bluuebunny/crossref_metadata_2025 huggingface dataset:
Combustion and Exhaust Emission Characteristics of a Passenger Car Diesel Engine Fueled With Biodiesel 30% Derived From Soybean
Authors: Kim Myung Yoon , Cho WooHeum , Lee Eun-Hyun , Chun Jerok
Published: January 2011

The impact of soybean methyl ester (SME) on the injection mass curve, exhaust emissions, engine performance, and exhaust gas temperatures of a common-rail direct injection diesel engine have been investigated. In this study, 30% SME blended diesel fuel (BD30) has been used as a fuel in the engine and results of the investigation were compared to those obtained using petroleum diesel fuel. The results of the investigation show that the change in injection mass curve when using BD30 instead of diesel was insignificant. A combustion analysis shows BD30 has a shorter ignition delay at part-load operating condition where heavy exhaust gas recirculation (EGR) rate is used. This difference in behavior is due to the oxygen contents and lower stoichiometric air-fuel ratio of BD30, which leads to higher O2 concentration in the exhaust gas. At part-load operating conditions, BD30 results showed 53% reduction in smoke at the expense of 18% increase in NOx emission. The full load engine power for BD30 was decreased by 2.1∼3.8% using EMS (engine management system) configurations without torque adjustment to compensated reduction in calorific value of BD30. When the engine power was so adjusted that BD30 produced the same power as diesel fuel, a lower exhaust gas temperature was observed at full load operating condition. Considering that the LHV (lower heating value) of BD30 is 2.6% lower than that of diesel fuel, there may be no factors that cause deterioration of thermal efficiency on using BD30 under all operating conditions.
Flanged Joints of Multi-Pass Shell-and-Tube Heat Exchangers Subjected to Non-Axisymmetric Thermal Loading
Authors: Petrova Natalia , Bouzid Abdel-Hakim
Published: January 2011

Despite the fact that multipass shell-and-tube heat exchangers operating at high temperature are subject to frequent problems related to flange sealing, there is neither detailed explanations for the reasons of the failures nor adequate solution to this problem. Specific geometry of multipass heat exchangers and the temperature difference between the inlet and the outlet fluids are responsible for the existence of a thermal circumferential gradient at the shell-to-channel bolted joint. However, existing flange design methods do not address non-axisymmetrical temperature loading of the flanged joint assembly. The circumferential thermal gradient, as the cause of frequent failures to seal the flanged joints, is ignored. This paper outlines the analytical modeling of a flanged joint with a tube sheet of a multipass heat exchanger subjected to a non-axisymmetrical thermal loading. A shell-and-tube heat exchanger of 51 in diameter with co-current flow was used for analysis. The main steps of the theoretical analysis used for the determination of the circumferential temperature profiles and the thermal expansion displacements and distortions of the bolted joint components are given. The results from the proposed analytical model are compared to those obtained from finite element models.
Assessment of the Hodograph Cone Method (HCM) for the Evaluation of the COD of Off-Centered Crack in Pipes Under Bending for LBB Assessment
Authors: Iannitti G.
Published: January 2011

In this work the applicability and the accuracy of the hodograph cone method (HCM) for estimating the COD distribution of off-centered cracks in pipe under bending has been verified by means of extensive finite element analysis and experimental investigation. The need to develop appropriated numerical model and the guideline to follows in order to get accurate results is discussed. Experimental measures performed by means of direct imaging correlation confirmed both the accuracy of the FEM model adopted as well as the robustness of the HCM. A correction for further improvement of the HCM accuracy and extension to large crack length is also proposed.
Dynamic Fragmentation Experiments Under Plane Strain and Uniaxial Stress Conditions
Authors: Lambert David E. , Weiderhold Joseph , Osborn John , Hopson Michael V.
Published: January 2011

The explosively loaded cylinder is further studied as an experimental method to improve dynamic fracture and fragmentation modeling. Details of the cylinder configuration are investigated to prescribe controlled loading conditions of uniaxial stress and plane strain. Commonly used fracture models, e.g. Johnson-Cook, are calibrated with strain at fracture under such controlled conditions. Earlier works by Goto, et al [1] had used thin-walled tubes to provide plane strain loading and shorter “rings” to establish uniaxial stress conditions. This paper extends on that work to look at alternative cylinder dimensions and metals of interest. A tungsten alloy, Aero 224, and a high strength steel, Eglin Steel (ES-1), are the subject metals. Dynamic, continuum-mechanics based modeling and simulations evaluated whether the stress triaxiality conditions are being met as design parameters of cylinder wall-thickness, explosive type, and initiation configuration. Experiments conducted for this effort, reported in greater detail by Weiderhold [2], provided precise measurement of the cylinder expansion process and fragmentation distributions. An explosively driven metal event is usually considered highly transient and multi-dimensional in stress; however, selective design of the system can result in a controlled experimental configuration. The analysis shows that the ductile ES-1 steel cylinder and rings do establish the desired plane strain and uniaxial stress conditions, respectively, as the cylinder expands to failure. Ultra-high speed photography experiments verify the time of fracture and correlate casewall expansion and velocity measurements. The analysis of the tungsten alloy had verified that if the material was capable of achieving at least a 25% strain to failure then the cylinder and rings would be viable controlled loading paths. However, fragments recovered from the explosively driven rings verified that the strain to failure was less than 14% and the triaxiality condition of uniaxial stress was not achieved by then. The data of this fragmentation under controlled loading conditions are to be used to determine coefficients for fracture-models and serve as benchmarks of relevant, dynamic fragmentation processes for future explosive/metal design opportunities.
Nonlinear Deformation Behavior of Bolted Flanges Under Tensile, Torsional and Bending Loads
Authors: Wu Zhijun , Nassar Sayed A. , Yang Xianjie
Published: January 2011

This paper investigates the nonlinear deformation behavior of bolted flanges under tensile, torsional and bending loads, using Finite Element Analysis (FEA). Even though the bolted flange may still deform elastically, the variation in contact area due to the external loading will cause nonlinear deformation. In this study, finite element simulation is used for investigating the respective non-linear deformation behavior of a preloaded bolted flange under tensile, torsional and bending loads, and to determine the corresponding stiffness values for each loading.
A Simple Criterion for Fracture Initiation at the Root of a U-Shaped Flaw
Authors: Smith Edwin
Published: January 2011

Motivated by the problem of Delayed Hydride Cracking (DHC) at the root of a blunt flaw in Zr-Nb CANDU pressure tube material, the author has developed a simple criterion which quantifies fracture initiation at the root of a blunt flaw. The criterion, which is based on a simplified version of the process zone procedure, is quite general and can be applied to a wide range of situations, and in this paper it is applied to the problem of fracture initiation at the root of a U-shaped flaw in a brittle material. The results compare favourably with finite element results obtained by other workers, the agreement providing useful underpinning for the simplified procedure. Moreover, and most importantly, since the finite element results have been shown to compare favourably with experimental results for a wide range of materials, the implication is that the author’s approach is also validated experimentally. This validation is important since it provides added confidence with regard to the application of the author’s application of the simplified version of the process zone procedure to the DHC problem.
Review of the Basis and Experience With Application of ASME BPV Code Case 2235
Authors: Hedden Owen F.
Published: January 2011

Code Case 2235 provides a technical basis for substitution of the ultrasonic method for radiography for examination for acceptance of welds in pressure vessels and piping. This paper first describes the background for the development of UT technique qualification by performance demonstration and the associated fitness-for-service flaw acceptance criteria of Code Case 2235. It then proceeds with review of the ASME and other standards based on the same or similar criteria, and continues with comments on typical examples of subsequent technical papers addressing field applications of Code Case 2235.
Advanced Finite Element Analysis (AFEA) Evaluation for Circumferential and Axial PWSCC Defects
Authors: Shim D.-J. , Kalyanam S. , Punch E. , Zhang T. , Brust F. , Wilkowski G. , Goodfellow A. , Smith M.
Published: January 2011

The Advanced Finite Element Analysis (AFEA) methodology has been developed by the US NRC and the nuclear industry to evaluate the natural crack growth of primary water stress corrosion cracking (PWSCC) in nickel-based alloy materials. The AFEA methodology allows the progression of a planar crack subjected to typical SCC-type growth laws by calculating stress intensity factors at every nodal point along the crack front, and incrementally advancing the crack front in a more natural manner. This paper describes the enhancements that have been made to the existing AFEA methodology. The most significant enhancement was the feature to evaluate axial crack growth where the crack was contained within the susceptible material. In this paper, this methodology was validated by performing an AFEA evaluation for the axial crack that was found in the V.C. Summer hot leg dissimilar metal weld. Other enhancements to the AFEA methodology include; upgrade to the PipeFracCAE© software developed by Engineering Mechanics Corporation of Columbus, feature to handle non-idealized circumferential through-wall cracks, mapping of weld residual stress for crack growth, and determination of limiting crack size using elastic-plastic J-integral analysis that included secondary stress (weld residual stress and thermal transient stress) effects.
Analysis Methodology Used in the Qualification of Westinghouse AP1000 Instrumentation Grid Assembly
Authors: Yu Lixin , Yang Jianfeng , Kielb John F. , Hunter Scott M. , Delport Gerrie W. , Bae Jun C. , Eisenhaure Jeffrey D.
Published: January 2011

The Instrumentation Grid Assembly (IGA) is a complex structure located in the upper head region of a nuclear reactor vessel (RV). It is used to support various in-core instruments running from the RV closure head (RVCH) penetrations to the reactor core. Qualification of the IGA per ASME Boiler and Pressure Vessel Code Section III is required by Westinghouse’s Design Specification. A structural analysis was carried out to demonstrate that the Code stress limits for various load levels were satisfied. These loads include deadweight, spring preload, pump pulsation load, random flow turbulence load, flow-induced vortex shedding load, seismic load, and loss-of-coolant-accident load. This paper describes the structural analysis methodology used in qualifying the IGA design for the Westinghouse AP1000 nuclear reactor.
Stress Intensity Factors and Weight Functions for Longitudinal Semi-Elliptical Surface Cracks Inside Thick-Walled Cylinders Using Highly-Refined Finite-Element Models
Authors: Hinkle Adam R. , Holliday James E. , Jones David P.
Published: January 2011

Fracture mechanics and fatigue crack-growth analysis rely heavily upon accurate values of stress intensity factors. They provide a convenient, single-parameter description to characterize the amplitude of the stress-field singularity at the crack tip, and are used to correlate brittle fracture and crack growth in pressure vessel and piping applications. Mode-I stress intensity factors that have been obtained for longitudinal semi-elliptical surface flaws on the inside of thick-walled cylinders using highly-refined finite element models are investigated. Using these results, weight function solutions are constructed and selected geometries are validated.
The Stress Analysis and the Sealing Performance Evaluation of the Pipe Flange Connection at Elevated Temperature
Authors: Takagi Yoshio , Torii Hiroyasu , Sawa Toshiyuki , Omiya Yuya
Published: January 2011

The authors have been evaluating the effects of the material properties of spiral wound gaskets (SWG) and the sealing performance of the pipe flange connections at elevated temperature with numerical and experimental analysis. The contact gasket stress increased by the mismatch of the thermal expansion between the gasket and flange/bolt as increasing the temperature and the sealing performance of the pipe flange connection was improved. The authors have also evaluated the effect of scatter in axial bolt force and revealed the assembly efficiency is not as high as expected in case of large nominal diameter pipe flange connection. Following the previous studies, the sealing performance of pipe flange connection and the assembly efficiency with SWG at elevated temperature were further evaluated with the experimental leakage test and 3-D FE analysis in this study. In order to make a precise evaluation, the experimentally obtained material properties of SWG were used in the analysis. The uniform axial bolt force tests and the scattered axial bolt force test were done to compare the sealing performance and the assembly efficiency evaluated by the ratio of the tightness parameter of each test at elevated temperature. Although the leak rate improved as increasing the temperature, the assembly efficiency decreased. The leakage based assembly efficiency was proposed according to the experimental results and numerical analyses.
Toward International Harmonization of Nuclear Codes and Standards
Authors: Faidy Claude
Published: January 2011

The objectives of this paper is to discuss technical harmonization of Nuclear Codes and Standards, based on French long experience in Codes and Standards used for design-fabrication and operation of nuclear components (mainly pressure retaining components). After a long period of use of ASME Section III code, during the Westinghouse licensing process, AFCEN (AREVA, EDF and the major manufacturers) decided to develop their own AFCEN French Codes. The 1st version has been issued in 1980 and the last one in 2007, completed by annual addendum. During more than 20 years the 2 Codes, RCCM and ASME Section III, have left separately, with different constraints like industrial history, localization of fabrication, more new plants in France than in USA, different R&D programs to support Code improvement. Recently a detailed review of differences for class 1 vessel has shown under a “general global quality equivalence”, a lot of differences in the Code development process, in the Code organization, in the scopes, in the State of the Art fulfillment, in ageing consideration at the design stage, in relation with national or international regulations, in term of standards used or complementary specification needs. The harmonization of Codes and Standards is possible under an important effort to move toward new ideas, more international rules and with a strong support of national safety authorities.
Guidance for Non-Intrusive Inspection of Pressure Vessels
Authors: Jaske Carl E.
Published: January 2011

Pressure vessels must undergo periodic inspections to help ensure their mechanical integrity and continued safe operation. Such inspections are usually mandated by regulations or prescribed in the integrity management programs of prudent operators. Traditionally, internal visual inspections have been employed. These can be costly because of the need to shut down the vessel, isolate it, prepare it for entry, and follow requirements for confined-space entry. Furthermore, vessel entry may even have an adverse effect on its future performance. For these reasons, it is desirable to utilize non-intrusive inspection methods where a vessel can be non-invasively inspected from its exterior. However, the use of non-intrusive inspections must not compromise safe and reliable vessel operation. Compared with traditional intrusive internal inspection, non-intrusive inspection is relatively new and there are a wide variety of inspection techniques available. Each technique has its strengths and weaknesses, and many engineers are not fully acquainted with the capabilities and limitations of the various non-intrusive inspection techniques. To address this issue, Recommended Practice DNV-RP-G103 on Non-Intrusive Inspection (NII) was developed [1]. This paper reviews the recommended practice and discusses example applications of the recommended practice. The recommended practice provides guidance on the following key aspects of non-intrusive pressure vessel inspection: (1) determining when its use is appropriate, (2) information that is needed for inspection planning, (3) defining requirements for inspection methods, (4) selecting inspection methods based on requirements, (5) evaluating inspection results, and (6) requirements for proper documentation of inspection results. The essential elements of the procedures covered in the recommended practice are performing a mechanical integrity review, deciding if non-intrusive inspection is possible, planning for the inspection, performing the inspection, and evaluating the results of the inspection. Finally, the inspection interval is evaluated.
Sealing Performance Test of Slip-On Type Pipe Flange Connections Subject to Internal Pressure and Bending Moment
Authors: Nagata Satoshi , Kobayashi Takashi , Tsuji Hirokazu , Sawa Toshiyuki
Published: January 2011

This paper presents the results of sealing performance test on the slip-on type pipe flange connections for 8 inch and 16 inch. The flange connections are subjected to internal pressure and bending moment. Internal pressure is applied by Helium gas and the bending moment is loaded through 4 points bending equipment. Gas leak rates are measured by pressure decay method. During the test, the variations in the axial bolt force are monitored for all the bolts by strain gages. The pipe stress at the junction of pipe and flange is also measured. Analyzing the measured data, the mechanical behaviors of the slip-on type flange connections under internal pressure and bending moment as well as the sealing performance are clarified.
Seismic Safety Margin Assessment for NPP Utilizing Full-Scale Tests: Overview
Authors: Kameda Hiroyuki , Nakagawa Masaki , Shibuya Akira , Fukunishi Shiro , Ebisawa Katsumi
Published: January 2011

Seismic safety margin assessment is discussed for structural systems and components of nuclear power plants (NPP). Emphasis is placed on utilizing full-scale test results. This paper presents an overview of the ongoing project at Japan Nuclear Energy Safety Organization (JNES). It proposes a conceptual framework of the issue, and provides a basis for the three companion papers that will present application examples on actual NPP equipments. Discussion is focused on 1) motivation of the project arising from the Kashiwazaki-Kariwa NPP earthquake experience in 2007, 2) problem identification with varying targets (verification of experienced plant performance, seismic risk assessment, etc.), 3) formulation of seismic safety margin, 4) needs for realistic assessment of seismic safety margin by incorporating full-scale test results, and 5) activities of the JNES project.
Through-Thickness Welding Residual Stress Profile in Dissimilar Metal Nozzle Butt Weld
Authors: Song Tae-Kwang , Kim Ji-Soo , Oh Chang-Young , Bae Hong-Yeol , Jeon Jun-Young , Kim Yun-Jae , Chai Young-Suck
Published: January 2011

This paper provides the through-thickness welding residual stress profile in dissimilar metal nozzle butt welds of pressurized water reactors. For systematic investigations of the effects of geometric variables, i.e. the thickness and the radius of the nozzle and the length of the safe end, on welding residual stresses, idealized shape of nozzle is proposed and elastic-plastic thermo-mechanical finite element analyses are conducted. Through-wall welding residual stress profiles for dissimilar metal nozzle butt welds are proposed, which take a modified form of existing welding residual stress profiles developed for austenitic pipe butt weld in R6 code.
Improved Incremental J-Integral Equation for Determining Crack Growth Resistance Curves
Authors: Zhu Xian-Kui , Leis Brian N.
Published: January 2011

The J-integral resistance curve is the most important material property used in structural integrity assessment. ASTM E1820 is a commonly used fracture toughness test standard for measuring the critical value of J-integral at the onset of ductile fracture and J-R curve. The recommended test procedure is the elastic unloading compliance method where multiple points are obtained from a single specimen test. For a stationary crack, the J-integral is simply calculated from the area under the load-displacement record using the η-factor equation. For a growing crack, the J-integral is calculated using the incremental equation proposed by Ernst et al. (1981) to consider the crack growth correction. In order to obtain accurate J-integral values, ASTM E1820 requires small and uniform crack growth increments. To allow larger crack growth increments in the unloading compliance test, an improved J-integral estimate equation is needed. Thus, this paper proposes a new incremental J-integral equation for determining J-R curves. An analytic approach is then developed and used to evaluate the accuracy of the proposed incremental equation using single edge bending and compact specimens for different hardening materials. Followed is an experimental evaluation using actual fracture test data for HY80 steel. The results show that the proposed incremental J-integral equation can obtain much improved results of J-R curves for larger crack growth increments, and thus is more accurate than the present ASTM E1820 equation.
Creep Rupture Ductility of Creep Strength Enhanced Ferritic Steels
Authors: Kimura Kazuhiro , Sawada Kota , Kushima Hideaki
Published: January 2011

Creep rupture strength and ductility of Creep Strength Enhanced Ferritic steels of Grades 23, 91, 92 and 122 was investigated with particular emphasis on remarkable drop in the long-term. Large difference in creep rupture strength and ductility was observed on three heats of Grade 23 steels. Remarkable drop of creep rupture strength in the long-term of T91 was comparable to those of Grades 92 and 122. Remarkable drop in creep rupture ductility in a stress regime below 50% of 0.2% offset yield stress was observed on Grade T23 steel, however, that of Grade P23 steel did not indicate any degradation of creep rupture ductility. Higher creep rupture ductility of Grade P23 steel was considered to be caused by its lower creep strength than that of T23 steels. Creep rupture ductility of Grades 92 and 122 steels indicated rapid and drastic decrease with decrease in stress at 50% of 0.2% offset yield stress. Stress dependence of creep rupture ductility of Grades 92 and 122 steels was well described by a ratio of stress to 0.2% offset yield stress, regardless of temperature. On the other hand, large drop in creep rupture ductility of Grade 91 steel was observed only in the very low stress regime at 650°C. Alloying elements including impurities and changes in precipitates may influence on creep rupture ductility, however, remarkable drop in ductility of the steels cannot be explained by chemical composition and precipitates. High ductility in the high stress regime above 50% of 0.2% offset yield stress should be provided by easy plastic deformation, and it has been concluded that a remarkable drop in ductility in the low stress regime is derived from a concentration of creep deformation into a tiny recovered region formed at the vicinity of grain boundary.
Three Dimensional FSI Simulation of Extruded Rod Bundles Immersed in Fluid Using Partitioned Coupling Technique
Authors: Kataoka Shunji , Minami Satsuki , Kawai Hiroshi , Yoshimura Shinobu
Published: January 2011

Dynamic response of extruded rod bundles immersed in fluid is an important feature as a seismic response of fuel rods. For their safety assessment, prediction of dynamic behavior is required. For the prediction, fluid structure interaction should be considered properly which significantly affects the dynamic behavior. However, actual behavior of the bundles includes complex modes of response and not only the interaction between fluid and structure but also the interaction between the bundles and external structure can affect its behavior. Therefore simulation method which can consider the interaction of complicated structures is expected. There are two different approaches for simulating their dynamic behavior. One is the monolithic method, in which one matrix constructed from two physics is solved, and the other is the partitioned method in which two different matrices are solved separately. The partitioned method enables us to utilize an advantage of existing simulation codes, for example their high parallel efficiency. One of the present authors developed a numerical simulation system ADVENTURE, which is a general purpose finite element simulation system which includes several finite element solvers designed to suite for large scale application in parallel computing environments. The authors have developed a simulation system of fluid structure interaction based on ADVENTURE system applying partitioned coupling technique. In this paper, the overview of the system is explained and several numerical simulation results of the dynamic response of the extruded rod bundles are shown. The result shows this coupling technique can give reasonable results and it can apply a larger scale problem of 9×9 arrays of extruded rod bundles.
Long-Term Creep Modeling of Modified 9Cr-1Mo Steel for a Sodium Cooled Fast Reactor
Authors: Kim Woo-Gon , Park Jae-Young , Kim Sung-Ho , Lee Chan-Bock
Published: January 2011

This paper focused on long-term creep modeling for describing total creep curves of up to rupture for modified 9Cr-1Mo steel (G91). Creep data was obtained by a series of constant-load creep tests at 600°C. Three modified constitutive equations of modified power-law method (MPM), modified theta method (MTM) and modified omega method (MOM), described as a sum of a decaying primary creep and an accelerating tertiary creep, were proposed. A nonlinear least square fitting (NLSF) analysis was carried out on the basis of the creep data so that they provide the best fit to experimental data in optimizing parameter constants of the individual equation. Results of the NLSF analysis showed that in the lower stress regions of 160MPa (σ/σys<0.65), the MTM matched well with the experimental creep data compared with the MPM and MOM, but that in the higher stress regions of 160MPa (σ/σy > 0.65), the MPM revealed better agreement than the MTM and MOM. It was found that the MTM was superior in the modeling of long-term creep curves to the MPM and MOM. Long-term creep curves for the G91 steel were numerically modeled and its creep life was predicted by the MTM.
Finite Element Analyses of Residual Stresses in Typical Welded Joints Used in Nuclear Power Plants and Comparisons With Experiments
Authors: Deng Dean , Ogawa Kazuo , Yanagida Nobuyoshi , Saito Koichi
Published: January 2011

Recent discoveries of stress corrosion cracking (SCC) at nickel-based metals in pressurized water reactors (PWRs) and boiling water reactors (BWRs) have raised concerns about safety and integrity of plant components. It has been recognized that welding residual stress is an important factor causing the issue of SCC in a weldment. In this study, both numerical simulation technology and experimental method were employed to investigate the characteristics of welding residual stress distribution in several typical welded joints, which are used in nuclear power plants. These joints include a thick plate butt-welded Alloy 600 joint, a dissimilar metal J-groove set-in joint and a dissimilar metal girth-butt joint. First of all, numerical simulation technology was used to predict welding residual stresses in these three joints, and the influence of heat source model on welding residual stress was examined. Meanwhile, the influence of other thermal processes such as cladding, buttering and heat treatment on the final residual stresses in the dissimilar metal girth-butt joint was also clarified. Secondly, we also measured the residual stresses in three corresponding mock-ups. Finally, the comparisons of the simulation results and the measured data have shed light on how to effectively simulate welding residual stress in these typical joints.
Fitness-for-Service Assessment of Hydrocarbon Storage Tanks
Authors: Ahmad Forhad , Hossain M. M. , Seshadri R.
Published: January 2011

Storage tanks are widely used in the industry to store hydrocarbon products. Corrosion damage is considered to be a serious threat to the structural integrity of the industrial storage tanks if it occurs on the primary pressure containment boundary. Therefore, fitness-for-service (FFS) assessment of these structures is performed periodically in order to ensure the operational safety and structural integrity. In this paper, evaluation methods are proposed for FFS assessment of storage tanks undergoing corrosion damage. The proposed methods are shown to give reasonably accurate and conservative assessment of the remaining strength factor. The methods are demonstrated through an example and the results verified by inelastic finite element analysis.
Considerations for Requiring Intermediate Stress Relief (ISR) for All Weld Types on 2 1/4 Cr-1 Mo-V Reactors
Authors: Shargay Cathleen , Moore Karly , Breig Timothy D. , Antalffy Les P. , Basic Michael M.
Published: January 2011

As an industry consensus, API 934-A is an excellent recommended practice on the materials and fabrication requirements for Cr-Mo reactors. However, it is cautious and somewhat vague on the topic of Intermediate Stress Relief (ISR) versus Dehydrogenation Heat Treatment (DHT) for the different types of welds — which reflects the industry’s varying practices. For the advanced steels, API 934-A states that DHT should only be used with Purchaser approval, and that it should not be used on restrained welds such as nozzle welds. As a result, it is common for a DHT to be permitted on longitudinal and circumferential seams to achieve the cost and schedule savings, and ISR is used for nozzle welds. There are risks to the fabricator however, as the welds remain extremely brittle after DHT (the toughness is restored after postweld heat treatment {PWHT}, and at intermediate levels after ISR), and welding defects that are acceptable per ASME Code criterias can lead to brittle fractures during subsequent fabrication steps. The costs of the repairs and delays can then be very high, especially if the cracking is not detected until after PWHT. This paper shows the risks of acceptable defects causing brittle fractures by fracture mechanics calculations, and presents some case histories of cracking. The relative costs of ISR versus DHT, versus repairs before and after PWHT are also reviewed.
Limit Load of Pre-Cracked Polyethylene Miter Pipe Bends Subjected to In-Plane Bending Moment
Authors: EL-Bagory Tarek M. A. A. , Younan Maher Y. A. , Sallam Hossam E. M. , Abdel-Latif Lotfi A.
Published: January 2011

The main purpose of the present paper is to investigate the effect of crack depth on the limit load of miter pipe bends (MPB) under in-plane bending moment. The experimental work is conducted to investigate multi miter pipe bends, with a bend angle 90°, pipe bend factor h = 0.844, standard dimension ratio SDR = 11, and three junctions under a crosshead speed 500 mm/min. The material of the investigated pipe is a high-density polyethylene (HDPE), which is used in natural gas piping systems. The welds in the miter pipe bends are produced by butt-fusion method. The crack depth varies from intrados to extrados location according to the in-plane opening/closing bending moment respectively. For each in-plane bending moment the limit load is obtained by the tangent intersection (TI) method from the load deflection curves produced by the testing machine specially designed and constructed in the laboratory. The study reveals that increasing the crack depth leads to a decrease in the stiffness and limit load of (MPB) for both inplane closing and opening bending moment. Higher values of the limit load are reached in case of opening bending moment. This behavior is true for all investigated crack depths.
Ratcheting Assessment of a Fixed Tube Sheet Heat Exchanger Subject to In Phase Pressure and Temperature Cycles
Authors: Mackenzie Donald , Behseta Khosrow , Hamilton Robert
Published: January 2011

An investigation of the cyclic elastic-plastic response of an Olefin plant heat exchanger subject to cyclic thermal and pressure loading is presented. The heat exchanger configuration is non-standard as the tube-sheet thickness is considerably less than that required by conventional design by formula rules. Ratchetting assessment is performed using the elastic stress analysis and stress categorization procedure, which indicates that shakedown occurs under the specified loading. The cyclic elastic-plastic response of the heat exchanger is also modeled by inelastic analysis, assuming both elastic perfectly plastic and a strain hardening material models. In the elastic-perfect plastic analysis, the vessel exhibits incremental plastic strain accumulation for 10 full load cycles, with no indication that the configuration will adapt to steady state elastic or plastic action; i.e. elastic shakedown or plastic shakedown. However, the strain increments are small and would not lead to the development of a global plastic collapse or gross plastic deformation during the specified life of the vessel. The strain hardening analysis indicates that the actual vessel will adapt to plastic shakedown after 6 load cycles.
Shakedown Behaviour of Composite Cylinders With Cross Hole
Authors: Chen Haofeng , Chen Weihang , Li Tianbai , Ure James
Published: January 2011

In this study, both the lower and upper bound shakedown limits of a closed-end composite cylinder with or without a cross hole subject to constant internal pressure and a cyclic thermal gradient are calculated by the Linear Matching Method (LMM). Convergence for upper and lower bound shakedown limit of the composite cylinders is sought and shakedown limit interaction diagrams of the numerical examples identifying the regions of reverse plastic limit and ratchet limit are presented. The effects of temperature-dependent yield stress, materials discontinuities, composite cylinder thickness and the existence of cross hole on the shakedown limits are discussed for different geometry parameters. Finally, a safety shakedown envelope is created by formulating the shakedown limit results of different composite material and cylinder thickness ratios with different cross hole sizes.
Failure Investigation of a 500 Gallon Liquid Nitrogen Storage Tank
Authors: Wilkowski Gery , Shim Do-Jun , Brust Bud , Rana Mahendra D.
Published: January 2011

A 500-gallon liquid nitrogen (LN2) storage tank failed while being filled by a pump truck. The failure of the tank was the first of its kind and quite unusual. The cryogenic storage tank was a typical double-wall construction. The inner and outer vessels were made of 5083-O aluminum and low-carbon ferritic steel, respectively. The inner liquid container was an ASME Section VIII, Div. 1 Code stamped vessel. The outer vessel was not Code stamped since it was designed for vacuum service. The outer vessel was made to support the inner vessel and insulation material and maintain this vacuum for thermal insulation purposes. The heads on both the outer carbon steel and the inner aluminum vessel were fractured at a girth weld resulting in a rocketing of the vessel. A detailed investigation was conducted to find the root cause. This investigation showed that a failure of a nozzle in the annular area between the two tanks caused LN2 to pour into that area. The warmer carbon steel outer shell caused the LN2 to vaporize and rapidly pressurize the annular area. This pressurization of the annular region caused the inner aluminum tank to buckle and resulted in the head separating from the main (inner) cylinder during the buckling process. The liquid LN2 from the inner tank flowed into the outer tank (along with possible flow from the truck) and the pressure continued to increase as the LN2 level increased. The pressure in the annular space reached critical level to cause the failure of the weld in the carbon steel tank. This paper describes the analyses that were carried out for this investigation which involved determining the crack-driving force from the combined weld residual stresses, thermal stresses from the LN2 liquid level, and pressure.
Effect of Load Angle on Limit Load of Polyethylene Miter Pipe Bends
Authors: EL-Bagory Tarek M. A. A. , Younan Maher Y. A. , Sallam Hossam E. M. , Abdel-Latif Lotfi A.
Published: January 2011

The aim of this paper is to investigate the effect crack depth a/W = 0 to 0.4 and load angle (30°,45°,and 60°) on the limit load of miter pipe bends (MPB) under out-of-plane bending moment with a crosshead speed 500 mm/min. The geometry of cracked and uncracked multi miter pipe bends are: bend angle, α = 90°, pipe bend factor, h = 0.844, standard dimension ratio, SDR = 11, and three junctions, m = 3. The material of the investigated pipe is a high-density polyethylene (HDPE), which is applied in natural gas piping systems. Butt-fusion welding is used to produce the welds in the miter pipe bends. An artificial crack is produced by a special cracking device. The crack is located at the crown side of the miter pipe bend, such that the crack is collinear with the direction of the applied load. The crack depth ratio, a/W = 0, 0.1, 0.2, 0.3 and 0.4 for out-of-plane bending moment “i.e. loading angle φ = 0°”. For each out-of-plane bending moment and all closing and opening load angles the limit load is obtained by the tangent intersection method (TI) from the load deflection curves produced by the specially designed and constructed testing machine at the laboratory. For each out-of-plane bending moment case, the experimental results reveals that increasing crack depth leads to a decrease in the stiffness and limit load of MPB. In case of combined load (out-of-plane and in-plane opening; mode) higher load angles lead to an increase in the limit load. The highest limit load value appears at a loading angle equal, φ = 60°. In case of combined load (out-of-plane and in-plane closing; mode) the limit load decreases upon increasing the load angle. On the other hand, higher limit load values take place at a specific loading angle equal φ = 30°. For combined load opening case; higher values of limit load are obtained. Contrarily, lower values are obtained in the closing case.
Evaluation of Wall Thinning of PWR Feed Water Piping With the Coupled Model of Static Electrochemical Analysis and Dynamic Double Oxide Layer Analysis
Authors: Naitoh Masanori , Uchida Shunsuke , Okada Hidetoshi , Ohira Taku , Koshizuka Seiichi
Published: January 2011

In order to confirm applicability and accuracy of FAC evaluation methods based on the coupled FAC model of static electrochemical analysis and dynamic oxide layer growth analysis, wall thinning rates calculated with the proposed methods were compared with those measured for the secondary piping of a PWR plant. Flow turbulence at major parts of the system was calculated with 3D CFD codes and extrapolated to the very surface of piping wall to obtain mass transfer coefficients at boundary layers of the structure surfaces. Then, wall thinning rates were calculated with the coupled FAC model by applying the mass transfer coefficients. Major conclusions are as follows: 1) Flow distribution calculated with 3D CFD codes could be extrapolated by applying 2/7 power law of turbulence energy as a function of distance from the surface to those at the very surface of the piping to obtain a precise distribution of mass transfer coefficients. 2) Wall thinning rates calculated for large scale piping of a PWR by applying the obtained mass transfer coefficients agreed with the measured rates within a factor of 2. 3) As a result of demonstration of the FAC evaluation model, it was confirmed that suitable amount of oxygen injection into the feed water resulted sufficient mitigation of FAC without any serious adverse effect on steam generator tubing.
Evaluation of Fracture Toughness Characteristic for Nuclear Piping Using Various Types of Specimens
Authors: Park Soo , Yoo Sang-soo , Min Jun-ki , Koo Jae-Mean , Seok Chang-Sung
Published: January 2011

The leak-before-break (LBB) concept is based on the fracture resistance curve obtained by J-R tests on various types of specimens. But it has been also known that the fracture toughness data by various types of specimens are different each other. For example, the estimates for fracture toughness of standard specimens are conservative when compared to the fracture toughness of real pipes owing to the difference of the constraint effect between real pipes and standard specimens. Therefore for estimating the integrity of real pipes on the basis of elastic-plastic fracture mechanics, we have to first establish the relations among real pipes, standard CT specimens and curved CT specimens. In this study, we performed the fracture toughness tests for nuclear piping material by various types of specimen. And each J-R curve considered in the constraint effect was compared.
Basic Study on Pressure Vessel for Vaporization of Cryogenic Fluids by Direct Contacting Normal Temperature Fluids
Authors: Watanabe Toshiaki , Iyama Hirofumi , Maehara Hironori , Itoh Shigeru
Published: January 2011

In recent years in Japan, the demand of cryogenic fluids like a LH2, LNG is increasing because of the advance of fuel cell device technology, hydrogen of engine, and stream of conciousness for environmental agreement. On the other hand, as for fisheries as well, the use of a source of energy that environment load is small has been being a pressing need. We paid attention to the effective use of cold heat of the liquid fuel which is a cryogenic fluid. That method is to use a cold heat which an cryogenic fluid has, without a heat exchanger. The mixture of the extreme low temperature fluid and the normal temperature fluid becomes the cause which causes pressure vessel and piping system crush due to explosive boiling and rapid freezing. Therefore, we carried out the experiments related to promotion of evaporating cryogenic fluids, in the contact directly of the room temperature fluids and cryogenic fluids.
Mechanical and Microstructural Characterization of Heat-Affected Zone Materials of Reactor Pressure Vessel
Authors: Katsuyama Jinya , Tobita Tohru , Nishiyama Yutaka , Onizawa Kunio
Published: January 2011

In order to monitor the neutron irradiation embrittlement of the reactor pressure vessel (RPV) steels for the safe operation of light-water reactors, surveillance specimens of representative materials, i.e. base metal, weld metal and heat affected zone (HAZ), are installed in the RPV during reactor operation according to the regulation. Among these materials, HAZ specimens exhibit a relatively large scatter in Charpy impact properties because of the microstructural inhomogeneity due to multi-pass welding. ASTM E185 and JSME S NC1 stipulate the exception of HAZ specimens from surveillance test. However, the technical basis on the exception has not been established. Therefore, we have started a research on the irradiation embrittlement in HAZ material of RPV steels. Typical RPV steel plates with different impurity levels and their weldments were fabricated to characterize the microstructures and subsequent mechanical properties of typical HAZ materials. Simulated HAZ materials were also made by applying several heat treatments representative of HAZ. Finite element analysis was conducted to draw maps of distributions of grain size and phase-fraction. Using simulated HAZ materials with different grain size and phase before irradiation, mechanical properties such as hardness, Charpy impact property and fracture toughness were measured in comparison with those of base metals and actual HAZ materials. Through the comparison, it was indicated that mechanical properties such as fracture toughness in some simulated HAZ materials were different from base metal and dependent significantly on the metallurgical structure, particularly phase but prior austenitic grain size. Higher fracture toughness in CGHAZ (Coarse-Grain HAZ) materials compared to base metal is due to mixed structure of martensite and lower-bainite phases. Upper-bainite phase in FGHAZ (Fine-Grain HAZ) and base materials causes lower fracture toughness than CGHAZ materials.
Classification of Defects in Fusion Joints of Polyethylene Pipes
Authors: Zheng Jinyang , Qin Yongquan , Shi Jianfeng , Guo Weican , Wang Hui , Wang Fei
Published: January 2011

To establish a comprehensive classification method of the defects in fusion joints of polyethylene (PE) pipes, the geometrical characters of typical defects in electrofusion (EF) and butt fusion (BF) joints were researched by means of ultrasonic phased array inspection and naked-eye observation. Then the results were comparatively analyzed, and a novel classification method of the defects in PE pipe joints was proposed. Typical defects in EF joints were classified as lack of fusion, voids, wire dislocation, and cold welding. And those in BF joints were classified as crack, voids, inclusion on fusion interface, and process defects. Furthermore, characteristics of the classified defects, together with their main causes were briefly described.
Analysis of Power Boiler Furnace Wall and Its Supporting Structure
Authors: Kim Jaecheol , Kim Taewoan
Published: January 2011

In this paper, wall tube stresses of power boiler furnace according to three different design options of furnace wall stiffening system were investigated. As the loading condition, furnace design gas pressure, fluid pressure inside the wall tube and the temperature difference between furnace wall and reaction plate were used. When the simplest design option is applied, wall tube stress levels are unsatisfactory. Furnace design gas pressure has strong influences on wall tube stress in this case. The second option using a reaction plate successfully decreased stresses on furnace wall tubes. However, another problem has arisen from using the reaction plate between furnace wall and wall stiffening H-beam called buckstay. When there are temperature differences between furnace wall and reaction plate, wall tubes are subjected to a large compression load. As final design option, the wall stiffening system using a space plate in addition to the reaction plate was analyzed. The space plate on reaction plate gives room to absorb differential thermal expansion between furnace wall and reaction plate, and satisfactory stress results on furnace wall tubes were obtained.