bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study on Stream-Wise Oscillation of Cylinder Arrays: Effect of Pitch Ratio
Authors: Nakamura Tomomichi , Yoshikawa Takafumi , Yoshimura Taku , Kondo Hironobu
Published: July 2010

The importance of the in-flow oscillation of a single cylinder in cross-flow has been spotlighted since an accident in a FBR-type reactor. However, the in-flow oscillation can be observed in tube arrays of heat exchangers. Previous reports show some interesting phenomena on the oscillation of cylinder arrays, which have a same pitch between cylinders. This paper shows the effect of the pitch ratio of a cylinder array on the characteristics of those phenomena, especially in in-flow direction, where every cylinder can move only in this direction. The motion of cylinders is measured by attached strain gages and by a high-speed digital video camera.
Prediction of Plastic Collapse Moments for Circumferential Cracked Pipes With Weld Overlays
Authors: Hasegawa Kunio , Li Yinsheng , Wilkowski Gery M. , Deardorff Arthur F.
Published: July 2010

Weld overlay (WOL) is one of the useful repair methods for cracked piping that has been successfully applied for piping in many nuclear power plants. In addition, ASME Boiler and Pressure Vessel Code Section XI provides a WOL method in Non-mandatory Appendix Q and a number of Code Cases. Currently, an analytical evaluation method for predicting failure stresses for WOL piping is under discussion in a working group of ASME Code Section XI. This paper proposes an approach for predicting the plastic collapse moment for WOL piping using a net-section collapse stress approach. In addition, the predicted collapse moments are compared with experimental data.
Comparison Between Different Approaches for the Evaluation of the Hot Spot Structural Stress in Welded Pressure Vessel Components
Authors: Muscat Martin , Degiorgio Kevin , Wood James
Published: July 2010

Fatigue cracks in welds often occur at the toe of a weld where stresses are difficult to calculate at the design stage. To circumvent this problem the ASME Boiler and PV code Section VIII Division 2 Part 5 [1] uses the structural stress normal to the expected crack to predict fatigue life using elastic analysis and as welded fatigue curves. The European Unfired Pressure Vessel Code [2] uses a similar approach. The structural stress excludes the notch stress at the weld toe itself. The predicted fatigue life has a strong dependency on the calculated value of structural stress. This emphasizes the importance of having a unique and robust way of extracting the structural stress from elastic finite element results. Different methods are available for the computation of the structural hotspot stress at welded joints. These are based on the extrapolation of surface stresses close to the weld toe, on the linearisation of stresses in the through-thickness direction or on the equilibrium of nodal forces. This paper takes a critical view on the various methods and investigates the effects of the mesh quality on the value of the structural stress. T-shaped welded plates under bending are considered as a means for illustration.
Stress Intensity Factor Influence Coefficients for External Surface Flaws in Boiling Water Reactor Pressure Vessels
Authors: Yin Shengjun , Dickson Terry L. , Williams Paul T. , Bass B. Richard
Published: July 2010

Over the service life of a nuclear power plant, the Boiling Water Reactor (BWR) may undergo many cool-down and heat-up thermal-hydraulic transients associated with, for example, scheduled refueling outages and other normal operational transients, or even possible overcooling transients. These thermal-hydraulic events can act on postulated surface flaws in BWRs and therefore impose potential risk on the structure integrity of Reactor Pressure Vessels (RPVs). Internal surface flaws are of interest for the BWRs under overcooling accidental scenarios, while external surface flaws are more vulnerable when the BWRs are subjected to heat-up transients. Stress Intensity Factor Influence Coefficient (SIFIC) databases for application to linear elastic fracture mechanics analyses of BWR pressure vessels which typically have an internal radius to wall thickness ratio (Ri/t) between 15 and 20 were developed for external surface breaking flaws. This paper presents three types of surface flaws necessary in fracture analyses of BWRs: (1) finite-length external surface flaws with aspect ratio of 2, 6, and 10. (2) infinite-length axial external surface flaws; and (3) 360° circumferential external surface flaws. These influence coefficients have been implemented and validated in the FAVOR fracture mechanics code developed at Oak Ridge National Laboratory (ORNL) for the US Nuclear Regulatory Commission (NRC). Although these SIFIC databases were developed in application to RPVs subjected to thermal-hydraulic transients, they could also be applied to RPVs under other general loading conditions.
J-Based Failure Assessment Diagrams for Axially Cracked Pipes Under Pressure
Authors: Chell Graham , Gardner Brian , Rhee Chong , Vargas Pedro
Published: July 2010

This paper describes the results of performing a comprehensive matrix of J-based finite element analyses (FEA) of external and internal surface axial cracks in pressurized pipes. The computations were performed for a range of stress-strain behaviors and pipe sizes typical of gas and liquid transmission pipelines. The J results for the deepest and surface points on flaws are presented in the form of failure assessment curves (FACs) plotted on failure assessment diagrams (FADs). The FACs are consistent with the Level 3C and material specific Level 2B FADs used in BS 7910. Yield pressures derived from the FEA results are used to evaluate the FAD parameter Lr (= pressure/yield pressure) for the Level 3C FACs. This choice of yield pressures facilitates the collapse of the Level 3C FACs in the fully plastic region of the FAD onto material specific curves relatively independent of geometric features. The Level 3C FACs generated from the FEA J results show a strong dependence on crack size in the elastic-plastic part of the FADs, particularly for long flaws. In these cases, the Level 3C FACs fall inside the corresponding material specific FACs derived according to Level 2B procedures. The reason for this is thought related to the development of local and global yield mechanisms and the incorporation in Level 3C FACs of geometry dependencies which are ignored in Level 2B. It is concluded that the Level 2B procedures may not always be conservative for long deep axial flaws in pressurized pipes when used in conjunction with accurate (e.g. determined from FEA) global yield pressures. Similarly, account has to be taken of the transition from local to global yielding in J estimation schemes that are formulated as the sum of elastic and plastic components if these are not to be non-conservative in the transition from elastic to fully plastic behavior. A method is suggested for incorporating the local to global yielding transition in J estimation schemes that also reduces the geometry dependence of Level 3C FADs to facilitate their representation by approximately material specific (Level 2B-type) FADs applicable to axially flawed pipelines.
A Procedure to Evaluate a B31.1 Welding End Transition Joint to Include the Fatigue Effects of Thermal Gradients for Design and Plant Life Extension
Authors: Creates David H.
Published: July 2010

Fatigue evaluation in B31.1 is currently done based on Equation 1 & 2 [B31.1-2007] which considers only displacement load ranges. Yet, fatigue damage is also occurring due to pressure cycling and thermal gradients. To exacerbate this, power plant design pressures and temperatures are rising, new materials are being introduced, pipes and attached components are become increasingly thick, and owners are requiring the power plants to heat-up and cool-down at faster rates. Also, power plant owners are more and more interested in extending the life of power plants beyond their original design life. Although the knowledge of thermal gradients has been available for many years, no attempt has been made to incorporate this into the B31.1 Code. This paper takes the first step in addressing this pressing need in today’s power plant environment. Granted there are several configurations where the effects of thermal gradients could be assessed. As the first step, this paper provides a procedure to evaluate the fatigue effects of thermal gradients in the prevalent Welding End Transition Joint (ASME B31.1 Fig 127.4.2) based on thermal gradients calculated as per [PVP2009-77147]. The disadvantage of this approach is that the conservatism in the calculation thermal gradients inherent in ASME Section III Sub-section NB-3600-2007 is inherent in these calculations as well, and may produce unacceptable results. If the results turn out to be unacceptable, it is a warning that something else needs to be done in the way of either monitoring or modifying or further evaluation. The advantage of this methodology is that it maintains the traditional B31.1 approach to fatigue by controlling SE with the same limit of SA except that there is now an additional term, f ‘, to account for the fatigue effects due to thermal gradients. In addition, it eliminates the need for a computer program to calculate this additional term, a computer program that is not normally accessible to the B31.1 designer anyway. Considering the fatigue effects of thermal gradients in this way will further help to preserve the integrity of the piping pressure boundary and consequently, the safety of personnel in today’s power plants and into the future.
Repair of an Externally Corroded Pressure Vessel Using Internal Lap Patches and Weld Buildup
Authors: Looyeh Reza , Taagepera Jaan , Bosi David , Carroll Martin
Published: July 2010

This paper presents a newly applied hybrid method for the repair of a tall pressure vessel which has been badly corroded in several areas with a couple of pin-holed leaks caused by corrosion under insulation (CUI). Due to the defective areas being on high elevations, and therefore lacking immediate accessibility, and due to adverse weather conditions, detailed inspection and planned external repair could not have been achieved to meet safety and technical requirements. As an alternative, the vessel was fully inspected internally by ultrasonic thickness measurements (UT) method to identify the extent of external CUI and shell thinning. Then it was repaired by applying combined weld buildup and lap patches to the inside surface in order to achieve an acceptable thickness to ensure the vessel would return to operation safely and will be fit for continued service. The required level of repair and the acceptability of the methodology have been assessed and verified by detailed calculations and the use of finite element technique.
Stress Index Development for Special Elbows
Authors: Kim J.-M. , Song H.-C. , Kang S.-Y. , Park S.-H. , Yang J.-S. , Kim Y.-H.
Published: July 2010

The reactor coolant piping system is designed to be in compliance with the requirements of Class 1 piping of Section III of the ASME Boiler and Pressure Vessel Code. Stress indices are required to evaluate the nuclear Class 1 piping. The reactor coolant system of Kori 1 nuclear power plant consists of a 2-loop system, each having two special elbows: one is the reducing elbow with a non-uniform thickness, and the other is the elbow with a splitter installed inside the elbow. However, stress indices for special elbows are not specified in NB-3683.7 of the ASME Code. In this paper, we computed the stress indices of special elbows for pressure and moment loads by the finite element analysis. The linear elastic method was used for the analysis with the finite element program, ANSYS, and the solid element (SOLID 45) was selected to model the geometry. The finite element model of the special elbows included a straight segment of pipe on each end of the elbows. The uniformly distributed internal pressure was applied to the pipe and elbow. The equivalent axial blow-off load was applied to one end, and the translational degree of freedom was fixed at the other end of the model. The moment was applied to one end, and the boundary condition was fixed at the other end of the model. Based on the analysis results, it is concluded that stress indices, except B1, in NB-3683.7 of the ASME Code can be used for special elbows conservatively. More analyses are required to apply B1 index to the special elbows.
Design Optimisation of a Ferritic Ring Weld Specimen Using FE Modelling
Authors: Gill Christopher M. , Hurrell Paul , Francis John , Turski Mark
Published: July 2010

This paper describes the design optimisation of an SA508 ferritic steel ring weld specimen using FE modelling techniques. The aim was to experimentally and analytically study the effect of post weld heat treatment upon a triaxial residual stress field. Welding highly constrained geometries, such as those found in some pressure vessel joints, can lead to the formation of highly triaxial stress fields. It is thought that application of post weld heat treatments will not fully relax hydrostatic stress fields. Therefore a ferritic multi-pass ring weld specimen was designed and optimised, using 2D finite element modelling, to generate a high magnitude triaxial stress field. The specimen thickness and weld-prep geometry was optimised to produce a large hydrostatic stress field and still allow efficient use of neutron diffraction to measure the residual stress. This paper reports the development of the test specimen geometry and compares the results of welding FE analysis and neutron diffraction measurements. Welding residual stresses were experimentally determined using neutron diffraction; both before post weld heat treatment. Three dimensional moving heat source weld finite element modelling has been used to predict the residual stresses generated by the welding process used. Finite element modelling examined the effect of phase transformation upon the residual stress field produced by welding. The relaxation of welding stresses by creep during post weld heat treatment has also been modelled. Comparisons between the modelled and measured as-welded residual stress profiles are presented. This work allows discussion of the effect of post weld heat treatment of triaxial stress fields and determines if finite element modelling is capable of correctly predicting the stress relaxation.
ASME B31.12 Hydrogen Piping and Pipeline Code Design Rules and Their Interaction With Pipeline Materials Concerns, Issues and Research
Authors: Hayden Louis E. , Stalheim Douglas
Published: July 2010

The ASME B31.12 Hydrogen Piping and Pipeline Code has just been published for use in designing hydrogen piping and pipeline systems. The B31.12 Committee has developed two design methods that take current steel specifications and chemical compositions into consideration. Due to the variability of chemistry and the lack of statistically meaningful test data these two methods place a design or testing burden on the owner of the pipeline or piping system. Research and development that can be applied to an understanding of the desirable microstructure along with a cleanliness level that is suitable in commercial grade steels for hydrogen service is imperative.
Progress in RI ISI Applications for WWER 440 and WWER 1000 Type Piping Systems
Authors: Horacek Ladislav
Published: July 2010

The technical publication contains a review of four risk informed inservice inspection pilot studies focused on WWER 440 and WWER 1000 type piping systems. All applications conducted in close co-operation with EPRI staff were based on modified EPRI RI ISI methodology for WWER type NPPs. Two of four pilot studies belonged to the EPRI methodology extension for Break Exclusion Region (high energy piping). All results and lessons learnt are shortly presented and discussed. The above RI ISI pilot studies were conducted for the following systems: 1. Primary piping including pressurizer piping surge lines at Dukovany NPP (WWER 440 type reactors, Czech Republic) 2. Low pressure emergency core cooling piping system (LP ECCS) at Temeli´n NPP (WWER 1000, Czech Republic) 3. No break zone (NBZ) application for steam line piping outside containment at Khmelnitskyi NPP (WWER 1000 type reactors, Ukraine). 4. No break zone application for steam line and feed water line piping outside containment at Temeli´n NPP (WWER 1000 type reactors, Czech Republic). Two studies are discussed in detail. The results for LP ECCS can be summarised as follows: from 115 welds in class 1 only 16 welds ranked in risk category 2 (RC2) with thermal fatigue potential, 42 welds in RC4 with no degradation mechanism identified (all welds with high consequence) and 57 welds in low RC6. From 671 welds in Class 2 only 19 welds ranked in RC5 with thermal fatigue or cavitation potential. The rest of 652 welds were ranked in low RC6 or RC7. The number of inspections applied were substantially changed from the point of inspections performed according to current ISI programme and proposed RI ISI examinations. The former 73 VT and PT examinations in the current ISI programme were proposed to be replaced by 12 UT inspections of which 5 are proposed as qualified mechanised UT examinations in case of identified potential to thermal fatigue damage mechanism. The pilot study at Khmelnitskyi NPP Unit 2 was ordered by IAEA. Based on the RI ISI pilot study results, nine of 67 Class 2 welds were selected for recommended qualified UT mechanized inspections. No Class 3 weld of total number 18 welds was included in the RI ISI programme. The risk impact acceptance criteria 1E−7 per system and 1E−8 per year for CDF and LERF were applied according to EPRI methodology in compliance with guidelines of the Czech Regulatory Body.
NDT Qualification Achievements for WWER Type RPV and Piping Systems
Authors: Horacek Ladislav
Published: July 2010

The technical publication contains the latest NDT qualification achievements in the following inspection areas of WWER type RPVs and piping systems: 1. TOFD examination of WWER 440 and WWER 1000 type RPV butt welds, 2. Pulse-echo examinations of longitudinal austenitic welds of elbows and 3. Phased array examinations of circumferential welds and longitudinal elbow welds of different piping systems. The progress in the TOFD RPV application is especially in high level involvement of computer modelling simulation by CIVA s/w (CEA, France). The level of compliance of TOFD examination and TOFD simulation results was confirmed for many defects in the 1:1 large scale test assemblies [1]. The progress and lessons learnt from pulse-echo examinations of longitudinal austenitic welds of elbows is related to Leak Before Break Concept Application for Primary piping and Pressurizer surge line piping at ANPP in Metsamor (Armenia) where there were increased requirements on in-service inspection including NDT qualification of pressurizer surge line longitudinal welds on elbows and primary piping longitudinal welds on elbows under the Main Circulation Pump. The progress in phased array applications on circumferential welds and longitudinal elbow welds of different piping systems is also accompanied by extended computer modelling simulation by CIVA s/w. Several examples of compliance of phased array (PA) examination and PA simulation results are given for many defects in the 1:1 piping weld test assemblies [2]. The paper contains also briefly the scope of the training of Armenian UT inspectors at NRI based on the contract sponsored by IAEA Vienna. Lessons learnt obtained within the UT training of Armenian inspectors coming from NDT qualification training, open and blind trials on available test assemblies are shortly presented, as well.
Technical Basis for Acceptance/Rejection Criteria for Flaws in High Pressure Gas Cylinder
Authors: Rana Mahendra D. , Smith John H. , Holroyd Henry
Published: July 2010

The objective of this paper is to present the technical basis used for developing acceptance/rejection limits for seamless, high pressure gas cylinders that can be used at the time of retesting the cylinders. The development of acceptance/rejection limits for cylinders is done in three steps. First, the “critical flaw sizes” (e.g. depth and length or area) for selected types of flaws are established by an analysis procedure that has been verified by experimental tests. Next the “allowable flaw sizes” are calculated by modifying (reducing) the size of the “critical flaw sizes” for each cylinder by adjusting for fatigue crack growth that may occur during the use of the cylinder. Finally the “acceptance/rejection criteria” is established to take into account other factors such as all the expected operating conditions that the cylinders may see in service and the reliability and detectability of the specific inspection equipment to be and to adjust the “allowable flaw sizes” to provide an additional margin of safety. This acceptance/rejection limits have been incorporated in recently published ISO Technical Report TR 22694: 2008 [1]. In this work, the API 579 “Recommended Practice for Fitness-for-Service” [2] was used to calculate the “critical flaw sizes” for a range of cylinder sizes and strength levels. For this study the “critical flaw size” is defined as the size of the flaw that will cause the cylinders to fail at the test pressure of the cylinder. The results of flawed-cylinder burst tests were used to experimentally verify the calculated “critical flaw sizes”. The “allowable flaw sizes” were then calculated by using well established fatigue crack growth rate data for steel and aluminum alloys to allow for the expected amount of fatigue crack growth that may occur during the specified retesting intervals. A limited number of tests were conducted to verify the “allowable flaw size” calculations. Further adjustments are made to the “allowable flaw sizes” to define the “acceptance/rejection criteria” to be used during cylinder retesting.
The Influence of Creep-Fatigue Interaction on High Temperature Crack Growth in 316 Steel Weldments
Authors: Davies C. M. , Dean David W. , Mehmanparast A. N. , Nikbin K. M.
Published: July 2010

High temperature crack growth in weldments is of great concern and generally occurs along the boundary between the heat affected zone (HAZ) and parent material (PM) of welded components in high temperature plants. Static creep and low frequency cyclic crack growth tests have been performed on compact tension, C(T), specimens manufactured from sections taken from a 316 steel weldment at 550 °C, where the crack tip was located along the fusion line within the HAZ. The data has been analyzed in terms of both the creep-brittle and creep-ductile crack tip parameters, K and C*, respectively. The cyclic test results have been compared to static creep crack growth tests on 316 steel weldments and homogeneous parent material specimens, and to crack growth models. The cracking rates of the cyclic crack growth tests are found to be higher than that of the of the static load creep crack growth tests on weldments. The data may be bounded by the high frequency fatigue and the static load creep crack growth predictions. However, further work is required to establish the fatigue and subsequently the creep component of the cyclic load crack growth tests on weldments.
Numerical Simulations of Dynamic Fracture in Thin Pipes
Authors: Shie Y.
Published: July 2010

We present a meshless methodology for large scale computations of fractureing thin shell structures subjected to internal pressure loads. The contribution is the first step of an efficient numerical methodology for such kind of events. In this paper, numerical simulations of large deformation dynamic fracture in thin shell structures using 3-D meshfree methods is presented. Due to the smoothness of the meshfree shape functions, they are well suited to simulate large deformation of thin shell structures while avoiding ill-conditioning as well as stiffening in numerical computations. The 3D meshfree representation allows high flexibility since thin structures as well as thick structures can be studied by the same methodology. The meshfree approach makes the methodology more flexible and independent as compared to finite elements, i.e. there is no need for creation of mesh. Dynamic fracture is modeled by a simple criterion, i.e. removing connectivity between adjacent nodes once a fracture criterion is met. The main advantage of such a 3-D meshfree continuum approach is its simplicity in both formulation and implementation as compared to shell theory approach, or degenerated continuum approach. Moreover, it is believed that the accuracy of the computation may increase because of using 3-D exact formulation.
Sloshing Characteristics of Single Deck Floating Roofs in Aboveground Storage Tanks: Natural Periods and Vibration Modes
Authors: Yoshida Shoichi , Sekine Kazuyoshi , Iwata Katsuki
Published: July 2010

The floating roofs are widely used to prevent evaporation of content in large oil storage tanks. The 2003 Tokachi-Oki earthquake caused severe damage to the floating roofs due to liquid sloshing. The structural integrity of the floating roofs for the sloshing is urgent issue to establish in the petrochemical and oil refining industries. This paper presents the sloshing characteristics of the single deck floating roofs in cylindrical storage tanks. The hydrodynamic coupling of fluid and floating roof is taken into consideration in the axisymmetric finite element analysis. It is assumed that the fluid is incompressible and inviscid, and the floating roof is linear elastic while the sidewall and the bottom are rigid. The basic vibration characteristics, natural periods and vibration modes, of the floating roof due to the sloshing are investigated. These will give engineers important information on the floating roof design.
Analytical Modeling of Flat Face Flanges With Metal-to-Metal Contact Beyond the Bolt Circle
Authors: Galai Hichem , Bouzid Abdel-Hakim
Published: July 2010

Design rules for flat face flanges with metal-to-metal contact beyond the bolt circle are covered by Appendix Y of the ASME Code. These design rules are based on Schneider’s work [1]. The prediction of tightness of these bolted joints relies very much on the level of precision of the O-ring gasket compression during operation. The evaluation of this compression requires a rigorous flexibility analysis of the joint including bolt-flange elastic interaction. This paper analyses flange separation and the bolt load change in flat face bolted joints. It proposes two different analytical approaches capable of predicting flange rotation and bolt load change during operation. The first method is based on beam theory applied to a continuous flange sector. This approach is an improvement of the discrete beam theory used by Schneider [1]. The second method is based on circular plate theory and is developed for the purpose of a more accurate assessment of the load changes. As in the Taylor Forge method, this approach is in general better suited than the beam theory for flat face flanges in particular when the flange width is small. The proposed models are compared to the discrete beam theory and validated using numerical FEA on different flange sizes.
Creep-Fatigue Prediction of Low Alloy Ferritic Steels Using a Strain Energy Based Methodology
Authors: Payten Warwick M. , Dean David W. , Snowden Ken U.
Published: July 2010

The accumulation of creep-fatigue damage over time is the principal damage mechanism which will eventually lead to crack initiation in critical high temperature equipment. A model that calculates the creep damage under conditions of strain control has been developed that assumes on a macroscopic level that the energy dissipated in the material may be taken as a measure of the creep damage induced in the material. This then assumes that the creep damage is directly proportional to absorbed internal energy density. The model developed is derived from considerations of mechanistic cavity growth. The model makes use of already existing creep data and relatively easily determined fatigue data for estimation of life under non-steady state conditions. The predictions of the energy-density exhaustion approach are compared with the results of creep-fatigue tests on a low alloy ferritic steel 1/2Cr-1/2Mo-1/4V (CMV) and with creep-fatigue calculations using a number of current models. The predicted results of the energy-density model are found to have good correlation with the measured creep-fatigue lives.
The J-Integral for a Single-Edge Cracked Panel Subjected to Combined Remote Tension and Bending
Authors: Matsubara Masaaki
Published: July 2010

On structural integrity evaluation, a single-edge cracked panel subjected to combined remote tension and bending is the typical one. The J-integral is a valid way for handling the ductile fracture problem immediately after stable crack initiation. The complimentary energy concept combined with fully plastic solutions to make it to estimate the J-integral of the panel. The proposed method is able to give us the J-integral as a function of the crack size/panel width and the strain hardening exponent.
Evaluation of Creep-Fatigue Damage for Hot Gas Duct Structure of the NHDD Plant
Authors: Lee Hyeong-Yeon , Song Kee-Nam , Kim Yong-Wan
Published: July 2010

Evaluation of creep-fatigue damage has been carried out for the HGD (hot gas duct) structure in the NHDD (Nuclear Hydrogen Development and Demonstration) plant. The core outlet and inlet temperature of the NHDD plant are 950°C and 490°C, respectively. Case studies on high temperature design codes of the draft Code Case for Alloy 617, ASME-NH and RCC-MR were carried out for the inner tube of the HGD for the candidate materials of Alloy 617 and Alloy 800H. Technical issues in application of the draft Code Case to a high temperature structure are discussed for Alloy 617 material. Code comparison between the ASME-NH and RCC-MR for Alloy 800H has been carried out. The candidate material of the outer pressure boundary (cross vessel) of the HGD is Mod.9Cr-1Mo steel. The damage evaluation according to the ASME-NH and RCC-MR for the cross vessel of Mod.9Cr-1Mo steel has been conducted and their results were compared.
Experimental Study on the Frequency of a Free Surface Fluctuation in a Vessel With or Without an Internal Structure
Authors: Nam Ho-Yun , Choi Byoung-Hae , Kim Jong-Man , Kim Byung-Ho
Published: July 2010

An experimental study has been performed to investigate the frequency of a free surface fluctuation in a vessel with and without an internal structure. Water flows in from the bottom nozzle and flows out at the side wall nozzles. There are two dominant frequency regions which are generated by a standing wave and a jet. In the standing wave region, the frequency is well described by f(4πdV/g)1/2 = 1.07 in a circular vessel. The frequency generated by a jet can be described by a dimensionless period and Froude number according to its fluctuation stability. In the case of a vessel with an internal structure, it needs a geometry factor which is described by a vessel diameter to a hydraulic diameter ratio in a standing wave region.
Preparation of Long Term Operation in Dukovany NPP, Czech Republic
Authors: Krivanek Robert
Published: July 2010

Dukovany NPP has 4 units with VVER440/213 type reactors and is in its 24th year of operation. Operational permission is valid for 30 years. Since 2004, NPP has started to prepare a LTO program which includes: • a detailed feasibility study, • an evaluation of safety aspects of LTO, • the preparation of a long-term modernization plan, • risk analysis etc. This program is now approved by company management and by the Czech regulatory body. It should enable operation up to 60 years. The article gives information about the status of the NPP Dukovany long-term operation (LTO) preparation. It gives an overview of results of the prepared LTO Assurance Program, Strategy of the NPP Dukovany LTO, along with risk analysis. The article details the procedure for the NPP Dukovany preparation for operation beyond the limits of original design lifetime, and ensuing planned stages.
Residual Stress Concentrations in a Stainless Steel Slot-Weld Measured by the Contour Method and Neutron Diffraction
Authors: Bouchard P. John , Turski Mark , Smith Mike C.
Published: July 2010

Arc-welding involves the deposition of molten filler metal and the localised input of intense heat. The surrounding parent material and, in the case of multi-pass welds, previously deposited weld metal, undergoes complex thermo-mechanical cycles involving elastic, plastic, creep and viscous deformations. These processes result in the development of large residual stress gradients around the welded region, which can be particularly detrimental to the structural integrity of plant components. The present study examines aggregated weld bead start and stop stress concentration effects in a three pass slot weld specimen that was designed to represent a multi-pass weld repair (without any original weld). The specimen design comprised a Type 316L stainless steel base-plate of nominal dimensions (300 × 200 × 25) mm3 with a 100 mm long by 10 mm deep central slot filled with 3 stringer manual metal arc weld beads, laid one on top of another. Residual stresses in three orthogonal directions were measured by neutron diffraction on a plane cutting through the centre of the plate, parallel to the welding direction, to show concentrations of tensile stress at both the weld start and stop positions. The transverse component of residual stress on the same plane in a second, nominally identical, specimen was mapped using the contour method. By applying two independent measurement techniques the residual stress field within the specimen type was determined with an increased level of confidence. Maximum transverse stress values of about 200 MPa at the weld start position and 300 MPa at the weld stop position were found. Peak tensile stresses in the longitudinal direction of 370 and 460 MPa were measured using neutron diffraction at the weld start and stop positions, respectively. The stresses measured by the contour method and neutron diffraction were in reasonable overall agreement with each other. However, the comparisons pointed to the possible presence of cutting artefacts in the contour results.
Amelioration of Microcracking in Multipass Weld Metal of Alloy 690 by Adding Rare Earth Metals
Authors: Nishimoto Kazutoshi , Saida Kazuyoshi , Fujiya Yasuyuki
Published: July 2010

The effect of the addition of rare earth metals (REM) to the weld metal on the microcracking susceptibility in the multipass welds of alloy 690 was examined by using the La or Ce containing filler metals. The amounts of the La and Ce in the filler metal were varied in several levels. The microcracking susceptibility of the reheated weld metal was evaluated by the spot and transverse-Varestraint tests using pre-welded specimens made by GTAW. The augmented strain levels were varied from 0.50–2.44%. Cracks that occurred in the reheated weld metal evaluated by the Varestraint test could be classified into three types; ductility-dip, liquation and solidification cracking. The ductility-dip cracking susceptibility could be significantly improved by adding 0.01–0.025mass%REM to the weld metal. Adversely, the excessive REM addition led to the liquation and/or solidification cracking in the weld metal. Microstructural analyses revealed that phosphide and sulphide of La or Ce were formed in the REM containing weld metals, and Ni-La or Ni-Ce intermetallic compound was additionally identified in the excessively REM containing weld metals. High temperature tensile test indicated that hot ductility of the weld metal was ameliorated by adding 0.01–0.03mass%REM, implying that the ductility-dip cracking susceptibility was decreased as a result of lowering the grain boundary segregation of impurity elements such as P and S due to the scavenging effect of REM. The liquation and solidification cracking in the excessively REM containing weld metals were considered to be due to the formation of liquefiable intermetallic compounds of Ni and REM. The multipass welding test confirmed that microcracks in the multipass welds of alloy 690 were completely prevented by using the filler metals containing approx. 0.03mass%REM.
Over Limit Oxygen Effect on Crack Propagation of WWER 440 RPV Steel in Primary Circuit Water
Authors: Ernestova Miroslava , Hojna Anna
Published: July 2010

Experience with operating nuclear power plants worldwide reveals that many failures may be attributed to fatigue associated with mechanical loading due to vibration and with corrosion effect due to exposure to high-temperature environment. In order to clarify the simultaneous influence on reactor pressure vessel (RPV) material testing of ferritic steel 15Ch2MFA used for RPV of WWER 440 was performed at Nuclear Research Institute (NRI) autoclaves. Cyclic and constant loadings were applied to Compact Tension (CT) specimens in WWER primary water environment at 290°C and simultaneous effect of different oxygen levels (< 20 ppb, 200 ppb, 2000 ppb) on crack propagation has been evaluated. Obtained crack growth rates are compared with ASME XI Code and VERLIFE curves and crack behaviour is discussed.
Coupled Discrete Element (DEM)–Continuous Fluid (CFD) Method for the Application of Pneumatic Conveyed Granular Media
Authors: Sturm Mira , Wirtz Siegmar , Scherer Viktor , Denecke Jens
Published: July 2010

A Coupled Discrete Element - Continuous Fluid Method is developed, which allows the numerical simulation of the behaviour of pneumatic conveyed granular media. While the fluid is simulated by computational fluid dynamics, the soft-sphere discrete element approach is used for the particle system. A “four-way coupling” is implemented to account for phase interaction on both sides and for the collisions among particles and with the pipe walls. The purpose of this work is to show the applicability of the presented simulation model to dense pneumatic conveying systems. Unfortunately, only few complete experimental data are available in this field. In this work a pneumatic conveying system for dense phase regime with a vertical pipe of 2 m height and a diameter of 50 mm is investigated. Periodic conditions are applied to both phases, the fluid and the particle system. The particles, which leave the pipe at one end, are inserted back at the other end of the pipe, so that a much larger simulation domain is represented. After an initial set up and some intermediate time steps a stable mode is reached and one single plug forms, which is then investigated in detail. The pressure distribution along the plug which coincides with the porosity distribution, the length of the plug and its velocity are important parameters which are examined and compared to experimental investigations. Variations of the conveying air velocity and their influence are also considered.
Update of the Tabulated «M and Y» Values in the New Revisions of French Codes CODAP® and CODETI®: Development of a Testing Procedure to Determine «M and Y» Values for Several Tightness Classes
Authors: Lejeune Hubert , Boulben Ce´dric
Published: July 2010

The existing tables giving “m and y” values, used in the Taylor Forge method for bolted flange connections calculation, have remained unchanged through years. Some gasket types do not appear in these tables and no reference is made to a Tightness Class associated to these values. The need for an update of the exiting tables has been raised by the supplier of French codes (CODAP® [1] and CODETI® [2]). A survey about the recommended values of “m and y” and their associated expected leakage rates for the gasket types available on the market has been performed. The wide discrepancy in the test procedures and the gasket parameter values showed the need for the development of a common test procedure. The new test procedure giving tables of “m and y” values depending on the tightness class is presented here. The application of this procedure on several gasket types, lead to the publication of new tables for “m and y” values, in the last French codes revision.
Preparation of High Strength Mo(Si, Al)2-SiC Composite by Melt Infiltration Process
Authors: Zhang XiaoLi
Published: July 2010

The Mo(Si, Al)2-SiC composite was prepared by infiltrating melted aluminum into MoSi2+C compacts at 1350°C, and the microstructure and mechanical property of this composite were analyzed. The results showed that the phases of these composite are Mo(Si1-x, Alx)2 and SiC, and a small amount of Mo5Si3C and Al. Increasing the value of x, the amount of Mo5Si3C and Al phases decrease and even disappear gradually. The microstructure of this composite is sheet-like Mo(Si, Al)2 with needle-like SiC distributed in its gap, and parts of SiC are whisker-like. When x = 0.2, the bending strength of the composite reaches the maximum, which was 770 MPa. The bending strength of designed composite prepared by melt infiltration in this study is better than that of the composite prepared by hot pressing reported in literature.
Approach for Selection of Rayleigh Damping Parameters Used for Time History Analysis
Authors: Spears R. E. , Jensen S. R.
Published: July 2010

Nonlinearities, whether geometric or material, need to be addressed in seismic analysis. One good analysis method that can address these nonlinearities is direct time integration with Rayleigh damping. Modal damping is the damping typically specified in seismic analysis Codes and Standards [1, 2]. Modal damping is constant for all frequencies where Rayleigh damping varies with frequency. An approach is proposed here for selection of Rayleigh damping coefficients to be used in seismic analyses that are consistent with given Modal damping. The approach uses the difference between the modal damping response and the Rayleigh damping response along with effective mass properties of the model being evaluated to match overall system response levels. This paper provides a simple example problem to demonstrate the approach. It also provides results for a finite element model representing an existing piping system. Displacement, acceleration, and stress results are compared from model runs using modal damping and model runs using Rayleigh damping with coefficients selected using the proposed method.
Web Based Nondestructive Evaluation Using Acoustic Emission
Authors: Ternowchek Samuel J. , Miller Ronnie K. , Cole Phillip T.
Published: July 2010

As operating equipment and structures age, the probability of failure increases. Increasing inspection cycles (over some fixed period of time) with conventional nondestructive evaluation (NDE) is one way to address this problem but it comes at a cost. In addition, an uncertainty exists that the right area(s) have been inspected during one of these inspection cycles. As a result, there is a need for a technique and method that provides the user with real time information about structural integrity or operating conditions. This technique and method must be cost effective and minimize the need for a person to be near the structure operating equipment in order to obtain data on a continuous basis.
A Radiofrequency Identification (RFID) Temperature-Monitoring System for Extended Maintenance of Nuclear Materials Packaging
Authors: Chen Kun , Tsai Hanchung , Fabian Bud , Liu Yung , Shuler James
Published: July 2010

A temperature-monitoring system based on radiofrequency identification (RFID) has been developed for extending the maintenance period of the nuclear material packaging for storage and transportation. The system consists of tags, readers, and application software. The tag, equipped with a temperature sensor, is attached to the exterior of a package. The application software enables remote reading, via radio waves, of the temperature from the sensor in the tag. The system reports any temperature violations immediately via e-mail or text message, and/or posts the alarm on a secure website. The system can monitor thousands of packages and record individual temperature histories in a database. The first type of packaging that will benefit from the RFID technology is Model 9977, which has been certified by the U.S. Department of Energy (DOE) to ship and store fissile materials such as plutonium and uranium. The recorded data can be correlated to the temperature of the containment O-ring seals, based on the decay heat load of the contents. Accelerated aging studies of the Viton® GLT O-rings have shown that temperature is one of the key parameters governing the life of the O-ring seals, which maintain the integrity of the containment boundary of the package. Use of the RFID temperature-monitoring system to verify that the surface temperature remains below a certain threshold will make it possible to extend the leak-test period of the package from one year to up to five years. The longer leak-rate testing interval will yield a cost savings of up to $10,000 per package over five years. This work was conducted by Argonne National Laboratory in support of the DOE Packaging Certification Program, Office of Environmental Management, Office of Packaging and Transportation (EM-63).
Recent Advances in Lower Bound Shakedown Analysis
Authors: Weichert Dieter , Hachemi Abdelkader
Published: July 2010

The special interest in lower bound shakedown analysis is that it provides, at least in principle, safe operating conditions for sensitive structures or structural elements under fluctuating thermo-mechanical loading as to be found in power- and process engineering. In this paper achievements obtained over the last years to introduce more sophisticated material models into the framework of shakedown analysis are developed. Also new algorithms will be presented that allow using the addressed numerical methods as post-processor for commercial finite element codes. Examples from practical engineering will illustrate the potential of the methodology.
Large-Scale Tests Performed in Support of LBB Projects Applied to WWER Type NPPs in the Czech Republic in Years 1992–1994
Authors: Lauerova Dana , Palyza Jiri , Zdarek Jiri
Published: July 2010

In the paper, an overview of large-scale experiments performed on components of WWER primary circuits within several LBB projects conducted in the Czech Republic in years 1992 – 1994 is presented. The tested components were replicas of the real ones; they contained a through-wall crack and were loaded by pressure and bending moment in two stages, as appropriate according to the LBB methodology. All tested components exhibited stable behaviour under normal operating loading superposed with safe shutdown earthquake loading (NOC + SSE) applied during 1st stage of experiment. During 2nd stage of experiment, under loading by bending moment only, the models usually exhibited stable tearing of the crack, in some cases limit load (maximum force at loading controlled by displacement) was reached. In the paper, the experiments are briefly described, with presenting the main experimental and (in some cases) FE computational results.
Flow-Induced Streamwise Vibration of a Flexibly-Mounted Cantilevered Cylinder in Steady and Pulsating Crossflow
Authors: Sherwood Joseph , Dusting Jonathan , Konstantinidis Efstathios , Balabani Stavroula
Published: July 2010

This paper describes an experimental study of the response of a freely vibrating cylinder with low mass ratio and high damping to steady and pulsating crossflow for Reynolds numbers in the range 120–2900. A rigid circular cylinder was cantilevered by means of a plate spring allowing it to oscillate in the stream-wise direction only. A camera-based technique was employed for tracking the cylinder vibration while the wake fluctuations were measured by a laser-Doppler system. The results show that the forced excitation from pulsating flow can take over control of the wake and/or the cylinder oscillations in a complex manner. The overall response depends strongly on two main parameters: the ratios of the pulsation frequency to the structural frequency and to the vortex shedding frequency from a fixed cylinder in steady flow. When the excitation frequency from both the wake and the external pulsation coincided with the natural frequency of the structure, the r.m.s. amplitude of the cylinder vibration increased up to 400% compared to that for the same reduced velocity in steady flow. In this case, maximum end displacements exceeded 35% of the cylinder diameter.