Papers by Keyword: Weldment

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Authors: Seung Se Baek, Il Hyun Kwon, Dong Whan Lee, Sung Mo Yang, Hyo Sun Yu
Abstract: Power plant weldments are composed of various microstructures. Due to welding and PWHT processes, the microstructure of the base metal adjacent to fusion line is transformed into entirely different microstructures, collectively known as heat affected zone (HAZ). Creep, on the other hand, is considered as the most important deterioration mechanism of heat resistant components found in power plants. Therefore it is essential to evaluate creep properties of HAZ, which is considered to be very hazardous in weldment. Recently, most of the creep tests for HAZ are conducted using cross weld type specimen. However there are some problems with this type of creep test due to the results being largely varied according to the volume fraction of HAZ. In this paper, SP-Creep test, which has confirmed the availability for creep properties evaluation, has been conducted on each of the weldment microstructures. The results showed that each microstructure has a different creep behavior. The overall creep properties of HAZ are worse than those of the weld metal. Among the HAZ structures, fine grained HAZ has the worst creep properties.
Authors: Jaroslav Balík, Miloš Janeček, Josef Pešička
Abstract: The growth of cracks in base steel P91 of 9Cr-1Mo class and in intercritical layer of HAZ is measured under creep coditions. For long term tests, a material degradation was detected consisting in an increase of crack growth rate and in a decrease of crack initiation time. An attempt is made to connect these effects with drop in ductility during thermomechanicalexposition.
Authors: F. Masuyama, M. Matsui, N. Komai
Authors: Jung Suk Lee, Kwang Ho Kim, Jae Hwan Han, Dong Il Kwon
Abstract: The material characterization on the weak points of the structural systems is essential to evaluate safety accurately. However, general material characterization methods such as uniaxial tensile test and CTOD (crack tip opening displacement) test are destructive, therefore, it cannot be applied to the system in use. To overcome this problem, the material characterization using instrumented indentation technique was developed. However, current researches on instrumented indentation technique focus on the hardness measurement. The evaluation of flow property, residual stress and fracture toughness using instrumented indentation technique is not sufficiently performed. In this paper, we introduce the evaluation method of the flow property, the residual stress near the weldment and the fracture toughness developed from damage mechanics. The algorithm of flow property evaluation, the residual stress evaluation model and the fracture toughness model by using indentation were verified comparing with the experimental results.
Authors: Tsuyoshi Takahashi, Yoshitaka Iwabuchi, Kazunori Ishitsuka
Abstract: The influence of residual stress and sensitizing on the electrochemical and corrosion behavior of type SUS304 stainless steels weldment has been studied in the Freeze-Thaw condition. After immersion test at Freeze-Thaw cyclic condition the severe corrosion damage was detected in the vicinity of weld boundary more than isothermal condition. The corrosion damaged zone corresponds to the location in which there are high residual stress and sensitization. The influence of residual stress and sensitization was distinguished and its magnitude was evaluated by voltammetry method.
Authors: Si Yon Bae, Bum Joon Kim, Byeong Soo Lim
Abstract: There exists strong environmental and economic pressure to increase the thermal efficiency of fossil fuel power stations and this has led to a steady increase in operating temperature and pressure resulting in the world wide construction plans for ultra super-critical power plants. Consequently, in order to improve the thermal efficiency of power plant, there has been a strong drive to develop more advanced heat resistant steels with excellent creep, high temperature fatigue and thermal fatigue resistant properties as well as superior oxidation and corrosion resistant properties. In this study, the test material was P122 alloy which was developed for ultra super-critical power plant. To measure the fatigue crack growth rate in low #K range, fatigue tests were performed on the P122 alloy welds by #K decreasing method at three different microstructure (Base metal, HAZ, Weld metal) regions. Microstructure observation and micro-hardness tests performed for all three regions to find the relationship among the crack growth rate, microstructure and hardness. Fatigue tests were performed with compact tension specimens at 600°C, 650°C and 700°C at the loading frequency of 20Hz.
Authors: Ju Young Kim, Jung Suk Lee, Kyung Woo Lee, Kwang Ho Kim, Dong Il Kwon
Abstract: Flow properties and stress state are indispensable factors for safety assessment of structural materials in operation, which were evaluated using instrumented indentation tests (IITs). Flow properties were obtained by defining representative stress and strain, and IIT results for 10 steel materials were discussed by comparing with those from uniaxial tensile tests. The indentation load-depth curve is significantly affected by the presence of residual stress, and the stress-induced load change was converted to a quantitative stress value. The stress state of a friction stir-welded joint of API X80 steel was evaluated and compared with that measured by energy-dispersive X-ray diffraction.
Authors: Robert Moskovic, N.P. O'Dowd, M. Priest, Peter E.J. Flewitt
Authors: Dulce Maria Rodrigues, Luís Filipe Menezes, Altino Loureiro, José Valdemar Fernandes
Authors: Xiang Ling, Hong Fang Ni, Gang Ma
Abstract: High residual tensile stress is an important factor contributing to stress corrosion cracking (SCC). Shot peening can impose compressive stresses on the surface of welded joints that negate the tensile stresses to enhance the SCC resistance of welded joints. In the present work, the distribution of residual stress caused by welding is measured by X-ray diffraction method. The maximum stress in the weld is close to the yield strength of AISI 304 stainless steel, and the stresses are negative at both ends of the weld and far from the weld. The X-ray method is also used to measure stress caused by shot-peening. The results show that the higher the peening coverage, the higher the residual compressive stresses in the surface of weldments. While under the same condition, the residual compressive stresses induced by glass beads shot-peening are larger than those by cast steel shots. Temperature and stress fields of welding are simulated by using ABAQUS codes. The 3-D solid elements are used in FEM. Temperature depending on material properties as well as the convection and radiation as boundary conditions are considered. The 3-D linear reduced-integration elements are used to simulate the shot peening process. The results of simulation have a good agreement with experimental data. All unpeened and peened weldments are immersed in boiling 42% magnesium chloride solution during SCC test. Unpeened specimens crack after immersion for 6 hours. The steel-peened specimens with 50% coverage crack after 310 hours, while the steel-peened specimens with 100% coverage crack for 3500 hours. However, steel-peened specimens with 200% coverage and glass-peened specimens with 50%, 100% and 200% coverage are tested for a total of 3500 hours without visible stress corrosion cracks in the peened surfaces. The experiment results indicate that shot peening is an effective method for protecting weldments against SCC and weldments peened by glass beads resist SCC better than those peened by steel shots.
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