A study on process parameters for cold U-bending of SUS304L heat transfer tube using rotary draw bending

Steam generator is one of enormous heat exchangers that use heat energy derived from a reactor of nuclear power plant for generating steam. The steam obtained is drained into a turbine, and plays an important role for power generation. The heat transfer tubes of each steam generator used in a pressurized water reactor (PWR) are composed of about 8,000 ～ 13,000 U-shaped tubes. These tubes act as the structural material and the thermal boundary. Furthermore, these tubes account for about 70% of the cooling surface area, transmitting thermal energy between the high-temperature (about 320°C), high-pressure (about 157 Kg_f/cm²) primary coolant derived from the reactor and the secondary coolant, which is at about 220°C and 60 Kg_f/cm², from the secondary system. These heat transfer tubes used in the steam generator within the PWR were fabricated from seamless tubes of stainless steel (SUS304L), Alloy 600 and Alloy690. In this study, numerical and experimental investigations are carried out on the U-bending process for fabricating heat transfer tubes from long straight SUS304L tubes. In the numerical simulation, 3-dimensional finite element analysis is performed using ABAQUS Explicit/Implicit. In detail, process parameters such as the angular speed, U-bending period, and bending angle taking into account elastic recovery after cold U-bending are considered. Additionally, experimental investigations are conducted to verify the suitability of the predicted U-shaped geometries in terms of the ovality and wall thickness of the U-shaped heat transfer tubes.     

Residual stress evaluation in dissimilar welded joints using finite element simulation and the L CR ultrasonic wave

Subsurface stresses in welded structures increase the likelihood of fatigue cracks and environmental induced material degradation. The ability to evaluate stresses at the surface as well as in the interior of welded structural members would substantially increase the accuracy of structure life estimation. The longitudinal critically refracted (L _CR) wave is a bulk longitudinal mode that travels within an effective depth underneath the surface. It may be used to detect in-plane subsurface stresses in the structures. This paper presents a three dimensional thermo-mechanical analysis to evaluate welding residual stresses in dissimilar plate-plate joint of AISI stainless steel 304 and Carbon Steel A106-B type. After finite element simulation, the residual stresses were evaluated by L _CR ultrasonic waves. Finally the results of two methods were compared and verified by hole-drilling method. This paper introduces a combination of ??Finite Element Welding Simulation?? and ??Ultrasonic Stress Measurement using the L _CR Wave?? which is called as ??FEL _CR??. The capabilities of FEL _CR??. The capabilities of FEL _CR in residual stress measurement are confirmed here. And also this paper evaluates residual stresses of dissimilar welded joints by LCR ultrasonic waves. It has been shown that predicted residual stress from three dimensional FE analyses is in reasonable agreement with measured residual stress from LCR method and also the results of both are verified with hole-drilling experimental measurements.     

Examining the Experience of Revealing Delayed Deformation Corrosion Cracking

The problem of skipping iron-oxide–filled damages in the welding junctions between the collector and Dn1200 branch pipe of the PGV-1000 steam generator in a VVÉR-1000 reactor facility is considered. The mechanism of crack nucleation and development is described. A hypothesis that cracks filled with corrosion deposits exhibit minimum reflectivity has been proposed and confirmed. Results of theoretical research into transmission and reflection of ultrasonic waves in the presence of a thin layer of corrosion products surrounded by pearlitic steel are provided. The reflectances of longitudinal and transverse waves from corrosion damages have been calculated and proved the viability of the hypothesis.     

拉伸载荷下穿透双裂纹干涉行为与合并准则研究

多裂纹的扩展与合并行为显著影响工程构件的剩余强度与使用寿命。为获得裂纹合并规律,对含不同长度和不同相对位置的非等长穿透双裂纹平板试样进行了拉伸试验,并基于延性损伤模型开展了有限元分析。结果表明,数值模拟中裂纹张口位移变化、扩展与合并行为与试验结果一致。此外,非等长穿透双裂纹长度及相对位置的变化,显著影响裂纹尖端的应力三轴度分布,进而影响双裂纹的合并行为。通过大量数值模拟分析,提出一种基于裂纹长度和相对位置的新合并准则。对照71组试验结果发现,新合并准则预测准确率高达84.5%;对照274组数值模拟结果发现,准确率高达91.2%。所提出的拉伸载荷下裂纹合并准则不仅具有显著高于现行含缺陷结构安全评定标准中合并准则的准确率,并且具有必要的保守性,可为工程构件中多裂纹合并与否提供有效判断。     

Experiments on thermal stratification in inlet nozzle of steam generator

Nuclear power plant components suffer pipe shedding, cracking, thermal fatigue, bending and supporting bracket breakage during their life span. Notably, the horizontal inlet nozzle of steam generator is prone to thermal stratification frequently due to its operational characteristics. As a result, PWRs in many countries including the U.S.A. suffered a lot of pipe cracks and leakages around the late 1970s, as the thermal stress inflicted by thermal stratification formed in the horizontal inlet nozzle of steam generator during transition (auxiliary feedwater injection) was not reflected on power plant design. Therefore, we classified the nuclear power plants in Korea into KSNP and Westinghouse-type(W) power plants (Kori # 1,2,3,4, Yeonggwang # 1,2 and Uljin # 1,2) and conducted an experiment on thermal stratification and thermal cycling in relation to the volume of auxiliary feedwater injected into the horizontal inlet nozzle of steam generator and hot water flowing back from steam generator. As a result, it was found out that KSNP was hardly prone to thermal stratification while thermal stratification occurred in the horizontal inlet nozzle of steam generator in Westinghouse-tvpe(W) power plants, necessitating a solution to address such a phenomenon.••     

Computational simulation of cold work effect on PWSCC growth in Alloy 600TT steam generator

The paper presents verification results for the validity of a numerical method considering the effect of cold work on Primary water stress corrosion cracking (PWSCC) growth rate in the Alloy 600TT steam generator tubes with a part-through single axial PWSCC. PWSCC growth simulations using Finite element (FE) analysis were performed with considering various cold work levels of the material. From the FE analysis results, the cold work effect was investigated from the variations of the PWSCC growth rate vs. Stress intensity factor (SIF) for the various cold work degrees and initial SIF values. Investigated results were compared with experimental test data available. It was identified that the numerical method could adequately assess the cold work effect on PWSCC growth in the Alloy 600TT tubes. In the simulation, it was found that the cold work could strongly influence the PWSCC growth rate even in a low degree of cold work, less than 2%.

     

蒸汽发生器堵头设计与堵管研究

堵管是核电站蒸汽发生器传热管破损的主要维修方法。调研并设计了堵头的结构，利用有限元软件ANSYS仿真分析了堵管过程，进行了堵管试验，并对被堵的传热管进行了密封性和力学性能检验。试验结果表明，堵头的结构设计合理，堵管通过了RCC—M规定的性能测试。     

蒸汽发生器管子管板液压胀保压时间数值模拟

第三代AP1000核岛主设备蒸汽发生器管子直径更小、管板厚度更厚、管子排列更密集、管子管板全长度液压胀管难度更大。采用ANSYS软件模拟蒸汽发生器管子与管板液压胀管的方法,着重用瞬态分析方法研究胀管压力和保压时间对接触压应力的影响,从而确定使接触压应力最大的平衡点。     

Application of modified mapping-collocation method to cracks emanating from a circular hole in an orthotropic finite plate

A modified mapping-collocation method is applied to the analysis of cracks emanating from a circular hole in an orthotropic finite plate under uniform stress. To check the effectiveness of this procedure, we present the various results for comparison with references. Then, the stress intensity factors are presented for several plate configurations of [0 _n /90 _m ] _s laminates. The results show that the modified mapping-collocation method is effectively applicable to analyzing such cracks in an orthotropic finite plate. The results also show that the stress intensity factors depend on the material orthotropy and geometry.     

Investigation of wire electrical discharge machining characteristics of Al6063/SiCp composites

In this investigation, the effect of wire electrical discharge machining (WEDM) parameters such as pulse-on time (T _ON), pulse-off time (T _OFF), gap voltage (V) and wire feed (F) on material removal rate (MRR) and surface roughness (R _a) in metal matrix composites (MMCs) consisting of aluminium alloy (Al6063) and silicon carbide (SiC_p) is discussed. The Al6063 is reinforced with SiC_p in the form of particles with 5%, 10% and 15% volume fractions. The experiments are carried out as per design of experiments approach using L₉ orthogonal array. The results were analysed using analysis of variance and response graphs. The results are also compared with the results obtained for unreinforced Al6063. From this study, it is found that different combinations of WEDM process parameters are required to achieve higher MRR and lower R _a for Al6063 and composites. Generally, it is found that the increase in volume percentage of SiC resulted in decreased MRR and increased R _a. Regression equations are developed based on the experimental data for the prediction of output parameters for Al6063 and composites. The results from this study will be useful for manufacturing engineers to select appropriate WEDM process parameters to machine MMCs of Al6063 reinforced with SiC_p at various proportions.     

Quality control of rolled rods by the electromagnetic-acoustic technique

Special features of testing of metal rods by the electromagnetic-acoustic technique were studied using rod waves (Pochhammer wave s ₀, torsional wave T ₀) and bulk waves (longitudinal l and transverse t waves of radial direction). It was shown that rod waves can detect not only a discontinuity but also a change in the chemical composition or length of rods. Bulk waves make it possible to perform nondestructive testing and structural analysis and to find a change in diameter. A combination of pivoting and bulk waves makes it possible to find the anisotropy of elastic properties and evaluate the texture of rolled metal.     

On the number of cracks in the axial splitting of ductile metal tubes

An analysis is given for the number of cracks which propagate in experiments on the splitting of ductile metal tubes when the ends are flared out. The number of cracks depends on the diameter of the tube (2r₀), the strength-to-toughness ratio of the metal ( ) and its hoop fracture strain _θ∫ (which may be related to microstructure via models of microvoid growth and coalescence). Since the expression for the number of cracks contains the product of ( ) and _θ∫, approximately the same number of cracks is predicted whether the tubes are annealed or work-hardened. Experiments by Reddy and Reid [Int. J. Mech. Sci. 28, 111 (1986)] give support to the predictions.     

蒸发器传热管堵管判据的研究

以传热管缺陷的伤深比α和当量长度比γ为参量,利用爆破压力拟合计算公式和强度条件,导出了含缺陷传热管的安全评定判据和堵管条件,提出了传热管在役检查的验收判据和堵管条件。     

Fluid dynamics analysis and optimized throttling design of L-shaped multi-stage high pressure reducing valve

Traditional high-pressure pressure reducing valves are mostly linear, occupying a lot of space and costing a lot. In this study, a L-shaped multi-stage high pressure reducing valve (L-HPRV) is newly designed, it can be widely used in space constrained pipelines, reducing floor space and thus lower costs. Then, the steam flow in L-HPRV is investigated with an experimental validated numerical method. Next, a parametric sensitivity study is conducted to investigate the effects of typical throttling components on fluid dynamics of the newly designed L-HPRV. Finally, based on the parametric sensitivity study, the optimized throttling design of L-HPRV is achieved. The results show that the rhombus-shaped perforated plates is considered to be the first choice for better fluid dynamics. Larger perforated plate diameter (D₁/D₀) and perforated sleeve diameter (D₂/D₀) relates to better aerodynamic performance. Chamfer radius has limited effects on fluid dynamics. N-stage adjustable perforated plate effectively disperses the pressure drop and velocity rising gradient in the throttling components at all levels. The preferred level ranking with better fluid dynamics for L-HPRV is obtained.     

Process improvement in laser hot wire cladding for martensitic stainless steel based on the Taguchi method

Laser hot wire cladding, with the prominent features of low heat input, high energy efficiency, and high precision, is widely used for remanufacturing metal parts. The cladding process, however, needs to be improved by using a quantitative method. In this work, volumetric defect ratio was proposed as the criterion to describe the integrity of forming quality for cladding layers. Laser deposition experiments with FV520B, one of martensitic stainless steels, were designed by using the Taguchi method. Four process variables, namely, laser power (P), scanning speed (V _s), wire feed rate (V _f), and wire current (I), were optimized based on the analysis of signal-to-noise (S/N) ratio. Metallurgic observation of cladding layer was conducted to compare the forming quality and to validate the analysis method. A stable and continuous process with the optimum parameter combination produced uniform microstructure with minimal defects and cracks, which resulted in a good metallurgical bonding interface.     

采油注汽锅炉爆管事故原因分析

通过对3个炉管爆裂断口金相及金属材料分析研究,为诊断和确定锅炉爆管事故发生的原因提供了依据,也为提出预防采油锅炉爆管事故的措施奠定了基础。通过分析比较3个爆破炉管的成分、宏观形貌及显微组织,注汽锅炉炉管产生爆管的主要原因是炉管壁温超温所致。     

Neuro-fuzzy and neural network-based prediction of various responses in electrical discharge machining of AISI D2 steel

In the present research, two neuro-fuzzy models and a neural network model are presented for predictions of material removal rate (MRR), tool wear rate (TWR), and radial overcut (G) in die sinking electrical discharge machining (EDM) process for American Iron and Steel Institute D2 tool steel with copper electrode. The discharge current (I _p), pulse duration (T _on), duty cycle (τ), and voltage (V) are considered as inputs to the network. A full-factorial design was used to conduct the experiments with various levels of I _p, T _on, τ, and V. The analysis of variance results reveal that I _p is the most influencing factor for MRR and G, having the highest degree of contributions of 87.61% and 81.90%, respectively. In case of TWR, T _on has the highest degree of contribution of 46.05% and is the most significant factor. The half of the experimental data set was used to train the networks and was tested for convergence with a different set of data to obtain appropriate number of neurons, epoch, and the fuzzy rule base. The mean square error convergence criteria, both in training and testing, came out very well. The developed models are found to approximate the responses quite accurately. Moreover, the predicted results based on above models have been confirmed with unseen validation set of experiments and are found to be in good agreement with the experimental results. The comparison results reveal that the artificial neural network and the neuro-fuzzy models are comparable in terms of accuracy and speed, and further, the proposed models can be employed successfully in prediction of MRR, TWR, and G of the stochastic and complex EDM process.     

在用蒸汽发生器开裂原因分析及对策

制氢装置中的蒸汽发生器壳体在使用时连续在不同部位开裂泄漏,通过实施全面的检验,并进行详细的分析,确定了其开裂失效的原因,并采取了相应的对策,取得了较好的效果。     

A study on fretting fatigue characteristics of Inconel 690 at high temperature

Inconel 690 alloy is used in nuclear power plant steam generator tubes. Fretting fatigue experiments were performed on Inconel 690 specimens at room temperature and at the nuclear power plant operating temperature of 320 °C. By comparing the fretting fatigue test data at room temperature and 320 °C, this study analyzed the change in characteristics related to the fatigue limit at 10⁷ cycles. In addition, this study attempted to measure changes in the friction force for repetitive cycles in fretting fatigue tests, and analyzed the mechanism of fretting fatigue by observing the fracture surfaces and performing spectrum analysis.     

Surface finish of bulk metallic glass using sequential abrasive jet polishing and annealing processes

Surface finish plays an important role in product quality due to its direct effects on product appearance. Hence, improvement of the surface finish is an essential requirement in industrial products. In an attempt to improve the surface finish of bulk metallic glass (BMG) material, several common methods have been used, such as milling, grinding, and lapping. However, the BMG surface finish has not yet been significantly improved by using these methods. Therefore, this paper proposes sequential abrasive jet polishing (AJP) and annealing processes that can considerably improve the BMG surface finish. In addition, this paper also takes into account optimal parameters for the AJP and annealing processes based on the Taguchi’s L ₁₈ and L ₈ orthogonal array experimental results, respectively. The experimental results show that using optimal AJP parameters, the surface roughness (R _a) of the ground specimens can be significantly improved from 0.675 to 0.016 μm. After the AJP process, the surface roughness (R _a) of the polished specimens can be further improved from 5.7 to 2 nm within an area of 5?×?5 μm by using optimal annealing parameters.