bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simplified Computation of the Welding Process on a Steam-Generator Divider Plate
Authors: Rossillon Frédérique , Depradeux Lionel 
Published: January 2014

The integrity of structures in nuclear power plants has to be assessed to meet given safety criteria. For a better understanding of the in-service loads in welded areas of PWRs components, the residual stresses resulting from the welding process have to be estimated. For that purpose, numerical simulations of welding have proved efficient but still require some improvement in terms of computation time reduction to be widely used in an industrial context.
This paper focuses on the residual stress fields in a double V butt weld on a steam generator divider plate. To set a reference, a 2D simulation of multi-pass welding was performed taking into account the whole non-linear thermo-mechanical history. Two simplified method were then carried out to estimate the residual stress field. The first method consists of modeling macro-beads by merging passes together. The second considers only a reduced number of appropriately selected passes in the analysis. Both methods are confronted to the full multi-pass simulation, set as a reference simulation, and their respective efficiency and robustness are discussed.
The main feature of this work, the RNP method, based on a reduced number of appropriately selected passes, gives a good reproduction of the stress fields and strongly reduce the computation time. A significant improvement is observed: CPU time is divided by 10 times with this predictive method.
Stress Classification for Tubesheet of Heat Exchanger With Semi-Ellipsoidal Heads
Authors: Yoshimura Naoki , Kataoka Shunji , Sato Takuya 
Published: January 2014

A fixed tubesheet type heat exchanger with semi-ellipsoidal heads which is dealt with in this paper has been adopted for refrigerant heat exchange process in LNG Plant. Since the conventional design standards, e.g. ASME Sec VIII Div.1 and TEMA, are not meant to be used for such a special type of heat exchanger, FEA should be performed to determine minimum required thickness of the tubesheet.
The elastic design procedure uses a stress classification methodology to guard against failure due to gross plastic deformation. According to the design standards, mechanical stresses in the tubesheet due to tube-side and/or shell-side pressure are defined as the primary membrane and bending stress and are evaluated by comparing with allowable values of the primary stress. For the special type of heat exchanger, however, stresses in the tubesheet obtained by FEA are actually complex combination of primary and secondary stresses. Application of this conventional design approach to the FEA-calculated stresses in tubesheet may lead to over-conservative design.
In helping to establish reliable and economical design of the tubesheet for such a special type of heat exchanger, authors conducted FEA investigation employing axisymmetric analysis model. Considering the geometric parameters, such as thickness of a tubesheet, heads type and shell dimension, the characteristics of tubesheet stresses was investigated and an appropriate stress classification was proposed.
Nuclear Reactor Pressure Vessel Integrity Assessment: Enhancement Provided by 3D Modeling Flaw Stability Calculations
Authors: Arrieta-Ruiz Adolfo , Meister Eric , Churier Henriette 
Published: January 2014

Structural integrity of the Reactor Pressure Vessel (RPV) is one of the main considerations regarding safety and lifetime of Nuclear Power Plants (NPP) since this component is considered as not reasonably replaceable. Brittle fracture risk associated with the embrittlement of RPV steel in irradiated areas is the main potential damage.
In France, deterministic integrity assessment for RPV is based on the crack initiation stage. The stability of an under-clad postulated flaw in the core area is currently evaluated under a Pressurized Thermal Shock (PTS) through a fracture mechanics simplified method.
One of the axes of EDF’s implemented strategy for NPP lifetime extension is the improvement of the deterministic approach with regards to the input data and methods so as to reduce conservatisms. In this context, 3D finite element elastic-plastic calculations with flaw modelling have been carried out recently in order to quantify the enhancement provided by a more realistic approach in the most severe events.
The aim of this paper is to present both simplified and 3D modelling flaw stability evaluation methods and the results obtained by running a small break LOCA event.
Reactor Pressure Vessel Nozzle Inner-Radius Examination
Authors: Glass S. W. , Thigpen B. , Guse G. , Brau E. 
Published: January 2014

Reactor pressure vessel nozzle inner radius (NIR) areas are identified as a specific target for ultrasound examination (UT) by many regulatory codes. This region represents a particularly challenging geometry to examine. Typically the examination is performed from inside the vessel with at least the upper internals removed. Normally the inspection is on the critical path so minimizing the schedule and vessel occupation time is important to the utilities outage planning and ultimate financial performance.
Although some inspection vendors have traditional qualifications for this NIR examination under various codes, this paper addresses several advanced techniques have been developed to minimize the critical path inspection time. Technology advancements include:
• Stereo-vision with laser reference for precise VT sizing of any observed indication
• A Small 5 degree-of-freedom arm to precisely track a transducer set along the inner-radius surface for immersion ultrasonic examination
• A simple nozzle-only tool with a passive mechanism to track the nozzle inner-radius surface for contact ultrasonic examination
• Advanced software (3-D iMaV) coupled with a 5-axis robot to analyze and control transducer placements and coverage from the nozzle and shell outside (OD)
The net result is a more efficient examination with shorter schedules and lower overall outage costs.
Challenging Hypers Performance
Authors: Giacomelli Enzo 
Published: January 2014

The production of LDPE may require huge heavy-duty reciprocating compressors to withstand the loads, deriving from the operating pressures, to satisfy the growing needs of the market. Safety, Performance and Reliability are normal expectations and therefore need a thorough evaluation of the specific service. The machine selection is based on positive experience in similar applications and cylinder performance. The cylinders are special pressure vessels, whose design and construction have to consider the extreme internal pressures and the process gas. The design must foresee all possible failure modes of each component, to have safe and smooth operation, thanks to innovative methods of modeling and simulation, like FEM and CFD, important for the design of cylinder parts.
Valves are simulated by mathematical models optimizing performance, to reach a correct mechanical behavior with minimum energy consumption and ensuring reliable operation.
The available technological improvements are a starting point, resulting from the developments of manufacturers and long experience of End Users.
The pulsation and vibration of the piping are usually investigated to keep the plant in operation without failures.
Many cylinder components are exposed to pressures fluctuating between suction and discharge and therefore to high fatigue loads. To reach high endurance capabilities they have to be pre-compressed to keep them operating under compressive stresses whenever possible. Special materials, shrink fitting and auto-frettage procedures are usually required.
The operation is the stage where all the parameters have to be kept under control and incipient problems have to be identified to minimize shut-downs and arrange various maintenance works. Automation, monitoring and diagnostic systems complete the efforts of operators to afford high safety levels, with increased availability and optimized maintenance interventions.
The continuing development of technology will help to challenge performance and high capacity demand of future plants.
On the Whistling of Corrugated Pipes With Narrow Cavities
Authors: Golliard Joachim , Belfroid Stefan , Gonzalez Diez Nestor , Bendiksen Erik , Frimodt Casper 
Published: January 2014

Pipes with a corrugated inner surface, as used in flexible pipes for gas production and transport, can be subject to Flow-Induced Pulsations when the flow velocities are higher than a certain onset velocity. The onset velocity for classical corrugated pipes can be predicted on basis of the geometry of the corrugations, the operational conditions and the geometry of the topside and subsea piping. A newly developed inner carcass design for flexible pipes features smaller corrugation cavities. The effect of narrow cavities on the whistling of corrugated cavities is evaluated.
In this paper, small-scale tests performed on corrugated tubes are reported. The tested geometries include both “classical” profiles, similar to the inner profile of agraff flexible risers, and profiles with less typical variations, such as deeper and narrower cavities. These tests were performed in order to evaluate the validity of a prediction model for the onset of pulsations, for corrugated pipes with these kinds of atypical variations. The experimental results show that the validity of the model remains reasonable, except when the cavities are very narrow. In this case, the model becomes overly conservative. The deviation is attributed to the momentum thickness of the boundary layer, which is too large compared to the cavity width. In this case, any instability of the shear layer is destroyed, which prevents whistling. Furthermore, the shift towards higher frequencies of the acoustic source term due to narrower cavities, and the possible coupling with higher acoustic modes, are considered.
Fatigue Behavior of Cladding Material for Nuclear Components
Authors: Herter Karl-Heinz , Schuler Xaver , Hoffmann Michael , Kopp Peter , Mahlke Jan 
Published: January 2014

To evaluate the fatigue behavior of the austenitic cladding of pressurized components, the fatigue design curves are usually based on experiments on specimens taken from plates, pipes or bars. Due to rapid heat transport into the ferritic base material, the cladding has a distinctive anisotropic structure that results from the manufacturing process. Therefore, it may not be assumed a priori that the fatigue curves of the various austenitic product forms used in the Safety Standards are also representative for the material of austenitic cladding. It is therefore necessary to determine and assure experimentally a fatigue curve of the cladding material and compare the results with the database of austenitic stainless steels used in German NPPs.
Flat specimens specially adapted to the geometric conditions were prepared out of the austenitic cladding of a RPV which had been manufactured according to nuclear specifications. To check a possible influence of the specimen geometry, flat specimens were prepared in advance from an austenitic pipe of known fatigue behavior and tested at different strain amplitudes. A comparison of the results with the fatigue curve determined with cylindrical specimens showed no influence at the higher strain amplitudes. Altogether, the fatigue data with flat specimens made of the austenitic cladding fit well into the scatter of the fatigue database of austenitic base materials tested with cylindrical specimens.
Fatigue Behavior of Dissimilar Welds Used for Nuclear Piping
Authors: Herter Karl-Heinz , Schuler Xaver , Hoffmann Michael , Kopp Peter 
Published: January 2014

Due to specific requirements in NPP piping different materials are used and connected by dissimilar welds (DM). The fatigue behavior of such welds must be known for design and safety evaluations. The overall fatigue behavior of welds depends on the properties of the different weld sections and their interaction. The welding may influence the fatigue behavior of the base materials in the vicinity of the weld.
The investigation deals with the fatigue behavior of DM typical for German NPP: ferritic steel 20MnMoNi5-5 welded to austenitic steel X6CrNiNb18-10 using nickel based alloy for buttering. Fatigue specimens were taken from each region of the weld (ferritic steel near weld, buttering, connection weld, austenitic steel near weld). Additionally specimens were taken containing two adjacent material regions and the respective fusion line. For each position specimens were tested in fully reversed strain controlled conditions at room temperature and total strain amplitude of 0.25%. The results were compared with the best-fit curves for austenitic and ferritic steels.
Waterhammer in a Horizontal Pipe Induced by Slug Formation and Rapid Condensation
Authors: Martin C. Samuel 
Published: January 2014

The phenomenon of condensation-induced waterhammer in an ammonia refrigeration system was investigated experimentally. Waterhammer was generated by introducing warm ammonia gas over static subcooled ammonia liquid placed in a horizontal 146.3 mm diameter carbon steel pipe approximately 6.0 m long. By means of fast response piezoelectric pressure transducers and a high speed data acquisition system rapid dynamic pressures were recorded whenever a condensation-induced event occurred. Employing top-mounted diaphragm pressure transducers to sense gas pressure the speed of liquid slugs propagating along the pipe was determined.
The occurrence of condensation-induced waterhammer depended upon three major variables; namely, (1) initial liquid depth, (2) liquid temperature, and (3) mass flow rate of warm gas. For given liquid depth and temperature, once the warm gas threshold conditions were exceeded, shocks occurred with greater magnitude as the mass flow rate of warm gas input was increased. With adequate subcooling condensation-induced waterhammer occurred for initial liquid depths ranging from 25% to 95% of internal pipe diameter. The threshold mass flow rate of warm gas necessary to initiate waterhammer was greater as the initial liquid depth was lowered. For numerous tests with sufficient gas mass flow rate a condensation-induced shock occurred at the end cap of the test pipe, generating an acoustic (pressure) wave that propagated at a modified speed of sound toward the gas-liquid interface at the back of the slug. Peak shock pressures could be correlated with the gas mass flow rate for various initial liquid depth and suction pressures and temperatures. As the initial liquid temperature and pressure were increased the hydraulic shocks became lower because of smaller subcooling.
Characterisation of Residual Stress Levels Retained in Fracture Mechanics Specimens Machined From Non-Stress Relieved Welds
Authors: McCluskey Robert J. A. , Zheng Gang , Sherry Andrew H. , Smith David J. 
Published: January 2014

The structural integrity assessment of weldments in engineering components, including piping, is dependent upon the acquisition of valid fracture toughness data. Test standards provide guidance for the preparation of fracture mechanics specimens machined from welds, recognising that under some circumstances retained weld residual stress in the specimens may influence the test, for example, by impairing the ability to establish a valid fatigue pre-crack. To date, however, there are little experimental data quantifying the level and distribution of retained residual stress in fracture mechanics specimens.
This paper describes an experimental study characterising the residual stresses retained in single-edge notched bend specimens machined from a non stress-relieved, narrow-gap Tungsten Inert Gas welded pipe, manufactured from 304L stainless steel. The original weld residual stress field was characterised using neutron diffraction and deep hole drilling. The residual stress levels retained in the test specimens were subsequently quantified using deep hole drilling.
The results indicated that reasonable levels of residual stress are retained within specimens, although for high toughness, ductile steel, this is insufficient to influence the fracture toughness measurement. The results, however, have implications for testing non stress-relieved welds manufactured from low toughness materials, where retained residual stresses could unduly influence fracture toughness measurements.
Comparison of Metal Temperatures Obtained From Conjugate Heat Transfer CFD Analysis and Thermal Finite Element Analysis of a Valve
Authors: Bowie Gareth , Fletcher Andrew , Reed Gary , Davenport Lewis , Hugill Peter 
Published: January 2014

This paper describes the results of a three dimensional Computational Fluid Dynamics (CFD) simulation of a rapid temperature increase in liquid water flowing through a relief valve, using Conjugate Heat Transfer (CHT) to predict the solid domain temperatures.
Surface Heat Transfer Coefficient (HTC) and bulk fluid temperature histories extracted from this simulation have been applied to a thermal structural Finite Element (FE) analysis of the valve body, providing an additional set of solid domain temperatures for comparison.
The aim of this paper is to compare the precision of the solid domain temperatures predicted by the CHT and HTC/FE simulations.
Three-Dimensional Finite Element Analysis of Rigid Flanged Shaft Coupling Subjected to Twisting Moment
Authors: Okayama Koichi , Fukuoka Toshimichi 
Published: January 2014

A reamer bolt is commonly used when clamping a rigid shaft coupling subjected to large shear force. Although some joint design procedures assume that the applied shear force transmits only through the reamer surface, it is also supported by the friction force on the contact surfaces. Accordingly, to design the coupling clamped by reamer bolts, it is important to evaluate the ratio of the shear forces supported by the reamer surface and the friction force, which is defined as shear force transfer ratio (SFTR) here.
In this study, distributions of SFTR and the bending stresses along the reamer surface are analyzed by three-dimensional FEM, focusing on the effects of the fit between the reamer bolt and bolt hole, the scatter of initial bolt stress and the misalignment of the connecting shafts. Numerical results quantitatively clarify how the amounts of the SFTR and the bending stresses as the friction coefficients, the fit and the magnitude of misalignment are changed. As for an offset misalignment, it is found that its effect on the bending moment generated in the shaft body is negligibly small, if the offset between two shafts in radial direction is less than 10mm which is 1% of the total shaft length.
Definition of a Cut-Off Natural Frequency for Small Bore Pipework Connections
Authors: McGhee James S. G. , MacDonald Stanislav , Hamilton John P. , Wally Gernot 
Published: January 2014

Vibration induced fatigue failures (VIFF) of pipework small bore connections (SBCs) due to turbulent flow excitation continue to occur in process piping systems, resulting in elevated safety risks and costly interruptions to normal operations. One of the primary causes of these failures is poor design.
When the valve and pipe components in an SBC assembly combine to produce a fundamental natural frequency that is low, the SBC can readily be excited into a high vibration condition. In this high vibration condition, the threat of VIFF increases significantly. One of the primary design goals for SBCs should therefore be to achieve a high natural frequency, however, this is very rarely considered in the existing design process. Reasons for this include the lack of understanding of the importance of natural frequency to the vulnerability of the design and a lack of information on how high this target natural frequency must be when it is considered.
In this paper, the concept of a cut-off natural frequency is defined, above which the probability of VIFF of SBCs is negligible. If this concept is incorporated into the design process for SBCs a decrease in the number of failures of SBCs due to vibration should be realised.
The Qualification of BWR Steam Dryer Weldments Exposed to Cyclic Loading Using Finite Element Methods
Authors: Breach Michael R. 
Published: January 2014

The qualification of welds other than full penetration groove welds exposed to cyclic loading using finite element methods requires an understanding of the basis behind classical methodologies. These methodologies usually address nominal stresses.
The nominal stress (S-N) method was the first approach developed to try to understand this failure process and is still widely used in applications where the applied stress is nominally within the elastic range of the material and the number of cycles to failure is large. From this point of view, the nominal stress approach is best suited to that area of the fatigue process known as high cycle fatigue. Cracks and discontinuities will cause stress redistribution and concentrations leading to secondary and peak stresses additive to the nominal stress when referencing the S-N curves.
Therefore, fundamental to the qualification of weldments of components and structures is the determination of the nominal stress field; however, this can be problematic for several reasons:
• Secondary, Peak stress arising from structural discontinuities can mask the actual nominal stress field.
• There may be an insufficient number of elements and/or integration points through the thickness to rely on linearization techniques, to separate the nominal stresses from the secondary and peak stresses due to the high cost of using bricks or tetrahedrons.
• In complex shell structures, the nominal stress field in weldments that satisfies equilibrium against externally applied loads is not readily distinguished; this is due to the shear preponderance of mesh sensitive discontinuities.
Herein, is a summary of methods to address the aforementioned problem and guidance in determining the true peak stresses and their qualification. Methods documented in ASME BPV Code Section VIII Div. 2, and various papers are compared. These methods will be used to assess existing methods that may be used in the industry. ASME BPV Code Section III Subsections NG and NB will be used as a basis to classify and qualify the weldment stresses.