bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite-Element Analysis of Crack Growth in Austenitic Stainless Steel Under Equibiaxial Loading
Authors: Dhahri H. , Gourdin C. , Maitournam H.
Published: October 2018

The lifetime extension of the nuclear power plants is considered as an energy challenge worldwide. That is why, the risk analysis and the study of various effects of different factors that could potentially represent a hazard to a safe long term operation are necessary. These structures, often of great dimensions, are subjected during their life to complex loading combining varying mechanical loads, multiaxial, with non-zero mean values associated with temperature fluctuations and also PWR environment.

Based on more recent fatigue data (including tests at 300°C in air and PWR environment, etc...), some international codes (RCC-M [2], ASME and others [3][4][5]) have introduced a modification of the austenitic stainless steels fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which has to be multiplied by the usual fatigue usage factor [6].

Unfortunately, experimental data on this issue are rare. In order to obtain fatigue strength data under structural loading, biaxial test means with and without PWR environment were developed at LISN in collaboration with EDF and AREVA [6]. Two kinds of fatigue device have been developed. Within the same specimen geometry, structural loads can be applied in varying only the PWR environment.

The first device (FABIME2) is devoted to study the effect of biaxiality and mean strain/stress on the fatigue life [9]. A second and new device called FABIME2e is for the study of the environmental effect. With these new experimental results, the PWR environment effect on the fatigue life of stainless austenitic steels will be quantified accurately on semi-structure specimen. This device combines the structural effect like equi-biaxiality and mean strain and the environmental penalty effect with the use of PWR environment during the fatigue tests.

The aim of this paper is to present the numerical interpretation of the results obtained with these two devices “FABIME2” and “FABIME2e”. Two important aspects will be addressed. The first concerns the mechanical behavior of austenitic stainless steel and the capabilities of the numerical model to reproduce the hardening of the material. And the second concerns the study of the crack growth during the equibiaxial fatigue test.
Simple Mechanical Testing Method to Evaluate Influence of High Pressure Hydrogen Gas
Authors: Ogata Toshio
Published: October 2018

A simple testing method to evaluate the influence of high pressure hydrogen gas up to 100 MPa on mechanical properties at the temperature between 20 K and up to 800 K had been developed. In this method, instead of using high-pressure gas vessels, high pressure gas was filled into a small hole in the hollow-type test piece from a hydrogen gas cylinder or a compressor for 10 MPa or 100 MPa test. A small inner diameter of the hole enables to evaluate also the reduction of area in the slow strain-rate tensile (SSRT) tests. The temperature of the test piece with the high pressure gas can be changed simply by surrounding coolant or heater between 20 K and 800 K. Lots of test results by this method proved that almost the same results were obtained between this method and the conventional method with high-pressure gas vessels where test piece is installed. The great advantages of this method are not only the less cost for the facilities of high-pressure vessels but also the ability of tests at lower or higher temperatures than those with the vessels. So, this method is proposed to be used world-widely to evaluate the mechanical properties of structural materials for extremely severe environments, such as high-pressure hydrogen applications and also to study the mechanism of the influence of high-pressure hydrogen for design and reliability of those facilities.

In this paper, the details of testing procedure of this method and results of tensile and fatigue tests in up to 70 MPa hydrogen gas on several kinds of stainless steels obtained by this method are presented.
Effect of Weld Strength Mismatch and Weld Width on the Fracture Toughness Determined From SENB Specimens
Authors: Moore Philippa L. , Garban Natalia , Bastid Philippe , Hughes Kevin
Published: October 2018

In fracture toughness test standard BS EN ISO 15653 for weld and HAZ specimens, there is limited guidance about how the weld width, and the weld metal to parent yield strength mismatch ratio can affect the fracture toughness of materials, nor how to interpret the results should these parameters fall outside the permitted limits given in the Standard. This research was carried out to evaluate how the values of J determined from fracture toughness test results are affected by the weld width and weld strength mismatch, by using FEA models of single edge notched bend (SENB) specimens.

Fracture toughness results from specimens notched into the weld centreline, of different mismatch ratios and weld widths, are compared with homogeneous materials specimens. The results show that for any mismatch ratio, fracture toughness for welds wider than 20mm are similar to homogeneous material. However, the fracture toughness decreases as the weld become narrower than 20mm. When this variation is taken as a percentage between a homogeneous material and a welded specimen, J varies for each weld width following the same trend for a specific mismatch ratio, independently of the material strength. To enable prediction of the fracture toughness behaviour of welded specimens, equations have been developed for comparison to homogeneous weld metal or homogeneous parent metal, as a function of the weld mismatch ratio and the weld width.

The real question is whether the Standard methods can nonetheless determine weld metal fracture toughness accurately in overmatched welds of different widths. From comparisons of J values extracted directly from the contour integral, and J values calculated using the standard equation (but based on load-CMOD data), it was found that standard methods vary by less than 5% in the majority of the cases. The exception was for the combination of mismatch ratio above 1.46 and welds narrower than 20mm. Therefore, it could be said that the Standard BS EN ISO 15653 is conservative with the overestimation percentage of 10%, since all model cases within the Standard limits of mismatch of 1.5, the largest over-estimation was only 6%, and typically less than 4%.
Research on Phased Array Ultrasonic Testing for the Girth Weld of 4mm~10mm Austenitic Stainless Steel Pipeline
Authors: Zhou Lu-yun , Fu Ming-hai , Xu Wei-pu
Published: October 2018

Austenitic stainless steel butt joints are widely used in the pressure piping system, and the quality of welded joints directly affect the safety of pressure special equipment. In this paper, phased array ultrasonic testing technology is used to study the feasibility of 4mm∼10mm wall thickness workpiece. Through the software CIVA (Developed by The French Alternative Energies and Atomic Energy Commission (CEA)) simulat to determine the parameters of the detection system, and it tests the 18 groups of 4mm∼10mm series simulation samples by PAUT (Phased Array Ultrasonic Testing).Through comparison with Radiographic testing, PAUT for the girth weld can be effectively for the 4mm∼10mm Austenitic Stainless Steel Pipeline.
Effect of Carburization on Creep Performance of Cr35Ni45Nb Heat Resistant Alloy
Authors: Cao Luowei , Xie Guoshan , Han Zhiyuan , Zhuang Fakun
Published: October 2018

The purpose of this paper is to describe the changes of the structure and the creep performance for Cr35Ni45Nb alloy after varying carburization. Carburizing layers with different thickness were produced in Cr35Ni45Nb alloy directly by vacuum carburizing experiment. The surface microstructure of Cr35Ni45Nb alloy was essentially changed after varying carburization. Creep performance of carburized only and carburization-creep treatment alloys were compared to study the effect of the carburization on creep for Cr35Ni45Nb heat resistant alloy. Mechanical properties of carburizing layer, carburizing transition layer and base alloy were characterized by micro-hardness, respectively. Results of creep rupture testing for the carburized and non-carburized specimens showed that carburization can influence the rupture time, failure strain and creep rate. Carburization also been proved to affect the constant of CMG and CMMG for different stress or carburizing level.
Development of a Program for High-Temperature Design Analysis and Defect Assessment According to RCC-MRx
Authors: Lee Hyeong-Yeon , Won Min-Gu , Huh Nam-Su , Kim Woo-Gon
Published: October 2018

A program for a high-temperature design analysis and defect assessment has been developed for an elevated temperature evaluation according to the RCC-MRx for Generation IV and fusion reactor systems. The program, called ‘HITEP_RCC-MRx,’ consists of three modules: ‘HITEP_RCC-DBA,’ which computerizes the design-by-analysis (DBA) for class 1 components such as the pressure vessel and heat exchangers according to RB-3200 procedures, ‘HITEP_RCC-PIPE,’ which computerizes the design-by-rule (DBR) analysis for class 1 piping according to RB-3600 procedures and ‘HITEP_RCC-A16,’ which computerizes high-temperature defect assessment according to the A16 procedures. It is a web-based program, and thus can operate on a smartphone as well as on a personal computer once it is connected to the URL. The program has been verified with a number of relevant example problems on DBA, Pipe, and A16. It was shown from the verification works that HITEP_RCC-MRx with the three modules conducts a design evaluation and a defect assessment in an efficient and reliable way.
Effect of High Pressure Gaseous Hydrogen on Fatigue Properties of SUS304 and SUS316 Austenitic Stainless Steel
Authors: Iijima Takashi , Enoki Hirotoshi , Yamabe Junichiro , An Bai
Published: October 2018

A high pressure material testing system (max. pressure: 140 MPa, temperature range: −80 ∼ 90 °C) was developed to investigate the testing method of material compatibility for high pressure gaseous hydrogen. In this study, SSRT and fatigue life test of JIS SUS304 and SUS316 austenitic stainless steel were performed in high pressure gaseous hydrogen at room temperature, −45, and −80 °C. These testing results were compared with those in laboratory air atmosphere at the same test temperature range. The SSRT tests were performed at a strain rate of 5 × 10−5 s−1 in 105 MPa hydrogen gas, and nominal stress-strain curves were obtained. The 0.2% offset yield strength (Ys) did not show remarkable difference between in hydrogen gas and in laboratory air atmosphere for SUS304 and SUS316. Total elongation after fracture (El) in hydrogen gas at −45 and −80 °C were approximately 15 % for SUS304 and 20% for SUS316. In the case of fatigue life tests, a smooth surface round bar test specimen with a diameter of 7 mm was used at a frequency of 1, 0.1, and 0.01 Hz under stress rate of R = −1 (tension-compression) in 100 MPa hydrogen gas. It can be seen that the fatigue life test results of SUS304 and SUS316 showed same tendency. The fatigue limit at room temperature in 100 MPa hydrogen gas was comparable with that in laboratory air. The room temperature fatigue life in high pressure hydrogen gas appeared to be the more severe condition compared to the fatigue life at low temperature. The normalized stress amplitude (σa / Ts) at the fatigue limit was 0.37 to 0.39 for SUS304 and SUS316 austenitic stainless steels, respectively.
Application of Genetic Algorithm on Optimal Pipeline Route Considering Complex Terrains and Obstacles
Authors: Hong Bingyuan , Li Xiaoping , Li Yu , Gao Jingjing , Zhou Yanhong , Wei Baocheng , Zhang Siqi , Gong Jing
Published: October 2018

Gathering network, which is usually characterized by various and complex structure, takes a large proportion of the overall construction cost of gas field. Optimization of pipeline routes is an effective way to reduce the investment. In this paper, a novel model for optimal route of pipeline considering complex terrains and obstacles is proposed and solved by Genetic Algorithm. Minimizing the total investment is the object of this model. Since the construction costs under different terrains are different, the distance factor Li, slope factor Di and elastic factor Si are introduced into the objective function to represent the length of the pipeline, the gradient of the pipeline, and the fluctuation of terrain. In addition, the performance of the model is verified by taking three typical situations of different terrains and obstacles as examples. The results illustrate that the proposed model can address the optimal design of pipeline routes in complex terrains. Moreover, the effects of different genetic operators on solutions are investigated, including three selection operators and two crossover operators. The study provides a guideline for designing pipeline routes in complex terrains and is also applicable to the analogous problem.
Load Line Displacement Partitioning in Creep Crack Growth Analyses of 316H Stainless Steel
Authors: Jones Michael D. , Nikbin Kamran M. , Davies Catrin M.
Published: October 2018

Accelerated creep crack growth tests in the laboratory can lead to greater levels of plasticity at the tip of a creep crack than would be experienced in service. This is problematic when trying to determine C* which is used to model the stress field ahead of a crack. Deflection partitioning methods must be used in order to determine the contribution to the load line displacement rate as a result of creep which in turn is used to calculate C*. This partitioning can lead to negative values of the creep load line displacement rate due to the high contribution from plasticity. The amount of assumed plasticity is likely to be erroneously high as it is currently assumed that the material behaviour fits a Ramberg-Osgood model, when in reality such a fit does not predict the behaviour well over a large range of stress.

This work compares the load line displacement determined from solutions based on a Ramberg-Osgood model with those calculated from finite element simulations using uniaxial tensile data to model the plasticity. The simulations formulated crack growth by means of a crack length vs time criterion using experimental crack growth data. It is found that the theoretical solutions do over predict the amount of plastic deformation compared to the numerical results. It is also found that for the short term test considered, the load-line displacement due to creep deformation was small compared to that from crack growth.
Effect of Clamping Failure on Flow Induced Vibration and Fretting Wear of Fuel Rods
Authors: Huan-huan Qi , Zhi-peng Feng , Fu-rui Xiong , Nai-bin Jiang , Qian Huang , Xuan Huang
Published: October 2018

Fuel rods are subjected to both axial and lateral flow in the reactor core. In this study, we present a study on the flow induced vibration (FIV) and fretting wear of fuel rod with failed clamping at grids. First, according to the flow distribution around a type of pressurized water reactor (PWR) fuel rod, the power spectral density (PSD) is obtained to characterize the turbulence excitation. Next, by combining the correlation PSD test parameters, the mean square value of the vibration displacement of each rod mode is found, and then the wear depth of dimple position is calculated based on the ARCHARD wear formula. The clamping of fuel rod at various grids may fail due to inaccurate manufacturing, fuel transportation and in-core irradiation. The absence of clamping force would significantly influence the rod mode and thereby changes its FIV responses. Simulation results show that the failure of the leaf spring has negligible effect on the rod natural frequency whereas the dimple failure near the location with larger FIV amplitude has a much significant effect. The lateral flow velocities at the inlet and outlet of the core are larger. For the fully clamped fuel rod, the response amplitude of turbulent excitation at the bottom and top of the fuel rod is larger. This is even more obvious with a failed dimple at these locations. Comparatively, the effect of dimple support failure in the middle is less influential. The influence of dimple support failure over the rod wear depth depicts basically the same trend as on the maximum FIV amplitude. In addition to the FIV amplitude, wear depth is also related to rod natural frequency. By examining the multiplication of amplitude and frequency at the top and bottom grid, we found that the dimple failure has greater impact at the top grid.
Transient Thermal Stress and Temperature Change Rate Analysis of Fixed Tubesheet
Authors: Wang Zhijian , Shi Qianyu , Li Qi , Wan Liping , Tang Hui
Published: October 2018

Some fixed tubesheet heat exchangers suffer amount of system startup and shutdown causing large thermal stress for tubesheets. It will make an impact on the fatigue damage of the equipment. Transient thermal and stress analysis were carried out in many papers, but the geometry models were simplified, the non-expanded part of the tube and tubesheet were not modeled in detail at the end of tube. In fact, there is a tiny gap enclosed by tube, tubesheet and weld. So in this paper, a simplified model and an accurate model are established, the transient thermal and stress analysis were performed in ANSYS Workbench. The difference between two models was compared and the influence of temperature change rate on thermal stress was discussed.
Flamanville EPR RPV’s Heads Carbon Segregation: Impact of the High Carbon Segregation on the Mechanical Properties of the RPV Steel
Authors: Marie Stéphane , Demarecaux Jérôme , Fichot Philippe , 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 have been organized by Framatome and performed in 3 laboratories.

Three sacrificial pieces have been used for this program, allowing the investigation of different carbon contents, coupled with different quenching conditions (thanks to a specimen sampling at different positions in the heads thickness).

As expected, the increase of the carbon content leads to an increase of the tensile properties, a shift toward the higher temperature of the brittle-to-ductile transition and a lowering of the toughness in the ductile regime. In the worst case, compare to the RTNDT measured in the frame of acceptance tests of the heads, the temperature to be considered to envelop all the experimental results with the toughness curve of the RCC-M code is 20°C higher. The extensive test program allows a quantification of these impacts for the integrity assessments of the RPV.

It is also demonstrated that the segregated material remains homogeneous, with a classical failure mode by cleavage. Master Curve approach is also applicable and used to characterize the carbon content impact on the toughness properties.
Numerical Study on the Creep Strain Characteristics for TMSR Reactor Coolant Piping Under Thermal Loading
Authors: Gong Wei , Zhang Xiaochun , Xie Mingqiang , Fu Yuan , Wang Xiao
Published: October 2018

Safety assessment and economy design of piping system at high temperature is highly important in power and nuclear engineering. ASME-NH code considers cyclic failure modes at elevated temperature and provides the rules and damage limits for creep-fatigue interaction. Based on the calculation methods for creep strain increment of ASME-NH code, this paper investigated the creep-fatigue damage of reactor coolant piping in Thorium Molten Salt Reactor-Solid Fuel (TMSR-SF0) loop. By designing different stress cycles, the different creep strain increment and creep-fatigue assessments are systematically conducted. It was found that the creep strain increment of SF0 loop accumulated in one stress cycle time was higher than that accumulated during the entire service life divided by the number of stress cycles. Similarly, the creep-fatigue damage was also lower. And thus, an economical design method for SF0/SF1 loop was given.
Case Study of Nonlinear Buckling With Shape Distortion due to Thermal Load
Authors: Shen Jun , Tang Yanfang , Peng Heng , Peng Hui , Liu Yinghua
Published: October 2018

Thermal load is one of the most important design conditions that should be considered carefully in engineering practice. Most inner-pressure vessels suffer thermo-mechanical ratcheting or unacceptable plastic deformation under cyclic thermal stress produced by inside heat source and pressure-induced primary stress. However, thermal load is also a crucial factor for external-pressure vessels where the failure model of buckling should not be ignored. The effect of thermal load on buckling is not only thermal stress itself but also shape distortion due to thermal load. In some cases, the latter is more important. In this paper, an external-pressure thin-walled ellipsoidal head with heating jackets has been studied. The temperature of this structure is uniformly distributed along the thickness direction but changes alternately between hot and cold along the meridional direction, which will have a significant effect on buckling behavior of this typical structure. Buckling load is sensitive to initial defect and small deformation. Several comparative calculations based on nonlinear buckling analysis have been conducted and some laws are established. Finally, some useful conclusions and suggestions are proposed for engineering design.
Fluid Structure Interaction Homogenization for Tube Bundles: Significant Dissipative Effects
Authors: Artini Gianluca , Broc Daniel
Published: October 2018

In the nuclear industry, tube arrays immersed in dense fluid are often encountered. These systems have a large amount of tubes necessary to increase the thermal power exchanged and their dynamical analysis for safety assessment and in life operation is one of the major concern of the nuclear industry.

The presence of the fluid creates a strong coupling between tubes which must be taken into account for complete dynamical analysis. However, the description of fluid’s effects on oscillating structures demands great numerical efforts, especially when the tube number increases making any direct numerical simulations impossible to achieve.

In this framework, homogenization methods are a possible solution in order to deal with tube bundle Fluid-Structure Interaction (FSI) problems; in fact, it gives the possibility to analyze the dynamics of the global coupled system in large domain with reasonable degree of detail and faster simulations times.

At the CEA of Saclay a method based on the linearized Euler equations has been developed. It was presented in a previous PVP conference and its main goal is to assess the effect of spatial deformations of the tube bundle displacement field on the dynamic behavior.

In the present paper, after an analysis on the modeling of fluid force where dissipative effects are significant, a homogenized model based on the Navier-Stokes equations is introduced. Simulations in bi-dimensional configurations for different excitations are performed.
Difference in Susceptibility to 475°C Embrittlement of Duplex Stainless Steel Base Metal and Weld Metal
Authors: Sakata Mikihiro , Kiso Tomoaki , Tanaka Masayuki , Sato Yasuhiro
Published: October 2018

Duplex and super duplex stainless steels are susceptible to thermal aging embrittlement, referred to as 475°C (885°F) embrittlement. The object of this study is to understand the difference in susceptibility to 475°C (885°F) embrittlement of the base metal and the weld metal of these steels. Isothermal aging heat treatment at 300–450 °C (570–840°F) up to 1,000 hours was performed on 22% Cr duplex stainless steel: UNS S32205 and 25% Cr super duplex stainless steel: UNS S32750 and S32760 and these weld metals made using their matching SMAW electrodes or GTAW rods. After heat treatment, the embrittlement behavior was evaluated by Charpy impact test and Vickers hardness test. The results revealed the time-temperature embrittlement curves of the weld metals were displaced to a significantly shorter period of time and extended to lower temperatures compared to those of the corresponding base metals. More importantly, these results suggested that the maximum design temperature limit on these steels currently specified in the ASME Pressure Piping Codes and Boiler and Pressure Vessel Code is not always sufficient to avoid the risk of 475°C (885°F) embrittlement in their welded components.
Transient Hydrogen Diffusion/Elastoplastic Coupling Analysis for Predicting Fatigue Crack Growth Acceleration of Low-Carbon Steel in Gaseous Hydrogen
Authors: Kawahara Kaito , Fujikawa Masaki , Yamabe Junichiro
Published: October 2018

In recent years, hydrogen, one of renewable energy, has attracted attention. For widespread commercialization of the hydrogen-energy systems, a useful and reliable evaluation method should be developed for capturing the degradation of strength and fatigue properties of metals in presence of hydrogen. This paper implemented transient hydrogen diffusion-elastoplastic coupling analysis program into a commercial software of Finite Element Analysis (Abaqus) to predict the fatigue crack growth (FCG) acceleration of a low carbon steel (JIS-SM490B) in high-pressure hydrogen gas. For this simulation, hydrogen-diffusion properties (concentration and diffusivity) depending on plastic strain were experimentally obtained. Our thorough numerical results proposed a practical technique to predict an onset of hydrogen-enhanced FCG acceleration measured in experiments, via the numerically obtained gradient of hydrogen concentration at the crack tip. In addition, a practical technique to predict the hydrogen-enhanced FCG acceleration ratio was also discussed based on the gradient of hydrogen concentration.
Management of Complex Loading Histories for Use in Probabilistic Creep-Fatigue Damage Assessments
Authors: Zentuti N. A. , Booker J. D. , Bradford R. A. W. , Truman C. E.
Published: October 2018

An approach is outlined for the treatment of stresses in complex three-dimensional components for the purpose of conducting probabilistic creep-fatigue lifetime assessments. For conventional deterministic assessments, the stress state in a plant component is found using thermal and mechanical (elastic) finite element (FE) models. Key inputs are typically steam temperatures and pressures, with the three principal stress components (PSCs) at the assessment location(s) being the outputs. This paper presents an approach which was developed based on application experience with a tube-plate ligament (TPL) component, for which historical data was available. Though both transient as well as steady-state conditions can have large contributions towards the creep-fatigue damage, this work is mainly concerned with the latter. In a probabilistic assessment, the aim of this approach is to replace time intensive FE runs with a predictive model to approximate stresses at various assessment locations. This is achieved by firstly modelling a wide range of typical loading conditions using FE models to obtain the desire stresses. Based on the results from these FE runs, a probability map is produced and input(s)-output(s) functions are fitted (either using a Response Surface Method or Linear Regression). These models are thereafter used to predict stresses as functions of the input parameter(s) directly. This mitigates running an FE model for every probabilistic trial (of which there typically may be more than 104), an approach which would be computationally prohibitive.
Fatigue Life Analysis of Storage Tanks In-Service Based on Exponential Curve Settlement Prediction Model
Authors: Zhang Delin , Chen Zhiping , Li You
Published: October 2018

In order to study the structural fatigue safety of in-service fixed roof storage tanks after uneven settlement, an exponential curve method of settlement prediction has been constructed. A finite element model based on the contact condition between the elastic ring beam foundation and the tank base was also proposed. On the basis of above, a fatigue life prediction method of in-service storage tanks based on the settlement prediction model has been established. Combined with the engineering example of an in-service tank, the structural fatigue safety under the actual uneven settlement was analyzed. The results indicate that the trend of foundation settlement with time could be predicted accurately and the contact condition between base and foundation could be simulated simultaneously. Subsequently, the in-service tank’s structural fatigue life under the uneven settlement could be predicted.
Influence of 70 MPa Hydrogen Gas on SUS 630 From 77 K to 373 K by Simple Testing Method
Authors: Ogata Toshio
Published: October 2018

The hydrogen environment embrittlement (HEE) on SUS 630 was evaluated by enclosing the hydrogen gas into a hole of the specimen at 77 K, 120 K, 190 K, 230 K, 260 K, 300 K, and 373 K. The pressure range of hydrogen gas was 10 MPa to 70 MPa. The slow strain-rate tensile (SSRT) tests were carried out and the relative reduction of area (RRA) was calculated by the ratio of the reduction of area (RA) in hydrogen gas and the RA in helium gas. The RA and tensile strength were smaller in the higher pressure of hydrogen gas. The RRA between 190 K and 260 K was almost zero, however, the HEE reduces at 77 K and 373 K. There was almost no HEE after changing to helium gas at the stress of just below the fractured stress in hydrogen during the SSRT tests.
Crack Remaining Repair Techniques in Japan
Authors: Ichikawa Hiroya , Kaminaga Takayuki , Miyoshi Yoshiyuki , Kimura Ryuji
Published: October 2018

Cracking on metal surface including Stress Corrosion Cracking (SCC) is a concern for nuclear power plant reactor system piping and components. Several repair techniques have been developed over the years that help address the cracking issues. In the United States, some crack remaining repair technologies such as Weld Overlay (WOL) technique have already been developed and also some technologies such as Excavate and Weld Repair (EWR) are still being actively discussed. Fitness-for-Service (FFS) codes in Japan also define some repair methods which allow repairing the components without removing the cracks. This paper introduces three repair methods which are described in the Fitness-for Service code in Japan, the WOL, the cap repair technique for Bottom Mounted Instrumentation (BMI) nozzles and seal welding.

WOL is a repair method that maintains structural integrity by depositing Intergranular Stress Corrosion Cracking (IGSCC) resistant weld to the outer surface of cracked circumferential welded joints in primary piping made of austenitic stainless steel. The cap repair technique for BMI nozzles is a method of repairing from the outer surface when leakage due to SCC occurs. The cap develops a new boundary outside the BMI nozzle to prevent the leakage by retaining the leakage inside the cap. The seal welding technique is also a repair method to cover the cracks by welding to prevent propagation of the cracks and to prevent leakage of reactor water.

Provided the cracks are adequately managed and evaluated, these crack remaining repair methods are very beneficial.
Study on Low Frequency AC Excitation Magnetic Flux Leakage Testing for Defects With Different Depths
Authors: Lu Xinyuan , Li Guanghai , Chen Liangchao , Chang Yu , Zhang Xiaozhu
Published: October 2018

Magnetic flux leakage (MFL) method is a non-destructive method commonly used for equipment with ferromagnetic material. This paper presents a low frequency alternating current (AC) excitation MFL method. This method uses low frequency AC current excitation to obtain a high detection depth, and to realize the examination of internal and external surface of the ferromagnetic structures. Based on the low frequency AC excitation simulation model built in ANSYS Electronics18.1 software, the amplitude and phase parameters of magnetic field were extracted and calculated. With the changes of the defect depths in different positions of the steel plate, the results of amplitude and phase parameters of magnetic field were studied and analyzed. Then the experiments of detection on artificial defects with different depths in different positions were conducted. The simulation and experimental results were discussed.
FA3 RPV Carbon Segregation Issue: Representativeness and Transferability of Sacrificial Parts
Authors: Lefrançois André , Berger Thierry , Lefever Benoît , Marie Stéphane
Published: October 2018

In order to demonstrate that the cover head and bottom head of the FA3 Reactor Pressure Vessel (RPV) exhibits sufficient toughness to withstand operational (from normal up to faulted) conditions, a dedicated experimental program was performed for three sacrificial forged parts (two cover heads and a bottom head) manufactured in Creusot Forge as-well, according to a similar process.

In order to be allowed to consider the mechanical properties (toughness) measured on these sacrificial parts, it was necessary to prove that they were representative of the FA3 ones.

Among all the parameters influencing the toughness properties it was defined that two of them had a major impact: the carbon content and the quenching effects.

For the first one, it was identified that it could be influenced by pouring conditions, forging conditions, including discard and upsetting ratios and machining (thickness).

For the second one, it was identified that it could be influenced by post-heat treatment machining and by quenching conditions.

Regarding these factors, for the five parts: manufacturing parameters and acceptance test results were compared, taking into account uncertainties.

In addition, for the three sacrificial parts, carbon content measured for various depths in the thickness were compared, after a transformation methodology allowing to convert depth inside part to ingot vertical location.

Finally, it was shown that the sacrificial parts could be considered to be representative of the FA3 parts to be used, for their mechanical properties.
The Research on Automatic Defect Recognition for Phased Array Ultrasonic Inspection of Polyolefin Butt Thermal-Fusion Joint
Authors: Zhong Haijian , Guo Weican , Miao Cunjian , Shi Jianfeng , Hou Dongsheng
Published: October 2018

Butt thermal-fusion joint is one of the main joints for polyolefin pipes. It could lead to different failure modes caused by factors such as different environments and operations, which will makes the joints become one of the most dangerous potential risks in polyolefin pipe system. As different defects could lead to different failure modes, defect recognition and classification are considered to be the critical issue for ultrasonic inspection. Based on the previous researches about defect recognition, simulation and experiments on artificial specimens in ultrasonic inspection, the imaging mechanism and identifying method were investigated for different defects, and the corresponding relations between joint defect characteristics and ultrasonic images were proposed. Furthermore, a defect recognition method was established. Many defect inspection, identification and dissection experiments were conducted on unknown defects, and the proposed method of automatic defect recognition was verified.
The Phased Array Ultrasonic Inner Inspection for the Butt Weld on the Head of High-Pressure Vessel
Authors: Miao Cunjian , He Qi , Du Xingji , Guo Weican , Ling Zhangwei , Xu Huiting
Published: October 2018

The layered high-pressure hydrogen vessels are widely used in hydrogen refueling stations. The head of the high-pressure vessel is made of austenitic stainless steel, and has thick walls, a pipe with a small diameter on the top and a butt-weld structure. It’s difficult to detect effectively, using conventional methods in the inspection of the butt weld on the head. To effectively detect the weld joint, a detecting method was investigated using ultrasonic phased array technique from the inner surface of the small-diameter pipe. By axial focusing and circumferential focusing, the ultrasonic field in austenitic stainless steel could satisfy the specific inspection requirement. Some ultrasonic field analysis and defect detection simulations were carried out with CIVA, for artificial defects such as side-drilled holes. Meanwhile, the test specimen and probe were designed and manufactured, and experiments were conducted. Furthermore, the feasibility and rationality of the detecting method and the simulation method were verified, and the detecting process parameters were determined.
Effects of Flaw Shape (Idealization) on the Interaction of Co-Planar Surface Flaws
Authors: Samadian Kaveh , Hertelé Stijn , De Waele Wim
Published: October 2018

Engineering Critical Assessment (ECA) guidelines contain amongst others, rules to assess flaw interaction. Major flaw dimensions (depth or height and length) are typically characterized assuming the flaws to be contained entirely within a bounding rectangle through a procedure known as flaw idealization. In (computational) fracture mechanics based calculations, flaws are often assumed to be (semi-)elliptical. This paper investigates the interaction between identical co-planar surface breaking flaws. Two flaw shapes are considered and compared: “canoe-shaped” (quarter-circular ends and constant depth elsewhere) and semi-elliptical. Especially for long shallow flaws, the canoe-shaped approximates the bounding rectangle, whereas the semi-elliptical shape only touches the bounding rectangle at three points (deepest point and two points at the surface). Several flaw dimensions and spacing distances are studied through an extensive parametric study comprising elastic and elastic-plastic finite element simulations. The results, based on Stress Intensity Factor (SIF) and J-integral analysis, show how the flaw shape can affect the degree of interaction. Notably, the inconsistency is less in linear-elastic analysis, but becomes more pronounced at higher (elastic-plastic) loading levels. This work highlights a challenge of comparing analytical and numerical based evaluations of interaction with ECA guidelines.
Research and Application of Ultrasonic Guided Wave With L(0,2) Mode for Elbow Tube Defect Inspection
Authors: Ding Ju , Zhang Min , Liu Shu-Hong , Tang Chen-huai , Wang Jie-Lu , Ren Bin , Yang Bo , Du Yan-Nan
Published: October 2018

Ultrasonic guided wave inspection technology has been widely for long distance pipeline inspection; however, the pipe elbow’s discontinuous structure and the dispersion of L-type wave are restricting the application of this technology. This paper proposes a method of L(0,2) mode guided wave excitation based on magnetostrictive effect and explores the optimization of the magnetization sensor arrangement. Test results shows that the proposed method can detect many types of defects in the pipe elbow. This paper encourages the use of L(0,2) mode guided wave excitation based on magnetostrictive effect in pipeline site inspections.
Buckling Assessment of Carbon Steel Pressure Vessels During PWHT
Authors: Kataoka Shunji
Published: October 2018

Post weld heat treatment (PWHT) is often applied to welded pressure vessels and piping to increase the mechanical and metallurgical properties. During the PWHT, a pressure component made of a carbon steel to which PWHT is applied, is heated up to the temperature around 620 deg.C with +/− 25 deg.C tolerances and that elevated temperature is kept for 1 to 2 hours. The local PWHT of the vertical pressure vessel is sometimes planned at a construction site with vertical position, because of some restrictions relating to construction, such as limited access route to the vessel location, and limited space large capacity cranes. In the situation, it is important to assure the structural stability during PWHT. Except wind loads, it is considered that the stress applied in the shell during PWHT is usually not significant, however there have been no published strength criteria corresponds to the PWHT conditions.

In this paper, the new elevated temperature tensile tests and constant stress creep strain tests of A516-Gr.70, a typical carbon steel material for pressure vessels, are conducted. Several examples of the numerical analysis using isochronous stress strain curve considering creep effect are presented.

From the test result, the importance of the consideration of the creep deformation on the structural integrity assessment of PWHT operation is clarified.
Investigation Into Thermal Stress Characteristics of Pipe-in-Pipe Under High Temperature Condition
Authors: Jeong Si-Hwa , Won Min-Gu , Huh Nam-Su , Kim Yun-Jae , Oh Young-Jin , Choi Jae-Boong
Published: October 2018

In this paper, the thermal stress characteristics of the pipe-in-pipe (PIP) system under high temperature condition are analyzed. The PIP is a type of pipe applied in sodium-cooled faster reactor (SFR) and has a different geometry from a single pipe. In particular, under the high temperature condition of the SFR, the high thermal stress is generated due to the temperature gradient occurring between the inner pipe and outer pipe. To investigate the thermal stress characteristics, three cases are considered according to geometry of the support. The fully constrained support and intermediate support are considered for case 1 and 2, respectively. For case 3, both supports are applied to the actual curved pipe. The finite element (FE) analyses are performed in two steps for each case. Firstly, the heat transfer analysis is carried out considering the thermal conduction, convection and radiation conditions. From the heat transfer analysis, the temperature distribution results in the piping system are obtained. Secondly, the structural analysis is performed considering the temperature distribution results and boundary conditions. Finally, the effects of the geometric characteristics on the thermal stress in the PIP system are analyzed.
Research on Reheat Cracking Criterion of CGHAZ in 2.25Cr1Mo0.25V Steel
Authors: Liu Chang-Jun , Zhou Shuang , Tan Jian-Ping , Zhang Hao-Yu
Published: October 2018

During the final post welding heat treatment (PWHT), residual stress relieves gradually with the accumulation of creep strain. However, reheat cracking with intergranular characteristic will occur when grain boundary cannot accommodate this kind of strain for some special steel welding, such as the welding coarse grained heat affected zone (CGHAZ) of 2.25Cr1Mo0.25V steel. Based on the principle of stress relaxation similar to the process of PWHT, two methods are applied to study the strain criterion of reheat cracking. Stress relaxation testing is performed on CGHAZ materials prepared by Gleeble thermomechanical simulator. The critical strain is calculated using the relationship between stress reduction and creep deformation. Self-loaded notched C-ring specimens are tested taken from the welding structure, coupled with finite element modeling and multiaxial creep coefficient to determine the critical strain. The results show that there is a large numerical difference between the critical strains from two methods. The possible reasons for the difference are given. Regarding the PWHT as a service process, whether the critical strain values obtained exceed the strain limits in ASME-NH is discussed.
Ductile Tearing Simulation of Circumferential Cracked Pipe Under Cyclic Loading Using Damage Criteria Determined by Monotonic Pipe Test Data
Authors: Hwang Jin-Ha , Youn Gyo-Geun , Miura Naoki , Kim Yun-Jae
Published: October 2018

To evaluate the structural integrity of nuclear power plant piping, it is important to predict ductile tearing of circumferential cracked pipe from the view point of Leak-Before-Break concept under seismic conditions. CRIEPI (Central Research Institute of Electric Power Industry) conducted fracture test on Japanese carbon steel (STS410) circumferential through-wall cracked pipes under monotonic or cyclic bending load in room temperature. Cyclic loading test conducted variable experimental conditions considering effect of stress ratio and amplitude. In the previous study, monotonic fracture pipe test was simulated by modified stress-strain ductile damage model determined by C(T) specimen fracture toughness test. And, ductile fracture of pipe under cyclic loading simulated using damage criteria based on fracture strain energy from C(T) specimen test data. In this study, monotonic pipe test result is applied to determination of damage model based on fracture strain energy, using finite element analysis, without C(T) specimen fracture toughness test. Ductile fracture of pipe under variable cyclic loading conditions simulates using determined fracture energy damage model from monotonic pipe test.
HRSG-Header Welds Residual-Stress Evaluation and Creep-Assessment Through the Application of Italian Code, American Standard
Authors: Grisolia Ottaviano , Scano Lorenzo
Published: October 2018

Joint design, preheating, post-weld-heat treatment and operator ability are key factors for the occurrence of critical residual stresses in the welds. In particular, they may affect creep life results of the analysis: to evaluate this, their characterization requires modeling welding process, such as that carried out in the present work for ASTM A 335-Grade P22 weld. It is a weld of the two analyzed in previous work on the high-temperature-section (superheater/reheater) lower headers of the bottom-supported heat-recovery steam generator (HRSG). Present study includes modeling the only weld-lay, gas tungsten arc, manual, for the finned-tube angle joint to the cylinder. It is the same as the first of the three weld-lays for the other previously analyzed, end-plug circumferential “V”-groove butt joint. The material considered for base metal is 2¼Cr 1Mo forged, normalized, tempered with creep strain rates higher than the weld’s as it appeared from analysis of previous work. Presently, the study first compares max tangential stress evaluated by thermal analysis on the circumferential weld with the average applied normally on the joint, sustained case. Roughly, the latter one has nearly same importance as axial membrane stress on the cylinder wall for the end-plug butt joint, pressure case; it is smaller for the finned-tube angle joint. Then, study compares previous creep results obtained considering SRF = 0.9 for the finned-tube joint weld with those counting the residual-stress increase in stress analysis (different creep law’s coefficients). Finally, study compares creep results for the finned-tube joint weld obtained with and without residual-stresses (same creep power-law). The objective is to comprehend residual-stress influence over creep-redistribution and creep relaxation.