bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Pressure-Temperature Limits for a Pressurized Water Reactor Pressure Vessel Considering Beltline and Extended Beltline Regions
Authors: Chou Hsoung-Wei , Shen Yu-Yu , Huang Chin-Cheng
Published: October 2018

To ensure the structural integrity of the embrittled reactor pressure vessels (RPVs) during startup or shutdown operation, the pressure-temperature (P-T) limits are mainly determined by the fracture toughness of beltline region material with the highest level of neutron embrittlement. However, other vessel parts such as nozzles with structural discontinuities may affect the limits due to the higher stress concentration, even though the neutron embrittlement is insignificant. Therefore, not only beltline material with the highest reference temperature, but also other components with structural discontinuities have to be considered for the development of P-T limits of RPV. In the paper, the pressure-temperature operational limits of a Taiwan domestic pressurized water reactor (PWR) pressure vessel considering beltline and extended beltline regions are established per the procedure of ASME Code Section XI-Appendix G. The three-dimensional finite element models of PWR inlet and outlet nozzles above the beltline region are also built to analyze the pressure and thermal stress distributions for P-T limits calculation. The analysis results indicate that the cool-down P-T limit of the domestic PWR vessel is still dominated by the beltline region, but the heat-up limit is partially controlled by the extended beltline region. On the other hand, the relations of reference temperature between nozzles and beltline region on the P-T limits are also discussed. Present work could be a reference for the regulatory body and is also helpful for safe operation of PWRs in Taiwan.
Numerical Study of Orifice Cavitation-Induced Instability and Pipe Vibration
Authors: Bai Wenjie , Duan Quan , Tijsseling Arris S.
Published: October 2018

Different kinds of orifice are widely used as a resistance element to reduce pressure in various piping systems. However, due to strong shear and turbulence mechanisms around the orifice, it is susceptible to instabilities that generate pressure fluctuations and pipe vibrations. Especially when cavitation occurs, this effect can be very strong. The present work tries to characterize orifice-induced instability by means of numerical simulations and assess pipe vibration levels. Firstly, by taking an elongated orifice as an example, the fluctuating pressure around the orifice is obtained by a Large Eddy Simulation with a 2D unsteady model of cavitation. Secondly, the pipe vibration response is studied with experiment. The variation trends of pressure fluctuation and pipe vibration are analysed under different operation conditions. The results of the simulations can provide a good explanation for pipe vibration. A relationship between orifice cavitation-induced instability and vibration is established based on numerical simulations and experimental results.
A Designer-Driven Welding Simulation Analysis to Define the Best Weld Sequence for Panel Structures
Authors: Asadi Mahyar , Tanbakuei Kashani Majid , Mohseni Mohammad , Smith Mathew
Published: October 2018

Distortion is a common problem in welded panel structures, historically techniques to mitigate this problem have been developed empirically. A usual approach involves defining an intermittent weld sequence, a process that is extremely difficult to optimize given the large number of possible combinations i.e. hundreds or even thousands for multi-pass welds. Typically, plans to control weld distortion are therefore largely intuitive with welding engineers relying on their experience combined with the results of a limited number of practical tests. However, with modern computing, welding engineers can now include all the physics of welding in a simulation allowing them to cheaply and efficiently optimize a welding sequence without the need for multiple physical samples. The final welding procedure is then physically qualified based on the simulation results. In this paper, the authors present their use of computer modeling to automate the implementation of welding patterns to minimize distortion in panel lines. We describe a signature technique based on the Joint Rigidity Method where a combinatorial algorithm optimizes the welding sequence based on the panel’s resistance to angular bending i.e. the welding sequence starts at the point in the panel with the highest rigidity and moves progressively toward the lowest rigidity thereby minimizing distortion. This enables the designer to carry out an optimization of this complex weld design without relying on empirical observations.
SCC Propagation Analyses in a Welded Joint Under Various Assumed Residual Stresses and Anisotropic SCC Propagation Law
Authors: Okada Hiroshi , Kikuchi Manabu , Ono Masahiro , Yusa Yasunori , Kamaya Masayuki
Published: October 2018

In this paper, the results of evaluations of the stress intensity factor and of natural SCC (stress corrosion cracking) growth simulations under weld residual stresses are presented. The results reveal some characteristic SCC propagation behaviors. A surface crack is assumed at the welded joint of a mock-up of a pressurized water reactor (PWR) pressurizer nozzle. SCC propagation law for the weld metal is assumed to be anisotropic. SCC propagation in the surface direction is assumed to be 10 times slower than that in the thickness direction of the welded joint. The anisotropy is caused by different solidification rates of the weld metal in these directions. The material in terms of mechanical properties is set to be homogeneous as differences in the Young’s moduli and the Poisson’s ratios are not large between the weld and the mother metal. The analytical procedures based on the finite element method with an automatic mesh generation scheme for cracked structures, the results of analyses under a various residual stress distributions and some discussions are presented in this paper.
Formulation of Three-Dimensional J-Integral for Finite Strain Elastic-Plastic Fracture Problems Under Any Load Histories (Monotonic and Cyclic Loads)
Authors: Arai Koichiro , Okada Hiroshi , Yusa Yasunori
Published: October 2018

In this paper, a redefined three-dimensional J-integral for the quadratic tetrahedral element along with some numerical examples are presented. It is known that the J-integral represents the energy release rate and can be computed on an arbitrary path or a domain of integration. This feature is called the “path-independent property”. It requires the assumption of proportional loading in the case of elastic-plastic material. Because of this assumption, when the J-integral is applied to a problem under a non-proportional loading condition, the computed J-integral value depends on the integral path or the integral domain.

To overcome this problem, the authors have proposed a formula to evaluate the energy dissipation inside a finite domain in the vicinity of the crack front, which is an extension of the conventional three-dimensional J-integral. The energy dissipating into a small but finite domain in the vicinity of crack front includes the energy released due to the opening of new crack faces and the deformation energy in the process zone. The numerical evaluation is carried out by the domain integral. In this formula, it is not necessary to evaluate any non-integrable terms at the crack front. Furthermore, the proposed formula has the feature of integral domain independence for any material models without any assumptions in their deformation histories. Therefore, it is possible to evaluate the J-integral for problems with non-proportional loads by using the proposed method.

In this paper, computational method using the quadratic tetrahedral element for the redefined J-integral under non-proportional loading is presented first. Some results of three-dimensional semi-circular surface crack problem are presented as numerical examples.
Blind Prediction of the Response of an Additively Manufactured Tensile Test Coupon Loaded to Failure
Authors: Gilkey Lindsay N. , Bignell John L. , Dingreville Remi , Sanborn Scott E. , Jones Chris A.
Published: October 2018

Sandia National Laboratories (SNL) conducted in the summer of 2017 its third fracture challenge (i.e., the Third Sandia Fracture Challenge or SFC3). The challenge, which was open to the public, asked participants to predict, without foreknowledge of the outcome, the fracture response predictions of an additively manufactured tensile test coupon of moderate geometric complexity when loaded to failure. This paper outlines the approach taken by our team, one of the SNL teams that participated in the challenge, to make a prediction. To do so, we employed a traditional finite element approach coupled with a continuum damage mechanics constitutive model. Constitutive model parameters were determined through a calibration process of the model response with the provided longitudinal and transverse tensile test coupon data. Comparison of model predictions with the challenge coupon test results are presented and general observations gleaned from the exercise are provided.
Importance of Accounting for Finite Particle Size in CFD-Based Erosion Prediction
Authors: Messa Gianandrea Vittorio , Wang Yongbo
Published: October 2018

Being capable in predicting the removal of material from a surface subjected to the impingements of solid particles within a carrier liquid is of considerable industrial interest. This phenomenon, called impact erosion, is of concern in many applications due to its severe technical and economic consequences. The use of Computational Fluid Dynamics (CFD) techniques for impact erosion prediction is a challenging approach to avoid the cost and complexity of laboratory testing. A well-established methodology exists for CFD-based erosion estimation, consisting in the simulation of the slurry flow by an Eulerian–Lagrangian two-phase model followed by the application of an empirical erosion correlation to estimate the loss of material produced by each particle-wall impact. One of the main assumptions of this approach is that the solids are treated as massive point particles, even if, from a theoretical point of view, this approximation may be too simplistic, as it requires the particle size to be infinitesimal. The objective of the present study was, primarily, to assess how the point–particle treatment of the dispersed phase may affect the accuracy of CFD-based erosion prediction models. Based on these findings, numerical strategies were proposed in order to correct for the induced error without the need of resorting to a fully-resolved description of the slurry flow, which would not be affordable in practical applications due to its excessive computational burden. As a first step, reference was made to the benchmark case of slurry abrasive jet impingement test. The obtained results will open the way for addressing more complex flows in future research.
Negative R Fatigue Crack Growth Rate Testing on Austenitic Stainless Steel in Air and Simulated Primary Water Environments
Authors: Platts Norman , Coult Ben , Zhang Wenzhong , Gill Peter
Published: October 2018

Light water reactor coolant environments are known to significantly enhance the fatigue crack growth rate of austenitic stainless steels. However, most available data in these high temperature pressurized water environments have been derived using specimens tested at positive load ratios, whilst most plant transients involve significant compressive as well as tensile stresses. The extent to which the compressive loading impacts on the environmental enhancement of fatigue crack growth, and, more importantly, on the processes leading to retardation of those enhanced rates is therefore unclear, potentially leading to excessive conservatism in current assessment methodologies.

A test methodology using corner cracked tensile specimens, and based on finite element analysis of the specimens to generate effective stress intensity factors, Keff, for specimens loaded in fully reverse loading has been previously presented. The current paper further develops this approach, enabling it to be utilized to study a range of positive and negative load ratios from R = −2 to R = 0.5 loading, and provides a greater understanding of the development of stress intensity factor within a loading cycle.

Test data has been generated in both air and high temperature water environments over a range of loading ratios. Comparison of these data to material specific crack growth data from conventional compact tension specimens and environmental crack growth laws (such as Code Case N-809) enables the impact of crack closure on the effective stress intensity factor to be assessed in both air and water environments. The significance of indicated differences in the apparent level of closure between air and water environments is discussed in the light of accepted growth laws and material specific data.
Evaluation of Stress Corrosion Crack Growth in Low Alloy Steel Vessel Materials in the BWR Environment
Authors: Ranganath Sampath , Carter Robert G. , Pathania Rajeshwar , Ritter Stefan , Seifert Hans-Peter
Published: October 2018

Low alloy steels (LAS) used in the fabrication of reactor pressure vessel (RPV) and nozzles have been resistant to stress corrosion cracking (SCC) in the Boiling Water Reactor (BWR) environment. The plate material is SA533 Grade B and the nozzle material is SA508 Class 2 for most operating BWRs. While BWR service field experience with the LAS materials has been very good for there have been a limited number of SCC incidents where cracking has been reported especially in Alloy 182 RPV attachment (dissimilar metal) welds. This paper describes the methodology for the assessment of SCC crack growth rate (CGR) of LAS RPV components in the BWR environment. Specifically, it describes the development of CGR disposition lines (also called reference crack growth rate curves) for normal water chemistry (NWC) and hydrogen water chemistry (HWC) in BWR environments. In addition, based on more recent data from tests on the effect of chloride transients in NWC environments are also proposed.
Creep Analysis for Pressurized Components Under Creep Conditions Based on Isochronous Stress-Strain Curve and Elastic-Perfectly Plastic Material Model
Authors: Xia Qi-Wei , Gong Jian-Guo , Xuan Fu-Zhen
Published: October 2018

This work is to address the creep analysis for components at elevated temperatures based on isochronous stress-strain curve and the elastic-perfectly plastic material model through numerical analyses. Numerical results presented that the creep deformation is very sensitive to the target inelastic strain chosen for analysis. A small inelastic strain, corresponding to a small yield stress, can cause very conservative result for the case studied. Moreover, the target inelastic strain, corresponding to the minimum inelastic strain along with the given path, is different from each other for various internal pressures.
Influence of W in Solid Solution on the Creep Rate of Nickel
Authors: Zhang Jing , Sandström Rolf
Published: October 2018

Ni and Ni-W binary alloys are basis for nickel based superalloys. For most nickel based superalloys, strengthening mechanisms include both solid solution hardening and precipitation hardening. W is a vital element to create solid solution hardening and to improve the creep strength. In spite of its wide usage to strengthening of high temperature alloys, the mechanisms for solid solution hardening are not fully quantified. From the assumption that it is due to the attraction of solute atoms to dislocations and formation of Cottrell atmosphere to slow down the motion of dislocations, a fundamental model has been formulated previously. In the present paper, the model is expanded by taking the stacking fault energy and strain induced vacancies into account. Important parameters in the model are the variation of the lattice constant and the shear modulus with alloying content. Models for these variations have been formulated as a function of solute content. Another important parameter is the maximum interaction energy between the dislocations and the solutes. The model can satisfactorily predict both the large difference in creep rate between pure Ni and Ni-W alloys and the comparatively smaller differences between the three investigated Ni-2W, Ni-4W and Ni-6W alloys.
Comparison Between the ASME BPVC Section VIII Division 3 and the Chinese Regulation TSG 21-2016 With Regard to the Design of High Pressure Vessels
Authors: Fuenmayor David , Wink Rolf , Bortz Matthias
Published: October 2018

There are numerous codes covering the design, manufacturing, inspection, testing, and operation of pressure vessels. These national or international codes aim at providing assurance regarding the safety and quality of pressure vessels.

The development of the Chinese economy has led to a significant increase in the number of installed high-pressure vessels which in turn required a revision of the existing regulations.

The Supervision Regulation on Safety Technology for Stationary Pressure Vessel TSG 21-2016 superseded the existing Super-High Pressure Vessel Safety and Technical Supervision Regulation TSG R0002-2005 in October of 2016.

This new regulation covers, among others, the design, construction, and inspection of pressure vessels with design pressures above 100 MPa. This paper provides a technical comparison between the provisions given in TSG 21-2016 for super-high pressure vessels and the requirements in ASME Boiler and Pressure Vessel Code Section VIII Division 3.
Effect of Heat Treatment on the Properties of Additively Manufactured Type 316L Stainless Steel
Authors: Korinko Paul S. , Morgan Michael J.
Published: October 2018

Thin wall test articles were made using Fusion Powder Bed processing of Type 316L stainless steel. This hollow structure was fabricated using a Renishaw AM250. The material was characterized in the as fabricated condition using optical, scanning electron microscopy, and tensile testing. The tensile behavior indicates high initial residual stress due to the higher than annealed material yield strength. A series of thermal treatments were investigated to determine the effect on mechanical properties and microstructural evolution. In order to determine these effects, miniature flat tensile test samples and metallographic samples were wire electrical discharge machined from the structure. These samples were vacuum heat treated at 870, 1040 and 1080°C for 30 to 120 minutes and metallographically examined to determine the microstructural evolution. The samples were tensile tested and the data are evaluated based on the power-law type relationships. AM Type 316L SS exhibits less strain hardening than wrought stainless steel. In addition, the ductility is somewhat lower in the as-fabricated condition compared to the heat-treated condition. The results of the testing and the rationale for these different behaviors will be discussed.
Numerical Simulation on Flow Induced Vibration and Fretting Wear of a Steam Generator
Authors: Tan Wei , Guo Kai , Fan Xiantao , Wang Yipeng , Zhu Guorui , Liu Liyan
Published: October 2018

The steam generator (SG) is a key component in the PWR nuclear power plant. U-shaped tube bundles are subjected to cross flow in inlet and bend sections. According to the design standards of steam generators, short-term flow induced vibration (FIV) damage could be avoided, but wear and corrosion of tubes still exists. Both fluid and structure parameters are needed in FIV analysis. As direct modeling of SG flow field is almost infeasible, the porous medium model has been widely used instead. Using porous medium model can only obtain the gap velocity approximately by mathematical methods with many other unclear parameters. A combination method of direct modeling and porous medium model was established in this research. The direct modeling section could give the details of fluid forces and the accurate gap velocity. Using the fluid forces, explicit dynamic analyses of tube with supports were carried out to get FIV response and contact forces. In this paper, a typical SG model was studied in designed experimental conditions, and the results were compared with published literatures. The results demonstrate that the numerical simulation along with the combination model and explicit dynamic analysis can provide new methods into the flow-induced vibration and fretting wear of multi-span U-tubes which can be applied into future design for steam generators and other heat exchangers with large size.
Mode I Ductile Crack Growth of 1TCT Specimen Under Large Cyclic Loading: Part II
Authors: Hojo Kiminobu , Kawabata Shinichi , Ogawa Naoki
Published: October 2018

The ductile crack growth calculation method under excessive cyclic loading has not been established in the rules for fitness for service, even for Mode I. On the paper for the PVP2017 conference, the authors simulated ductile crack growth behavior of CT specimens under cyclic loading within a committee of the Japan Welding Society, and showed that the Chaboche model and bilinear kinetic hardening rules underestimated the load in compression. The discrepancy between the prediction results and the experimental results were also shown to become larger with increasing load cycle number. In this paper, the authors tried to establish how to determine the parameters of the combined hardening rule and then applied it to simulate the ductile crack growth behavior of the 1TCT specimens for loading levels different from that of last year. Also, the simplified ΔJ calculation, for example the reference stress method, and the crack growth rate from the JSME rules for FFS were applied to estimate the ductile crack growth. Based on this approach, the crack growth analysis method was investigated in order to incorporate into the JSME rules for large cyclic loading.
Fracture Analysis of Ductile-Brittle Transition Temperature Region Considering Specimens With Different Constraints
Authors: Hojo Kiminobu , Hirota Takatoshi , Ogawa Naoki , Yoshimoto Kentaro , Nagoshi Yasuto , Kawabata Shinichi
Published: October 2018

Fracture toughness from a CT specimen is used as a material constant for fracture evaluation, but it has a large constraint, which provides too conservative evaluation results. In ductile to brittle transition temperature (DBTT) region ferritic steel which is material of RPV has a large scatter and it becomes important to know the accurate scatter of an irradiated material because of less margin of RPV’s integrity after a long term operation. In this paper to establish a more precise fracture evaluation method in DBTT region for an irradiated RPV with a postulated surface flaw, fracture analysis procedures considering constraint effect, the Beremin model and damage mechanics model and a coupled model of these models were applied to the specimens with different constraints, which were 1/2TCT specimens and flat plate specimens with a semicircular flaw under tensile load. For evaluation of pure cleavage fracture of flat plate specimens, a Beremin model with plastic strain effect was applied with incorporation of plastic strain effect. Further, for ductile fracture, the local strain criterion of ASME Section VIII was applied to the specimens with different geometries and its applicability was discussed.
Construction of 3D Primary Structure and Stress Classification of Cylindrical Shell With Nozzle
Authors: Duan Chenghong , Wei Xinchen , Huang Jinhao , Lu Mingwan
Published: October 2018

The primary structure method is one of the effective methods to distinguish the primary stress and secondary stress. The knotty problem of stress classification can be solved by using the primary structure method and the equivalent linearization of stresses. The primary structure method has been successfully used to the finite element analyses with 2D axisymmetric elements and shell elements. A method to construct the primary structures with 3D solid elements is given in this paper, and the stress classification of cylindrical shell with nozzle is discussed in a new point view.
Modelling of Fatigue due to Thermal Mixing by Using a Spectrum Method
Authors: Timperi Antti
Published: October 2018

Turbulent mixing of cold and hot fluids can lead to high-cycle thermal fatigue in T-junctions, but modelling of the thermal load induced to the structure is challenging. The spectrum method has been recently proposed as an efficient modelling method, which uses a theoretical turbulence spectrum to represent the fluctuating thermal load. In this work, further development and application of the method is presented. Estimation of the frequency of the largest-scale temperature fluctuations is considered in particular, as this is an essential input parameter for the model spectrum.

The method is applied to a T-junction including a mixer pipe and a high temperature difference that induces significant buoyancy effects. The frequency scale of the fluctuations is determined for the flow case based on temperature spectra obtained from a Computational Fluid Dynamics (CFD) simulation. A formula for the frequency scale is proposed, which can be used in approximating the frequency scale for other flow conditions. Fatigue and crack growth analysis of the T-junction wall are carried out by using the spectrum method, and the results are compared with those obtained with sinusoidal and CFD temperature loads. The results indicate improvement in accuracy over the highly simplified sinusoidal method.
Temperature Dependence of Fatigue Crack Growth in Low-Alloy Steel Under Gaseous Hydrogen
Authors: Takakuwa Osamu , Matsuoka Saburo , Okazaki Saburo , Yoshikawa Michio , Yamabe Junichiro , Matsunaga Hisao
Published: October 2018

In order to elucidate the temperature dependence of hydrogen-enhanced fatigue crack growth (FCG), the FCG test was performed on low-alloy Cr-Mo steel JIS-SCM435 according to ASTM E647 using compact tension (CT) specimen under 0.1–95 MPa hydrogen-gas at temperature ranging from room temperature (298 K) to 423 K. The obtained results were interpreted according to trap site occupancy under thermal equilibrium state. The FCG was significantly accelerated at RT under hydrogen-gas, that its maximum acceleration rate of the FCG was 15 at the pressure of 95 MPa at the temperature of 298 K. The hydrogen-enhanced FCG was mitigated due to temperature elevation for all pressure conditions. The trap site with binding energy of 44 kJ/mol dominated the temperature dependence of hydrogen-enhanced FCG, corresponding approximately to binding energy of dislocation core. The trap site (dislocation) occupancy is decreased with the temperature elevation, resulting in the mitigation of the FCG acceleration. On the basis of the obtained results, when the occupancy becomes higher at lower temperature, e.g. 298 K, hydrogen-enhanced FCG becomes more pronounced. The lower occupancy at higher temperature does the opposite.
Calculation of Leakage Rate for Bolted Flanged Joint During the Long Term Service at High Temperature
Authors: Xue Jilin , Chen Xuedong , Fan Zhichao , Wang Lu
Published: October 2018

Bolted flange joints (BFJs) are widely used in the process industries, and there is a large proportion served in the high temperature environment. During the long term service at high temperature, the creep relaxation of each component of BFJ will cause the decline of the residual gasket stress, which will further affect the sealing effect. So, it is very important to make sure the change rule of the leakage rate of BFJ during the long term service at high temperature. Firstly, according to constructing the relationship between the leakage rate and the service time, the leakage rate calculation method of BFJ during the long term service at high temperature was proposed. Secondly, the stress distributions of the gasket during the long term service at high temperature, which was time-dependent, were calculated at the tightness level T2 and T3 by using the numerical simulation method. Finally, based on the time-dependent average gasket stress and maximum gasket stress, the change rule of the time-dependent leakage rate of BFJ during the long term service at high temperature was obtained. The research results will play an important role in mastering the attenuation rule of the leakage rate of BFJ and supporting the leakage rate control of BFJ during the long term service at high temperature.
Light-Weight Mechanism of Pressure Strengthening of Cryogenic Vessels From Austenitic Stainless Steel
Authors: Lu Qunjie , Huang Gai , Wu Yingzhe , Ding Huiming , Zheng Jinyang
Published: October 2018

Pressure Strengthening (PS) is a technology widely used to increase the allowable stress and thus reduce the weight of Austenitic Stainless Steel (ASS) cryogenic vessels. Pre-strain and low temperature are two important factors enhancing the strength. However, standards such as EN 13458-2, ASME VIII-I, AS 1210 and ISO 21009-1, state that the strengthening is based on work hardening of ASS, while the effect of low temperature was ignored or not mentioned. Therefore, in this work, the influence of low temperature on cryogenic mechanical properties of S30408 stainless steel and its welded joints were studied firstly, then a numerical analysis on the influence of pressure strengthening of a large transportable cryogenic storage tank was conducted. Finally, after the technical significance of PS was discussed, a new understanding was proposed. Conclusions come that: (a) At room temperature, the strength of ASS can be increased by pre-strain; while at −196 °C, the strengthening of low temperature plays a leading role (2/3 or more) for strength increment; (b) The purpose of PS technique is to stabilize the dimensions of the internal vessel. It is unnecessary to consider insufficient strengthening or over strengthening at different location because the strength enhancement is mainly due to low temperatures.
Study on Hydrogen Compatibility of S31603 Weld Joints in 98MPa Gaseous Hydrogen
Authors: He Qi , Hua Zhengli , Zheng Jinyang
Published: October 2018

Austenitic stainless steel of the 300 series and their welds are widely employed in the production, storage and distribution infrastructures of gaseous and liquid hydrogen. However, hydrogen compatibility of their welds has not been completely understood, especially in high-pressure hydrogen environment. In this study, the influence of 98MPa high pressure gaseous hydrogen on the tensile properties and fracture behaviors of three kinds of S31603 weld joints were investigated, including SMAW, SAW and TIG welds. The tensile data indicated that hydrogen caused the ductility loss of the SAW and TIG weld joints, particularly for the TIG welds. For the SMAW weld joints, hydrogen had little impact on its ductility. Fractographic analysis revealed that hydrogen scarcely induced a change in the fracture mode of the SMAW welds. Different from this, the SAW and TIG welds were found to exhibit an obvious susceptibility to hydrogen embrittlement in this study, particularly for the TIG welds, based on the change of fracture features from dimples to facets, striations and secondary cracks. Additionally, both fracture surfaces of the SMAW and SAW welds contained some inclusions where the secondary cracks were promoted.
A Study on Damping Ratio in the Design Code of Vertical Vessels Supported by Skirt
Authors: Tan Wei , Fan Xiantao , Du Yian , Jia Zhanbin , Liu Liyan
Published: October 2018

The vertical vessels supported by skirt are sensitive to dynamic loads, that might oscillate intensely under earthquake and wind loads. Therefore, calculating the dynamic loads and response accurately, especially the damping ratio, influences the amplitude of vessels vibration greatly and is vital for safe operation of the vertical vessels. In Chinese design code, the damping ratio is 0.01 for steel structure, and in American code, it consists of structural damping βs and aerodynamic damping βa, while in European code, the additional damping βd is also considered. With full-scale field tests, the damping ratios of vertical vessels, through a thorough data collection, is recommended as 0.002∼0.005. The damping ratio is 2/3 less than the design value 0.01 in empty condition, that makes the vessel in a crucial state. A new design concept is proposed that the damping ratio of vertical vessels should be determined based on various conditions. Fatigue checking is required in empty condition besides designing by code in operating condition. In addition, the allowable placement time [Tp] is calculated in empty condition. The actual placement time Tp should satisfy Tp < [Tp] and the damper should be installed on the vertical vessel to provide additional damping ratio in the case of Tp > [Tp]. An experiment was carried out to illustrate the new design concept that the damping ratio was enlarged by installing dampers. The damping ratio with other research could provide fundamental parameters for the amendment of the design code.
Study of Alternative Assembly Patterns Using Finite Element Analysis and Lab Tests
Authors: Jung Gong H. , Pudwill Wesley , Sheu Elysia J.
Published: October 2018

A total of 24 lab tests were performed to evaluate two different joint assembly patterns (legacy and an alternative pattern), two lubricant types (Nickel based and Moly-Disulphide based), and two types of torque wrenches (Hydraulic and Pneumatic). Bolt stress was measured during assembly using load indicating bolts (SPC4). Assembly time was also measured since alternative assembly patterns have been recognized as a potential method for improving assembly efficiency without negatively impacting bolt pre-load scatter. In order to understand the bolt stress distribution in both of the legacy and alternative assembly patterns, a finite element model was developed to simulate wrench sequences specified by ASME PCC-1. The FEA model included the effect of elastic interaction of the bolts and flange. The FEA results indicate similar behavior when compared to the lab test results, and the FEA study was extended to two other alternative assembly patterns. This paper summarizes the results of the FEA and lab tests on a 24” NPS Class 300 flange and may provide validation and supporting information for users who are considering the use of a more efficient assembly method such as the alternative assembly patterns presented in ASME PCC-1.
Application of Flaw Updating Process on Probabilistic Structural Evaluation for a Reactor Pressure Vessel Under Pressurized Thermal Shocks
Authors: Huang Pin-Chiun , Chou Hsoung-Wei , Ferng Yuh-Ming
Published: October 2018

The structural integrity of a reactor pressure vessel (RPV) is one of the most important issues for the operation of nuclear power plant. Nowadays, the probabilistic fracture mechanics (PFM) technique is widely used in evaluating the structural integrity of RPVs. However, the flaw characteristics used for PFM analysis are mainly derived from the Pressure Vessel Research User Facility (PVRUF) and Shoreham vessel inspection database, which may not be able to truly represent the vessel-specific condition of the analyzed RPV. In this work, the NUREG-2163 procedure which modifies the flaw characteristic parameters is employed. The Bayesian updating process which combines the prior flaw data with non-destructive examination (NDE) results as well as uncertainties is used to develop the posterior vessel-specific flaw distributions. Subsequently, the updated flaw files are used for PFM analysis to investigate the effects of NDE updated flaw characteristics on the fracture probability of RPV subjected to pressurized thermal shocks. Considering the updated flaws based on the NDE data, the analyzed results could be more plant-specific to predict the fracture risks of RPVs during operation.
Guideline on Application Process of Techniques Developed for Repair, Replacement and Mitigation Activities
Authors: Koyama Koji , Kobayashi Hiroyuki , Hojo Kiminobu
Published: October 2018

The process from the engineering development to actual application of the new techniques used for the maintenance activities for Japanese nuclear power plants’ (NPPs) component in operation, the JANTI Guideline, “Guideline on Application Process of Techniques Developed for Maintenance Activities” was developed to propose clarification activities to be checked or examined in each stage throughout process. The guideline focuses on techniques used for especially such remedial activities as repair, replacement and mitigation of ageing. In engineering development stage, all information on the new techniques are provided to be checked or examined at each stage of the process followed further, such as code/standard formulation stage. It is important to carry out share recognition for the activities, which should be performed in each process in the prompt application to the actual plant system efficiently, among the persons or organizations concerned.
Damage Behavior of Filament-Wound Composite Cylinder Under Impact by Flat-Ended Impactor
Authors: Wu Qiaoguo , Chen Xuedong , Fan Zhichao , Jiang Yong , Zhang Xiaoqiang , Nie Defu
Published: October 2018

Numerical simulations were performed on the damage behavior of carbon-fiber-wrapped composite cylinder subjected to impact by a flat-ended impactor. The simulation results were in agreement with the test in terms of both the damage morphology of the cylinder and the impact acceleration-time curve of the impactor. The relationship between the impact acceleration-time curve characteristics and the initiation and propagation process of the various damages was analyzed. The effects of the internal pressure on the damage morphology of the cylinder, the impact acceleration-time curve of the impactor, and the critical perforation energy of the cylinder wall were discussed. Change law of the residual burst pressure of the cylinder with different impact energies was obtained. The conclusions in this paper are helpful for the safety assessment of the composite cylinders subjected to impact by foreign objects.
Study on the Influence of Strain Rate on Crack Initiation and Growth in Simulated Reactor Coolant Environment of Type 316 Stainless Steel
Authors: Nose Takahisa , Nakamura Takao , Kitada Takanori
Published: October 2018

In order to conduct effective and rational maintenance activity of components in nuclear power plants, it is proposed to manage fatigue degradation based on crack size corresponding to an extent of cumulative fatigue damage. The purpose of this study focuses on the influence of strain rate in simulated reactor coolant environment for fatigue crack initiation and growth. 3-dimensional replica observations were conducted for environmental fatigue test specimens in different strain rates. Crack initiation and growth were observed in the experiments. It is clarified that low strain rate influences crack propagation and coalescence and increases crack growth rate that finally decrease fatigue life.
Flamanville EPR RPV’s Heads Carbon Segregation: Characterization of the Segregation in the Heads
Authors: Fichot Philippe , Calonne Olivier , Segond Mathieu , Marie Stéphane , Desnoyers Yvon , Hajjaj Mejido , Miller Cecile
Published: October 2018

To characterize the mechanical properties of the residual carbon segregation of the Flamanville EPR RPV heads, a testing program has been defined by Framatome using three sacrificial representative heads. The first step of this program was a 3D characterization of the carbon content inside each piece.

A specific strategy has been defined using two methods for the carbon measuring:

- In situ measurements using a mobile arc spark spectrometer. This device allows a higher number of non-destructive measurements in a particularly constrained environment and in a short time,

- Conventional spectrometry performed on chips sampled from the pieces. This technique is more accurate but is destructive and more time consuming.

Also, to consolidate the representativeness of the sacrificial vessels heads, the results were analysed using a geostatistical approach. This paper presents how these two techniques have been used to characterize the carbon content in the segregated part of the pieces and the conclusion of the geostatistical analyses.
Stress Intensity Factors for Circular-Arc Cracks in Plates
Authors: Shim D. J. , Tang S. , Kim T. J. , Huh N. S.
Published: October 2018

Stress intensity factor solutions are readily available for flaws found in pipe to pipe welds or shell to shell welds (i.e., circumferential/axial crack in cylinder). In some situations, flaws can be detected in locations where an appropriate crack model is not readily available. For instance, there are no practical stress intensity factor solutions for circular-arc cracks which can form in circular welds (e.g., nozzle to vessel shell welds and storage cask closure welds).

In this paper, stress intensity factors for circular-arc cracks in finite plates were calculated using finite element analysis. As a first step, stress intensity factors for circular-arc through-wall crack under uniform tension and crack face pressure were calculated. These results were compared with the analytical solutions which showed reasonable agreement. Then, stress intensity factors were calculated for circular-arc semi-elliptical surface cracks under the lateral and crack face pressure loading conditions. Lastly, to investigate the applicability of straight crack solutions for circular-arc cracks, stress intensity factors for circular-arc and straight cracks (both through-wall and surface cracks) were compared.
Layout Optimization for Progressive Development of Stellated Natural Gas Gathering Network
Authors: Hong Bingyuan , Li Xiaoping , Li Yu , Gao Jingjing , Zhou Yanhong , Wei Baocheng , Zhang Siqi , Gong Jing
Published: October 2018

Gathering pipeline network, as one of the most important parts of oil and gas field construction, is characterized by complex topological structure and high investment costs. Therefore, optimization of gathering pipeline network can reduce total investment of field significantly. This paper focuses on stellated pipeline network, a common connection structure of gathering pipeline, and presents a layout optimization model for progressive development of gathering pipeline network. Minimizing the production length is the object of the model. Constraints of wells, valve groups, gathering radius and flow rate are taken into consideration. The optimal position of valve groups and central processing facility and the connection of each pipeline are obtained by solving this model with a heuristic algorithm proposed in this paper. In addition, three typical cases, namely new production block, well pattern infilling and rolling development, are taken as examples to verify the reliability and practicality of the proposed model. The results demonstrate that the proposed method can tackle the layout optimization problem of expanding a pre-existing gathering pipeline network.
Experimental Measurement of the Shank Torque As a Function of the Stiffness and Frictional Characteristics of the Bolted Joint
Authors: Croccolo Dario , De Agostinis Massimiliano , Fini Stefano , Olmi Giorgio , Robusto Francesco , Cavalli Omar , Vincenzi Nicolò
Published: October 2018

During tightening, the amount of torque given by the difference between the tightening torque, which is directly applied by the torque wrench, and the underhead torque, flows through the screw shank towards the threaded portion. This torque combines with the axial preload to bring about the overall stress state of the screw at tightening. Upon release of the torque wrench, a certain amount of the shank torque is released due to the elastic springback of the screw-plates system. In the literature [1], this phenomenon is just briefly treated by a few authors: they generally agree that approximately a half of the initial shank torque is released just a few seconds after torque wrench removal. This indication is given regardless of the frictional [2] and stiffness [3] parameters, which govern the joint. The present contribution aims at assessing, if there is any effect of the following parameters on the amount of shank torque being released after wrench removal: (i) the ratio between the torsional stiffness of the screw and of the plates, (ii) the friction coefficients in the underhead and in the thread. The experimentation has been run on a M20 8.8 class socket head screw, which has been instrumented by a double array of strain gauges, to simultaneously measure both the axial preload and the torque acting on its shank. Two different types of joined members have been examined: a cylindrical sleeve whose diameter is twice the screw diameter (compliant joint) and a rectangular plate whose transverse dimensions are more than ten times larger than the screw diameter (stiff joint). The underhead and thread friction coefficients have been controlled by properly selecting lubrication conditions. The main outcome of the work is that the torsional stiffness of the joined members does have an impact on the residual shank torque. A simple mathematical model has also been implemented, in order to predict the residual shank torque during the design phase.
Fatigue and Corrosion Fatigue Life Assessment With Application to Autofrettaged Parts
Authors: Okorokov Volodymyr , MacKenzie Donald , Gorash Yevgen
Published: October 2018

This study investigates an effect of autofrettage on the fatigue and corrosion fatigue life of high pressure parts made from low carbon structural steel. To estimate the beneficial effect of autofrettage application, an extensive experimental program and advanced theoretical modelling are conducted and analyzed in this study. Accurate calculation of compressive residual stresses is achieved by application of a cyclic plasticity model which can precisely simulate a cyclic plasticity response of material. In terms of a fatigue life prediction methodology, a non-local stress based approach with a modified critical distance theory is used for prediction of the crack initiation stage providing conservative fatigue assessment. Because of the fact that the crack propagation stage can take a considerable part of the total life for autofrettaged parts, more accurate fatigue life calculation is performed by the use of a fracture mechanics approach. The total fatigue life time of autofrettaged parts is then calculated as a sum of the crack initiation and propagation stages.
Multiscale Stress-Diffusion Analysis of Notch-Tip Hydrogen Profiles in Zircaloy-4
Authors: El Chamaa Said , Patel Mitesh , Wenman Mark R. , Davies Catrin M.
Published: October 2018

Hydrogen pick-up in zirconium alloys can lead to their structural failure, which is an important problem in the nuclear industry. This investigation focuses on modelling the accumulation of hydrogen in the vicinity of loaded V-notches in four-point bend Zircaloy-4 specimens. In order to account for the anisotropic diffusivity of hydrogen in hexagonal close-packed α-zirconium, a multiscale methodology is proposed to compute notch-tip hydrogen profiles. This methodology unifies continuum scale stress analysis, using the finite element approach, and atomistic scale stress analysis, using the elastic dipole tensor of point defects. The steady state notch-tip hydrogen profiles are determined for different notch geometries and crystal orientations. It was found that hydrogen enhancement is greater but more localised for sharper notches with a smaller flank angles, which is the expected effect of stress. It was also found that hydrogen enhancement is greater if the notch opening plane coincides with the prism plane as opposed to the basal plane. This anisotropic effect is a consequence of the trigonal symmetry of the hydrogen interstitialcy.