bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Properties of High Nitrogen - High Strength Stainless Steels in High Pressure Gaseous Hydrogen Environment
Authors: Nakamura Jun , Omura Tomohiko , Tomio Yusaku , Hirata Hiroyuki , Terunuma Masaaki , Dan Etsuo , Osuki Takahiro
Published: January 2014

The susceptibility to hydrogen embrittlement and the fatigue properties of several high nitrogen stainless steels were evaluated by SSRT (Slow Strain Rate Test) and external fatigue test. The tensile properties were evaluated by SSRT in gaseous hydrogen pressurized up to 90MPa in the temperature range from −40 degree C to room temperature. Despite the increase of nitrogen content, high nitrogen stainless steels showed no degradation by hydrogen. The susceptibility to hydrogen embrittlement depended on the chemical compositions. Fatigue properties in high pressure gaseous hydrogen were evaluated by the external cyclic pressurization test using tubular specimens. In this test the tubular specimen was filled with high pressure hydrogen gas filled with hydrogen pressurized up to 90MPa, and the outside of the specimen was cyclically pressurized with water pressurized up to 90MPa. The difference of fatigue life between hydrogen and inert gas was extremely small. Susceptibility to hydrogen embrittlement was discussed based on stability of an austenitic structure.
U-RANS Model for the Prediction of the Acoustic Sound Power Generated in a Whistling Corrugated Pipe
Authors: Golliard Joachim , González-Díez Néstor , Belfroid Stefan , Nakiboğlu Güneş , Hirschberg Avraham
Published: January 2014

Corrugated pipes, as used in flexible risers for gas production or in domestic appliances, can whistle when a flow is imposed through the pipe. Nakiboğlu et al [1, 2] have developed a method to compute the acoustic source term for axi-symmetric cavities. The method is based on the resolution of incompressible Navier-Stoke equations without turbulence modeling. This is a quasi-laminar flow model. A single cavity in a short pipe is considered with, as inlet boundary condition, a pipe flow with an imposed harmonic velocity perturbation. At low Reynolds numbers most of the effect of the turbulence is accounted by the steady velocity profile imposed at the inlet. However, this model fails when applied to high Reynolds number flows as encountered in gas-transport systems (Re = 106 or higher). In this paper, a modified model, using a 2-D unsteady Reynolds Averaged Navier Stokes turbulent solver, is presented. Turbulence determines the development of the approaching boundary layer and of the shear layer above the cavity. The shear-layer velocity profile controls the acoustic power generated by the cavity in response to the imposed acoustic oscillations. Comparison with experimental results obtained for a single cavity shows that the modification of the method considerably increases its accuracy for a deep cavity.
Cleavage Fracture Modelling for RPV Steels: Discrete Model for Collective Behaviour of Micro-Cracks
Authors: Abu-Muharib Andrew , Jivkov Andrey P. , James Peter , Yates John R.
Published: January 2014

The ability to predict variations in cleavage fracture toughness behaviour of ferritic RPV steels, accounting for the effects of irradiation and defect geometry, is vital to safety assessment and life extension decisions. Local approaches to cleavage fracture offer a promising methodology to accomplish such calculations. However, the limited progress achieved by improving the local failure probability expression suggests that the methodology for calculating global cleavage might not be adequately representing real material. The basis for the existing methodology is the weakest-link assumption that all individual failure events are independent and non-interacting. Here an approach is considered which utilises a microstructure-informed model incorporating the experimental knowledge needed to postulate deterministic criteria for particle rupture and micro-crack propagation, whilst accounting for the probabilistic distribution of particle sizes. This is then used in a lattice model that can help detail the evolution of the formation of micro-cracks on global failure, therefore inferring the suitability of the weakest-link assumption. Predicting the probability of cleavage fracture requires such models, as the macroscopic cleavage phenomenon is governed by a number of micro-structural features.

The material microstructure is represented by a regular lattice of truncated octahedral cells forming a computational site-bond model, with sites located at the cell centres and connected by two distinct sets of bonds. These bonds are modelled with structural beam elements, which represent all the possible relative deformations between coordinated sites. Particles of various sizes are distributed in the bonds, based on an experimentally determined distribution of cleavage initiating particles in RPV steel (Euro Material A). Although only elastic deformations are considered here, the results demonstrate that the interactions between individual failure events could potentially have a strong effect on the way global failure is reached.

Nucleation of micro-cracks by rupturing second-phase particles affects their subsequent formation. In particular, it was found that once formed there is a reduced probability of further development of micro-cracks at particles outside the crack planes and an enhanced probability of formation at particles along the crack planes. This will therefore influence the distribution of micro-crack sizes that could in principle be used to calculate the global probability of failure, and could lead to substantially different distributions of particle sizes, then used in the current local approach methods.
Pseudo-Dynamic Heterogeneous Testing With Dynamic Substructuring of a Piping System Under Earthquake Loading
Authors: Reza Md. Shahin , Bursi Oreste S. , Abbiati Giuseppe , Bonelli Alessio
Published: January 2014

In recent years, both pseudo-dynamic and real time heterogeneous testing with dynamic substructuring — hybrid testing — have gained significant popularity for their applicability to testing several types of nonlinear structures/systems. In a hybrid test, a heterogeneous model of the emulated system is created by combining a Physical Substructure (PS) with a Numerical Substructure (NS) that describes the remainder of the system. Nevertheless, an efficient implementation of this technique requires overcoming certain problems, e. g., proper dynamic substructuring, reduction of external forces and actuator delay compensation. This paper presents a pseudo-dynamic test campaign undertaken by the University of Trento, Italy, on a typical full-scale industrial piping system subjected to earthquake loading in order to investigate its seismic performance. Some challenges faced during the implementation are shown and strategies adopted to overcome these problems are illustrated. Experimental activities will be described and performances of different components of the piping system, i.e., elbows, tee-joints, bolted flange joints and straight pipes under earthquake loading with the presence of an internal pressure of 3.2 MPa will be presented and commented.
Semi-Active Control of Structural Systems Aiming to Approximate the Performance of the Targeted Active Control Law: Output Emulation Approach
Authors: Hiramoto Kazuhiko , Matsuoka Taichi , Sunakoda Katsuaki
Published: January 2014

As a method for semi-active control of structural systems, the active-control-based method that emulates the control force of a targeted active control law by semi-active control devices has been studied. In the active-control-based method, the semi-active control devices are not necessarily able to generate the targeted active control force because of the dissipative nature of those devices. In such a situation, the meaning of the targeted active control law becomes unclear in the sense of the control performance achieved by the resulting semi-active control system. In this study, a new semi-active control strategy that approximates the control output (not the control force) of the targeted active control is proposed. The variable parameter of the semi-active control device is selected at every time instant so that the predicted control output of the semi-active control system becomes close to the corresponding predicted control output of the targeted active control as much as possible. Parameters of the targeted active control law are optimized in the premise of the above “output emulation” strategy so that the control performance of the semi-active control becomes good and the “error” of the achieved control performance between the targeted active control and the semi-active control becomes small.
Detail Investigation of Omega Method for Creep Analysis of Pressure Vessel Components
Authors: Vivio Francesco , Gaetani Luca , Ferracci Michele , Masia Alessandro
Published: January 2014

A comprehensive creep material model for evaluation of high temperature applications of ferritic, martensitic and austenitic steels is available in API 579-1/ASME FFS and in ASME VIII Div 2 CC-2605-1 codes based on MPC Project Omega.

Although the model can be used directly to analyze pressure vessels components behavior in a non-linear finite element creep analysis, several numerical and theoretical limits are to be taken into account in the implementation of the FE user-subroutine of the material model.

In this context, a deep parametric analysis, both theoretical and numerical, based on different possible operating conditions and material behavior (temperature, pressure, stress field, elastic-plastic material properties and plastic flow rules) has been performed to review the model results on a high pressure vessel component.

Based on results of these analyses, a theoretical critical review of the method is presented.
Experiments to Determine the Influence of Residual Stress and Elastic Follow-Up on Creep Crack Initiation
Authors: Shirahatti A. M. , Truman C. E. , Smith D. J.
Published: January 2014

Components used in the power generation sector are often continuously exposed to high temperatures and corrosive environments. Failure processes, such as net section rupture, creep crack growth or fatigue crack growth therefore occur within the high temperature regime. The presence of residual stresses plays an important role in the subsequent failure of engineering components and structures. Residual stresses can arise from almost all manufacturing and fabrication processes and can also arise during service. Tensile residual stresses may combine with in-service loads to promote failure at a load the designer would view as safe. A quantitative understanding of how residual stresses interact with applied service loads is thus required for accurate safety assessments.

In this paper a test rig based on a three bar structural model is used to introduce long range residual stresses in a 316H steel C(T) specimen at high temperature. The residual stresses induced are characterized easily without use of time consuming residual stress measurement techniques. The complete test rig is then subjected to an applied load. The magnitude of the residual and applied stress in the 316H C(T) specimen is a function of the initial misfit displacement, applied load and relative stiffness of the components of the test rig. The experimental results show that a test rig with a higher elastic follow-up value will have more crack growth compared to a rig with a lower elastic follow-up. Also, both tests demonstrate that as the crack grows, relaxation of residual stress in the C(T) specimen occurs, and it is compensated by a change in residual stress distribution in other parts of the rig. Furthermore, creep crack initiation data is compared with load controlled tests conducted. It is found that the time for the crack to initiate is increased in the case of mixed boundary conditions compared to load controlled conditions.
The Effect of Different Types of Surface Preparation on Lap Shear Strength of a Typical Ambient Cured Carbon Fiber Composite Repair System
Authors: Mally Timothy S. , Keller Michael W. , Walker Roger H.
Published: January 2014

A crucial factor in a composite repair installation is the degree of surface preparation that is available. The surface profile that is created is directly proportional to the bond strength of the composite repair to the substrate. A NACE-2 near-white metal sandblast is ideal surface preparation for a composite repair. However, this degree of surface preparation is not available for every installation for various reasons. As a result, this paper details the effects of several different kinds of surface preparation on composite bond strength.

Details are presented for the lap shear testing of a carbon fiber reinforced polymer (CFRP) according to ASTM D5868. Five different surface preparation techniques are tested, including NACE-2 sandblast, bristle blast, wire brush, carbide grinder, and sand paper. The testing is used to calculate the necessary degree of surface preparation required to sustain an acceptable field repair.

Test samples are fabricated according to the ASTM standard, and are tensile tested on an MTI-5K tensile machine. The lap shear values are compared to acceptable values required in the ASME Post Construction Code 2. Industry experience is also considered as it is determined whether these surface preparation methods are acceptable for in-situ composite repair.
Creep Property Evaluation for Stress Mitigation Simulation in Post Weld Heat Treatment
Authors: Yanagida Nobuyoshi , Saito Koichi
Published: January 2014

Creep properties for stress mitigation simulation in post weld heat treatment (PWHT) were studied. Materials tested in this study were both deposited metal and base metal of a nickel base alloy, an austenitic stainless steel, and a low alloy steel. First, creep tests were conducted at 625 °C, which is a holding temperature in PWHT of a low alloy steel. Test specimens were subjected to certain stress and the amount of creep strain was measured. A Norton-Bailey law model was used to simulate the amount of creep strain. Material parameters for the Norton-Bailey law model were determined from the creep strain measurement data. Stress relaxation tests were also conducted at 625 °C. Test specimens were subjected to a constant total strain and stress relaxation was measured. The experimentally measured stress relaxation data were calculated using the Norton-Bailey law model with the material parameters determined from the creep tests. The calculation data showed good agreement with the experiment data. Accordingly, the material parameters determined in this study can be considered valid.
The Simplified Method for Fatigue Assessment of the European Pressure Vessel Standard EN 13445
Authors: Lidonnici Fernando
Published: January 2014

The European Pressure Vessel Standard EN 13445 provides in its part 3 (Design) a simplified method for fatigue assessment. Use of the simplified method is limited to cases where the cyclic load is mainly given by pressure fluctuations. The stress ranges needed for the evaluation of the allowable number of cycles are calculated only on the basis of the pressure range and of the maximum allowable pressure of each vessel component, obtained from the normal design formulae. Suitable tables are provided in order to establish, for each vessel component, a relationship between the stress range and the pressure range. Other tables are provided in order to define a suitable fatigue curve on the basis of the so called “Weld Class”: curves with higher values of stress ranges are given for full penetration welds having better NDT testing, while curves with lower stress ranges are given for not fully penetrated welds with poor or no NDT testing. Since only the plain Design by Formulae is needed for the use of the method, no FEM calculations are required. The simplified method may therefore give a suitable simple and economic solution in many common cases of cyclic loading. In this paper two worked examples have been provided in order to compare the results of fatigue calculations made with the simplified method with the results obtained by means of a complete F.E.M. stress analysis.
Hyper Compressor Tungsten Carbide Plunger Repair
Authors: Manuel Randy
Published: January 2014

Solid Tungsten carbide plungers are the primary choice for hyper compressors for manufacturing Low Density Polyethylene (LDPE.) However, tungsten carbide plungers in this severe service is susceptible to premature failures and/or short runs due to gas leakage from the running combinations of lubrication, packing and plunger surface. Thermal fatigue (heat checking), fretting, corrosion and scoring are common problems found on the plunger surface resulting in premature leakage or even plunger breakage. This paper elaborates on these plunger problems, repairs and possible reasons for these surface defects.
Study on Structural Integrity Analysis of Tubular Reactor With Corrosion Pits in LDPE Plant
Authors: Zhao Jianping , Miao Chunsheng , Chen Jiang , Guan Xinchun
Published: January 2014

Ultrahigh pressure polyethylene tubular reactors were widely used in Petrochemical Industry. Because of corrosion, fatigue crack and other defects easily caused by a high operating pressure and complicated operating conditions for tubular reactor, their safety was a concerned issue in the engineering field. This paper conducted genetic mechanism analysis on ultrahigh pressure polyethylene tubular reactors with corrosion pits in LDPE plant. The ultimate bearing capacity analysis was carried out for tubular reactor with pits by three-dimensional finite element method. The effects of depth, length and width of pits on structural bearing capacity were discussed. The results indicated that the critical pit depth of tubular reactor was 8mm.
Development and Validation of Inverse Analysis of Heat Conduction and Thermal Stress for Elbow: Part II
Authors: Hojo Kiminobu , Ochi Mayumi , Ioka Seiji , Kubo Shiro
Published: January 2014

A heat conduction inverse method for piping elbow was developed to estimate the temperature and stress distribution on the inner surface by measuring the outer surface temperature. In the Part I paper, the derivation and verification of the heat conduction inverse method were described. In the Part II paper, the accuracy for the thermal stress calculation was confirmed by assuming several thermal stratification patters and comparing with the reference results from normal FE heat conduction and thermal stress analyses. As a result, in the case of the measured-basis fluid temperature input from a high temperature-pressure test, the inverse method estimated the maximum stress change by 7% conservative comparing the normal FE analyses. For the assumed temperature change pattern the estimation accuracy was conservatively improved by attaching the additional thermocouples on the outer surface adjacent to the thermal stratification phase. The developed method is practically useful because of short calculate time of 1–2 seconds for 500 time data points after providing the transfer functions.
Comparison of R5 and ASME NH Creep-Fatigue Damage Assessment Methodologies
Authors: Sheridan Michael , Knowles David , Montgomery Oliver
Published: January 2014

The R5 volume 2/3 procedures [1] were developed by British Energy (now EDF Energy) to assess the high temperature response of uncracked metallic structures under steady state or cyclic loading. They contain the basic principles of:

• Application of reference stress methods

• Consideration of elastic follow up

• A ductility exhaustion approach to calculate creep damage accumulation.

These considerations represent a fundamental distinction from ASME BPVC Section III, Subsection NH [2].

This paper draws on literature review and experience to explain the principal differences in the limits of application, cycle construction and damage calculation between these codes/procedures focusing on creep-fatigue damage determination. The implications of the differences between the codes and standards are explored.

The output of this work is aimed at two groups of structural integrity engineers; those using these codes and standards to assess existing conventional and nuclear plant, and also those looking to ASME and R5 to design Generation IV PWRs with design temperatures much elevated from those of Generation III and III+.

The conclusions from this paper offer some practical guidance to structural integrity engineers which may assist in selecting the more appropriate procedure to assess creep-fatigue damage for a particular situation.
A Design Approach Based on Historical Test Data and Bayesian Statistics
Authors: Wei Zhigang , Yang Fulun , Konson Dmitri , Nikbin Kamran
Published: January 2014

Testing is still the final verification for a design even though there are substantial number of analytical and simulation methods available. Testing is seen to be also an indispensable part in the foreseeable future. Numerous test data have been generated in many testing institutions over the years and it is clear that future new tests will be conducted. Historical data with similar design and operating conditions can shed light on the current and future designs since they would share some common features when the changes are not dramatic. To effectively utilize the historical data for future design, two steps are necessary: (1) finding an approach to consistently correlate test data obtained from various conditions; (2) Use of Bayesian statistics which can provide a rational mathematical tool for extracting useful information from the historical data.

In this paper, the basic Bayesian statistical procedure based on the historical data is outlined. With this information the reduction of sample size number or improving the accuracy and confidence with the same sample size are becoming possible. Examples of utilizing the historical data are also presented and the benefit of using the Bayesian statistics are highlighted.
Statistical and Probabilistic Analysis of Thermal-Fatigue Test Data Generated Using V-Shape Specimen Testing Method
Authors: Wei Zhigang , Lin Burt , Ellinghaus Kay , Pieszkalla Markus , Harlow D. Gary , Nikbin Kamran
Published: January 2014

V-shape specimen testing is a relatively new, simple and useful technique to characterize the thermal-fatigue resistance of materials subjected to combined thermal/mechanical loadings, and to rank and select materials. However, the V-shape specimen test data, similar to many other life test data, always contain an inherent scatter not only because of material non-uniformity but also of the difficulties in operating control, such as loading, boundary conditions, and environment. Therefore, statistical and probabilistic approaches have to be used to interpret the test data in order to implement the observations into new product designs. In this paper, the V-shape specimen test data are selected, analyzed and the scatter properties of the test data are fitted using several continuous probability distribution functions. The results are compared, and the root failure mechanisms of the V-specimens are also discussed. Finally, the main observations are summarized, and a recommendation is provided.
A Study on Controllable Aseismic Device With Inertia Mass and MR Fluid
Authors: Sodeyama Hiroshi , Shibata Kazuhiko , Sato Yusuke , Tomizawa Tetsuya , Fujitani Hideo
Published: January 2014

The authors have developed a new aseismic device, which has a ball screw and rotational mass. It not only generates the resistive inertial force originating in the rotational mass but also dissipates the energy of vibration through a viscous damping mechanism. Furthermore, the damping capability of the device can be controlled externally with an applied magnetic field. A magneto-rheological (MR) fluid is used to change the dynamic characteristics of the device. Through comprehensive experimental testing of a prototype device, the dynamic characteristics of the device have been verified. The test results show that the force-displacement relationship varies with an applied magnetic condition. Only a few amperes of electric current is required to generate a magnetic field effective for the prototype device with a capacity of 100kN.
Creep Strength of Dissimilar Weld Using High B-9Cr Steel for A-USC Boiler
Authors: Tabuchi Masaaki , Hongo Hiromichi , Abe Fujio
Published: January 2014

The research project aiming to commercialize 700°C class pulverized coal power system; advanced ultra-super critical (A-USC) pressure power generation has been conducted in Japan from 2008. In A-USC boilers, Ni base or Ni-Fe base alloys are used for high temperature parts at 650–700°C and advanced high Cr ferritic steels are planning to be used at the temperatures lower than 650°C. Because the high B-9Cr steel developed in National Institute for Materials Science (NIMS) has improved creep strength in weldments, it is one of the candidate materials for A-USC boilers. In the present paper, the creep tests of the dissimilar welds between high B-9Cr steels and Ni base alloys were conducted. In the heat affected zone (HAZ) of the high B-9Cr steels, fine-grained microstructures were not formed and grain size of the base metal was retained. Free boron on the grain boundaries is considered to affect the mechanisms of the α-γ transformation during weld thermal cycle. Consequently, the creep rupture lives of the dissimilar welds between high B-9Cr steels and Ni base alloys were 5–10 times longer than those of the conventional 9Cr steel welds at 650°C.
Application of the Transfer Matrix Method to the Analysis of Hydro-Mechanical Vibration of NPP Piping
Authors: Orynyak Igor , Radchenko Sergii , Dubyk Iaroslav
Published: January 2014

The transfer matrix method (TMM) was used for description of harmonic vibrations of piping with transported medium. Apart from 12 well-known mechanical parameters which characterize the state of piping system in each cross section two additional parameters that characterize the vibration of the medium, namely its translation and pressure pulsations were considered. The solution of these equations, which take into account the Poisson contraction of the pipe wall, in the form suitable for the transfer matrix method application was derived. The biggest uncertainty in the analytical modeling is to adopt the boundary conditions for above mentioned 2 parameters for the considered piping section. To solve this problem of identification of the most probable induced frequency we developed the technique of choosing such boundary conditions at which the maximum of energy is confined within the considered piping section. The validity of the approach was tested on some analytical examples. This method was used to analyze the forced vibration of the second circuit loop of unit 1 Zaporizhia Nuclear Power Plant (ZNPP) with VVER-1000 (from Russian: Vodo-Vodyanoi Energetichesky Reactor; Water-Water Power Reactor) arising from turbulent eddies in the flow of steam. Natural frequencies and forms of mechanical, hydrodynamic, and related hydro-mechanical vibration were found, a number of recommendations were given to reduce the vibration levels.
Influence of Phase Transformations on Residual Stresses in Welded Structures
Authors: Dennis R. J. , Kulka R. , Muransky O. , Smith M. C.
Published: January 2014

A key aspect of any numerical simulation to predict welding induced residual stresses is the development and application of an appropriate material model. Often significant effort is expended characterising the thermal, physical and hardening properties including complex phenomena such as high temperature annealing. Consideration of these aspects is sufficient to produce a realistic prediction for austenitic steels, however ferritic steels are susceptible to solid state phase transformations when heated to high temperatures. On cooling a reverse transformation occurs, with an associated volume change at the isothermal transformation temperature.

Although numerical models exist (e.g. Leblond) to predict the evolution of the metallurgical phases, accounting for volumetric changes, it remains a matter of debate as to the magnitude of the impact of phase transformations on residual stresses. Often phase transformations are neglected entirely. In this work a simple phase transformation model is applied to a range of welded structures with the specific aim of assessing the impact, or otherwise, of phase transformations on the magnitude and distribution of predicted residual stresses. The welded structures considered account for a range of geometries from a simple ferritic beam specimen to a thick section multi-pass weld. The outcome of this work is an improved understanding of the role of phase transformation on residual stresses and an appreciation of the circumstances in which it should be considered.
Determination of the Transition Temperature Scatter Using the Charpy Data Scatter
Authors: Orynyak Igor , Zarazovskii Maksym , Bogdan Andrii
Published: January 2014

For a pressure vessels integrity assessment it is necessary to know the transition temperature of metal. It is defined from the hyperbolic tangent curve, which best approximates the Charpy V-notched (CVN) impact tests data, as the temperature corresponding to some fixed Charpy impact energy.

However, when planning experiments, processing of the results, and interpreting of the resulting transition temperature, two problems arise which have not been studied in the literature. First — sufficiency of the CVN impact tests data for a curve fit building and transition temperature determination. Second — experimental data scatter accounting while determining the transition temperature.

This work proposes to define two quantitative characteristics: the “importance” of each CVN impact test for the defined transition temperature; the transition temperature scatter which is calculated from the Charpy impact energy data scatter with consideration of the above “importance”. Also the data points sufficiency criterion for adequate defining the transition temperature is formulated.

Numerical experiments carried out on sets of test data have shown a good correlation between transition temperatures scatter calculated by the standard method and by the one developed in the present paper. Analysis of RPV weld metal surveillance data in the initial and irradiated conditions for Unit 1 and 2 of South-Ukrainian NPP shows that the transition temperature scatter, determined in this way, reaches 26°C.
Study of Prolonged Service Degradation of Superheater Tubes and its Effects on Remaining Life Predictions
Authors: Al-Obaidi Khalid A. , Merah Nesar
Published: January 2014

This study investigates the degradation of superheater tubes that has been in service for very long time. It also discusses the degradation effects on tube remaining life predictions. The tubes, utilized in this study, belong to an industrial boiler that has been in service for 232 000 h in a petrochemical plant and generate steam at 47 barg and 410 °C. Outcomes of this study will contribute to better understanding and development of scientific procedures to make reasonable estimate of tube remaining life considering the tubes aging while in service. This is beneficial in preventing failures and forced plant shutdown when life is consumed. It also helps industry to avoid capital expenditures on premature replacements of boiler tubes that can still serve longer time. In this study, comparison is made between short-term life predictions and actual properties found after about 26.5 years of service. The tubes condition is assessed by metallographic, mechanical and stress rupture testing. According to the results, it is found that prolonged service degradation has strong effects on remaining life predictions. Both effects that would lead to overestimating or underestimating tube remaining life were found if existing procedures are used without consideration for material degradation during service.
Comparison of Handbook and 3-D Finite Element Analysis LEFM Solutions for a Threaded Fastener
Authors: Sommerville Daniel , Qin Minghao , Walter Matthew
Published: January 2014

As part of license renewal activities, many Boiling Water Reactor utilities must assess the integrity of bolted components within the reactor pressure vessel. Since inspection techniques capable of identifying cracking in the threaded regions of the core plate bolting do not currently exist it is important for flaw tolerance evaluations to be performed with as much accuracy as possible in order to obtain realistic inspection intervals and to assess the degree of redundancy in the bolted joint designs. Both 3-D finite element analysis and handbook linear elastic fracture mechanics solutions are used to assess the flaw tolerance of a core plate bolt design. Consideration of the relevant degradation and crack growth mechanisms is given for both initial crack configuration(s) and crack growth calculations. The 3-D finite element analysis is performed to investigate the effects of various simplifications in the available handbook solutions presented in the literature. The results of the flaw tolerance evaluations using both methods are compared and conclusions drawn regarding the applicability of the available handbook solutions for similar work in the future.
Deflection of Gaskets and its Effect on Tightness of Flanged Connections in Long Term
Authors: Kobayashi Takashi , Nishiura Kengou , Hiratsuka Masaaki , Itoi Katsutoyo
Published: January 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 PTFE gaskets are used. The visco-elastic characteristic of gaskets is the main cause for the phenomenon. It has been shown that the tightness improved even if the bolt forces reduced in the long term. The reason was thought that gaskets became packed under a high gasket stress. Because of this effect, the leak rate decreased. It is important to estimate the thickness change of gaskets to evaluate the tightness of flanged connections.

In this paper, a model of a flanged connection, in which the flange, the bolts and the gasket are represented by spring constants, is proposed. Using the model, the relationship between the gasket deflection and the tightness are discussed.
Experimental Investigation on Minimum Design Metal Temperature of Q345R Steel
Authors: Shu Xiangyu , Zheng Jinyang , Shou Binan
Published: January 2014

Q345R is the most widely used material in manufacture of pressure vessels in China. It is recently permitted in ASME Code Case 2642 for the fabrication of pressure vessels with design temperature above −10°C without concern about the low stress conditions. However, it’s allowed to be used at above −20°C in Chinese standards. For understanding its properties under low temperature, a large amount of toughness test data of Q345R were collected from recent literature, and lots of Charpy V-notched (CVN) impact tests at a series of lower temperature were also conducted. Several Ductile-Brittle Transition (DBT) curves were drawn from the test results and some reference temperatures for DBT region and CVN energies at certain temperatures were obtained and discussed. Results show that its toughness at −20°C is much better than that required both in Chinese standards and American Codes. The reference temperature of Q345R was determined as −24.7°C by using a conservative statistical estimation. And It is suggested that the allowable Minimum Design Metal Temperature (MDMT) of this material in American codes should be extended to a lower region.
Proposal of Fatigue Life Equations for Carbon and Low-Alloy Steels and Austenitic Stainless Steels as a Function of Tensile Strength
Authors: Kanasaki Hiroshi , Higuchi Makoto , Asada Seiji , Yasuda Munehiro , Sera Takehiko
Published: January 2014

Fatigue life equations for carbon & low-alloy steels and also austenitic stainless steels are proposed as a function of their tensile strength based on large number of fatigue data tested in air at RT to high temperature. The proposed equations give a very good estimation of fatigue life for the steels of varying tensile strength. These results indicate that the current design fatigue curves may be overly conservative at the tensile strength level of 550 MPa for carbon & low-alloy steels. As for austenitic stainless steels, the proposed fatigue life equation is applicable at room temperature to 430 °C and gives more accurate prediction compared to the previously proposed equation which is not function of temperature and tensile strength.
Creep Rupture Strength Evaluation With Region Splitting by Half Yield
Authors: Kimura Kazuhiro
Published: January 2014

Creep strength of ferritic and austenitic steels has been investigated on the correlation between stress vs. creep rupture life curve and 50% of 0.2% offset yield stress (half yield) at the temperatures. Inflection of stress vs. creep rupture life curve was recognized on ferritic creep resistant steels with martensitic or bainitic microstructure. However, no identifiable correlation was observed on ferritic steels with ferrite and pearlite microstructure, as well as austenitic steels and superalloys except for several alloys. Ferritic steel with martensitic or bainitic microstructure indicates softening during creep exposure, however, hardening due to precipitation takes place in the ferritic steel with ferrite and pearlite microstructure and austenitic steels. This difference in microstructural evolution is associated with indication of inflection at half yield. Stress range of half yield in the stress vs. creep life diagram of creep strength enhanced ferritic steels is wider than that of conventional ferritic creep resistant steels with martensitic or bainitic microstructure. As a result of wide stress range of boundary condition, risk of overestimation of long-term creep rupture strength by extrapolating the data in high-stress regime to low-stress regime is considered to be high for creep strength enhanced ferritic steels.
Experimental Evaluation of Resonance Frequency at Branch Section in Each Dry and Wet Steam Flow
Authors: Uchiyama Yuta , Morita Ryo
Published: January 2014

Flow-induced acoustic resonances of piping system containing closed side-branches are sometimes encountered in power plants. In U.S. NPP, the steam dryer had been damaged by high cycle fatigue due to acoustic-induced vibration under a power uprating condition. The steam piping systems of actual power plants often have nearly saturated wet steam condition. Resonance frequency at branch section is one of important factors for evaluation and prediction of acoustic resonance. However, the resonance frequency in steam condition could not be estimated by using theoretical equation since the end correction under steam condition is not clarified. In addition, sound speed in wet steam, which is evaluated by theoretical isentropic equation, may be different from practical sound speed in wet steam. Although there are several previous studies about acoustic resonance, most of them are not steam flow but air flow. In the present study, the end correction in each dry and wet steam and sound speed of wet steam was evaluated from experimental results of dominant frequency of fluctuating pressure. As a result, method for predicting resonance frequency by using theoretical equation in each dry and wet steam condition was proposed.
Development of Design Procedure for Gasketed Pipe Flange Connections Based on Allowable Leak Rates
Authors: Nagata Satoshi , Oyama Yasuro , Sawa Toshiyuki , Kobayashi Takashi , Kurosawa Ryou
Published: January 2014

The development of a design procedure for bolted gasketed pipe flange connections based on allowable leak rates has been carried out by the technical committee for sealing technology of pressure equipment organized in the High Pressure Institute of Japan. This procedure covers the design of flange connections used at room temperature. The point preeminent of this procedure is that the maximum allowable leak of the flange connection is obtained by the minimum required initial bolt preloads determined by the elastic interaction analysis of flanges, bolts, and gasket considering thier flexibilities and stiffnesses. The paper explains the design process of this procedure and gives the technical background. The paper also shows some of examples obtained through the validation of this design procedure and the design studies for actual applications.
Multiple Crack Extension and Temperature Effect of Perforated Plate in Elevated Temperature Fatigue Test
Authors: Kinoshita Keisuke , Suzuki Yoshitaka , Kumagai Takuya , Watanabe Osamu , Matsuda Akihiro
Published: January 2014

The present paper presents the experimental results for fatigue crack propagation of SUS304 steel perforated plate at an elevated temperature of 550°C. (1) The specimens have two holes placed at an angle of 30°, 60° and 90°. Crack initiation cycle is determined from the pictures showing crack propagation process, which are measured with a CCD camera at a regular interval cycle. The stress concentration is larger in the order of 60°, 90° and 30°, the number of cycles to failure Nf follows this order. By using the inelastic strain amplitude, cycles to crack initiation for each specimen can be predicted. Hereafter, multiple cracks at different sites propagate according to the strain concentration contours. (2) The effect of high temperature on fatigue strength is also investigated for temperature from 500°C to 700°C. Cracks occurring at hole sides are measured by a CCD camera and the crack growth is calculated from photographs. Some specimens show the multiple small cracks at hole-side. (3) This paper also discusses fatigue evaluation of the circular notched plate under the inter-laminar shear loading at elevated temperature. FEM analysis of a specimen shows the distribution of stress under inter-laminar shear loading. Fatigue tests were conducted, and compared with results of analysis. The stress distribution under the inter-laminar shear loading shows unique distributions compared with those under the tensile loading, which is consistent with experimental results.
Development of Inverse Analysis of Heat Conduction and Thermal Stress for Elbow: Part I
Authors: Ioka Seiji , Kubo Shiro , Ochi Mayumi , Hojo Kiminobu
Published: January 2014

Thermal fatigue may develop in piping elbow with high temperature stratified flow. To prevent the fatigue damage by stratified flow, it is important to know the distribution of thermal stress and temperature history in a pipe. In this study, heat conduction inverse analysis method for piping elbow was developed to estimate the temperature history and thermal stress distribution on the inner surface from the outer surface temperature history. In the inverse analysis method, the inner surface temperature was estimated by using the transfer function database which interrelates the inner surface temperature with the outer surface temperature. Transfer function database was calculated by FE analysis in advance. For some patterns of the temperature history, inverse analysis simulations were made. It was found that the inner surface temperature history was estimated with high accuracy.
Application of Surface Roughness Parameters to the Evaluation of Low Cycle Fatigue Damage in Austenitic Stainless Steel
Authors: Fujimura Nao , Nakamura Takashi , Oguma Hiroyuki
Published: January 2014

Changes in the surface roughness of SUS316NG during cyclic loadings were investigated, and the relations between those changes and the crack initiation and propagation processes are discussed on the basis of microscopic observations and cellulose acetate replica observations. Strain-controlled fatigue tests were conducted at three constant strain ranges. Surface roughness was measured periodically during the tests, and three roughness parameters were calculated: arithmetic mean roughness Ra, surface profile maximum height Rmax, and maximum valley depth Rv. Until the middle of fatigue life, all three increased linearly with the number of cycles regardless of the strain range, and their rates of increase became smaller with decreasing strain range. Surface observation revealed that small cracks initiated very early in fatigue life, propagated slowly until the middle of fatigue life, and then grew rapidly. Changes in surface roughness are therefore sensitive to fatigue loading even when cracks are very small and crack detection is difficult. The results suggest that surface roughness can probably be used to assess fatigue damage because until the middle of fatigue life it increases linearly with the number of cycles. The definition of each roughness parameter and the changes show that Rmax and Rv are suitable for damage assessment.
Use of the Alternating Current Potential Drop (ACPD) Technique to Monitor Creep Behaviour of Austenitic Steels
Authors: Narayanan Aditya , Davies Catrin M. , Mahmoud Yasser K.
Published: January 2014

The Alternating Current Potential Drop (ACPD) strain sensor has been developed as a tool to monitor the condition of a material. It is comprised of a square array of sensors that measures the resistance in two orthogonal directions, using the changes in the material’s resistance over time as a measure of its deformation and evolution of damage within it due to creep. The method expresses the change in resistance as the ratio of axial to lateral resistance, suppressing temperature-related effects on material resistivity, which are mostly isotropic.

Previous experiments have seen this method applied to samples of ferritic (2.25CrMoV) steel at 650°C [1]. Within this paper, the method has been extended to include work on the austenitic stainless steel 316H (17Cr11NiMo). Results of a series of interrupted creep tests are presented that show the resistance behaviour of the material at different points in its creep life. Metallographic studies have also been performed so as to establish how data gained using this technique is related to the condition of the material.
Long-Term Design of Composite Pipes and Tanks
Authors: Faria Hugo , Guedes Rui M. , Marques A. Torres
Published: January 2014

In order to improve the reliability and confidence of composite solutions for piping and tanks in the several industrial applications they serve, deeper knowledge on the long-term behavior is needed. In this work a practical predictive approach for the long-term properties of these structures was established. It is based on experimental data previously obtained in comprehensive experimental programs for different types of GFRP pipes, thus covering a wide range of laminate constructions and manufacturing processes. In this paper, the principles, applicability and validation of the design criterion developed are presented and discussed.
The Effect of Punching Plates to Suppress the Sloshing in a Gas Liquid Separator
Authors: Suzuki Hayato , Kaneko Shigehiko
Published: January 2014

Natural gas is relatively clean and its demand is increasing these days. In most of the case, gas fields are located at the bottom of the sea. Therefore, Floating Production, Storage and Offloading (FPSO) system is now attracting big attention. This paper is related to dynamical design of FPSO system, specially focused on the free surface elevation in the horizontal cylindrical and axisymmetric liquid vessel with end caps induced by the wave. In this study, the theory on the wave height and resonant frequency in a horizontal cylinder subjected to longitudinal external excitation is developed. Then, the theory capable of taking account of the effect of punching plates is described. Finally, experimental data of resonant wave height up to 3rd mode are shown in comparison with theoretically derived results.