bluuebunny/crossref_metadata_2025 huggingface dataset:
Static Deflection Control of a PVC Pipe Joint Using Piezoelectric Actuation
Authors: Meyer Ryan , Pang Su-Seng
Published: January 2011

This paper investigates the use of surface bonded piezoelectric induced strain actuators and their effectiveness at inducing deflection in a PVC (polyvinyl chloride) simply supported adhesively bonded pipe joint structure. The purpose using piezoelectric actuation is to reduce the high shear stress concentrations at the ends adhesive layer by reducing the joint end deflections caused by external loading; effectively enhancing the strength of the joint. Euler-Bernoulli beam theory is implemented to derive the elastic curves for two possible surface bond scenarios; on the pipe joint itself and on the separate spans of piping. The derived equations account for the physical and geometrical parameters of the piping and piezoelectric actuators. The effects of reducing the detrimental effects of a distributed external load caused by the weight of the fluid within the piping system are examined. A numerical study is carried out to evaluate the effectiveness of the piezoelectric actuation based on the two proposed actuator bond scenarios. Bonding two pairs of actuators on separate pipe sections was shown to be capable of inducing greater joint end deflections than bonding a single pair of actuators on the pipe joint. Bonding two pairs of actuators on the separate sections of piping was shown to be capable of reducing joint end deflections caused by external loading by 70%, while bonding one pair of actuators on the pipe joint was shown to be capable of reducing joint end deflections by 20%.
Comparison of Analytical Methods to Study the Impact of a Postulated Closure Head Drop Accident on the Structural Integrity of the Bottom-Mounted Instrumentation System
Authors: Castillo William C. , Loy Geoffrey M. , Remic Joseph M. , Molitoris David P. , Demetri George J. , Roarty David H.
Published: January 2011

During typical nuclear power plant refueling activities for a pressurized water reactor (PWR), the reactor vessel closure head assembly must be removed from the reactor vessel (RV), transported for storage, and returned to the RV after refueling. This is categorized as a critical heavy load lift in NUREG-0612 [1] because a drop accident could result in damage to the components required to cool the fuel in the RV core. In order to mitigate the potentially severe consequences of a closure head drop, the United States Nuclear Regulatory Commission (USNRC) has mandated that nuclear power plants upgrade to a single failure-proof crane, show single failure-proof crane equivalence, or perform a head drop analysis to demonstrate that the core remains covered with coolant and sufficient cooling is available after the head drop accident. The primary coolant-retaining components associated with the RV are the inlet and outlet nozzles and the hot and cold leg main loop piping. Typical head drop analyses have considered these components to ensure that their structural integrity is maintained. One coolant-retaining component that has not been included in head drop evaluations on a consistent basis is the bottom-mounted instrumentation (BMI) system. In a typical Westinghouse PWR, 50 to 60 BMI nozzles are connected through the bottom hemisphere of the RV to one-inch diameter guide tubes which run under the vessel to a seal table above. Failure of the BMI system has the potential to adversely affect core coolability, especially if multiple failures are postulated within the system. A study was performed to compare static and dynamic methods of analyzing the effects of a head drop accident on the structural integrity of the BMI system. This paper presents the results of that study and assesses the adequacy of each method. Acceptability of the BMI system pressure boundary is based on the Nuclear Energy Institute Initiative (NEI 08–05 [2]) criteria for coolant-retaining components, which are based on Section III, Appendix F of the ASME Code [3].
Residual Deformation of a Hard-Coated Valve Seat Subjected to Thermal Shocks
Authors: Mathieu Jean-Philippe , Rit Jean-Franc¸ois , Ferrari Je`roˆme , Hersant David
Published: January 2011

Most safety related valves in EDF’s nuclear plant must prove their ability to sustain thermal shocks of approximately 240K amplitude. This paper evaluates the simulation of a globe valve tested for thermal shocks. Since the physical test campaign showed inadequate internal sealing, the simulation focuses on the residual deformation of the hard alloy, planar seat, welded on successive body designs. This deformation is the result of the thermal loadings first induced by the welding process, then by fluid flow inside the valve. A chain of 3D simulations successively computes: a welding temperature transient in the body, the resulting strain hardening — especially in the seat vicinity —; temperature transients in the flow and the valve parts, and the resulting strains in the body causing a bump deformation of the seat surface. This end result agrees with measurements on the tested valve specimen. We show that inaccurate results are obtained on simpler assumptions, such as no welding, and we give insights on the dominant effect of the first hot, cold, hot transient over other profiles. Finally, the agreement we obtain on deformation predictions is toned down by an unsatisfactory sealing prediction, as well as the complexity and duration of the simulation chain compared with physical testing.
Creep Behavior of the Newly Developed Advanced Heat Resistant Austenitic Stainless Steel Grade UNS S31035
Authors: Ho¨gberg Jan , Chai Guocai , Kjellstro¨m Patrik , Bostro¨m Magnus , Forsberg Urban , Sandstro¨m Rolf
Published: January 2011

The UNS S31035 austenitic stainless steel grade is a newly developed advanced heat resistant material for use in coal fired boilers at material temperatures up to about 700°C. This new grade has good resistance to oxidation and hot corrosion, and shows higher creep rupture strength than other austenitic stainless steels available today. This paper will mainly focus on the study of the creep mechanisms in this grade from 550°C up to 800°C by using TEM, SEM and LOM. The creep mechanisms at different temperatures and loading conditions have been identified. The interaction between dislocations and precipitates and their contribution on the creep rupture strength and fracture mechanisms have been discussed. In this paper, different models have been used to evaluate the long-term creep behavior of the grade. A creep rupture strength near 100MPa at 700°C for 100 000h has been predicted. This makes it an interesting alternative for super-heaters and reheaters in future high-efficient coal fired boilers.
Universal Weight Function Consistent Method to Fit Polynomial Stress Distribution for Calculation of Stress Intensity Factor
Authors: Scarth Douglas A. , Xu Steven X.
Published: January 2011

Procedures for analytical evaluation of flaws in nuclear pressure boundary components are provided in Section XI of the ASME B&PV Code. The flaw evaluation procedure requires calculation of the stress intensity factor. Engineering procedures to calculate the stress intensity factor are typically based on a polynomial equation to represent the stress distribution through the wall thickness, where the polynomial equation is fitted using the least squares method to discrete data point of stress through the wall thickness. However, the resultant polynomial equation is not always an optimum fit to stress distributions with large gradients or discontinuities. Application of the weight function method enables a more accurate representation of the stress distribution for the calculation of the stress intensity factor. Since engineering procedures and engineering software for flaw evaluation are typically based on the polynomial equation to represent the stress distribution, it would be desirable to incorporate the advantages of the weight function method while still retaining the framework of the polynomial equation to represent the stress distribution when calculating the stress intensity factor. A method to calculate the stress intensity factor using a polynomial equation to represent the stress distribution through the wall thickness, but which provides the same value of the stress intensity factor as is obtained using the Universal Weight Function Method, is provided in this paper.
Simulation and Measurement of Through-Wall Residual Stresses in a Structural Weld Overlaid Pressurizer Nozzle
Authors: Marlette Stephen , Freyer Paula , Smith Michael , Goodfellow Andrew , Pitoiset Xavier , Voigt Bradley , Rishel Rick , Kingston Ed
Published: January 2011

Full structural weld overlays (FSWOLs) have been used extensively as a repair/mitigation technique for primary water stress corrosion cracking (PWSCC) in pressurizer nozzle dissimilar metal (DM) welds. To support an approved FSWOL design and safety submission for British Energy pressurized water reactor (PWR) nozzles, an in-depth evaluation was performed to assess the effects of a FSWOL on the through-wall residual stress distribution in safety/relief pressurizer nozzles. Two safety/relief pressurizer nozzle mockups were fabricated based on British Energy’s PWR nozzle design. One mockup included the nozzle to safe-end DM weld and the safe-end to stainless steel weld while the second mockup included the DM weld, the stainless steel weld and a Westinghouse-designed structural weld overlay. The mockups were fabricated utilizing materials and techniques that represented the plant-specific nozzles as closely as possible and detailed welding parameters were recorded during fabrication. All welds were subsequently nondestructively evaluated (NDE). A thorough review of the detailed fabrication records and the NDE results was performed and several circumferential positions were selected on each mockup for subsequent residual stress measurement. The through-wall residual stress profiles were experimentally measured through the DM weld centerline at the selected circumferential positions using both the deep hole drilling (DHD) and incremental deep hole drilling (iDHD) measurement techniques. In addition to experimental residual stress measurements, the through-wall residual stress profiles were simulated using a 2-D axisymmetric ANSYS™ finite element (FE) model. The model utilized kinematic strain hardening and the temperature constraint method which greatly simplified the simulation as compared to detailed heat source modeling methods. A range of residual weld stress profiles was calculated by varying the time at which the temperature constraints were applied to the model. The simulation results were compared to the measurement results. It was found that the effects of the FSWOL were principally three fold. Specifically, the FSWOL causes a much deeper compressive stress field, i.e., the overlay shifts tension out towards the outside diameter surface. Further, the FSWOL reduces tension in the underlying dissimilar metal weld, and finally, the FSWOL causes higher peak compressive and tensile residual stresses, both of which move deeper into the nozzle wall after the overlay is applied. Relatively good agreement was observed between the FE results and the measurements results.
Comparative Review of Risk-Informed Inservice Inspection Methodologies
Authors: Chockie Alan D. , Graybeal M. Robin , Kulat Scott D.
Published: January 2011

In the 1970’s and early 80’s there was a reevaluation of the role of inservice inspection programs. Inservice inspection programs as originally developed under the ASME Section XI Code requirements were based on the best information available at the time and helped establish the safety of the subject components. However, it was determined that the examination requirements were not efficient because examinations were being focused on many welds, components, and systems that are not as important as originally thought when the ASME Section III Classes 1, 2, and 3 categories were developed. It was determined that the appropriate locations were not being inspected and that the most effective types of examinations were not being performed. It was felt that a more optimal inspection approach was needed. This eventually led to the development of the risk-informed inservice inspection (RI-ISI) methodology. RI-ISI provides a structured and systematic framework for allocating inspection resources in a cost-effective manner while improving plant safety. It helps focus inspections where failure mechanisms are likely to be and where enhanced inspections are warranted. This paper examines the foundations for the current RI-ISI initiatives and how the RI-ISI methodology may be used in the future for current and next generation plants.
Modeling Heat Transfer in Spent Fuel Transfer Cask Neutron Shields: A Challenging Problem in Natural Convection
Authors: Fort James A. , Cuta Judith M. , Bajwa Chris S. , Baglietto Emilio
Published: January 2011

In the United States, commercial spent nuclear fuel is typically moved from spent fuel pools to outdoor dry storage pads within a transfer cask system that provides radiation shielding to protect personnel and the surrounding environment. The transfer casks are cylindrical steel enclosures with integral gamma and neutron radiation shields. Since the transfer cask system must be passively cooled, decay heat removal from the spent nuclear fuel canister is limited by the rate of heat transfer through the cask components, and natural convection from the transfer cask surface. The primary mode of heat transfer within the transfer cask system is conduction, but some cask designs incorporate a liquid neutron shield tank surrounding the transfer cask structural shell. In these systems, accurate prediction of natural convection within the neutron shield tank is an important part of assessing the overall thermal performance of the transfer cask system. The large-scale geometry of the neutron shield tank, which is typically an annulus approximately 2 meters in diameter but only 10–15 cm in thickness, and the relatively small scale velocities (typically less than 5 cm/s) represent a wide range of spatial and temporal scales that contribute to making this a challenging problem for computational fluid dynamics (CFD) modeling. Relevant experimental data at these scales are not available in the literature, but some recent modeling studies offer insights into numerical issues and solutions. However, the geometries in these studies, and for the experimental data in the literature at smaller scales, all have large annular gaps that are not prototypic of the transfer cask neutron shield. This paper proposes that there may be reliable CFD approaches to the transfer cask problem, specifically coupled steady-state solvers or unsteady simulations; however, both of these solutions take significant computational effort. Segregated (uncoupled) steady state solvers that were tested did not accurately capture the flow field and heat transfer distribution in this application. Mesh resolution, turbulence modeling, and the tradeoff between steady state and transient solutions are addressed. Because of the critical nature of this application, the need for new experiments at representative scales is clearly demonstrated.
Impulse Response Reduction Using Harmonically Varying Damping
Authors: Iba Daisuke , Spencer B. F.
Published: January 2011

This paper proposes a new impulse response reduction method using harmonically varying damping considering a single-degree-of-freedom isolation system. In general, a low damping system is better than a high damping system with respect to steady-state isolation performance at high frequencies. On the other hand, as the mass of the low damping system is subjected to an impulse input, attenuation of the response is slow. In this study, an ideal variable damper is employed to achieve impulse response reduction. If the additional harmonic response caused by the variable damping and the base excitation are at the same frequency as the impulse response and with opposite-phase, the impulse response of the system can be reduced. An expression for the variable damping is developed and the reduction performance is confirmed by numerical simulation.
A New Idea of Pure Mode-I Fracture Test of Bonded Bi-Materials
Authors: Ouyang Zhenyu , Ji Gefu , Li Guoqiang , Pang Su-Seng , Ibekwe Samuel
Published: January 2011

Bi-material systems in which two dissimilar materials are adhesively joined by a thin adhesive interlayer have been widely used in a variety of modern industries and engineering structures. There are two fundamental issues that need to be adequately addressed: (1) Fracture of bonded bi-materials is mixed mode: Mode-I (pure peel) and Mode-II (pure shear). Fracture test implementation of bi-material systems with the traditional Mode-I methods will induce a noticeable mixed mode fracture due to the disrupted symmetry by the bi-material configuration; (2) The popular cohesive zone models (CZMs) for accurate fracture simulations require more than a single parameter (toughness) as is the case in the traditional linear elastic fracture mechanics (LEFM). Thus, J-integral is highly preferred. It can not only capture more accurate toughness value by considering the root rotation effect, but also facilitate the experimental characterizations of the interfacial cohesive laws, which naturally include all required parameters by CZMs. Motivated by these two important issues, a novel idea is proposed in the present work to realize and characterize the pure Mode-I nonlinear interface fracture between bonded dissimilar materials: Despite the approximation with the elementary beam theories, the accuracy is validated by numerical simulations. The proposed approach may be considered as a promising candidate for the future standard Mode-I test method of adhesively bonded dissimilar materials due to its obvious simplicity and accuracy.
Effect of Shear and Torsion on the Plastic Collapse Load of a Pipe Section With a Circumferential Flaw
Authors: Yen Lingyah , Al-Shawaf Taha , Kim Dae-Jin
Published: January 2011

This paper focuses on the effect of shear force and torsion moment on the plastic collapse load for circumferentially flawed pipe sections with small and large diameter-thickness (D/t) ratios. Rigorous elastic-plastic finite element analyses are performed using bilinear kinematic hardening and Von Mises yield criteria. The comparison between the numerical results and predictions by the ASME B&PV Code Section XI Appendix C shows that including the effect of shear and torsion (separate from bending moment) may result in plastic collapse loads varying from those predicted by the ASME Section XI Appendix C.
Background on the New ASME PCC-1:2010 Appendix P “Guidance on Troubleshooting Flanged Joint Leakage Incidents”
Authors: Payne James R. , Neely Clyde C. , Hayman Edward W.
Published: January 2011

A revised ASME PCC-1 “Guidelines for Pressure Boundary Bolted Joint Assembly” [1] has recently been published and includes several new appendices. Among them is the new Appendix P “Guidance on Troubleshooting Flanged Joint Leakage Incidents”. It is a significant addition to the PCC-1 document that outlines what should be considered when leakage of a pressure boundary bolted joint occurs. This paper outlines the development background of this new appendix. It also provides an outline of its contents along with discussion on its use.
Economic and Technical Efficiency of High Performance Abrasive Waterjet Cutting
Authors: Henning Axel , Liu Peter , Olsen Carl
Published: January 2011

Abrasive water jets have recently become a popular tool for mechanical machining. With its great advantages of geometric and material flexibility and its ability to cut hard-to-machine materials the technology is quickly spreading throughout many industries. With this near net-shape production becomes feasible, while significantly reducing the time necessary for secondary operations like programming, clamping, or tool changing. This allows a significant optimization of the overall manufacturing process chain. In this paper different approaches to increase the economic and technical efficiency of cutting with abrasive water jets are analyzed. Experimental analysis of the speed of abrasive particles show that the kinetic power of the particles mainly depends on the hydraulic power of the waterjet. Merely increasing the pressure of the jet did not yield any improvement in its acceleration capability. To obtain the most effective cutting performance a high level of hydraulic power through large nozzles should therefore be utilized. Additionally, recent advancements in cutting path control software have proven to significantly decrease the total ‘time to product’ and to increase the precision of the part. Those improvements in both software control and cutting power enable abrasive water jets to become an integral part of many industrial manufacturing processes. This will widen the scope of possible applications of this innovative and promising technology.
Estimation Procedures for J and CTOD Fracture Parameters Experimental Evaluation Using Homogeneous and Mismatched Pin-Loaded SE(T) Specimens
Authors: de Oliveira Gabriel P. , Donato Gustavo H. B.
Published: January 2011

Experimental evaluation of geometry-dependent material’s fracture resistance using constraint-designed SE(T) specimens has proved to be an accurate option to assess the structural integrity of pipelines and pressure vessels reducing excessive conservatism. In this context, this work presents procedures for experimental J-integral and CTOD (δ) evaluation using the eta (η) method applied to tension pin-loaded SE(T) specimens made of homogeneous materials and also containing mismatched joints. Initially, the conceptual background is presented, followed by the description of the refined non-linear finite element models developed, which provide the necessary evolution of load with increased load-line and crack mouth opening displacement. As results, are presented η factors for J-integral estimation and CTOD calculations, which are not available in current standardized procedures. The main objective is to allow fracture resistance experimental evaluation using specimens of different a/W-ratios, material flow properties, weld joint configurations and levels of weld strength mismatch. The main motivation is the possibility of enhancing accuracy of pressure vessels and piping integrity assessments, since these later present very close fracture conditions if compared to SE(T) specimens. The present results, when taken together with previous developments, extend the knowledge about the use of pin-loaded SE(T) specimens. The reader should enhance the studies about the topic with the complimentary paper with the same title beginning but involving clamped SE(T) specimens.
Uncertainties in NDE Reliability and Assessing the Impact on RI-ISI
Authors: Doctor Steven R. , Anderson Michael T.
Published: January 2011

A major thrust in the past 20 years has been to upgrade nondestructive examinations (NDE) for use in inservice inspection (ISI) programs to more effectively manage degradation at operating nuclear power plants. Risk-informed ISI (RI-ISI) is one of the outcomes of this work, and this approach relies heavily on the reliability of NDE, when properly applied, to detect sources of expected degradation. There have been a number of improvements in the reliability of NDE, specifically in ultrasonic testing (UT), through training of examiners, and improved equipment and procedure development. However, the most significant improvements in UT were derived by moving from prescriptive requirements to performance based requirements. Even with these substantial improvements, NDE contains significant uncertainties and RI-ISI programs need to address and accommodate this factor. As part of the work that PNNL is conducting for the U. S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research, we are examining the impact of these uncertainties on the effectiveness of RI-ISI programs. One of the primary objectives of in-service inspection, including a RI-ISI program, is to manage potential degradation that may occur, but that had not been foreseen through previous operating experience. However, RI-ISI programs in the U.S are primarily based on history, looking back at past failures in the operating fleet. Therefore, RI-ISI may not adequately manage degradation events that are yet to occur, such as those that may have a long incubation (initiation) time, but a potentially fast growth rate. For this reason, RI-ISI will always be reactive to such failure events. Successful ISI needs to determine what NDE is required, when and how frequently it needs to be applied, how effective the NDE must be and where the NDE needs to be applied. Both flaw detection and accurate characterization need to be addressed. This paper will examine the reliability and uncertainties of NDE, and how these may impact RI-ISI.
An Ultrasonic Phased Array Evaluation of Cast Austenitic Stainless Steel Pressurizer Surge Line Piping Welds
Authors: Diaz Aaron A. , Cinson Anthony D. , Crawford Susan L. , Moran Traci L. , Anderson Michael T.
Published: January 2011

A set of circumferentially oriented thermal fatigue cracks (TFCs) were implanted into three cast austenitic stainless steel (CASS) pressurizer (PZR) surge-line specimens (pipe-to-elbow welds) that were fabricated using vintage CASS materials formed in the 1970s, and flaw responses from these cracks were used to evaluate detection and sizing performance of the phased-array (PA) ultrasonic testing (UT) methods applied. Four different custom-made PA probes were employed in this study, operating nominally at 800 kHz, 1.0 MHz, 1.5 MHz, and 2.0 MHz center frequencies. The CASS PZR surge-line specimens were polished and chemically etched to bring out the microstructures of both pipe and elbow segments. Additional studies were conducted and documented to address baseline CASS material noise and observe possible ultrasonic beam redirection phenomena.
The Computation of Accurate Buckling Pressures of Imperfect Thin-Walled Cylinders
Authors: de Paor Caitri´ona , Kelliher Denis , Cronin Kevin , Wright William M. D.
Published: January 2011

The buckling capacity of thin cylindrical shells subject to uniform external pressure is investigated in this paper. Thin cylindrical shells are known to be highly sensitive to geometric and material imperfections such as wall thickness variation, non-circularity and random geometric imperfections. The effect of imperfection on the buckling load is studied using finite element (FE) models and laboratory experiments. Imperfection measurements are taken on small scale steel cans and these measurements are modelled and analysed using a geometrically nonlinear static finite element analysis. The cans are then tested in the laboratory and the results compared with those predicted by the FE models and theory.
Development and Validation of Online Monitoring Techniques for Composite Overwrapped Pressure Vessels
Authors: Faria Hugo , Frias Clara , Fraza˜o Orlando , Vieira Pedro , Marques Anto´nio Torres
Published: January 2011

In this research programme, methodologies for structural health monitoring (SHM) of composite overwrapped pressure vessels (COPV) were addressed. This works fit in the development of a COPV laboratorial prototype incorporating non-destructive sensing technologies, in order to detect and identify critical aspects that can occur during operation, aiming to reduce possible unwanted and unpredicted failures. Fibre Bragg grating (FBG) optical sensors and polyvinylidene Fluoride (PVDF) polymeric piezoelectric were the selected sensing technologies. These sensors were embedded in the liner-composite interface during its manufacturing and monitored the prototype while being tested under cyclic internal pressure loading. The data collected from the different sensors type were compared. The Analysis of the data, together with the assessment to the suitability of the two sensing technologies in SHM applications are discussed.
An Experimental Approach for Delayed Stress Corrosion
Authors: Keller Scott G. , Gordon Ali P.
Published: January 2011

Failures of structural and mechanical components have long been attributed to environmentally assisted cracking (EAC). The umbrella of EAC encompasses several phenomena, including stress corrosion cracking (SCC), corrosion fatigue (CF), hydrogen embrittlement (HE) and liquid metal embrittlement (LME). The latter, LME, has resulted in the failure of components in petrochemical and aeronautical industries, among others. The effects are detrimental, with crack tip velocities on the order of centimeters per second and failures occurring rapidly. Previous research has provided numerous underlying microstructural failure mechanisms aimed at identifying the true failure mode. Conflicting experimental data has extended the debate over the true mechanism promoting renewed interest in novel experimental regimes. Utilizing fracture mechanics specimens, the solid-liquid Al-Hg couple was analyzed to extend or reject current theories. Through the implementation of an original environmental chamber capable of testing notched and pre-cracked components in corrosive environments, C(T) specimens were subjected to experiments submersed in liquid mercury. Upon the application of an initially applied stress intensity factor (under load-control), incubation periods preceding failure were observed. Crack initiation and propagation were observed to occur along the starter notch, as well as other regions on the specimen. Results provided evidence that additional factors, such as a critical load or critical microstructural orientation, were factors in crack initiation and propagation. In the quest to observe the influence of these additional factors, a variation of the experimental setup was implemented and initial tests have begun.
Formulation of a Criterion for Preventing Self-Loosening of Threaded Fasteners Due to Cyclic Transverse Loading
Authors: Yang Xianjie , Nassar Sayed , Wu Zhijun
Published: January 2011

In the paper, a novel criterion is developed for preventing the self-loosening of preloaded threaded fasteners under cyclic transverse loading. For a known cyclic excitation, the system parameters are used in the formulation of a closed form solution for the minimum fastener preload required for preventing self-loosening. The effect of several key variables is investigated; this includes bearing and thread friction coefficients, bolt grip length, thread pitch, material, and the cyclic amplitude of the transverse excitation. An experimental setup and test procedure is established. Comparison between the experimental and analytical clamp load variation results shows that the proposed criterion can accurately predict the requirements for preventing self-loosening.
Crack Branching and Its Effect on Environmentally Assisted Cracking in High Temperature Water Environments
Authors: Lu Zhanpeng , Xue He , Shoji Tetsuo
Published: January 2011

Crack kinking or branching has been observed in laboratory stress corrosion cracking tests and in some components suffering from stress corrosion cracking in nuclear power plant coolants. There are several types of crack branching: i.e., macroscopic multiple branching cracks, local crack branching or the combination of both. Crack branching affects the crack tip stress/strain distribution in terms of stress intensity factor and crack tip strain rate, and consequently affects crack growth behavior. The crack tip mechanical fields in some typical crack branching systems are quantified using empirical, analytical and numerical simulation methods. The effect of crack branching is less significant in contoured double cantilever beam specimens than in compact tension specimens for the same size and configuration of branched cracks. The applications of the analysis results to some observed crack branching phenomena of austenitic alloys in high temperature water environments are discussed based on the theoretical crack growth rate formulation.
Domestic Gas Cylinders Manufactured by Using a Composite Hybrid Steel Glass Reinforced Thermoplastic Matrix Solution
Authors: Nunes Joao P. , Silva Joao F. , Antunes Paulo J.
Published: January 2011

The use of polymer composites allows effectively minimizing the weight, improving aesthetics, promoting handling, and also increasing the vessels mechanical, impact, and corrosion behavior [1]. Since filament winding technique appeared in late 1950s as very suitable production process to manufacture rotationally advanced structures [2–7], such as rocket engine cases, an extensive work has been carried out on the development of new processing possibilities. The improvements occurred until the 1980s as consequence of the computer evolution, give finally birth to the modern polar and multi-axle CNC-controlled filament winding machines that are easily integrated in CAD/CAM environments and allow process almost all exotic shapes with very high accurate fiber placement, speed, and quality control [8]. In this work, continuous glass/polypropylene (GF/PP) commingled fiber tapes were employed to produce wrapped pressure gas vessels for domestic applications by using filament winding. The vessel structural-wall was built using a hybrid solution consisting in a very thin steel liner over wrapped by the filament wounded GF/PP commingled fiber tape layers. FEM analysis was used to evaluate if the composite gas pressure vessel based on the hybrid solution (steel liner plus glass fiber reinforced thermoplastic) is capable to withstand the following pressure requirements: the metallic liner, alone, a minimum burst pressure of 4MPa and whole hybrid composite vessel minima internal test and burst pressures of 3MPa and 6.75 MPa, respectively. Finally, gas pressure vessel prototypes manufactured in industrial conditions were submitted to burst pressure and electrostatic tests to prove that they accomplish all European standard strength requirements. The electrostatic tests were made to evaluate the risk of dangerous electrostatic discharges occurring in the worst service conditions described in the Annex C of the EN 13463-1 standard [9]. Two types of electrostatic discharge risks were evaluated: i) possibility of the brush discharge occur from the external non-conductive surface of the composite cylinders due to the accumulation of electrical charges generated in service by rubbing or contact of the cylinder with a high voltage power supply, and ii) possibility of the brush discharge occur through the gas cylinder metallic conductive filling valve due to the accumulation of electrical charges on the internal steel liner as result from the normal service cylinder shaking.
Fracture and Fatigue of Commercial Grade API Pipeline Steels in Gaseous Hydrogen
Authors: San Marchi Chris , Somerday Brian P. , Nibur Kevin A. , Stalheim Douglas G. , Boggess Todd , Jansto Steve
Published: January 2011

Gaseous hydrogen is an alternative to petroleum-based fuels, but it is known to significantly reduce the fatigue and fracture resistance of steels. Steels are commonly used for containment and distribution of gaseous hydrogen, albeit under conservative operating conditions (i.e., large safety factors) to mitigate so-called gaseous hydrogen embrittlement. Economical methods of distributing gaseous hydrogen (such as using existing pipeline infrastructure) are necessary to make hydrogen fuel competitive with alternatives. The effects of gaseous hydrogen on fracture resistance and fatigue resistance of pipeline steels, however, has not been comprehensively evaluated and this data is necessary for structural integrity assessment in gaseous hydrogen environments. In addition, existing standardized test methods for environment assisted cracking under sustained load appear to be inadequate to characterize low-strength steels (such as pipeline steels) exposed to relevant gaseous hydrogen environments. In this study, the principles of fracture mechanics are used to compare the fracture and fatigue performance of two pipeline steels in high-purity gaseous hydrogen at two pressures: 5.5 MPa and 21 MPa. In particular, elastic-plastic fracture toughness and fatigue crack growth rates were measured using the compact tension geometry and a pressure vessel designed for testing materials while exposed to gaseous hydrogen.
Using Thermoplastic (HDPE) Liners and Glass Fiber Reinforced Thermosetting and Thermoplastic Structural Wall Matrices to Produce Filament Wound Pressure Vessels
Authors: Silva Joao F. , Nunes Joao P. , Velosa Joao C.
Published: January 2011

Polymer composites are an excellent alternative to replace more traditional materials in the fabrication of pressure cylinders for common applications. They minimize the weight and improve the mechanical, impact and corrosion behavior, which are relevant characteristics for almost all current and future large scale pressure cylinder applications, such as liquid filters and accumulators, hydrogen cell storage vessels, oxygen bottles, etc. A new generation of composite pressure vessels has been studied in this work. The vessels consist on a thermoplastic liner wrapped with a filament winding glass fiber reinforced polymer matrix structure. A conventional 6-axis CNC controlled filament winding equipment was used to manufacture the thermosetting matrix composite vessels and adapted for production of thermoplastic matrix based composite vessels. The Abaqus 6.4.2 FEM package was used to predict the mechanical behavior of pressure vessels with capacity of approximately of 0.068 m3 (68 liters) for a 0.6 MPa (6 bar) pressure service condition according to the requirements of the EN 13923 standard, namely, the minimum internal burst pressure. The Tsai-Wu and von-Mises criteria were used to predict composite laminate and thermoplastic liner failures, respectively, considering the elasto-plastic behavior of the HDPE liner and the lamina properties deducted from the micromechanical models for composite laminates. Finally, the results obtained from the simulations were compared with those obtained from the experimental pressure tests made on the thermoplastic liners and final composite vessels.
Fracture and Fatigue Tolerant Steel Pressure Vessels for Gaseous Hydrogen
Authors: Nibur Kevin A. , San Marchi Chris , Somerday Brian P.
Published: January 2011

Fatigue crack growth rates and rising displacement fracture thresholds have been measured for a 4130X steel in 45 MPa hydrogen gas. The ratio of minimum to maximum load (R-ratio) and cyclic frequency was varied to assess the effects of these variables on fatigue crack growth rates. Decreasing frequency and increasing R were both found to increase crack growth rate, however, these variables are not independent of each other. Changing frequency from 0.1 Hz to 1 Hz reduced crack growth rates at R = 0.5, but had no effect at R = 0.1. When applied to a design life calculation for a steel pressure vessel consistent with a typical hydrogen trailer tube, the measured fatigue and fracture data predicted a re-inspection interval of nearly 29 years, consistent with the excellent service history of such vessels which have been in use for many years.
Detailed Finite Element Modeling of US EPR™ Nuclear Island for Seismic SSI Analysis
Authors: Tabatabaie Mansour , Sumodobila Basilio , Wong Calvin , Fisher Daniel E. , Oswald J. Todd
Published: January 2011

The US EPR™ standard design currently under development by AREVA consists primarily of a nuclear island (NI) and several other significant structures outside of and in close proximity to the NI. The NI structures consist of the Reactor Building (RB), Fuel Building (FB), Safeguard Building 1 (SB1), Safeguard Building 2/3 (SB2/3), Safeguard Building 4 (SB4), and Reactor Building Internal Structures (RBIS) — all of which share a common foundation basemat. The Nuclear Island is embedded approximately 11.6 m below the ground surface. Seismic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in the frequency domain using a lumped-mass stick and/or coarse finite element model of the structure. These models are designed to capture the global dynamic response of the system, the results of which provide the inertia forces that are used for foundation stability assessment as well as input to a static detailed finite element model of the structure for design. The in-structure response spectra is calculated from a separate dynamic analysis of detailed structural model on fixed base excited by the base motion developed from the SSI analysis or often by including single-degree-of-freedom (SDOF) oscillators representing the local response in the stick/coarse finite element SSI models. With recent advances in computer software and hardware technologies, it is now possible to perform SSI analysis of detailed structural models in the frequency domain. This paper presents the results of the seismic SSI analysis of the US EPR™ nuclear island using both a stick and detailed finite element representation of the structure. The soil profile corresponds to a medium stiff soil case used for the standard design. Because the EPR™ nuclear island is a complex, unsymmetric structure, the stick model consists of multiple interconnected sticks developed and calibrated against a detailed finite element model of the structure on a fixed base. Both models are analyzed using SASSI [1]. The results of the detailed finite element model in terms of maximum accelerations and response spectra, as well as total interstory forces and moments, are calculated and compared with those of the lumped-mass stick model.
Tri-Axial Shake Table Test on the Thinned Wall Piping Model and Damage Detection Before Failure
Authors: Nakamura Izumi , Otani Akihito , Sato Yuji , Takada Hajime , Takahashi Koji
Published: January 2011

In order to investigate the influence of degradation on dynamic behavior of piping systems and clarify the failure mode of piping systems with local wall thinning, tri-axial shake table tests using three-dimensional piping system models were conducted. The degradation used in this study was wall thinning at elbows and a tee, which was considered to be caused in piping systems due to the effects of aging. The test results show that the dominant frequency and the maximum response acceleration would be reduced due to the existence of wall thinning. Nondestructive inspections such as ultrasonic inspection tests and penetrant inspection tests were applied in the interval of the shake table test in order to detect the damage caused by the repeated shaking. As a result, nondestructive inspection methods would be useful for detecting the damage before the failure caused by the seismic load.
The Potential Impacts of Recent Transportation Accidents Involving Severe Fires on the Safe Shipment of Spent Nuclear Fuel
Authors: Bajwa Christopher S. , Easton Earl P.
Published: January 2011

In 2007, two severe transportation accidents occurred in the state of California. The first occurred in Oakland on a section of Interstate 880 known as the “MacArthur Maze” and involved a tractor trailer carrying gasoline which impacted an overpass support column and burst into flames. The subsequent fire caused the collapse of a portion of the Interstate 580 overpass onto the remains of the tractor trailer in less than 20 minutes, due to a reduction of strength in the structural steel exposed to the fire. The second incident was a chain-reaction accident involving over thirty tractor trailers in the Interstate 5 “Newhall Pass” truck bypass tunnel in Santa Clarita. This accident also involved an intense fire, fueled mostly by produce and other food commodities, that damaged the concrete walls of the tunnel and required the tunnel to be closed for repairs. The US Nuclear Regulatory Commission (NRC) is in the process of studying both of these accidents to examine any potential regulatory implications related to the safe transport of spent nuclear fuel in the United States. This paper will summarize work recently completed on these severe transportation accidents by the NRC.
Crack Tip Constraint Under Biaxial Loading in Elastic-Plastic Materials
Authors: Wang Z. X. , Huang Jian-ye , Chao Y. J. , Lam P. S.
Published: January 2011

Crack tip constraint is known to affect the fracture resistance of materials. The effect of biaxial loading on a center crack in an X100 steel plate has been investigated. The crack driving force and the constraint parameter are estimated based on the two-parameter J-A2 theory in elastic-plastic fracture mechanics with the aid of finite element analysis. The center-cracked plate is subject to various degrees of biaxiality (defined as the ratio of the transverse stress parallel to the crack and the opening stress normal to the crack). Using the constraint parameter (A2) in uniaxial loading condition as a reference value, a Constraint Enhancement Factor is introduced to facilitate the investigation of crack tip constraint under biaxial loading. The analysis carried out in this paper has established a relationship between the Constraint Enhancement Factor and the biaxiality. With the J-A2 fracture model, the critical applied load and the critical crack driving force can be expressed as functions of biaxial loading ratio. The methodology and analysis results can be used in structural integrity assessment of a pressure vessel or piping which contains a crack under biaxial loading.
Stress Analysis and Qualification of Vessels Containing Large Internal Vessels and Piping: Methodology
Authors: Prakash Ajay , Wilcox Wade , Minichiello John , Julyk John
Published: January 2011

Vessels used for hazardous waste treatment have passive systems for mixing, sampling, and monitoring that require sizeable internal vessels and piping. Stress analysis and code qualification of such safety related vessels, their internal components and associated supporting structures pose some unique analytical and design challenges. Pertinent issues encountered in the process of developing finite element analysis and design code evaluation methodology are reviewed, and proposed resolutions are presented.
Evaluation of Fracture Toughness by Master Curve Approach Using Miniature C(T) Specimens
Authors: Miura Naoki , Soneda Naoki
Published: January 2011

The fracture toughness Master Curve gives a universal relationship between the median of fracture toughness and temperature in the ductile-brittle transition temperature region of ferritic steels such as reactor pressure vessel (RPV) steels. The Master Curve approach specified in the ASTM standard theoretically provides the confidence levels of fracture toughness in consideration of the inherent scatter of fracture toughness. The authors have conducted a series of fracture toughness tests for typical Japanese RPV steels with various specimen sizes and shapes, and ascertained that the Master Curve can be well applied to the specimens with the thickness of 0.4-inches or larger. Considering the possible application of the Master Curve method coexistent with the present surveillance program for operating RPVs, the utilization of miniature specimens which can be taken from broken halves of surveillance specimens is quite important for the efficient determination of the Master Curve from the limited volume of the materials of concern. In this study, fracture toughness tests were conducted for typical Japanese RPV steels, SFVQ1A forging and SQV2A plate materials, using the miniature C(T) specimens with the thickness of 4 mm following the procedure of the ASTM standard. The results showed that the differences in test temperature, evaluation method, and specimen size did not affect the Master Curves, and the fracture toughness indexed by the reference temperature, T0, obtained from miniature C(T) specimens were consistent with those obtained from standard and larger C(T) specimens. It was also found that valid reference temperature can be determined with the realistic number of miniature C(T) specimens, less than ten, if the test temperature was appropriately selected. Thus, the Master Curve method using miniature C(T) specimens could be a practical method to determine the fracture toughness of actual RPV steels.