bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental Investigation of the Factors That Contribute to the Creep-Relaxation of Compressed Non-Asbestos Gaskets
Authors: Veiga Jose´ C. C. , Cipolatti Carlos F. A. , de Sousa Ana M. F. , Reeves David W.
Published: August 2009

The adequate tightness of flanged joints contributes to maintaining safe working conditions in numerous equipment and industrial installations. The new sealing technologies and materials can require more careful selection, handling and installation than previous asbestos equivalents. Many research studies have been conducted to understand and improve the assembly bolt load of piping joints in order to minimize the likelihood of leakage. The selection of the bolt load must consider many factors, such as: minimum gasket stress to achieve a seal; the maximum stress that will damage the joint components and the amount of gasket stress lost to creep-relaxation under room temperature and service condition. It is well known that the bolt load decrease to some degree after the initial assembly due to creep-relaxation characteristics of the gasket. ASME PCC-1 recommends restoring the gasket load, after a minimum 4 hours, due to short-term creep-relation. This paper intends to investigate factors which may influence the creep-relaxation characteristic of the compressed non-asbestos gasket. In order to reproduce real field condition, ASME B16.5 class 300lbs flanges were used in this experimental investigation.
Technical Justification for Increasing Temperbead Welding Area Limits on Low Alloy Steel
Authors: Herrera Marcos L. , Tang Shu S. , Peterson Artie
Published: August 2009

This paper presents the results of the analytical evaluation supporting the technical justification of increasing the amount of temperbead welding, currently limited to an area of 100 in2, that can be performed on low alloy steel (LAS) nuclear power plant components. The need to expand the application area limitations is increasing for ambient temperature Gas Tungsten Arc Weld (GTAW) temperbead weld overlay repairs on LAS components. As nuclear power plants age and as inspection techniques continue to improve increasing the area limit becomes increasingly important since more indications are being identified. Existing limitations of temperbead welding area of 100 in2 imposed in the ASME Code and in Code Cases 606 and 638 for ambient temperature temper bead welding are arbitrary and overly conservative. This paper presents the analyses supporting: 1) a weld overlay repair greater than 100 in2 on a Reactor Pressure Vessel (RPV) nozzle and 2) a weld cavity repair on an RPV of 500 in2 vertical shell weld. Based on the results of these cases, conclusions regarding temperbead welding in excess of the current 100 in2 limit are made.
An Update on Selecting the Optimum Bolt Assembly Stress for Piping Flanges
Authors: Brown Warren , Reeves David
Published: August 2009

In order to minimize the likelihood of leakage from flanged piping joints, it is a good practice to maximize the initial bolt assembly stress. Present bolting guidelines (ASME PCC-1 [1]) outline the use of a percent of bolt yield across all flange sizes and classes to set the assembly stress level. These guidelines do indicate that aspects such as component strength and gasket stress should be considered, however the most common application of the approach is to use a standard percentage of bolt yield across all flange sizes and classes. This approach does allow for adjustment for differences in material yield strengths (carbon steel versus stainless steel) and raised face (RF) versus ring type joint (RTJ) flange configurations. It does not, however, adjust for the difference in strength between standard pipe flange sizes nor the actual gasket stress achieved across all flange sizes and classes. Since there is no assessment of flange strength, such an approach may cause failure of joint components. In addition, because the standard percentage of bolt yield technique does not look at gasket stress, it is prone to gasket leakage due to low stress or gasket destruction due to over-compression for some joints. In addition, some joints may require bolt loads well in excess of the standard value to develop an acceptable gasket stress level in order to prevent leakage. This paper is a continuation of the paper presented during PVP 2006 in Vancouver (Brown [2]), which examined the variables that must be considered and drew some preliminary conclusions regarding the use of flange stress limits in determining the maximum allowable bolt load for a given flange size. Subsequent to writing that paper, further investigation found that the code calculated flange stresses are a poor indicator of the maximum acceptable bolt load. The most practical measure of this load is obtained by using elastic-plastic finite element analysis (FEA) to determine the point of gross plastic deformation of the flange. This paper details the maximum bolt load limit results of elastic-plastic FEA on most sizes of standard ASME weld neck flange sizes. The practical application of this method is in the development of standard bolt assembly stress (or torque) tables for standard pipe flanges using a given gasket type. In addition, a new code equation and additional limits are developed, by comparison to the elastic-plastic FEA results, which allow the determination of the maximum assembly bolt load for non-standard weld-neck flanges and standard weld-neck flanges with different bores, materials or gaskets than used in the elastic-plastic FEA presented in this paper.
Experimental Evaluation of Deformation and Constraint Characteristics in Precracked Charpy and Other Three-Point Bend Specimens
Authors: Nanstad Randy K. , McCabe Donald E. , Sokolov Mikhail A. , Merkle John G.
Published: August 2009

To enable determination of the fracture toughness reference temperature, T0, with reactor pressure vessel surveillance specimens, the precracked Charpy (PCVN) three-point bend, SE(B), specimen is of interest. Compared with the 25-mm (1 in.) thick compact, 1TC(T), specimen, tests with the PCVN specimen (10×10×55 mm) have resulted in T0 temperatures as much as 40°C lower (a so-called specimen bias effect). The Heavy-Section Steel Irradiation (HSSI) Program at Oak Ridge National Laboratory developed a two-part project to evaluate the C(T) versus PCVN differences, (1) calibration experiments concentrating on test practices, and (2) a matrix of transition range tests with various specimen geometries and sizes, including 1T SE(B) and 1TC(T). The test material selected was a plate of A533 grade B class 1 steel. The calibration experiments included assessment of the computational validity of J-integral determinations, while the constraint characteristics of various specimen types and sizes were evaluated using key curves and notch strength determinations. The results indicate that J-integral solutions for the small PCVN specimen are comparable in terms of J-integral validity with 1T bend specimens. Regarding constraint evaluations, Phase I deformation is defined where plastic deformation is confined to crack tip plastic zone development, whereas Phase II deformation is defined where plastic hinging deformation develops. In Phase II deformation, the 0.5T SE(B) BxB specimen (slightly larger than the PCVN specimen) consistently showed the highest constraint of all SE(B) specimens evaluated for constraint comparisons. The PCVN specimen begins the Phase II type of deformation at relatively low KR levels, with the result that KJc values above about 70 MPa√m from precracked Charpy specimens are under extensive plastic hinging deformation. For the second part, about twenty specimens of each type and size (65 PCVN) have been tested to enable statistically reliable comparisons of T0 for the various cases, with tests completed at temperatures from −28 to −37°C. The KJc test data obtained for HSST Plates 13B and 13A show PCVN bias values from −30 to −40°C relative to 1TC(T), but the standard 1TSE(B) specimen shows a bias of about −10°C. However, the SE(B) specimens exhibit a tendency for decreasing T0 with decreasing specimen size (B and/or b). The results are compared with those from other materials and observations are noted regarding potential effects of test temperature and metallurgical factors.
Identification of Quad Cities Main Steam Line Acoustic Sources and Vibration Reduction
Authors: DeBoo Guy , Ramsden Kevin , Gesior Roman , Strub Brian
Published: August 2009

The Quad Cities Nuclear Power Station, Units 1 and 2, have a history of steam line vibration issues. The implementation of an Extended Power Uprate resulted in significant increases in steam line vibration as well as acoustic loading of the steam dryers, which led to equipment failures and fatigue cracking of the dryers. This paper discusses the extensive data collection on the Quad Cities Unit 2 replacement dryer and the Main Steam Lines. This data was taken with the intent of identifying acoustic sources in the steam system. Review of the data confirmed that vortex shedding coupled column resonance in the relief and safety valve standpipes were the principal sources of large magnitude acoustic loads in the main steam system. Modifications were developed in subscale testing to alter the acoustic properties of the valve standpipes and add acoustic damping to the system. The modifications developed and installed consisted of acoustic side branches that were attached to the Electromatic Relief Valve (ERV) and Main Steam Safety Valve (MSSV) attachment pipes. Subsequent post-modification testing was performed in plant to confirm the effectiveness of the modifications. The modifications have demonstrated a reduction in the acoustic pressure loads at full Extended Power Uprate (EPU) conditions to levels below those at Original Licensed Thermal Power (OLTP).
Crack Growth Rates of Irradiated Austenitic Stainless Steels in BWR Environments at 289°C
Authors: Chopra O. K. , Gruber E. E. , Alexandreanu B. , Chen Y. , Shack W. J.
Published: August 2009

Crack growth rate (CGR) data have been obtained in boiling water reactor environments on several grades of austenitic stainless steels, including weld heat-affected-zone and cast materials, that were irradiated up to 2.0 × 1021 n/cm2 (E > 1 MeV) (≈3 dpa). Crack growth tests were conducted on 1/4-T compact tension specimens subjected to either a sawtooth waveform with load ratios up to 0.7 and rise times up to 1000 s, or a constant load with or without periodic partial unloading. The results indicate significant enhancement of crack growth rates in the irradiated steels. The results are compared with data obtained from other studies. The existing CGR data are also reviewed to evaluate the effects of material composition, irradiation, and water chemistry on the CGRs in austenitic SSs. The significance of specimen size criteria is discussed.
Contributions of Dr. Spencer H. Bush to the Successful Development of Risk-Informed Inservice Inspection Technology
Authors: Balkey Kenneth R. , Simonen Fredric A.
Published: August 2009

The development and implementation of risk-informed inservice inspection (ISI) approaches, providing an alternative to ASME Section XI Code requirements for the selection of examination locations in nuclear power plant piping systems, has been recently identified by industry leaders as the most successful voluntary application of risk technology in the United States. This technology improves the effectiveness of examination of piping components, i.e. concentrates inspection resources and enhances inspection strategies on high-safety-significant locations, and reduces inspection requirements on others while maintaining or enhancing overall plant safety (in terms of core damage and large, early release frequency). Risk-informed ISI has been successfully implemented in more than 90% of U.S. reactors and in nuclear power plant ISI programs in at least eight other countries. Beginning almost 20 years ago, Dr. Spencer H. Bush played an instrumental role in the development of this technology as a Steering Committee member of the ASME Research Project on Risk-Based Inspection Guidelines. He later became a member of the ASME Section XI Working Group on Implementation of Risk-Based Examination participating in the development and review of ASME Code Cases allowing for trial use of this new technology. Dr. Bush, having a long leadership role with ASME Section XI, played an instrumental role in the development of an overall structure and process for integrating the technologies inherent to a risk-informed ISI program, including piping failure data and non-destructive examination reliability results. He also played a key role in garnering ASME and regulatory acceptance of this alternative approach. The authors, along with many other colleagues, had the honor and privilege of working closely with Dr. Bush on this initiative over the last two decades, and via this paper, the authors would like to highlight some of Dr. Bush’s key contributions to this successful development in his memory.
Stress Relaxation in Aluminum Welding Using Ultrasonic Method
Authors: Andrino Marcilio H. , dos Santos Auteliano A. , Bray Don E. , Trevisan Roseana E.
Published: August 2009

Stress relaxation of welded joints can increase the safety of structures. Although it is not absolutely clear why it happens, several researches have proved the phenomenon. This work presents the application of the ultrasonic technique to evaluate the stress relaxation in welds of 5052 aluminum. A special geometry was developed, so each welded plate had uni-axial stresses in the measurement region. Twenty-two plates were tested, eleven in the rolling direction and the remaining in the perpendicular direction. The plates were stress relief using a heat treatment to set an initial stress free reference state. After that, they were welded to create the stress field in the area of investigation. A final step was to cut each of the samples after different periods of time from the welding. The stress was measured in the uni-axial stress region. A calendar of the process was established to record precisely the time for each step. Longitudinal critically refracted waves were used to measure the stresses. The results showed a clear effect of relaxation. The magnitude was not as pronounced as in steel, but kept the same relation with the ultimate strength of material.
Analytical Modeling of Hydraulically Expanded Tube-to-Tubesheet Joints
Authors: Laghzale Nor Eddine , Bouzid Abdel-Hakim
Published: August 2009

The loss of the initial tightness during service is one of the major causes of failure of tube-to-tubesheet joints. The initial residual contact pressure and its variation during the lifetime of the joint is among the parameters to blame. A reliable assessment of the initial contact pressure value requires accurate and rigorous modeling of the elasto-plastic behavior of the tube and the tubesheet during the expansion process. This paper deals with the development of a new analytical model used to accurately predict the residual contact pressure resulting from a hydraulic expansion process. It is based on the elastic perfectly plastic material behavior of the tube and the tubesheet and the interaction between them. The model results have been compared and validated with those of the more accurate numerical FEA models. Additional comparisons have been made with existing methods.
Fatigue Strength Reduction Factors for Welded Joints: Another View
Authors: Kalnins Arturs
Published: August 2009

The paper distinguishes between FSRFs that are used for two different purposes. One is to serve as a guideline for an initial estimate of the fatigue strength of a welded joint. That is the purpose of the FSRFs that are given in the ASME B&PV Code and various accompanying documents. If that estimate renders the fatigue strength inadequate, an FSRF can be sought that is limited to the joint under consideration. The paper shows how such FSRFs can be determined from fatigue test data. In order to make it possible to read the allowable cycles from the same design fatigue curve as that used for the FSRFs of the guidelines, a Langer curve [defined by equation (2) in the paper] is used to curve fit the data. The appropriate FSRF is obtained by minimizing the standard deviation between this curve and the data. The procedure is illustrated for girth butt-welded pipes. The illustration shows that for the data used in the analysis, a constant FSRF is applicable to less than one million cycles but not to the high-cycle regime.
Reflection of Blast Waves Off Cylindrical Pipes
Authors: Geng J. , Thomas K.
Published: August 2009

In this paper, the interaction between a blast wave and an array of cylindrical objects (pipe or vessel) has been numerically investigated to evaluate blast load distribution around the objects. It was found that the interaction leads to a blast focusing within the gap between two adjacent pipes, and that the focused overpressure may exceed a fully reflected overpressure. This paper examines the effects of a combination of the arrangement of pipes (diameter, gap distance) and incident blast wave characteristic parameters (positive phase duration) on the focusing phenomena and the resultant blast load distribution.
Accuracy and Margin in Creep-Fatigue Evaluation for Modified 9Cr-1Mo Steel
Authors: Takahashi Yukio
Published: August 2009

Modified 9Cr-1Mo steel (ASME SA-213, Grade 91) is regarded as a promising candidate for structural materials in some of the nuclear power generation plants considered in Generation-IV project. If it is used at high temperature conditions, consideration of creep-fatigue interaction in addition to simple creep rupture is needed in component design. The author has been conducting many creep-fatigue tests for the steel at temperatures between 550°C and 650°C in order to search for a suitable creep-fatigue assessment method. It was found that creep damage at failure estimated by applying the time fraction approach to measured stress relaxation data strongly depended on the test temperature and became quite small at 550°C. However, application of calculated stress relaxation brought about the increase of creep damage over the linear damage summation line. Furthermore, addition of design factors significantly increased the values of creep and fatigue damages, making margin against failure quite large. A new definition of creep damage as a ductility consumer in strain based approach gave a simple method to estimate creep damage more properly and stably with a much smaller sensitivity on the stress relaxation behavior.
Mechanical Testing of Roll Repaired Boiling Water Reactor Control Rod Drive Housings
Authors: Corchon Fernando , Gorrochategui In˜aki , Ranganath Sam
Published: August 2009

Cracking and occasional leaks have been reported in some Boiling Water Reactor (BWR) control rod drive (CRD) stub tubes. Roll expansion of the housing against the Reactor Pressure Vessel (RPV) bottom head penetration has been used successfully to provide a leak barrier. The recently approved ASME Code Case N-730 “Roll expansion of Class 1 Control Rod Drive (CRD) Bottom Head Penetrations in BWRs, Section XI, Division 1” provides the specific criteria for the application of roll expansion. The minimum roll band length in the Code Case was based on the requirement that the roll joint capability exceed the scram forces on the CRD. The roll joint capability was based on a simplified analytical model with assumed friction factors. The predictive model was then compared with the results of extensive testing on mockups. This paper describes the results of the testing that has been performed to determine the load capability of roll repairs for different roll band lengths, material combinations (stainless steel and Alloy 600), percent wall thinning, thermal cycling and surface condition. The mock-ups were rolled using procedures and rolling equipment similar to those used in actual plant application. The mock-ups were tested in a testing machine by applying a ‘push force’ on the housing. In addition to measuring the force using a load cell, strain gages were also used to measure the strains on the housings. LVDTs were used to monitor the displacement during the test. The results showed that the resistance of the rolled joint (i.e. the load capability) is proportional to the roll length. The load capability was not a strong function of wall thinning or thermal cycling. It was strongly affected by the surface condition (e.g. oxidation) and the housing material yield strength. The predictive model was consistent with the test results and confirmed that the roll expansion joint has substantial load capability. Thus, the roll joint is not only a leak barrier, but also a structural load-carrying joint that is sufficient to resist the upward scram loads on CRDs.
Residual Stresses in CANDU Feeder Bends: Comparison of Measurements and Predictions
Authors: Yetisir M. , Khajehpour S. , Ding Y.
Published: August 2009

In one CANDU® nuclear station, 11 outlet feeder pipes have been replaced because of cracking in the bends (9 of them were detected before leaked). The cracked feeder bends, which were made out of SA-106 Grade B material, were 2.5 inches (64 mm) in nominal diameter and with a small bend radius of 3.75 inches (95 mm). In all cases, cracks were primarily axial in orientation and were initiated either on the inside surface along the flanks of the bends or on the outside surface along the extrados of the bends. Root cause analyses indicated that the residual stress played a significant role in these failures. Measured residual stresses data from ex-service and spare feeder bends have been used to identify possible crack locations, to evaluate susceptibility to cracking of various feeder bends and to develop inspection strategies in limited-scope inspection campaigns. This paper documents the numerical prediction of residual stresses in feeder bends and compares these data with field measurements.
Study on Isolation Device for Decrease of Displacement by Using Control of Friction
Authors: Shintani Masanori , Taguchi Naoya
Published: August 2009

This paper deals with reduction of horizontal relative displacement by using a frictional force for a seismic isolator. First, a compression spring is attached to the base. Next, a slope plate is superimposed on it. The frictional force acts on the slope plate. The restoring-force is given to the seismic isolator by the compression spring attached to the base. In the equation of motion of the analytical model, the frictional force changes in proportion to the displacement. The restoring-force is also proportional to the displacement. The restoring-force always works in the direction of the center. Therefore, the frictional force and the restoring-force are both proportional to the displacement. Simulation analysis was performed under various conditions using this analysis model. As a result of conducting the analysis and an experiment with this model, it was shown that response acceleration and relative displacement can be reduced successfully. In order to reduce response acceleration and relative displacement more, analysis was carried out with the actual earthquake waves under the conditions to change the coefficient of friction by relative displacement. As a result, the coefficient of friction that reduces relative displacement most effectively without impairing the performance of the seismic isolator was established. However, the coefficient of friction that reduces the response acceleration and relative displacement effectively depends on by seismic waves. Therefore, in this report, the coefficient of friction that reduces response acceleration and relative displacement most effectively is determined by using white noise. It is analyzed with actual seismic waves by using the decided parameters. The performance of the seismic isolator is examined.
Environmental Crack Growth Predictions for Piping Components
Authors: Ranganath Sam , DeBoo Guy
Published: August 2009

Structural integrity assessment of reactor components requires consideration of crack growth. A key input to this is the development of reference stress corrosion crack (SCC) growth rate curves for use in the structural evaluation. The ASME Section XI Task Group on SCC Reference Curve is looking into available SCC data for stainless steel and nickel based alloys and associated weldment in both pressurized water reactor (PWR) and boiling water reactor (BWR) environments. The test data show significant data scatter in crack growth rates (CGR). The conservative approach is to develop reference curves that bound all available data so that upper bound crack growth predictions. While this approach may be conservative, it may lead to excessive estimates of crack growth and result in unrealistic (and often meaningless) structural margin predictions. Selection of the appropriate SCC reference curves requires realistic interpretation of test data so that the predictions are consistent with field behavior and provide reasonable, but conservative assessment. This paper describes crack growth assessment for stainless steel piping and Alloy 600 safe end components with Alloy 182/82 welds in BWR environment. The results from the crack growth analysis for piping can be used to determine whether a proposed reference curve provides reasonable results. The objective is to use the piping and safe end crack growth predictions to develop optimal SCC Reference Curves for use in ASME Code evaluations.
Comparison of Methods for Predicting the Influence of Residual Stresses on Brittle Fracture
Authors: Mirzaee-Sisan Ali , Hadidi-Moud Saeid , Smith David John
Published: August 2009

This paper compares different methods for predicting the influence of residual stresses on brittle fracture. Comparison is made between fracture predictions of a local statistical approach based on the Beremin type model, with those of a well-known fracture assessment procedures, BS7910 and R6 that uses a failure assessment diagram (FAD). The results from both methods are discussed and compared. The study focuses on the behaviour of a ferritic steel pipe containing a part-through circumferential thumb-nail crack on the outer surface of the vessel.
A Review of K-Solutions for Through-Thickness Flaws in Cylinders and Spheres
Authors: Sisan Ali Mirzaee , Hadley Isabel , Smith Sarah E. , Smith Mike
Published: August 2009

This paper reviews different stress intensity factor solutions for a wide range of configurations and loading conditions for a cylinder with axial and circumferential through thickness cracks and a sphere with through thickness meridional (equatorial) cracks. The most appropriate solutions to use are identified.
Effect of Location and Type of Separating Load on Joint Clamp Load and Bolt Tension
Authors: Nassar Sayed A. , Gandham Satya Vijay Teja
Published: August 2009

This study investigates the change in the tension of a tightened bolt, and the corresponding change in the joint clamp load due to various forms of dynamic separating load that is placed at different distances from the bolt center. Dynamic finite element analysis is performed using ABAQUS on a single-bolt joint using a separating force in the form of a step, shifted sinusoidal, ramp, cyclic ramp and square functions. The separating force is symmetrically placed at locations (from the bolt center) that are equal to 2, 3, 4, and 5 times the nominal diameter of the bolt. Changes in the bolt tension and the clamp load are investigated for three levels of the peak separating load. Dynamic FEA results are compared with those of static separating loads.
Study of Two-Stage Tightening of Threaded Fasteners Using Various Tool Speed Combinations
Authors: Ganeshmurthy Saravanan , Nassar Sayed A.
Published: August 2009

This paper investigates the effect of various tool speed combinations on the torque-tension relationship in a two-stage torque control process for the tightening of threaded fasteners. The tightening speed has a considerable affect on the thread and bearing friction coefficients. Hence, the amount of clamp load generated by a specified level of the tightening torque is significantly influenced by the tool speed combinations in many high volume applications. In two-stage processes, the fastener is first tightened to an intermediate torque level beyond which the tool speed is changed but the tightening is continued until the full target torque is reached. The effect of tightening speed combinations (for stages one and two) on the torque-tension relationship is investigated. Data on the coefficients of thread and bearing friction as well as the Nut Factor K is investigated. The findings of this study are helpful in predicting the clamp load generated in bolted joints, which enhance its reliability and safety. Additionally, the study provides helpful data that may be utilized for developing reliable assembly strategies in mass production applications such as the automotive industry.
Steam Plant Piping Vibration Study and Resolution
Authors: Zysk Gregory , Giamarino John
Published: August 2009

The world’s largest district steam co-generation plant was successfully brought on line following major modifications in the spring of 2005. During the initial “shake-down” operation of the high pressure steam send-out system, piping vibrations were experienced, which disrupted flow meters and other equipment. Operation of one of five identical flow control valves, used in parallel to regulate steam flow to the street distribution system, resulted in the high vibration levels. To investigate the cause of the vibrations, a project was undertaken, which included testing of the piping system utilizing dynamic pressure transducers and accelerometers and engineering analysis of the acoustics and piping structural dynamics. Multiple combinations of open and closed valves were investigated, and the likely root cause was identified as flow-induced vibration originating at a tee in the system. A piping layout modification was designed. The modification consisted of rerouting the piping downstream of one flow control valve to bypass the source of the flow-induced vibration. Following the piping modification, further tests were conducted that showed the reconfiguration successfully mitigated the vibration.
Statistical Initiation and Crack Growth Models for Stress Corrosion Cracking
Authors: Shack W. J. , Chopra O. K.
Published: August 2009

Statistical distributions of initiation times and crack growth rates are needed for probabilistic fracture mechanics models. Times to failure in laboratory tests on small specimens are about a factor of 1000 shorter than the times to failure of comparably sized “specimens” in the field would have to be in order to get realistic component failure rates. Thus while specimen tests are useful in identifying parametric dependencies, it is unlikely that they can be used directly to develop initiation models for field components without using field data. A scaling approach is proposed to provide a method for pooling data from different size components and for extrapolating experience from one set of components to another set. Estimates of statistical distributions for initiation of stress corrosion cracks are developed from field data for BWR pipe cracking and CRDM cracking. Estimates of statistical distributions of crack growth rates are developed by combining phenomenological models for crack growth rates with expert judgment on the range of input parameters to those models.
Determination of the Elastic-Plastic Fracture Mechanics Z-Factor for Alloy 182 Weld Metal Flaws for Use in the ASME Section XI Appendix C Flaw Evaluation Procedures
Authors: Wilkowski G. , Xu H. , Shim D.-J. , Rudland D.
Published: August 2009

One of the ways that the ASME Section XI code incorporates elastic-plastic fracture mechanics (EPFM) in the Section XI Appendix C flaw evaluation procedures for circumferential cracks is through a parameter called Z-factor. This parameter allows the simpler limit-load (or net-section-collapse) solutions to be used with a multiplier from EPFM analyses. Traditionally the EPFM solution was determined by using the GE-EPRI J-estimation scheme to determine the maximum load by EPFM, and Z = limit load / EPFM solution. The Z-factor is a function of the material toughness as well as the pipe diameter. With the advent of primary water stress-corrosion cracks (PWSCC) in pressurized water reactor (PWR) dissimilar metal welds (DMW), there is a need to develop Z-factors for Alloy 82/182 nickel-based alloy welds that are susceptible to such cracks. Although there have been Z-factor solutions for cracks in stainless and ferritic pipe butt welds, the DMW are somewhat different in that there is a much lower yield strength material on one side of the weld (typically forged or wrought 304 stainless steel) and on the other side of the weld the low alloy steel has a much higher strength than even the weld metal. This paper shows how 3D finite element analyses were used for a particular pipe size to determine the sensitivity of the crack location in the Alloy 182 weldment (crack in the center of weld, or closer to the stainless or low alloy steel sides), and how an appropriate stress-strain curve was determined for use in the J-estimation schemes. A Z-factor as a function of the pipe diameter was then calculated using the LBB.ENG2 J estimation scheme using the appropriate stress-strain curves from the finite element analysis. The LBB.ENG2 analysis was used rather than the GE-EPRI estimation scheme since it has been found that the LBB.ENG2 analysis is more accurate when compared with full-scale pipe tests. From past work, the GE-EPRI method was found to be the most conservative of the J-estimation schemes in predicting the maximum loads for circumferential flaws when compared to full-scale circumferentially cracked-pipe tests. The proposed Z-factor relationship should be restricted to normal operating temperatures (above 200C) with low H2 concentrations, where the Alloy 182 weld metal exhibits high toughness.
Benchmarking of a Thermal Finite Element Approximation Scheme for Externally Cooled Spent Fuel Storage Casks
Authors: Bajwa Christopher S. , Spivack Ian F.
Published: August 2009

The US Nuclear Regulatory Commission (NRC) is responsible for licensing spent fuel storage casks under Title 10 of the Code of Federal Regulations Part 72 (10 CFR Part 72). Under these regulations, storage casks must be evaluated to verify that they meet various criteria, including acceptable thermal performance requirements. The purpose of the evaluation described in this paper is to establish the effectiveness of a medium-effort modeling approach and associated simplifying assumptions in closely approximating spent fuel cask component temperature distributions. This predictive evaluation is performed with the ANSYS® code, and is applicable to externally cooled cask designs. The results are compared against experimental measurements and predictions of the COBRA-SFS finite-difference code developed at Pacific Northwest National Laboratory.
Material Removal Simulation of Aluminum Compound Tubes With Incorporating Real Unloading Behavior
Authors: Mohammadi M. , Farrahi G. H. , Hoseini S. H.
Published: August 2009

Real loading-unloading behavior of an A5083 aluminum alloy was recorded experimentally. This real behavior was incorporated in the variable material properties (VMP) numerical algorithm to predict residual stresses resulted from autofrettage and shrink fit in two kinds of autofrettage compound tubes. Using an analytical method, residual stresses induced by bore material removal via machining were calculated. Using developed VMP code and isotropic hardening rule in both autofrettage compound tubes, residual stresses resulted from shrink fit and autofrettage processes and via post machining, were estimated. Machining process simulation was performed for 10 mm bore material removal. ANSYS commercial FEM software was used for validating the results of VMP code. The results of VMP method and ANSYS were in good agreement with each other. Finally with the help of recorded real unloading behavior of A5083 aluminum alloy, also aforementioned simulations were performed on various tubes. The material removal simulation was modeled for 5 mm to 15 mm material removal from the bore.
Simplified Limit Load Estimation of Components With Cracks Using the Reference Two-Bar Structure
Authors: Adibi-Asl R. , Seshadri R.
Published: August 2009

Limit loads for different crack configurations are determined in this paper by invoking the concept of equivalence of “static indeterminacy” that relates a multidimensional component configuration to a “reference two-bar structure.” Simple scaling relationships are developed that enable rapid determination of limit loads. The method is applied to different crack configurations, and the limit loads are compared with corresponding results obtained from inelastic finite element analysis.
Assessing the Effect of Intrinsic Microscale Heterogeneity on Brittle Fracture of a Ferritic Steel
Authors: Zhao Xinglong , Lidbury David , da Fonseca Joa˜o Quinta , Sherry Andrew
Published: August 2009

Brittle fracture can have potentially catastrophic consequences on the safety and integrity of engineering components. For this reason, the accurate prediction of cleavage failure probability is of importance in assessing the defect tolerance of high-integrity ferritic steel components, given the possibility of operation in the presence of significant loads at temperatures in the ductile-brittle transition range. In current safety assessments, fracture mechanics treats polycrystalline steels as homogeneous continua. In reality, deformation is heterogeneous, due to the elastic and plastic anisotropy of their constituent (often randomly orientated) grains. Heterogeneity at the micro (grain) scale is currently not considered by conventional fracture mechanics. This paper describes the initial results of a programme of work on a 22NiMoCr37 steel forging to assess the effect of micro-scale heterogeneity on cleavage fracture probability using an adaptation of the Beremin local approach model. The results of cleavage fracture modelling allowing for the effects of micro-scale heterogeneity are compared with the results of modelling based on the assumption of homogeneous materials behaviour. Application of the micro-scale heterogeneity model is providing some new insights into the prediction of cleavage fracture probability.
High Performance Coatings for Spent Fuel Containers and Components
Authors: Farmer J. C. , Choi J.-S. , Day S. D. , Lian T. , Hailey P. D.
Published: August 2009

It has been found that the corrosion resistance of Fe-based amorphous-metal alloys can be improved dramatically through additions of chromium, molybdenum, and tungsten. The addition of yttrium lowers the critical cooling rate of these materials, but complicates the gas atomization process. High concentrations of boron enable these alloys to serve as effective neutron absorbers for criticality control applications. Since these alloys are Fe-based, any substitution of these for Ni-based alloys in the storage of spent nuclear fuel (SNF) applications could result in significant cost savings. Large quantities of amorphous alloy powders have now been successfully produced in multi-ton quantities with gas atomization, and applied to several half-scale SNF containers and criticality control (basket) structures with the high-velocity oxy-fuel (HVOF) thermal spray process. Corrosion rates determined with linear polarization in a variety of repository-relevant brines, and the results of recent salt fog testing of large-scale prototypes are presented.
Field Experience With Code Case N-659: Ultrasonic Examination in Lieu of Radiography
Authors: Henry Douglas O.
Published: August 2009

Code Case N-659 Revision 0 was approved in 2002 to allow ultrasonic examination (UT) an alternative to radiography (RT) for nuclear power plant components and transport containers under Section III of the ASME Code. The Nuclear Regulatory Commission has not approved N-659 and its subsequent revisions (currently N-659-2) for general use, but they have been used on a case-by-case basis mainly where logistic problems or component configuration have prevented the use of radiography. Like the parallel Code Case 2235 for non-nuclear applications under Section I and Section VIII, Code Case N-659 requires automated, computerized ultrasonic systems and capability demonstration on a flawed sample as a prerequisite for using UT in lieu of RT. Automated ultrasonic examination can be significantly more expensive than radiography, so a cost-benefit evaluation is a key factor in the decision to use the Code Case. In addition, the flaw sample set has recently become an issue and a topic of negotiation with the NRC for application of the Case. A flaw sample set for a recent radioactive material transport cask fabrication project was successfully negotiated with the NRC. The Code Case N-659 approach has been used effectively to overcome barriers to Code required radiography. Examples are examination of welds in an assembled heat exchanger and in a radioactive material transport cask assembly where internal shielding prevented radiography of the weld. Future development of Code Case N-659 will address sample set considerations and application-specific Code Cases, such as for storage and transport containers, will be developed where NRC concerns have been fully addressed and regulatory approval can be obtained on a generic basis.
Study and Analysis of the Fluid-Structure Interaction Between Apple and Underwater Shock Wave
Authors: Oda Asuka , Moatamedi Moji , Itoh Shigeru
Published: August 2009

Shock wave treatment of an apple can produce a soft apple similar to a sponge containing water. Therefore, without needing to cut and grate apples, apple juice can be easily obtained by squeezing by hand. In a previous result, it was reported that more than 40MPa shock pressure was needed to make a soft apple. From observation for the shock treatment for the apple, an oblique wave was produced from a detonating fuse and the wave reflected at the surface of the apple. The resulting shock wave data was obtained. In the result of further observations, there was the possibility that the wave passing through the apple was attenuated faster than the wave passing through water. In this report, the same method in the previous research was used. Apples, detonating fuse, and electric detonator were set in water tank, with the fuse initiated by electric detonator. In this research, the behavior of shock wave passing through an apple was researched as exploratory experiment for numerical analysis. In the future, we want to attempt to analyze the fluid-structure interaction between the apple and underwater shock wave by using computer finite element analysis.
Magnetostrictive Sensor Long-Range Guided-Wave Technology for Long-Term Monitoring of Piping and Vessels
Authors: Kwun Hegeon , Kim Sang Y. , Light Glenn M.
Published: August 2009

Long-range guided-wave technology is a recently developed inspection method for surveying large areas of structures and is widely used as a screening tool for corrosion defects in piping. Because of its ability to examine a structure over a long distance, this technology with permanently installed probes is ideal for on-line long-term structural health monitoring of pressure vessels or piping for improved safety, operation, and maintenance. The magnetostrictive sensor (MsS) technology is a guided-wave technology developed at authors’ institution. It uses a probe that consists of thin ferromagnetic strip and coil for guided-wave generation and detection. The MsS probe is inexpensive and can be used on components up to 300°C. Applications of the MsS for long-term monitoring of pressure vessels and piping are presented, including the configuration of MsS probes, types of guided-wave mode used, defect types detectable with guided waves, and example data.
Acoustic Noise Reduction in Large-Diameter Steam-Line Gate Valves
Authors: Janzen Victor P. , Smith Bruce A. W. , Luloff Brian V. , Pozsgai Jonathan , Dietrich Andrew R. , Bouvier James M. , Errett Alan J. , Kitko Gregory T. , Roberts Thomas C.
Published: August 2009

High levels of tonal noise continue to be a potential problem for piping systems that include inline gate valves, particularly for valves located in large-diameter steam lines of power plants. In such cases the large amounts of energy available in the flowstream, and the ineffectiveness of design guidelines in avoiding acoustic excitation, combine to provide a very real possibility of severe noise problems and potentially high levels of piping vibration. This paper presents results of a scale-model testing program designed to investigate the excessive noise and vibration produced by a 28"-diameter gate valve in a recently constructed power plant. After model testing of the original valve configuration indicated that the noise was caused by vortex shedding over the valve’s interior cavity, numerous tests were conducted to investigate the dependence of noise production on interior valve geometry. Results showing how the noise was reduced and recommendations for avoiding such problems are presented.
Analysis and Comparison of Pad Reinforcement of Pressure Vessel by Elastic and Elastoplastic FEM
Authors: Liang Lihua , Gao Zengliang , Xu Yangjian , Zhang Kangda , Fan Zhaohui
Published: August 2009

Considering reinforcement pad and the cylindrical shell as an integral model and a contact model, stress analysis for opening-reinforcement structures of a cylindrical shell is performed by elastic and elastoplastic FEM. By comparison of two sub-models and two material constitutive relations (elastic and elastoplastic), the stress distribution of cylindrical shell intersections by the contact model is similar to that by the integral model, but there are some differences of the stress at contact surfaces of the shell and the reinforcement pad between by the contact model and by the integral model. In general, the stress analysis of the integral model for pad reinforcement can approximately represent that of the contact model. Finite element analyses for different nozzle diameters and different oblique angles in nozzle and cylinder shell intersections are carried out. The stress distribution and the maximum stress are affected by oblique angle. But the difference of the maximum stress intensity among different diameters is small.
Stress Categorization Using the Reference Two-Bar Structure
Authors: Hossain M. M. , Adibi-Asl R. , Seshadri R.
Published: August 2009

The ASME Boiler and Pressure Vessel Codes and Standards used for designing pressure vessel and piping provide guidelines to classify the linear elastic stresses into primary, secondary and peak categories. Although these guidelines cover a wide range of pressure components, they are sometimes difficult to apply to the three-dimensional components with complex loading and geometries. The concept of “reference two-bar structure” is used in this paper to categorize the stresses in pressure components and structures, using linear elastic finite element analyses. The method is applied to a number of components and structures from simple to relatively complex geometric configurations. The results compare well with those obtained from commercial finite element codes.