , Sugawara Seiji
Published: November 2014

In this paper, the tensile fatigue tests using small compact specimen were conducted by the corrosion and hydrogen embrittlement fatigue testing method which authors have proposed. Based on these results, the quantitative separated estimations of the sensitivity of Corrosion, Hydrogen Embrittlement (HE) and Facet-like Fracture Hydrogen Induced Dislocation Pile-up (F-HIDP) were made by using the acceleration factor, D*, that is the ratio of fatigue crack growth rate to that under atmospheric condition.
The Analysis of Hydrogen Diffusion Behaviors Coupled With the Analysis of Heat Transfer Around the Heat Affected Zone of Welding
Authors: Ohmi Toshihito , Yokobori Toshimitsu , Takei Kenichi , Konishi Yuki
Published: November 2014

Hydrogen penetrates into the metal and causes Hydrogen embrittlement due to the increase in hydrogen concentration. This is caused by the local stress fields such as residual stress field at the site of welding or local stress field around a crack tip. It accompanied with incubation time of several hours since the components were exposed to hydrogen atmospheric condition. This incubation time is time lag of hydrogen diffusion and concentration at the site where the hydrogen embrittlement occurs. Therefore, clarification of the hydrogen diffusion behavior is important to prevent from fracture of hydrogen embrittlement.

In this paper, the numerical analyses of hydrogen diffusion around weld part including HAZ (Heat Affected Zone) under residual stress coupled with that of heat transfer during the cooling process before and after weld were conducted and the behaviors of hydrogen concentration were analyzed. On the basis of these analyses, the method of heat treatment to prevent from hydrogen concentration at the weld part was investigated. Results obtained by these analyses showed that pre weld heat treatment is effective in the prevention of hydrogen concentration and combined pre weld heat treatment with post weld heat treatment was found to be the most effective treatment.
Probabilistic Fracture Mechanics Analysis for Degraded Reactor Pressure Vessel in Pressurized Water Reactor Nuclear Power Plant
Authors: Huang Kuan-Rong , Huang Chin-Cheng , Chou Hsoung-Wei
Published: November 2014

Cumulative radiation embrittlement is one of the main causes for the degradation of PWR reactor pressure vessels over their long term operations. To assess structural reliability of degraded reactor vessels, the FAVOR code from the Oak Ridge National Laboratories of the United States is employed to perform probabilistic fracture analysis for existing Taiwan domestic PWR reactor vessels with consideration of irradiation embrittlement effects. The plant specific parameters of the analyzed reactor vessel associated with assumed design transients are both considered as the load conditions in this work. Further, two overcooling transients of steam generator tube rupture and pressurized thermal shock addressed in the USNRC/EPRI benchmark problems are also taken into account. The computed low failure probabilities can demonstrate the structural reliability of the analyzed reactor vessel for its both license base and extended operations. This work is helpful for the risk assessment and aging management of operating PWR reactor pressure vessels and can be also referred as its regulatory basis in Taiwan.
The Effect of Inspection on Maintenance Planning for Fossil Fuel Fired Power Plant
Authors: Takahashi Jun , Sakai Shinsuke
Published: November 2014

Periodical inspection is necessary for stable operation of the plant. But usually, inspection cost and inspection period are limited, and it is difficult to inspect all of the objective location of the plant in allowed cost and period. Therefore, for maintenance planning, probability of failure is presumes by the obtained sample size inspection data. In that case, presumed probability of failure includes uncertainty, and the one-side tolerance limit of the probability is changed by the sample size of the inspection.

For maintenance on boiler tubes of fossil fuel fired power plants, only limited sample size inspection data can be used for maintenance planning. On the other hand, the conditions of the tubes for maintenance are different because environmental conditions of the tubes like actual temperature are different. Then the inspection results don’t demand enough information to presume probability of failure because the standard deviation is not known. But usually to presume probability of failure for maintenance, the standard deviation is not considered only the average is used.

Therefore, considering mainly uncertainties depend on sample size of the inspection data, presumed probability of failure is related to rational maintenance planning.
Proposal of Surface Finish Factor on Fatigue Strength in Design Fatigue Curve
Authors: Fukuta Yuichi , Kanasaki Hiroshi , Asada Seiji , Sera Takehiko
Published: November 2014

The published papers related to the effects of surface finish on fatigue strength are reviewed in order to formulate its factor in the design fatigue curve in air environment.

Firstly, some of regulations and literatures were examined to verify the surface finish effect on fatigue strength and formulation of that in design fatigue curve.

The fatigue strength of carbon and low alloy steels is decreased with an increase of its surface roughness and tensile strength but that of stainless steel is not decreased except for special conditions.

After screening the data of carbon and low alloy steels, a surface finish factor is formulated with these data which is a function of tensile strength, surface roughness and mean stress.
Statistical Model of Micro Crack Growth for the Evaluation of Accumulated Fatigue in NPPs
Authors: Abe Shigeki , Nakamura Takao
Published: November 2014

In order to establish sophisticated management of aging degradation and to achieve high reliability of components in nuclear power plants (NPPs), it is required to reveal the mechanism of aging degradation and to quantify its deterioration. Present design code requires the assessment of CUF (cumulated usage factor) using design fatigue curve to prevent the occurrence of low-cycle fatigue failure in class 1 components of NPPs. This assessment of CUF prevents the low-cycle fatigue failure effectively up to the present date. However, the margins of structural factor (safety factor) and environmental fatigue reduction factor Fen need to be clarified for the quantitative assessment of aging degradation based on the mechanism of fatigue accumulation in NPPs,. Structural factor and environmental factor are defined in NUREG/CR6909, etc, but they do not clearly explain the technical basis of these factors according to the mechanism of fatigue and environmental effect. In this study, we quantify the dispersions of crack initiation and crack growth in fatigue test in a certain condition aiming at more sophisticated management of aging degradation based on the mechanism of crack growth. Applying these dispersions, we establish a statistical model of micro crack growth to predict fatigue life. We will propose the application of this prediction model of fatigue crack growth to the management of actual components degradation and establish proper maintenance program in order to achieve high reliability of components in NPPs in future.
Fatigue-Life and Leak-Before-Break Assessments of Cr-Mo Steel Pressure Vessels With High-Pressure Gaseous Hydrogen
Authors: Yamabe Junichiro , Itoga Hisatake , Awane Tohru , Matsunaga Hisao , Hamada Shigeru , Matsuoka Saburo
Published: November 2014

Pressure cycle tests were performed on two types of Cr-Mo steel pressure vessels with inner diameters of 306 mm and 210 mm and notches machined on their inside under hydrogen-gas pressures, varied between 0.6 and 45 MPa at room temperature. One of the Cr-Mo steels had a fine microstructure with tensile strength of 828 MPa, while the other had a coarse microstructure with tensile strength of 947 MPa. Fatigue-crack growth (FCG) and fracture-toughness tests of the Cr-Mo steels were also carried out in gaseous hydrogen. The Cr-Mo steels showed accelerated FCG rates in gaseous hydrogen compared to ambient air with an upper bound corresponding to an approximately 30-times higher FCG rate. Furthermore, in gaseous hydrogen, the fracture toughness of the Cr-Mo steel with coarse microstructure was significantly smaller than that of the steel with fine microstructure. Four pressure vessels were tested; then, all of the pressure vessels failed by leak-before-break (LBB). Based on the fracture-mechanics approach, the LBB failure of one pressure vessel could not be estimated by using the fracture toughness in gaseous hydrogen. The fatigue lives could be estimated by using the upper bound of the accelerated FCG rates in gaseous hydrogen.
Stress Analysis and Design of Bolted Flange Connections Under Internal Pressure
Authors: Omiya Yuya , Sawa Toshiyuki , Takagi Yoshio
Published: November 2014

In the present paper, the gasket stress distributions, hub stress and a variation in axial bolt force in bolted gasketed pipe flange connections under internal pressure are analyzed using elasto-plastic FEM taking into account the nonlinearity of gasket behavior. Non-asbestos spiral wound gaskets were employed. The effect of nominal flange diameter is examined on the gasket contact stress distributions, the hub stress and the variation in axial bolt force (the load factor) is examined. Using the obtained gasket contact stress distribution and the fundamental data of the relationship between gasket compressive stress and gasket leak rate according to JIS B 2490, a method for predicting the leak rate is demonstrated. Experiments to measure the amount of leakage, the hub stress and the variation in axial bolt force when the joint is under internal pressure were carried out. The numerical results of the leak rate, hub stress and the load factor are in a fairly good agreement with the measured results. Then, a method is demonstrated for determining the bolt preload under given conditions, that is, taking into account assembly efficiency, leak rate and internal pressure In addition, bolt preload is determined using the actual gasket contact stress which can be estimated using the value of the load factor. As a design example, the procedure for determining the bolt preload in 3″ and 20″ nominal diameter pipe flange connections is shown for the allowable leak rate of 1.0−3Pa • m3/s. The results are validated by the experiments.
Study on Simplified Prediction Method of Thermal Ratchet Deformation Based on Parallel Bar Model
Authors: Kokufuda Toshiaki , Kasahara Naoto
Published: November 2014

For elevated temperature structures such as fast breeder reactor components, inelastic deformation is likely to occur because of reduction of yield stress and occurrence of creep deformation. The typical failure modes for elevated temperature structures are excessive deformation caused by the accumulation of inelastic deformation and creep fatigue caused by inelastic strain concentration at structure discontinuities. In order to prevent such failures, it is necessary to evaluate inelastic deformation adequately.

Thermal ratchet deformation, namely the progressive plastic deformation induced by cyclic thermal stress with uniform primary stress, has some possibility resulting in excessive deformation. ASME boiler & pressure vessel code provides elastic evaluation methods for thermal ratchet. However, these methods are so focused on preventing thermal ratchet deformation, that it could be too conservative under some conditions. Therefore, a simplified elastic evaluation method to quantify thermal ratchet deformation is desired.

In this paper, the simplified prediction method for thermal ratchet deformation is proposed using parallel bar model, which represents stress redistribution mechanism of cylindrical vessels. The solution of thermal ratchet deformation of parallel bar model was derived and compared with FEM calculation results of cylindrical vessels. This theoretical solution is proposed as a prediction method for thermal ratchet deformation of cylindrical vessels. The applicable area of the proposed prediction method is the cylindrical vessel under linear and parabolic temperature distribution through the wall thickness.
Formulation of the Aeroelastic Instability Problem of Rectangular Plates in Uniform Flow Based on the Hamiltonian Mechanics for the Constrained System
Authors: Hara Kensuke , Watanabe Masahiro
Published: November 2014

This paper addresses a formulation and an aeroelastic instability analysis of a plate in a uniform incompressible and irrotational flow based on the classical variational principle framework. Because of an intrinsic algebraic relation between the plate displacement and the velocity potential, this system has to be formulated as the constrained system. In this study, we tried to apply the Hamiltonian mechanics to the formulation of the fluid-structure interaction problem with mixed boundary condition. As a result, we obtain the canonical equations, that consist of the evolution equations for the plate displacement, the velocity potential, the Lagrange multiplier and canonically conjugate momenta for those physical quantities. In particular, it was found that the Lagrange multiplier was just the pressure. In other words, the equations of time evolution could be derived for not only the plate displacement and the velocity potential but also the pressure (the Lagrange multiplier). The stability of this system was analyzed by the eigenvalue analysis. Then, flutter modes, their frequencies and growth rates were discussed. The proposed technique has the advantage that it can reduce iteration procedures in the stability analysis. As a consequence, it can be expected that the stability of this system can be evaluated efficiently. This paper introduces a formulation of the only two dimensional problem, and the stability analysis of a clamped-free plate is implemented as an numerical example. Howerver, this formulation can be applied to three dimensional problems without intrinsic difficulties.