bluuebunny/crossref_metadata_2025 huggingface dataset:
Verification of Probabilistic Fracture Mechanics Analysis Code PASCAL Through Benchmark Analyses With FAVOR
Authors: Li Yinsheng , Uno Shumpei , Katsuyama Jinya , Dickson Terry , Kirk Mark
Published: October 2017

A probabilistic fracture mechanics (PFM) analysis code called PASCAL has been developed by the Japan Atomic Energy Agency to evaluate failure frequencies of Japanese reactor pressure vessels (RPVs) during pressurized thermal shock (PTS) events based on Japanese data and Japanese methods published for or provided in Japanese codes and standards. To verify this code, benchmark analyses were carried out using the FAVOR code, which was developed in the United States and has been utilized in nuclear regulation. The results of these analyses confirmed with great confidence the applicability of PASCAL to failure probability and frequency evaluation of Japanese RPVs. An outline of PASCAL, the benchmark analysis conditions and analysis results are reported in this paper.
Numerical Analysis of Mechanical Interaction of Pipe-in-Pipe Flowline
Authors: Akolawole M. T. , Pu Yongchang
Published: October 2017

Pipe-in-pipe (PIP) flowline is a unique solution for long subsea tie-backs in deepwater and ultra-deepwater fields. This is because of its optimum thermal performance over wet insulation. However, pipelines are subjected to the highest loading condition during installation. Significant limitation imposed on existing installation vessel in deepwater, is peculiar to S-lay installation method. Contrary to the level of stress experienced with the S-lay installation method at specific locations such as overbend and sagbend region, this method is still widely utilized because of its high production rate. These regions are dominated by bending curvatures which are defined by different load conditions. Due to the composition of PIP system, it is important to understand the structural response of the flowline, the mechanical interaction occurring between various components and the amount of load transfer at this location.

Although, the mechanical interaction within the PIP system are case specific. However, it has been observed that prior to case study analysis; simple pipe models are being developed to assess the mechanical interaction of this system. This paper addresses the impact of the centralizer material on the structural response and load transfer between the outer pipe and inner pipe. The numerical analysis was carried out using Ansys software and was based on Euler Bernoulli bending theory. The centralizer was clamped on to the inner pipe with the clearance between the centralizer and the outer pipe included in the model. The core of the analysis, was modeling the visco-elastic response of nylon rings (Polyamide 6), from which centralizers are made. The centralizer was spaced based on S-lay or J-lay installation criteria against heat sink.

The results demonstrated the relationship between spacing of the centralizer and areas of first contact, amount of force transferred through the centralizer material, non-linearity introduced by contact formulation, alongside the time and temperature dependent behavior of visco-elastic material. The result correlated accurately with the bending principle. Different material model was assessed to determine accuracy of results obtained, in the absence of experimental test data to model visco-elastic response. In addition, the bending curvature was used to predict the mechanical interaction in installation and operation analysis, where limitations of explicitly modeling centralizers exist.
Laser Peening Qualification for the U.S. Application
Authors: Adachi Hiroyuki , Ito Akira , Imasaki Kazuto , Yoda Masaki , Chida Itaru , Uraguchi Kohei , Marlette Stephen
Published: October 2017

Primary water stress corrosion cracking (PWSCC) is a degradation process that has plagued nickel alloy components and welds in the nuclear industry for decades. Numerous mitigation techniques have been developed over the years that help reduce the potential for cracking in nickel alloy components exposed to the primary water environment. One such method is Laser Peening (LP), which improves the stress properties and helps to reduce the potential for crack initiation. The LP process has been applied in Japan to both boiling water reactors (BWR) and pressurized water reactors (PWR) for stress corrosion mitigation. The first application of LP in the US for the nuclear industry was applied in the fall of 2016 to the bottom mounted instrumentation (BMI) nozzles of a PWR. The bottom mounted nozzles are made from Alloy 600 tubing and attached with Alloy 82/182 welds, which are known to be susceptible to PWSCC. In order to prevent crack initiation, it is important for the peening mitigation process to induce sufficient compressive stress on the surface of the susceptible materials. However, it is not practical to take stress measurements directly on the reactor components in order to verify compression. Thus, the magnitude of compression induced by the LP process was verified prior to the application at the plant using mockups of the BMI nozzles. As a part of the qualification process, test coupons were peened and stress measurements were taken using X-ray diffraction (XRD). The results of the stress measurements demonstrate that sufficient surface compression was achieved by the LP process in order to provide PWSCC mitigation. This paper presents and discusses key stress measurement results taken during the qualification process for the first application of LP at a U.S. nuclear plant. Although not directly applicable in this case, the guidance in ASME Code Case N-729 Mandatory Appendix II and MRP-335 for PWR upper head nozzles was generally followed.
Numerical Modelling of the Cooling System at ALBA Synchrotron Radiation Facility to Understand its Performance
Authors: Escaler Xavier , Prieto Montserrat , Quispe Marcos , Kjeldsen Morten , De La Torre Oscar
Published: October 2017

The ALBA Synchrotron Light Source in Barcelona (Spain) requires a reliable, stable and adequate cooling system for its optimal operation. The current design with four long and intricate consumption lines with a ring type piping layout (270 m perimeter) and a common return pipe is believed to compromise the operability and to promote the trapping of air pockets. In order to improve its performance, a better understanding of the thermo-fluid dynamic behaviour is required that permits to opmitize the system and to anticipate unexpected failures. For that, a detailed 1D model has been built with Flowmaster® software comprising all the components and the various regulation mechanisms to control fluid temperature and pressure. Preliminarily, the model has been validated in steady state operating conditions against experimental measurements showing good agreement. Then, a series of specific steady and transient numerical simulations have been carried out to determine the system response. In particular, the effects of blockage and leakage as well as the increase or decrease of heat duty have been analysed. Furthermore, the best flow distribution through the rings has also been found to reduce the air content by maximizing the velocities.
Models for Calculating the Effect of Environment on Fatigue Life (Fen) for Complex Waveforms and/or Non-Isothermal Conditions
Authors: Currie Chris , Morley Andrew , Platts Norman , Twite Marius , Wright Keith
Published: October 2017

Environmentally assisted fatigue of nuclear plant materials in the Pressurised Water Reactor (PWR) coolant environment is a phenomenon that has been extensively studied over the past 30 years. Methods for accounting for the PWR environment in an ASME III fatigue assessment are presented in NUREG/CR-6909. The deleterious effect of environment is described through a Fen factor dependent upon strain rate, temperature and the dissolved oxygen content of the water. The formulae which describe the Fen are based upon correlations observed in test data predominantly from tests conducted with constant temperature and strain rate (triangular or sawtooth loading). Actual loading histories encountered during service are far more complex, with both strain rate and temperature, and therefore Fen, varying through the cycle. NUREG/CR-6909 recommends a modified rate approach method for accounting for this, whereby the load cycle is broken up into a number of strain increments and then integrated to give the Fen for the cycle.

There is a substantial and growing body of data for conditions in which the strain rate or temperature or both changes. The NUREG/CR-6909 modified rate approach does not generally perform well in describing the deleterious effect of environment in these complex conditions. In particular, the modified rate approach does not predict a difference in life when the temperature is varied in-phase or out-of-phase with the strain waveform, or when the slow portion of the strain rate is moved from the top to the bottom of the waveform.

This paper presents new data from strain-controlled fatigue endurance testing of two casts of 304L with complex waveforms and temperature cycling. The paper then presents and compares a number of models for integrating the Fen through the cycle, including methods which weight Fen increments depending on position in the strain cycle.

It is concluded that greater weighting on the environmental effect in the top of the cycle is necessary to describe the differences in life observed. This is further validated by a review of test data in the wider literature. An improved method is presented to account for the effects of the PWR environment on fatigue lives of austenitic stainless steel materials, which has similarities to the “Weighted K Rate” method previously presented by Rolls-Royce, PVP2016-63497, for environmentally assisted fatigue crack growth.
Development of Secondary Stress Weighting Factor and Plastic Reduction Factor From Moment-Rotation Curves of Surface Cracked Pipe Tests
Authors: Pothana S. , Wilkowski G. , Kalyanam S. , Hioe Y. , Hattery G. , Martin J.
Published: October 2017

In flaw evaluation criteria, the secondary stresses (displacement controlled) may have different design limits than primary stresses (load-controlled stress components). The design limits are based on elastic stress analysis. Traditionally the elastic design stresses are used in the flaw evaluation procedures. But realistically a flaw in the piping system can cause non-linear behavior due to the plasticity at the crack plane as well as in the adjacent uncracked-piping material. A Secondary Stress Weighting Factor (SSWF) was established which is the ratio of elastic-plastic moment to the elastic moment calculated through an elastic stress analysis. As long as the remote uncracked pipe stresses are below yield, the SSWF is 1.0, and if the uncracked pipe plastic stresses are above the yield stress, the SSWF reaches a limit which is called the Plastic Reduction Factor (PRF).

Four-point-bend tests were conducted on pipes with varying circumferential surface-crack lengths and depths. The moment-rotation plots obtained from various pipe tests were used in the determination of PRF. A lower-bound limiting PRF can be calculated from a tensile test, but pipe systems are not uniformly loaded like a tensile specimen. The actual PRF value for a cracked pipe was shown to have a lower bound, which occurs when the test section of interest is at a uniform stress (such as the center region in a four-point pipe bend tests). When multiple plastic hinges develop in a pipe system (a “balanced system” by ASME Section III NB-3650 design rules), this gives a greater reduction to the elastically calculated stresses since there is more plasticity. It was found that the plastic reduction is less when most parts of the pipe system remains elastic, or if the crack is located in the high strength/ lower toughness pipe or welds, or if the pipe size is large enough that elastic-plastic conditions occur even for a higher toughness material. Interestingly, it was shown that the same system with different loading directions could exhibit different actual PRF values if the change in the loading direction changes how much of the pipe system experiences plastic stresses. For smaller cracks, where the bending moments are high, the actual PRF is controlled by plasticity of the uncracked pipe, which is much larger than the plasticity that occurs locally at the crack. However, for large cracks where the bending moments are lower (closer to design conditions), the plasticity at the crack is equally important to the smaller amount of plasticity in the uncracked pipe for the actual PRF. Hence the plasticity of both the uncracked pipe and at the cracked sections is important to include in the determination of actual PRF values.
Modeling of Pipe System Behavior With Circumferential Surface Crack for Secondary Stress Margin Assessment
Authors: Uddin M. F. , Brust F. W. , Wilkowski G. M. , Kalyanam S. , Martin J.
Published: October 2017

In flaw evaluation criteria, the design limits for the secondary stresses is frequently different than the primary stresses. The evaluation procedure for primary stresses are load-controlled based which is independent of pipe deformation. The evaluation procedures for secondary stresses are displacement controlled which are dependent on pipe deformation. Certain stress components such as thermal expansion, thermal striping, welding residual stress, misalignment/cold-springing, dynamic anchor motion are historically considered secondary stresses and their design limits are based on elastic stress analysis. In reality, there can be much more rotation/displacement of the pipe with nonlinear fracture behavior due to nonlinear material behavior and plasticity at the crack plane providing extra margins on the elastically calculated rotation values that come from uncracked-pipe design analyses. In assessing secondary stress margin, a secondary stress reduction factor is defined as the ratio of elastic-plastic moment to elastic moment. This is equivalent to another concept using a Plastic Reduction Factor (PRF) as well as the inverse of structural (or safety) factor (SF) in ASME Section XI flaw evaluation criteria for various service levels.

In this work, the secondary stress reduction factor was determined for a representative pipe system with multiple crack sizes, crack locations, and loading conditions. Nonlinear finite element (FE) analyses of a whole uncracked-pipe system were performed using ABAQUS® under various loading combinations to determine the critical locations for cracks in the pipe system. Next, FE analyses of the cracked-pipe system were carried out using cracked-pipe element — a methodology developed by the authors. Cracked-pipe system analyses were conducted for two loading conditions — one producing contained plasticity or single-hinge system and the other producing larger plasticity in the pipe system. Several analyses were conducted for each loading conditions with a combination of two crack sizes at two key locations. Secondary stress reduction factors were then calculated for both loading conditions in the pipe system. Finally, the margin in secondary stress was assessed for the pipe system by comparing the secondary stress reduction factors with that for straight pipe sections (determined for experimental bend tests) as well as with the recommended equivalent PRF and the equivalent ASME secondary stress correction factors.
Welding of Internally Clad X65 Pipes With Precipitation Strengthened Ni-Based Filler Metals
Authors: Penso Graciela C. , Alexandrov Boian T.
Published: October 2017

X65 steel pipes internally clad with Alloy 625 used in subsea oil extraction are normally welded together with Alloy 625 filler metal. For pipe reeling applications, DNV-OS-F101 requires pipe girth welds to overmatch base metal yield strength with 100 MPa. Since Alloy 625 filler metal does not meet this requirement, Ni-base super alloys 718 and 282 were considered as potential welding consumables for reeling applications.

The solidification behavior in weld metal of these alloys diluted with Alloy 625 pipe ID cladding was evaluated using thermodynamic simulations. The response to precipitation hardening by multiple reheat cycles was studied by producing multilayer buildups with cold metal transfer (CMT) and pulsed gas metal arc welding (GMAWp) processes. Weld buildup of Alloy 718 exhibited insufficient hardening response and yield strength, while Alloy 282 met the DNV overmatch requirement. Successful narrow groove welding of X65 pipes with Alloy 282 was performed using CMT process. Welding parameter optimization allowed resolving centerline solidification cracking and lack of fusion defects. The weld metal yield strength was lower than in the multipass buildup, which was attributed to lower number of reheats in groove welding. Meeting the overmatch requirement for yield strength in Alloy 282 groove welds requires further parameter optimization.
Fracture Initiation in Pressure Tube Specimens of Hydrided Irradiated Zr-2.5Nb Materials With Split Circumferential Hydrides
Authors: Sung Shin-Jang , Pan Jwo , Lam Poh-Sang , Scarth Douglas A.
Published: October 2017

Fracture initiation for axial cracks in pressure tube (PT) specimens of hydrided irradiated Zr-2.5Nb materials with split circumferential hydrides at room temperature is examined by conducting three-dimensional finite element analyses. With a strain-based fracture criterion with consideration of stress triaxiality, the location for the earliest crack initiation is determined near the middle of the axial crack front. For PT specimens with split circumferential hydrides, three types of strain concentration are observed in the ligaments ahead of the crack front. The computational results suggest that the internal pressure for crack initiation of hydrided irradiated PT specimens with many randomly distributed split circumferential hydrides needs only 55% to 70% of that for unhydrided irradiated PT specimens. The computational results can be used to explain the near 40% reduction of the fracture toughness at room temperature obtained from hydrided irradiated PT specimens when compared with that from unhydrided irradiated ones.
Bounding Surface Flaw Configuration Susceptible to Stress Corrosion Cracking Under Welding Residual Stress in a Multiple-Purpose Canister
Authors: Lam Poh-Sang , Sindelar Robert L. , Duncan Andrew J. , Carter Joe T.
Published: October 2017

The part-through-wall crack perpendicular to the circumferential weld on the outside surface of a spent nuclear fuel (SNF) multiple-purpose canister (MPC) can be shown to be the most limiting fracture configuration driven by the welding residual stress (WRS). A series of semi-elliptical cracks of various sizes is chosen to calculate the stress intensity factors (K) under a bounding residual stress (i.e., the stress distribution that bounds all WRS in a canister). The threshold stress intensity factor (KISCC) of the canister material in the storage environment is used to determine a critical flaw size, below which the stress corrosion cracking would be unlikely to take place. This result can be considered as the flaw disposition criterion should a surface flaw be detected during the inservice inspection as required by the aging management program (AMP), and can be proposed to American Society of Mechanical Engineers (ASME) Section XI Code Case N-860, “Examination Requirements and Acceptance Standards for Spent Nuclear Fuel Storage and Transportation Containment Systems.”
Acceptance Criterion of Ductile Failure and Plastic Collapse for Safe-Shutdown Earthquakes Using Nonlinear Dynamic Analysis
Authors: Tamura Ichiro , Matsuura Shinichi , Shimazu Ryuya , Kimura Koji
Published: October 2017

We investigated the ductility factors of nonlinear inelastic SDOF systems at Level D Service Limits “using elastic analysis” in ASME BPVC Sec. III, and confirmed that the ductility factor depends on the natural frequencies of the systems, seismic motions and constant loads. Based on the above results, an acceptance criterion of components to prevent ductile failure and plastic collapse is proposed. The criterion is given as a limit of ductility factor for Level D Service Limits “using plastic analysis”. The proposed limit of ductility factor allows single state for nonlinear inelastic systems, and is not depending on the natural frequencies of the systems, seismic motions and constant loads.
Tube Expansion and Hybrid Friction Diffusion Bonding of Cu-Ni and ASTM A516 G70 Tube-to-Tubesheet Joints
Authors: Hbbani Abdulellah , Al-Badour Fadi , Bazoune Abdelaziz
Published: October 2017

Hybrid Friction Diffusion Bonding (HFDB) is a solid-state welding process. The development of HFDB process in achieving quality joints in tube-to-tubesheet heat exchangers is constrained on tube thickness of 1 mm and similarity of tube and tubesheet materials. In nuclear and petrochemical industries, there is significant demand on steel, copper-nickel, and dissimilar shell and tube (tube-tubesheet) heat exchangers. The present study evaluates the feasibility of HFDB on copper-nickel tubes into steel tubesheets with a tube thickness of 1.26 mm. To avoid relative movement of tubes with respect to the tubesheet, tubes are expanded prior to HFDB using commercial roller expander. The effect of tool rotational speed on joint strength and developed macrostructure was investigated employing mechanical pull-out tests to validate safe operation of the joint, and optical microscopy, respectively. Moreover, a comparison between expanded and welded-and-expanded tube-to-tubesheet joints is carried out.
Simulation of Lamb Wave Propagation Using Excitation Potentials
Authors: Faisal Haider Mohammad , Giurgiutiu Victor , Lin Bin , Yu Lingyu
Published: October 2017

Acoustic emission (AE) can be used to measure energy associated with inelastic deformation such as slip, twinning, and microcracking, etc. in a structure. By obtaining AE information during a damage process, the failure indication can be detected. Therefore, better understanding of AE from a damage process is essential for proper damage detection. Elastic waves emission from a damage process due to energy release can be generalized by excitation potentials. There are two types of potentials exists in a plate for straight crested Lamb waves: pressure potential and shear potential. Theoretical formulation showed that due to excitation potentials the elastic waves in a plate followed the Raleigh-Lamb wave equation. The total energy released from damage can be decomposed as pressure potential and shear potential. Each potential has contribution to different wave modes. A numerical simulation was conducted to identify different wave modes due to excitation potentials. Out of plane displacement was calculated numerically on top of the plate at 500 mm distance from excitation point in each of 2mm, 6mm and 12 mm thick stainless steel plate. There were large losses in peak signal amplitude of anti-symmetric fundamental mode (A0) with increasing plate thickness from 2mm to 12 mm.
Relating ASME Flaw Evaluation to ASME Task Group on Carbon Fiber Repairs
Authors: Jimenez Tomas , Houston Eric , Meyer Nico
Published: October 2017

As most nuclear power stations in the US have surpassed their initial 40 years of operability, the industry is now challenged with maintaining safe operations and extending the operating life of structures, systems and components. The US Nuclear Regulatory Commission (NRC), Nuclear Energy Institute (NEI), and Electric Power Research Institute (EPRI) have identified safety related buried piping systems as particularly susceptible to degradation. These systems are required to maintain the structural factors of the ASME Construction Codes under pressure and piping loads, which includes seismic wave passage. This paper focuses on evaluation approaches for metallic buried piping that can be used to demonstrate that localized thinning meets the requirements of the Construction Code. The paper then addresses a non-metallic repair option using carbon fiber reinforced polymers (CFRP) as the new pressure boundary.
Internal Repair of Buried Pipes With CFRP Composites
Authors: Ojdrovic Rasko , Pridmore Anna
Published: October 2017

A design framework for internal repair of buried pressure pipes was recently proposed and is under development by AWWA and ASME committees. This paper discusses the design approach and quality control procedures prior to, during, and after CFRP liner installation in buried pressure pipes. We discuss the importance of and the requirements for prequalification of materials and installers, onsite verification of quality of construction prior to commencement of repairs, inspection procedures during construction, and post-installation inspection and testing of installed CFRP.
Comparison Between Test and Analysis for Spent Nuclear Fuel Transportation Cask
Authors: Choi Woo-Seok , Cho Sangsoon , Seo Ki-Seog , Bang Kyoung-Sik , Lee Ju-Chan , Yu Seunghwan
Published: October 2017

The storage and transport system are being developed in Korea. The spent fuels stored temporarily in wet storage at reactor site are scheduled to be transported to the interim storage in near term in Korea. To prepare the spent fuel transportation and storage, the dual purpose cask and concrete cask have been developed and submitted for the license approval.

Safety evaluation test was conducted with 1/3 scaled model and so was analysis. Since numerical simulation results can be different based on the analysis models, the reliable FE model was generated through several revising process. The comparison between simulation and test was conducted by numerical simulation using this FE model.

The reliable FE model made it possible to be proceeded stably by analysis and generated more realistic results compared to those of test. By the comparison between analysis and test results, the validity and appropriateness of the modeling technique and analysis methodology were verified.
A Historical Review and Additions to SIFs and Stress Indices for Trunnion Elbows
Authors: Williams Dennis K. , Nargund Shrikant
Published: October 2017

The development of primary and secondary moment loading stress indices and analytical derivations of stress intensification factors (SIF) has matured over the past 35 years. The original development work for the ASME piping Codes SIF definitions was empirically derived well over 65 years ago and still, debates linger over the equivalence of the physical fatigue testing of piping fittings and the rapid evolution of stress classification techniques as applied specifically, to the finite element method. The trunnion elbow geometry has always presented significant mathematical challenges in the determination of stress intensification factors, which is primarily due to the complexity of the intersection created by a right circular cylinder (forming the trunnion) to a toroid (forming the elbow). This paper traces the maturation of the SIF definition for the trunnion-elbow geometry from the original roots of the Markl tests, to the early analytical formulations presented by Williams and Lewis, to the WRC and EPRI results published in the late 1990s, through today’s rendition as contained in the Appendices to the ASME B&PV Code, Section III. In addition, geometry combinations are introduced herein that have not been covered in any of the previously referenced publications. Finally, a comparison of the various formulations is tendered for consideration of the reader to determine if in fact there has been significant progress in this subject area since the early analytical work published by Williams and Lewis in the early 1980s.
Closed-Form Stress Intensity Factor Solutions for Deep Surface Cracks in Plates
Authors: Azuma Kisaburo , Li Yinsheng , Hasegawa Kunio , Xu Steven
Published: October 2017

Materials made of Alloy 82/182/600 used in light-water reactors are known to be susceptible to stress corrosion cracking. It is known that the depth a of some cracks due to primary water stress corrosion cracking is larger than the half-length c. The stress intensity factor solution for cracks plays an important role to predict crack propagation and failure. However, Section XI of the ASME Boiler and Pressure Vessel Code does not provide the solutions for cracks with large aspect ratios a/c.

In this study, closed-form stress intensity factor influence coefficients for deep surface cracks in plates are discussed. The crack tip stress distribution is represented by a fourth degree polynomial equation. Influence coefficient tables obtained by using finite element analysis in previous studies are used for curve fitting. The closed-form solutions for the coefficient were developed at the surface points and the deepest points of the cracks with aspect ratio a/c ranged from 1.0 to 8.0. The solutions for the points where the stress intensity factor reaches maximum were also investigated.
Validation of the Proposed R6 Method for Assessing Non-Sharp Defects
Authors: Horn Anthony J. , Cicero Sergio , Bannister Adam , Budden Peter J.
Published: October 2017

Structural integrity assessment codes such as R6 [1] and BS7910 [2] provide guidance on the assessment of flaws that are assumed to be infinitely sharp using the Failure Assessment Diagram (FAD). In many cases, such as fatigue cracks, this assumption is appropriate, however it can be pessimistic for flaws that do not have sharp tips such as lack of fusion, porosity or mechanical damage. Several Notch Failure Assessment Diagram (NFAD) methods have been proposed in the literature to quantify the additional margins that may be present for non-sharp defects compared to the margins that would be calculated if the defect were assumed to be a sharp crack. This paper presents the second stage of validation work, using 3D Finite Element (FE) Analyses and a wide range of test data on non-sharp defects, to validate an NFAD method proposed for inclusion in R6 and to quantify the errors caused by various approximations in the method.
Finite Element Analysis of the Effect of Mechanical Stress Improvement Process on Weld Residual Stress and Flaw Growth in a Thick-Walled Pressurizer Safety Nozzle
Authors: Facco Giovanni G. , Raynaud Patrick A. C. , Benson Michael L.
Published: October 2017

The Mechanical Stress Improvement Process (MSIP) is generally accepted as an effective method to modify the residual stress field in a given component to mitigate subcritical crack growth in susceptible components [1] [2] [3]. In order to properly utilize MSIP, residual stress prediction is needed to determine the parameters of the MSIP application and the expected final residual stress field in the component afterwards. This paper presents the results of a 2D axisymmetric finite element study to predict weld residual stresses (WRS), and associated flaw growth scenarios, in a thick-walled pressurizer safety nozzle that underwent mitigation by application of MSIP. The authors have developed a finite-element analysis methodology to examine the effect of MSIP application on WRS and flaw growth for various hypothetical welding histories and boundary conditions in a thick-walled pressurizer safety nozzle. In doing so, a wide range of repair scenarios was considered, with the understanding that some bounding scenarios may be impractical for this geometry.
Crack Growth Rate Testing With Instrumented Bolt-Load Compact Tension Specimens Under Chloride-Induced Stress Corrosion Cracking Conditions in Spent Nuclear Fuel Canisters
Authors: Duncan Andrew J. , Lam Poh-Sang , Sindelar Robert L. , Carter Joe T.
Published: October 2017

Stress corrosion cracking (SCC) may occur when chloride-bearing salts and/or dust deliquesce on the external surface of the spent nuclear fuel (SNF) canister at weld residual stress regions. An SCC growth rate test is developed using instrumented bolt-load compact tension specimens using the American Society for Testing Materials (ASTM) specification E1681 with an experimental apparatus that allows an initially dried salt to deliquesce and infuse naturally to the crack front under temperature and humidity parameters relevant to the canister storage environmental conditions. The shakedown tests were conducted over a range of relative humidity controlled by the guidance in ASTM E104 at 50 °C with salt assemblages of (1) mixture of artificial dust and deliquescent salts (2) a mixture of artificial dust and salt from dehydrated sea water. After five months exposure the specimens were examined for evidence of chloride induced stress corrosion cracking (CISCC) and observations are reported for both salt/dust mixtures. The test specimen and apparatus designs will be modified to enhance the interaction between the deliquescing salt and the crack front for more accurate characterization of the crack growth rate as a function of stress intensity factor, which is an essential input to the determination of in-service inspection frequency of SNF canisters.
Jagged Cracking in the Heat-Affected Zone of Weld Overlay on Coke Drum Cladding
Authors: Wang Yiyu , Kannan Rangasayee , Li Leijun , Suzuk Yasin , Ting Darren , Yuen Simon , Garcia Maria Marilin
Published: October 2017

Jagged cracks were observed in SA240 Type 405 stainless steel cladding of Inconel 625 overlay repaired coke drums. It is found that intergranular cracking is the dominant fracture mode in the fine-grained heat-affected zone (FGHAZ) of the boat specimens. The sensitization effect from the operation and welding thermal cycles leads to the depletion of Cr with the preferential precipitation of Cr-rich M23C6 carbides along the grain boundaries. The cladding FGHAZ has the largest frequency of grain boundaries with higher local strain levels and the highest fraction of grain boundary Cr-rich M23C6 carbides. Thermal stress distributions predicted by finite element analysis clearly show the maximum shear stress to exhibit the typical “jagged” pattern near the cracked regions. Thermal expansion coefficient and strength mismatch among the shell base metal, cladding, and overlay is believed to have caused the unique jagged maximum shear stress distribution in the cladding HAZ of Inconel 625 overlay. The magnitude of this thermal stress can reach the yield strength of the cladding at 900 °F (482 °C) service temperature, therefore, provides the driving force for the jagged cracking formation in the sensitized HAZ.
Application of Flexible Ultrasonic Phased Array Technique on Detection of Fillet Welds in Small-Diameter Pipe Holder
Authors: Guo Weican , Miao Cunjian , Du Xingji , Wang Min , Xia Junfang
Published: October 2017

Fillet welds in small-diameter pipe socket of pressure vessels always have complicated structures and groove types, which make it easy to produce porosity, lack of fusion, incomplete penetration and other flaws during welding. Therefore, nondestructive testing is a significant and meaningful approach to ensure the quality of welding for pressure vessels’ safety. Ultrasonic testing is the main method for nondestructive testing of pipe fillet welds. However, it is difficult to distinguish between the interference wave and the flaw echo, or to recognize the defect signal, while utilizing conventional ultrasonic testing technology. Additionally, the coupling effect is bad for traditional rigid probe on the concave surface when the probe is inserted into the small-diameter pipe to do the inner scanning. To obtain a good coupling effect, flexible phased array technology was put forward, with a bendable probe made from flexible materials. The probe could be bent and inserted into the inner pipe for longitudinal wave scanning, giving a good matching with the inner wall and replacing the traditional rigid probe. Besides, it is more convenient to conduct the ultrasonic testing, and the focal law could be changed easily according to the curve shape of the inner pipe, without replacing the probe. Thus, scanning and dynamic focusing in multiple angles and directions can be carried out, and the position, distribution and size of the flaws could be displayed intuitively combined with real-time imaging technology. This technology is able to obtain better coupling and detecting effects and solve the technical problem for concave ultrasonic inspection of fillet welds.
Application of CFRP for Steel Pipeline Upgrades at Surry Power Station
Authors: Sealey Janean , Gordon Lars , Ojdrovic Rasko , Pridmore Anna
Published: October 2017

The Surry Power Station completed a proactive upgrade of 96-inch, 42-inch and 30-inch steel pipelines in circulating and service water systems using a structural upgrade approach with internally applied carbon fiber-reinforced polymer (CFRP) composites. This paper provides an overview of the two-year project from options analysis and pre-planning to completion of the CFRP lining. This will include the discussion of the process Surry Power Station used for options analysis, technical vetting of the repair solutions, procurement method and award criteria. The project implementation discussion will include: (i) Design approach for stand-alone carbon fiber upgrade of steel pipelines; (ii) Extensive pre-planning and contingency planning process; (iii) Success strategies for challenge meetings on pipeline repair projects; (iv) Effective safety programs; (v) quality control programs; and (vi) Step-by-step view of the carbon fiber installation. The installation portion of the paper will include a discussion of challenges encountered and overcome during construction, along with lessons learned which are being applied for future similar projects.
Research on Weight-Reduced Optimization Design of Large Nuclear Power Low Pressure Cylinder
Authors: Hu Yifeng , Ye Xingzhu , Chen Gang
Published: October 2017

Steam turbines need to be safer and more reliable when used in nuclear power plants. In order to ensure long-term reliability of nuclear power equipment, a high safety factor is usually adopted in the design of low-pressure (LP) inner casing of steam turbines. It not only leads to larger self-weight of LP outer casings and fundamental load, but also causes higher manufacturing and transportation costs. In this paper, the stress and deformation behaviors of the LP outer casings of steam turbines are first evaluated using the numerical finite element analysis. Then, two optimization design methods, size optimization and topology optimization are used to conduct the weight reduced optimization design of inner casing, in combination with the design standards, so that the structural efficiency and performance of LP inner casings are achieved. At the same time, the self-weight and related costs are also greatly reduced. This study proposes a more optimized structural design of LP inner casings of steam turbines, and it offers considerable economic benefits.
Development of a Partial Structural Factor Approach for Direct Fracture Toughness Implementation Into the ASME Boiler and Pressure Vessel Code
Authors: Erickson Marjorie , Kirk Mark
Published: October 2017

Direct implementation of best estimate fracture toughness models is a growing priority to enable an accurate assessment of the fracture safety of nuclear pressure boundary components for extended licensing periods. Models currently adopted for use in ASME Section XI of the Boiler and Pressure Vessel Code are based in linear elastic fracture mechanics methodologies developed 40 or more years ago at a time when drop weight tear tests and Charpy V-notch impact tests were the accepted standards used for characterizing a material’s resistance to brittle fracture. The current ASME guidance uses:

• a conservatively estimated RTNDT reference temperature,

• to index the linear elastic, lower-bound KIc curve that describes a material’s resistance to fracture, and

• then divides this lower-bound curve by a structural factor.

This approach includes multiple implicit and explicit treatments of uncertainty. It is not transparent, it produces inconsistent levels of conservatism, and it makes it difficult to incorporate improved knowledge, obtained from either new data or new models, into a flaw evaluation.

Code Case N830-R1 proposes use of a suite of best-estimate models to describe the temperature dependence and scatter of fracture toughness from lower shelf through upper shelf. CC-N830-R1 proposes that the 5th percentile lower bound of these models be used in flaw evaluations along with the current IWB 3611 and 3612 requirements that includes division of this 5th percentile curve by a structural factor. The intent in the next revision of this Code Case (Revision 2) is to move away from these current methods that inconsistently, and in some cases multiply, treat uncertainties.

Uncertainty treatment that relies on combinations of lower bound models, structural factors that do not consistently bound data, and margins needlessly complicate and confuse the characterization of material toughness and make it nearly impossible to assess the true level of safety. CC N830-R2 will therefore propose the use of a partial structural factor (PSF) approach. PSFs will be assigned to each of the key terms (i.e., toughness, stress, flaw size) in the fracture mechanics equations used in assessing safety of flaws. The value of each PSF will be defined to account for the uncertainty contribution of that term in a consistent manner. Partial safety factors have been successfully adopted by other codes and standards as will be further described in this paper, along with a proposed approach for defining partial safety factors for use with the CC N830-R1 models.
Spent Fuel Canister Probabilistic Confinement Integrity Assessment
Authors: Broussard John E. , Chu Shannon , Fuhr Kevin
Published: October 2017

A probabilistic model was developed that considers the likelihood of through-wall penetration of chloride-induced stress corrosion cracking (CISCC) in austenitic stainless steel canisters and compares different population-based sample inspection regimes. This paper describes the inputs and methods used to simulate multiple canisters with a range of susceptibilities. This paper also summarizes results of key illustrative cases.
Experimental Damping of a Heat Exchange Tube With a Large Number of Supports in Air and Water
Authors: Park Tae-Jung , Ha Chang-Hoon , Cho Min-Ki , Kang Heung Seok , Lee Kang Hee
Published: October 2017

The flow induced vibration occurs frequently in a steam generator in the nuclear power plant. The large-scale steam generator has a large number of tube supports whose cell has rhombus-type shape, and there is a tiny clearance between tube and its support grid. The damping is very complex because of non-linearity and randomness.

The experiment for damping was performed to investigate it with a number of 13 support spans both in air and water environment. The lower part of multi-span fixture was excited by root-mean-square random force with the range of 1∼10 newton to get the frequency response function. The half-power bandwidth method was applied to obtain the damping ratio. The sensitivity of a number of spans was investigated in the range of 9 ∼ 13. In addition, the damping was reviewed from a comparison with Pettigrew [1∼4] and ASME B&PV Code [5].
Laminated Type Isolation Device for Light Weight Structure Using Urethane Elastomer
Authors: Goda Kengo , Furuya Osamu , Imamura Kohei , Ishihana Kenta
Published: October 2017

At the present, base isolation system has been recognized by general earthquake resistant technique since the Great Hanshin Earthquake 1995. The seismic isolation will be aggressively applied to not only architectural and civil structures but also various structures, because the effectiveness on seismic safety had been demonstrated again in the Great East Japan Earthquake. In generally, although the base isolation system is divided into laminated rubber bearing type and friction sliding bearing type. In the case of former type, shape factor, maximum or minimum outer shapes and so on are restricted by the material characteristics in visco-elastic material. In general, the isolation structure is used in high damping rubber. However, we pay attention to base isolation using urethane elastomer. Urethane elastomer has excellent elasticity, mechanical strength, abrasion resistance, weather resistance, oil resistance, impact resistance the absorbent, anti-vibration and excellent low-temperature properties. Furthermore, it is possible to impart various characteristics by a combination of isocyanate and polyol and chain extender, requires no large-scale apparatus, it has the advantage molecular design is easy.

In previous study, the research and development of laminated type base isolation device using urethane elastomer was carried out to upgrade a seismic safety for various structures. The fundamental characteristics was investigated from several loading test by using various experimental devices, and the design formula for the stiffness and equivalent damping coefficient is formulated as an approximate expression of mechanical characteristics until now. It was confirmed that urethane elastomer is not hardening up to 500% shear strain. Moreover, the experimental examination for aged deterioration in the urethane material has been continuously carried out. As the results, it was confirmed that the laminated type seismic isolation device using urethane elastomer is possible to develop as a practicable device from the stable mechanical properties as considering in design step.

In this study, the small-scale laminated type base isolation device using urethane elastomer is advanced to the direction of further technical upgrading and of scale down for light-weight structure as a sever rack. The first stage, basic properties of the urethane elastomer has been investigated by loading test. Furthermore, the design equation is created by loading test using urethane elastomer. The validity of the design equation has been confirmed. The second stage, the compression creep test with laminated type base isolation device has been investigated to confirm an effect on light-weight mechanical devices.
Fracture Tests of Flat Plate and Pipe With Non-Aligned Multiple Flaws
Authors: Iwamatsu Fuminori , Miyazaki Katsumasa , Saito Koichi
Published: October 2017

Fracture tests of flat plates and pipes with non-aligned multiple flaws were conducted to investigate an appropriate flaw characterization rule for ductile fracture evaluation. Worldwide fitness-for-service codes, such as the JSME Code and the ASME Boiler and Pressure Vessels Code provide flaw characterization rules for flaws detected by in-service inspection. Since the flaw characterization rules seems to be determined based on linear-elastic fracture mechanics, developing appropriate rules remains a ductile fracture evaluation issue. Although experimental approaches have been attempted to establish an evaluation method for ductile fractures of non-aligned multiple flaws, further efforts are required. Hence, this study deals with expanding the experimental data of a flat plate subjected to tensile load and a pipe subjected to bending load. Each specimen was given one, two, or three through-wall flaws by electrical discharge machining. The tensile tests of flat plate specimens and the 4-point bending tests of pipe specimens were conducted to observe the collapse behavior and obtain load-displacement relationships. Flaw interactions, which depend on the distances between two flaws, were observed from the test results. The experimental data to investigate an evaluation method were expanded by performing fracture tests on the flat plate and pipe specimens.
Load and Resistance Factor Design of Dual Criterion Against Gross Plastic Deformation and Collapse
Authors: Duan Cheng-Hong , Li Xing-Xu , Sun Yu , Lu Ming-Wan
Published: October 2017

ASME VIII-2 code [1] and EN 13445 standard [2] give the design criterion against plastic collapse and gross plastic deformation respectively. Duan et al. [3] propose a new criterion combining the advantages of both. This paper introduces two characteristics of the new criterion, and points out that it is a dual criterion against gross plastic deformation and collapse. The Load and Resistance Factor Design form of the new criterion and an application example are given.