bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissecting the Dinosaur; Problems With B16.5 and B16.47 Flange Standards
Authors: Brown Warren
Published: January 2014

ASME B16.5 and B16.47 flanges have been in existence for a very long time with very few changes made since their creation. That might lead the casual observer to think that the designs contained in those documents have been optimized and represent best in technology. While that may have been the case when they were first introduced, it is anything but the case at the moment. In fact, in many cases the design of these standard flanges is far from optimal. However, even worse than that, there are presently several significant issues with the flange standards that could be easily resolved, without adding cost to the flanges or requiring dimensional modifications.

These changes would eliminate some existing or potential joint integrity failures. This paper outlines a list of improvements, complete with justification for the need, which the author would like to see made to the ASME standard flange standards. Some of these suggestions have already gained support in industry and been relayed on to the B16.5 committee, however they have not yet been incorporated. These simple improvements can, for the most part, be implemented within existing company standards in order to immediately circumvent potential or existing joint leakage issues. The paper details suggestions for modification of the standard B16.5, B16.47 and B16.20 wording, both for consideration by the B16 committees and incorporation into corporate standards in the interim.
Improved Analysis of External Loads on Flanged Joints
Authors: Brown Warren
Published: January 2014

External loads on bolted flanged joints must be assessed in order to be in compliance with ASME and other international pressure vessel and piping codes. However, in the case of the ASME B31.3 piping code or ASME VIII, Division 1 pressure vessel code, there is not specific guidance on how to assess these loads. This has created a situation where piping designers have employed a variety of methods, ranging from very conservative to possibly non-conservative. A review of historical joint external load experiments is made in this paper, which highlights the relatively low risk of joint leakage due to external loads. In addition, an improved method of assessing the acceptability of external loads for any given joint is introduced and compared to both test results and existing assessment methods. The method presented is based on probability of leakage for standard piping joints using the method outlined in Appendix O of ASME PCC-1 [1]. This allows, in some cases, a much higher acceptable load than typically employed when using traditional methods such as the Equivalent Pressure method. By allowing higher external loads, it is possible to reduce the footprint of a process unit, which saves money, while maintaining safety.
Investigations on Creep Behavior of P91-Type Steel Using Combined Creep Damage Model
Authors: Liu Fujun , Tang Ping , Kong Shuai , Ling Zhangwei , Zheng Muling , Zhao Liwei
Published: January 2014

P91-type steel is widely used for the high-temperature pipe work components in advanced power plants. The creep behavior of the P91-type steel has been studied by many researchers during the past years. Since it is well known that the creep behavior of P91-type steel cannot be satisfactorily described by a simple, Arrhenius-type, power-law constitutive model. While Norton-Bailey creep is a deviatoric temperature-dependent creep model, furbished with a time-hardening creep model, which is the most common model for modeling primary and secondary creep together, and Kachanov-Rabotnov creep damage theory described with Norton creep model can be used to model tertiary creep. Both of them based on Norton creep constitutive equation. In this paper, based on the Norton-Bailey creep law and Kachanov-Rabotnov creep damage theory, a new combined constitutive model has been developed, in which the creep and damage function are both considered as nonlinear variables. The damage parameters in the model have clear physical meaning and can be determined from the benchmark experiment. The results indicated that this combined damage model was applicable to describe the full damage evolution for P91-type steel.
Inquiry Into Characteristic of Multiple Friction Pendulum System With Multiple Sliding Surfaces Under Bidirectional Loadings
Authors: Tsai C. S. , Wang Y. M. , Su H. C.
Published: January 2014

In order to investigate the bidirectional characteristic of a multiple friction pendulum system (MFPS) with multiple sliding surfaces, a series of component tests were performed by using the shaking table in the National Center for Research on Earthquake Engineering, Taipei, Taiwan. The multiple friction pendulum system with multiple sliding surfaces consists of double concave surfaces, more than one intermediate sliding plates and one articulated slider located between the concave surfaces and intermediate sliding plates. These devices can continuously change their horizontal stiffness, damping, and displacement capacities during ground shaking by virtue of the properties such as radii and friction coefficients of multiple sliding surfaces. In this study, both uni- and bidirectional component tests of a multiple friction pendulum system with three and four sliding surfaces were carried out to investigate its mechanical characteristic. Furthermore, results obtained from the shaking table tests of an isolated steel structure demonstrate that the MFPS isolation system with multiple sliding surfaces could properly change its stiffness and damping effect, and effectively reduce the excitation force during ground shaking.
FEM Contact Stress Analysis at the Bearing Surfaces in Bolted Joints With Washer Under Tensile Loadings
Authors: Sawa Toshiyuki , Omiya Yuya , Kuwaki Kengo
Published: January 2014

High strength bolts with washers are utilized widely for high reliability. The usage of the high strength bolts enables higher bolt preload, thus the contact stress at the bearing surfaces increase. When a bolted joint is under external axial load W, the axial bolt force increases by Ft and the contact stress increases at the bearing surface. This may cause the plastic deformation and a decrease in the axial bolt force. Consequently, it is important to determine the initial axial bolt force (bolt preload) considering external load. In this paper, The characteristics of hollow cylindrical bolted joints with plain washers under external tensile loadings are analyzed using elasto-plastic FEM such as the contact stress distributions, plastic displacement (permanent set) at the bearing surfaces and the load factor Φ = (Ft/W). The effect of thickness of the plain washers on the contact stress distributions and the plastic displacements are clarified. It is found that the effect of the plain washer specified in JIS B 1256 is small on the contact stress distributions and the plastic displacements. Also, the effect of the external load on the changes in the contact stress distributions and the plastic displacements at the bearing surfaces using the values of load factor is observed to be small. The prediction for the reduction in axial bolt force was compared with the experiment. As a result, it was found that a higher bolt preload shows a small reduction in axial bolt force.
Effect of Local Wall Thinning on Low-Cycle Fatigue Behaviors of Elbow With Internal Pressure: Estimation of Fatigue Life Based on Revised Universal Slope Method
Authors: Takahashi Koji , Sato Kyohei , Matsuo Kazuya , Ando Kotoji , Urabe Yoshio , Hidaka Akitaka , Hisatsune Masakazu , Miyazaki Katsumasa
Published: January 2014

Low-cycle fatigue tests and finite element analysis were conducted using 100A elbow specimens made of STPT410 with local wall thinning in order to investigate the influences of local wall thinning on the low-cycle fatigue behaviors of elbows with internal pressure. Local wall thinning was machined on the inside of the elbow in order to simulate metal loss by flow-accelerated corrosion. The local wall thinning located in three different areas, called extrados, crown and intrados. Eroded ratio (eroded depth/wall thickness) was 0.5 and 0.8. The elbow specimens were subjected to cyclic in-plane bending under displacement control with internal pressure of 0 or 9 MPa. Fatigue failure was classified into two types. The one is the type of fatigue crack initiation and another is the type of crack initiation after local buckling. In the type of fatigue crack initiation, fatigue crack initiated at crown and propagates to the axial direction. In the type of crack initiation after local buckling, at first local buckling occurs and secondary, crack initiates at the same place and propagates to the circumferential direction. The low-cycle fatigue lives of elbows were predicted conservatively by the revised universal slope method.
Study on Weld Residual Stress and Crack Propagation Evaluations for a Saddle-Shaped Weld Joint
Authors: Katsuyama Jinya , Masaki Koichi , Onizawa Kunio
Published: January 2014

Stress corrosion cracking (SCC) have been observed in reactor coolant pressure boundary piping system at nuclear power plants. When an SCC is found, the structural integrity of piping should be assessed according to a fitness-for-service rule. However, the rule stipulates the assessment procedures for crack growth and failure only for a simple structure such as cylindrical or plate-wise structure. At the present, the methodology even of an SCC growth evaluation for a geometrically complicated piping such as saddle-shaped weld joints has not been established yet. This may be because analyses on the weld residual stress distribution which affects the SCC growth behavior around such portion are difficult to conduct. In this study, we established a finite element analysis model for a saddle-shaped weld joint of pipes. The residual stress distributions produced by the tungsten inert gas (TIG) welding were calculated based on thermal-elastic-plastic analysis with moving and simultaneous heat source models. Analysis results showed complicated weld residual stress distributions, i.e., residual stresses in both hoop and radial directions were tensile at the inner surface near the nozzle corner in branching pipe. SCC growth simulation based on S-version finite element method (S-FEM) using the weld residual stress distributions in saddle-shaped weld joint was also performed. We confirmed an applicability and the accuracy of S-FEM to saddle-shaped weld joint.
Improvement in Fatigue Limit by Shot Peening for High-Strength Steel Containing Crack-Like Surface Defect: Influence of Surface Crack Aspect Ratio
Authors: Nakagawa Makiko , Takahashi Koji , Osada Toshio
Published: January 2014

The effect of shot peening (SP) on the bending fatigue limit of high-strength steel (SUP9A) containing a semi-elliptical surface slit was investigated. SP was conducted on specimens containing a semi-elliptical surface slit with an aspect ratio (a/c) of 0.4, where a was the crack depth (a = 0.1, 0.2, and 0.3 mm) and c was half the surface length of the crack. Bending fatigue tests were carried out under a stress ratio R equal to 0. The results showed that the fatigue limit of the shot-peened specimens with slits having a depth of less than 0.2 mm was almost the same as that of the shot-peened specimens without slits. Meanwhile, some of the specimens fractured at the surface in areas other than the slit. Thus, the maximum depth of the slit that could be rendered harmless by SP was 0.2 mm. The maximum depths of cracks with various aspect ratios that could be rendered harmless by SP were predicted, assuming that the cracks were arrested when the apparent stress intensity factor at the slit tip was less than the threshold stress intensity factor of the material. The estimated values were in good agreement with the experimental values. A harmless crack assessment diagram was proposed based on this estimation method.
Applicability of Miniature C(T) Specimen to Evaluation of Fracture Toughness for Reactor Pressure Vessel Steel
Authors: Yoshimoto Kentaro , Hirota Takatoshi , Sakamoto Hiroyuki , Sugihara Takuji , Sakaguchi Shohei , Oumaya Toru
Published: January 2014

Irradiation embrittlement of Japanese reactor pressure vessels (RPV) is usually monitored by conducting tests on irradiated RPV material according to surveillance test program. Although fracture toughness specimens are contained in Japanese PWR surveillance capsule, the number of specimens is limited due to capacity of capsule. In order to evaluate lower bound of fracture toughness considering its scatter with higher reliability, it is expected to obtain additional fracture toughness data using remaining broken specimens of irradiated materials.

One of solutions to this problem is specimen reconstitution technique. However, it is difficult to make numbers of specimens by reconstitution because of need for specific equipments and time-consuming machining operations. As an alternative method, fracture toughness test using miniature C(T) specimens with dimension of 4×10×10mm, which can be taken from broken halves of Charpy specimen, is proposed and the studies to verify the reliability and robustness of evaluation method have been conducted in the Japanese round robin program since 2010.

In this study, fracture toughness tests were performed on Japanese SA 533 Gr.B Cl.1 steel using miniature C(T) specimens and the effect of specimen size on reference temperature T0 was studied by the Master Curve approach. In addition, the issues related to application to irradiated materials were discussed.
Study on Piping Response Under Multiple Excitation: Part 2 — Validation for Multiple Excitation Analysis of Piping
Authors: Kai Satoru , Watakabe Tomoyoshi , Kaneko Naoaki , Tochiki Kunihiro , Moriizumi Makoto , Tsukimori Kazuyuki
Published: January 2014

The piping in a nuclear power plant is laid across multiple floors of a single building or two buildings, which are supported at many points. As the piping is excited by multiple-inputs from the supporting points during an earthquake, seismic response analysis by multiple excitations is needed to obtain the exact seismic response of the piping. However, few experiments involving such multiple excitation have been performed to verify the validity of multiple excitation analysis. Therefore, analysis of the seismic design of piping in Japan is performed by the enveloped Floor Response Spectrum (FRS), which covers all floor response spectra at all supporting points. The piping response estimated by enveloped FRS is conservative in most cases compared with the actual seismic response by multiple excitations. To perform rational seismic design and evaluation, it is important to investigate the seismic response by multiple excitations and to verify the validity of the analytical method by multiple excitation test.

This paper reports the validation results of the multiple-excitation analysis of piping compared with the results of the multiple excitations shaking test using triple uni-axial shaking table and a 3-dimensional piping model (89.1mm diameter and 5.5mm thickness). Three directional moments from the analysis and the shaking test were compared on the validation. As the result, it is confirmed that the analysis by multiple time history excitation corresponds with the test result.
Study on Leakage Diffusion and Force Analysis of Double-Layer Structure of Oil Storage Tank
Authors: Zhao Liwei , Liu Fujun , Kong Shuai , Ling Zhangwei , Wang Liqin
Published: January 2014

Given the limitation of existing inspection technology and the severity of corrosion in tank floor, a double-layer structure of oil storage tank was proposed in this paper. It was verified that the reliability of the calculated values based on the comparison between stress test values and calculated ones. Then, the numerical simulation method was put forward to research the stress distribution and deformation of tank floor under six different support schemes. Generally considering the strength and the stiffness of tank floor, the weight of the support structure and the ease of manufacture, an optimizing design of the support structure was adopted. Furtherly, the influencing rule of leak positions and volume of leak (Q) on the leakage diffusion was studied by using 93# gasoline. The results show that for the same amount of leakage, the leakage on the center of tank floor diffused quickly, was the most easily detected part, and the edge of the tank floor was the most difficult to be detected. For leakage occurred in same position, the volume fraction (φ) in pipeline increased with the increase of leakage.
Basic Study on Mitigation of Annular-Flow-Induced Vibration by Considering Variability in Parameters of Structure and Fluid
Authors: Shintani Atsuhiko , Isono Hirokazu , Ito Tomohiro , Nakagawa Chihiro
Published: January 2014

In this study, the stability of a structure and mitigation of the vibration of a structure subjected to annular flow are investigated when the parameters of the structure and fluid have variability or uncertainty. The equations of motion of the structure and fluid are given by the Euler-Bernoulli-type partial differential equation and the Navier–Stokes equation, respectively. Hence, the fluid–structure coupled system has variability. The fluid–structure coupled equation considering variability is derived from the above-mentioned equations. By drawing the root locus of the coupled equation, the stability of the coupled system with variability is investigated. Because the parameters of structure and fluid have variability, the critical flow velocity also varies. The effect of parameter variability on the critical flow velocity variability is investigated. Furthermore, to reduce the coupled vibration of the system with variability, a control input is used. Through adequate control, the coupled system with variability is stabilized.
Analysis of Wave Propagation in Overhead Contact Wire of Trains Using the Transfer Matrix Method
Authors: Fukui Takahiro , Asami Toshihiko , Ise Tomohiko
Published: January 2014

In this paper, we propose a method for analyzing the vibration properties of contact wires (trolley wires) using the transfer matrix method (TMM), by treating them as a periodic structure. When the speed of the train increases, self-excitation vibration of the wires may occur. When the trolley wires repeatedly contact and separate from the pantograph, the pantograph is worn by the sparks. Therefore, the vibration of the trolley wires must be kept as small as possible. For such problems, many researchers have proposed vibration analysis of the wires. However, these methods are not suitable for the vibration analysis of wires because of the very complicated wave propagation phenomenon. The TMM proposed in this study is an easy technique for studying wave propagation since the vibration properties can be simplified greatly by handling the smallest unit of repetition of the structure. Using this method, we can identify the frequencies of the vibration-attenuating domain (stop-band) and the vibration-amplifying domain (pass-band). If we can bring the excitation frequency of the wire to the stop-band domain, wear of the pantograph can be reduced. Here, we introduce three cell models; two of them do not take into account the elasticity of the trolley wire, and the other does. Then, we discuss how the stop-band appears in these models.
Transient Behavior of Water Hammer in a Two-Pipe System
Authors: Inaba Kazuaki , Kamijukkoku Masaya , Takahashi Kosuke , Kishimoto Kikuo
Published: January 2014

We experimentally investigated the propagation behavior of pressure waves in fluid coupled with elastic stress waves in tubes across a straight junction of two different tubes with different diameters and materials, named discontinuity. We measured wave speeds of water hammers upstream and downstream of the discontinuity and the transmission and reflection ratios of water hammer pressures at the discontinuity. To obtain the ratios, strain gages were attached at constant intervals in the hoop direction and the axial direction. Strain signals were converted into pressure histories and used to obtain the ratios. It is confirmed that propagation speeds upstream and downstream of the discontinuity can be estimated by the Korteweg wave speed. Furthermore, the impact responses of tubes in the hoop direction can be evaluated by characteristic impedance with an area change. However, we found that the axial strains due to the area change from the larger diameter tube to the smaller diameter tube were clearly different from values evaluated by the Poisson coupling. It is confirmed that when the tube cross-sectional area suddenly decreases by half at the straight junction of two tubes, the reflected pressure loading in the axial direction can cause the axial peak strain that is 0.6 times as large as the hoop peak strain.
Technical Basis for Proposed Code Case of Alternative Rules for Cladding Repair by Underwater Electrochemical Deposition in Class 1 and 2 Applications
Authors: Kim Myong-Jin , Kim Dong Jin , Kim Joung Soo , Kim Hong Pyo , Hwang Seong Sik
Published: January 2014

A reactor vessel consists of carbon/low alloy steel (SA508) as the structural material, and a cladding layer (SS309) as a protective layer. Cladding layer experiences damage by accidents such as thermal sleeve detachments. Carbon/low alloy steel is weak to corrosion when exposed to the primary water especially during refueling time, which is a potential threat against the integrity of a reactor vessel. Therefore, the damaged cladding part should be repaired. Repairing the inside of the reactor vessel is difficult because of high radiation levels, poor accessibility, and the underwater condition. One promising repair technology is the electrochemical deposition (ECD) of nickel.

Nickel plating through ECD has a lot advantages such as excellent corrosion resistance, no heavy thermal effect (near room temperature process), and proper mechanical properties for long-term nuclear operation. Moreover, the plating layer can be easily removed and is applicable to underwater conditions. The ECD technology used to repair the inside of the steam generator tube has been approved in the ASME code case N-569, titled “Alternative Rules for Repair by Electrochemical Deposition of Class 1 and Class 2 Steam Generator Tubing.” It is expected that an ECD layer can protect the corrosion/erosion of the exposed surface of damaged cladding/ carbon steel.

The ECD process consists of many processes, such as surface cleaning, strike layer formation for the adhesion between ECD layer and cladding/carbon steel, activation, and a main electrodeposition process. “Alternative Rules for Cladding Repair by Underwater Electrochemical Deposition in Class 1 and 2 Applications” is proposed based on the Code Case N-569. This proposed code case includes material requirements, qualification, essential variables, and examination requirements.
Study on Minimum Wall Thickness Requirement of Reactor Vessel of Fast Reactor for Seismic Buckling by System Based Code
Authors: Takaya Shigeru , Watanabe Daigo , Yokoi Shinobu , Kamishima Yoshio , Kurisaka Kenichi , Asayama Tai
Published: January 2014

In this paper, minimum wall thickness requirement of reactor vessel of fast reactor for seismic buckling is discussed on the basis of the System Based Code (SBC) concept. One of key concepts of SBC is the margin optimization. To implement this concept, reliability design method is employed, and the target reliability for seismic buckling of reactor vessel is derived from nuclear plant safety goals. Input data for reliability evaluation such as distribution type, mean value and standard deviation of random variable are prepared. Seismic hazard is considered to evaluate uncertainty of seismic load. Wall thickness needed to achieve the target reliability is evaluated, and as a result, it is shown that the minimum wall thickness can be reduced from that required by a deterministic design method.
J Integral in Elasto-Plasticity by Path Integral Method and Virtual Crack Extension Method in 2-Dimensional Problem
Authors: Chang Kexin , Ohmura Yuki , Watanabe Osamu , Matsuda Akihiro
Published: January 2014

This paper shows the two calculation method of J Integral in elastic-plastic behavior of central crack in 2-dimensional problem. The analysis of the J integral and the increment of J for a plate with a central crack under cyclic fatigue loadings are carried out by using path integration based on the numerical results of Finite Element (FE) analysis. The J integral is calculated by both elastic analysis and elasto-plastic analysis. The accuracy of numerical results for the increment of J is proved by comparison with the simplified method results. In this study, we also analyzed the J-integral using the virtual crack extension method based on the finite element method. Analysis model is a two-dimensional flat plate with a central crack, and by changing the crack length in the different FE analysis, the fundamental feature of J-integral by the virtual crack extension method under cyclic fatigue analysis is discussed.
J-Resistance Properties of Cr-Mo Steels With Internal Hydrogen Measured by Means of Potential Drop Method
Authors: Konosu Shinji , Shimazu Hidenori , Fukuda Ryohei , Horibe Tadashi
Published: January 2014

The tearing resistance dJ/da of three kinds of 2.25Cr-1Mo steels and 2.25Cr-1Mo-0.3V steel with internal hydrogen was measured using the potential drop method. Internal hydrogen refers to test specimens that are precharged (thermally charged) prior to testing. In general, Cr-Mo steels used widely in the refining and petrochemical industry are susceptible to temper embrittlement. However, there are very few studies concerning the effects of hydrogen and temper embrittlement on J-resistance properties. The test specimens were prepared by subjecting them to normalizing, tempering and post-weld heat treatments which simulated actual conditions. Some specimens were embrittled by step cooling (Socal-1 treatment). Hydrogen substantially reduces the dJ/da of the steels other than the V-bearing steel and temper embrittlement additionally causes adverse effects on the dJ/da of the steels with internal hydrogen where the temper embrittlement parameter J-factor is larger than around 300.
Analysis of a Feed Water Distribution Ring for a Water Hammer Load Following a Pipe Break
Authors: Olsson Anders , Möller Mikael
Published: January 2014

In a nuclear pressurized water reactor (PWR) the steam is created in steam generators (SG). The water is returned to the SG via the feed water line and is mixed with the warmer water inside the SG by means of a feed water distribution ring. In the feed water line just outside the SG there is a check valve that will close at pipe break upstream the valve. When the valve closes the water flow through the valve halts and a severe pressure pulse will move into the feed water distribution ring. The pressure pulse is much higher than what the feed water distribution ring can resist statically. However, taking FSI and plasticity into account the magnitude of the pressure pulse is reduced significantly. In this paper an analysis of a feed water distribution ring taking FSI into account with acoustic elements is presented. Without FSI the calculated pressure was 3.7 times higher than the allowable static pressure but taking FSI into account it could be shown that the piping system could be qualified for the event. One of the key issues is the valve model that is elaborated in order to model the closing of the valve as accurately as possible.
Simulation of Low-Reynolds Number Flow Around a Circular Cylinder Following a Slender Elliptical Path
Authors: Baranyi László
Published: January 2014

Two-dimensional flow around a circular cylinder forced to follow an elliptical path at low Reynolds numbers is investigated numerically using a thoroughly tested in-house code based on the finite difference method. Time-mean (TM) and rms values of lift, drag and base pressure coefficients are investigated within the lock-in region against the transverse oscillation amplitude for Reynolds number Re = 150 at frequency ratios of 0.8, 0.9 and 1.0 while the ratio of in-line and transverse cylinder oscillation amplitudes is kept at six different values yielding slender elliptical cylinder paths. The objective of the paper is to investigate the effect of the shape of the path, or amplitude ratio, on force coefficients. Findings show that for the cases investigated the rms of lift and TM of drag and base pressure are hardly affected by the amplitude ratio, while its effects are pronounced on the TM of lift and rms of drag and base pressure.
Fracture Toughness Evaluation of Reactor Pressure Vessel Steels by Master Curve Method Using Mini-CT Specimens
Authors: Tobita Tohru , Nishiyama Yutaka , Ohtsu Takuyo , Udagawa Makoto , Katsuyama Jinya , Onizawa Kunio
Published: January 2014

To examine the applicability of Mini-CT (0.16T-CT) specimens to fracture toughness evaluation by Master Curve method, we conducted fracture toughness tests using specimens with different size and shapes such as pre-cracked Charpy-type, 0.4T-CT and 1T-CT in addition to 0.16T-CT specimens for commercially manufactured five kinds of SA533B Cl.1 steels with different ductile-to-brittle transition temperature. Reference temperature To determined by 0.16T-CT specimens were approximately equal to those of 1T-CT specimens for all materials. The Weibull slope of 0.16T-CT specimens was similar to those of other larger specimens. We also examined a loading rate effect on To of 0.16T-CT specimens within the quasi-static loading range prescribed by ASTM E1921. There was no loading rate effect peculiar to 0.16T-CT specimens, while the higher loading rate gave rise to slightly higher To.
Applicability of Optical Fiber Bragg Grating Sensors in the Structural Health Monitoring of Composite Overwrapped Pressure Vessels
Authors: Pereira Gilmar , Figueiredo Joana , Faria Hugo , Marques A. Torres
Published: January 2014

Composite overwrapped pressure vessels (COPV) have been increasingly pointed to as the most effective solution for high pressure storage of liquid and gaseous fluids. Reasonably high stiffness-to-weight ratios make them suitable for both static and mobile applications. However, higher operating pressures are sought continuously, to get higher energy densities in such storage systems, and safety aspects become critical. Thus, reliable design and test procedures are required to reduce the risks of undesired and unpredicted failures. An in-service health monitoring system may contribute to a better product development, design and optimization, as well as to minimize the risks and improve the public acceptance.

Within the scope of developing different COPV models for a wide range of operating pressures and applications, optical fiber Bragg grating (FBG) sensors were embedded in the liner-composite and composite-composite interfaces during their manufacture in order to allow the online strain monitoring during preliminary testing and service-life. The ability of these measuring systems to effectively assess the strain fields was to be investigated. Simultaneously, a finite element analysis (FEA) was made using the ABAQUS® platform. In this numerical analysis, accurate and realistic simulation of the different materials, geometry and loading conditions was approached. Particularly, the anisotropic nature of the wound laminate and the varying orientation of the fibers were attained. However, the cohesive zones were not attributed independent properties.

Comparison between experimental and numerical data was addressed. In general, although the experimental-numerical data agreement was not as good as desired, a preliminary insight to both the structural health monitoring (SHM) system and the numerical modeling approaches was actually achieved. Full characterization and validation shall be further addressed in the continuation of the present work.

The first set of results and difficulties on the development and implementation of this SHM system to COPV are presented and discussed in this paper.
An Innovative Precise Integration Method in Solving Structural Dynamic Problems
Authors: Wu Chiun-lin , Chuang Ching-Chiang
Published: January 2014

An innovative time integration method that incorporates spurious high-frequency dissipation capability into the so called “high precision direct integration algorithm” is presented, and its numerical stability and accuracy is discussed. The integration algorithm is named “high precision” to emphasize its numerical capability in reaching computer hardware precision. The proposed procedure employs the well-known state space approach to solve the simultaneous ordinary differential equations, the exact solution of which contains an exponential matrix to be efficiently computed using the truncated Taylor series expansion together with the power-of-two algorithm. The proposed method, belonging to the category of explicit methods, is found to provide better accuracy than many other existing time integration methods, and the integration scheme remains numerically stable over a wide range of frequencies of engineering interest. This paper is also devoted to study numerical accuracy of the Precise Integration Method in solving forced vibration problems, particularly near resonance conditions. The numerically obtained transfer functions are then compared with the analytical exact solution to detect spurious resonance. Finally, numerical examples are used to illustrate its high performance in numerical stability and accuracy. The proposed method carries the merit that can be directly applied to solve momentum equations of motion with exactly the same procedure.
New Challenges in the Production of Ultra Large Forgings for the Manufacturing of Pressure Vessels
Authors: Talamantes-Silva Jesus , Bates Paul , Al-Bermani Sinan , Davies Peter , Hambleton Andrew , Bunney David
Published: January 2014

The latest designs of Pressure Vessels (PV), coupled with recently introduced ASME section VIII Division 3 revised code requirements, have brought about new challenges in both alloy suitability and manufacture for these safety critical components. Sheffield Forgemasters International has produced and reconditioned numerous PV forgings during the last fifty years and current demand on section sizes conveys a real challenge when trying to meet specified mechanical properties. This paper describes the technological concerns encountered when manufacturing these components and discusses the limits of what can be achieved with current practice and alloy compositions. Particular attention is given to current code testing requirements and the difficulties in obtaining an acceptable balance of strength and toughness in the mid wall of thick section large forgings.
A Parametric CFD Analysis of the Valve Pocket Losses in Reciprocating Compressors
Authors: Balduzzi Francesco , Ferrara Giovanni , Maleci Riccardo , Babbini Alberto , Pratelli Guido
Published: January 2014

The increasing demand for high efficiency in the field of energy production has also had an impact on reciprocating compressors. In this case, the need to reduce losses is one of the most important challenges. In the past, most studies were focused only on the analysis of valve pressure losses. More recently, interest has been extended to the prediction of the losses through pocket valves and cylinder ducts, these losses being a crucial aspect of a more accurate estimate of the absorbed power.

The use of CFD simulation has shown great potential for the study of the entire reciprocating compressor, but is still limited by high computational costs. Recently the authors have presented a simplified CFD approach: the actual valve geometry is replaced with an equivalent porous region, which has significantly increased the speed of calculation while ensuring accuracy as well.

Based on this approach, a new methodology for the evaluation of pocket valve losses is presented. Since the pocket losses have been proven to be independent of the actual valve installed, a set of CFD simulations using a parameterized geometry of the pocket valve was performed and the relationship between the losses of the pocket and its geometrical features was obtained. An analytical response surface was defined using the values of the geometrical dimensions as inputs and the pocket flow coefficient as output. Finally, the response surface was validated through a set of test cases performed on different geometries with the actual valve and the results have shown good predictability of the tool.
Numerical Analytic Approach to a Calculation of a Thermal Stress State of Shell and Tube Heat Exchangers
Authors: Laskin Igor , Volfson Boris
Published: January 2014

Nowadays, a stress calculation of shell and tube heat exchangers’ elements is based either on analytic methods described in ASME, TEMA, EN, GOST and other standards or on numerical modeling using FEA. The main disadvantage of the analytic methods is that they can be applied only to certain apparatuses’ designs and it is very difficult or even impossible to use them with non-typical constructions. Otherwise, such a calculation is easy to perform with modeling by FEA. However, a direct finite element simulation of several thousands of tubes, which can be designed in one heat exchanger, makes the task very time-consuming and the resulting model very big and computation-intensive. This paper examines a typical model, which includes 3.5 million nodes and more than 3 million elements. We offer a numerical analytic solution of this task, which consists in modeling of a tube bundle by an orthotropic continuum with equivalent properties. The comparison of the results of a temperature distribution calculation and the stress-strain distribution calculation using direct numerical modeling of the tubes in the tube bundle by shell elements from one hand, and of the suggested numerical analytic solution from another, shows that these results do match closely enough to practice.
CANDU Owners Group Risk-Informed In-Service Inspection (RI-ISI) Project
Authors: Lafreniere Paul , O’Regan Patrick , Rezaie-Manesh Mehdi , Chesworth Scott
Published: January 2014

The Canadian Nuclear Safety Commission (CNSC) has prepared “Guidelines for Risk-Informed In-service Inspection (RI-ISI) for Piping.” This document provided instructions and acceptance criteria for licensees to develop an RI-ISI program integrating both risk insights and traditional analysis as an alternate to the current programs for piping inspection. In response to the CNSC guideline, a CANDU Owners Group (COG) project was initiated to develop a best-fit methodology for nuclear systems within the CANDU design. The traditional EPRI RI-ISI methodology was selected as a starting point for the CANDU best-fit methodology development. Since characterization of risk requires knowledge of both failure potential and the consequence of failure, these values were determined for in-scope piping welds. Once the risk associated with each component was established, the components were ranked accordingly, elements were selected based upon the sampling percentages of EPRI RI-ISI, and a comparison was made between plant risk under the current CSA N285.4 / augmented programs and RI-ISI. Application to a number of nuclear and non-nuclear systems has been completed and has shown where inspection allocation can be improved and where low-value added inspections can be reduced. Work is underway to extend the results of this project to conventional systems and components beyond piping welds.
Proposed Modifications to the EN 1591-1 Flange Calculation Procedure
Authors: Schaaf Manfred
Published: January 2014

At present, the European Standards EN 1591-1 which is used for the calculation of bolted flanged joints and EN 13555 in which the determination of the required gasket characteristics are defined are under revision.

Several studies on gasket testing and on flange calculation have been performed in order to verify the suggested modifications of the standardization working groups. As a result of these studies several optimizations in respect of the testing procedures, the definition of the gasket characteristics and the calculation procedure can be derived.

In this paper, an advanced calculation procedure will be presented which is based on the use of additional or modified gasket characteristics such as the stiffness-independent gasket deflection caused by creep of the gasket material or formulas for the description of the gasket compression curves are presented.
Evaluation of Excessive Loading Effect on Fatigue Crack Growth Behavior Based on Crack Blunting and Stress Distribution in Front of the Crack Tip
Authors: Yamaguchi Yoshihito , Katsuyama Jinya , Onizawa Kunio , Li Yinsheng
Published: January 2014

It is very important to establish an evaluation method of the structural integrity of piping beyond the small scale yielding condition due to large earthquakes. One of the key issues is the effect of excessive loading on the fatigue crack growth behavior. We performed fatigue crack growth tests under constant amplitude cyclic loading with a single excessive tensile/compressive load. The stress distribution in front of crack tip and crack blunting were estimated by FEM analyses. After the crack tip was blunted by the excessive tensile loading, the effect of the excessive loading on crack growth rate varied depending on the magnitude of the subsequent compressive loading. When a compressive load is enough to close the crack, the crack growth rate became higher than that before the excessive tensile loading while increasing the tensile stress in front of crack tip. A crack growth prediction method has been proposed considering the effects of the excessive loading based on the variation of the stress distribution in front of crack tip and the crack blunting. The predicted crack growth rate by the proposed method was correlated with the experimental ones.
Improved Gasket Testing
Authors: Schaaf Manfred
Published: January 2014

At present, the European Standards EN 1591-1 which is used for the calculation of bolted flanged joints and EN 13555 in which the determination of the required gasket characteristics are defined are under revision.

Several studies on gasket testing and on flange calculation have been performed in order to verify the suggested modifications of the standardization working groups. As a result of these studies several optimizations in respect of the testing procedures, the definition of the gasket characteristics and the calculation procedure can be derived.

In this paper, additional or modified gasket characteristics such as the stiffness-independent gasket deflection, caused by creep of the gasket material or formulas for the description of the gasket compression curves, are presented. Several tests with diverse gasket materials were performed in order to generate generally admitted procedures to determine these required characteristics which are the basis for the advanced calculation procedure which will be presented in a second paper.
Effect of Flaw Orientation on Delayed Hydride Crack Initiation in Zr-2.5Nb Pressure Tubes
Authors: Shek Gordon K. , Cui Jun , Scarth Douglas A. , Xu Steven
Published: January 2014

The Zr-2.5Nb pressure tubes of CANDU reactor are susceptible to a cracking mechanism known as Delayed Hydride Cracking (DHC), which is a repetitive process that involves hydrogen diffusion, hydride precipitation and fracture at a stress concentrator such as a flaw or a crack. Service-induced flaws are present in some pressure tubes and they need to be assessed for susceptibility to DHC initiation. An engineering procedure based on the process-zone methodology has been developed and incorporated into the Canadian standard to determine the susceptibility of flaws in pressure tubes to DHC initiation. The engineering procedure was validated against experiments on flaws which were oriented in the axial direction of the pressure tube. However, many of the service-induced flaws are oriented at some oblique angle with respect to the axial direction of the tube and they may have higher threshold stresses for DHC initiation than those of the axial flaws. It would be advantageous to apply the process-zone evaluation procedure to such angled blunt flaws. For this purpose, an experimental study was carried out to measure the threshold stresses for DHC initiation from machined V-notches with different orientations (0°, 15°, 30° and 45°) with respect to the axial direction of an unirradiated pressure tube. The experimental results were used to support the development of the evaluation procedure for angled blunt flaws. The experimental program and the validation of the engineering procedure for angled blunt flaws are described in this paper.
Method for Estimation of Pressure Vessel Internals Lifetime on IASCC Criterion
Authors: Fedorova Valentina , Margolin Boris
Published: January 2014

Austenitic stainless steels are used extensively as structural materials in the internal components of reactor pressure vessels. However, high neutron doses lead to a significant reduction in the fracture resistance of these steels in water environment. Irradiation assisted stress corrosion cracking (IASCC) of internals has been observed in pressurized water reactors (PWRs).

In the present work the IASCC model of the irradiated austenitic steels in PWR water has been developed.

On the basis of analysis of available experimental data IASCC mechanism is proposed. Based on this mechanism, the dependence of fracture stress under IASCC on neutron dose is derived. For its construction the following assumptions were made.

1. Creep rate due to grain boundary sliding does not depend on neutron dose.

2. Fracture strain due to grain boundary sliding decreases when neutron dose increases.

3. There is an apparent stress threshold below which IASCC initiation does not occur in PWR environment.

Life prediction analysis for IASCC is performed on the basis of linear rule of damage accumulation.
Brittle Fracture Analysis of a Dissimilar Metal Weld
Authors: Blouin A. , Chapuliot S. , Marie S. , Bergheau J. M. , Niclaeys C.
Published: January 2014

One important part of the integrity demonstration of large ferritic components is based on the demonstration that they could never undergo brittle fracture. Connections between a ferritic component and an austenitic piping (Dissimilar Metal Weld — DMW) have to respect these rules, in particular the Heat Affected Zone (HAZ) created by the welding process and which encounters a brittle-to-ductile transition.

Within that frame, the case considered in this article is a Ni base alloy narrow gap weld joint between a ferritic pipe (A533 steel) and an austenitic pipe (316L stainless steel). The aim of the present study is to show that in the same loading conditions, the weld joint is less sensitive to the brittle fracture than the surrounding ferritic part of the component. That is to say that the demonstration should be focused on the ferritic base metal which is the weakest material.

The bases of this study rely on a stress-based criterion developed by Chapuliot et al., using a threshold stress (σth) below which the cleavage cannot occur. This threshold stress can be used to define the brittle crack occurrence probability, which means it is possible to determine the highest loading conditions without any brittle fracture risk.