• Steel and Composite Structures
• /
• v.28 no.3
• /
• pp.349-362
• /
• 2018

This paper presents a semi-analytical solution for the creep analysis and life assessment of 304L austenitic stainless steel thick truncated conical shells using multilayered method based on the first order shear deformation theory (FSDT). The cone is subjected to the non-uniform internal pressure and temperature gradient. Damages are obtained in thick truncated conical shell using Robinson's linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson-Miller Parameter (LMP). The creep response of the material is described by Norton's law. In the multilayer method, the truncated cone is divided into n homogeneous disks, and n sets of differential equations with constant coefficients. This set of equations is solved analytically by applying boundary and continuity conditions between the layers. The results obtained analytically have been compared with the numerical results of the finite element method. The results show that the multilayered method based on FSDT has an acceptable amount of accuracy when one wants to obtain radial displacement, radial, circumferential and shear stresses. It is shown that non-uniform pressure has significant influences on the creep damages and remaining life of the truncated cone.

• Proceedings of the KSME Conference
• /
• 2000.04a
• /
• pp.31-36
• /
• 2000

High temperature and pressure materials in power plant are degraded by creep damage, if they are exposed to constant loads for long times, which occurs in the load bearing structures of pressurized components operating at elevated temperatures. Many conventional measurement techniques such as replica method, electric resistance method, and hardness test method for measuring creep damage have been used. So far, the replica method is mainly used for the Inspection of High temperature and pressure components. This technique is, however, restricted to applications at the surface of the testpieces and cannot be used to material inside. In this paper, ultrasonic evaluation for the detection of creep damage in the form of cavaties on grain boundaries or integranular microcracks are carried out. And the absolute measuring method of quantitative ultrasonic velocity technique for Cr-Mo material degradation is analyzed. As a result of ultrasonic tests for crept specimens, we find that the sound velocity is decreased as the increase of creep life fraction$({\Phi}_c)$ and also, confirmed that hardness is decreased as the increase of creep life fraction$({\Phi}_c)$ but the coefficient of ultrasonic attenuation is increased as the increase of creep life fraction$({\Phi}_c)$. Finally based on the result in this paper, it can be recognized that the ultrasonic techniques using velocities and attenuation coefficient factor are very useful non-destructive methods to evaluate the degree of material degradation in fossile power plants.

• Journal of Ocean Engineering and Technology
• /
• v.15 no.2
• /
• pp.46-52
• /
• 2001

In this paper, the real-time prediction of high temperature creep life was carried out for the friction welded joints of dissimilar heat resisting steels (SUH3-SUH35). various life prediction method such as LMP (Larson_miller Parameter) and ISM (initial strain method) were applied. The creep behaviors of those steels and the welds under static load were examined by ISM combined with LMP at 500, 600 and $700^{\circ}C$, and the relationship between these two methods was investigated. A real-time creep lie (tr, hr) prediction equation by initial strain (${\varepsilon}_0$, %) under any creep stress ($\sigma$, MPa) at any high temperature (T, K) was developed as follows: $t_r={\alpha}{\varepsilon}_0^{\beta}{\sigma}^{-1}$ where, ${\phi}=16: {\alpha}=10^{51.412-0.104T+5.375{\times}10^5T^2}$, $ {\beta}=-83.989+0.180T-9.957{\times}10^{-5}T^2,{\phi}=20:$ ${\alpha}=10^{69.910-0.146T+7.744{\times}10^{-5}T^2$, ${\beta}=-51.442+0.105T-5.595{\times}10^{-5}T^2$ for SUH3-SUH35 friction weld of =16mm and 20mm, respectively.

• Transactions of Materials Processing
• /
• v.17 no.8
• /
• pp.558-563
• /
• 2008

The initial strain, the applied stress exponent, the activation energy, and rupture time in AZ31 magnesium alloy have been measured in order to predict the deformation mechanism and rupture life of creep over the temperature range of 423-443K. Creep tests were carried out under constant applied stress and temperature, and the lever type tester and automatic temperature controller was used for it, respectively. The experimental results showed that the applied stress exponent was about 9.74, and the activation energy for creep, 113.6KJ/mol was less than that of the self diffusion of Mg alloy including aluminum. From the results, the mechanism for creep deformation seems to be controlled by cross slip at the temperature range of 423-443K. Also the higher the applied stress and temperature, the higher the initial strain. And the rupture time for creep decreased as quadratic function with increasing the initial strain in double logarithmic axis.

• Journal of Ocean Engineering and Technology
• /
• v.18 no.2
• /
• pp.58-63
• /
• 2004

Reduced Activation Ferritic/Martensitic Steels (RAFs) are leading candidntes for structural materials of a D-T fusion reactor. One of the RAFs, JLF-l (9Cr-2W-V, Ta) has been developed and has shown to have good resistance against high-fluency neutrino irradiation and good phase stability. Recently, in order to clarify the strengthening mechanisms at high temperatures, a new scheme to improve high temperature mechanical properties is desired. Therefore, the test technique development of high temperature creep behaviors for this material is very important. In this paper, the creep properties and creep life prediction, using the Larson-Miler parameter method for JLF-l to be used for fusion reactor materials or other high temperature components, are presented at the elevated temperatures of 50$0^{\circ}C$, 55$0^{\circ}C$, $600^{\circ}C$, $650^{\circ}C$ and 704$^{\circ}C$. It was confirmed, experimentally and quantitatively, that a creep life predictive equation, at such various high temperatures, is well derived mr the LMP method.

• Journal of Ocean Engineering and Technology
• /
• v.12 no.2 s.28
• /
• pp.71-78
• /
• 1998

In this report for the assessment of creep properties of high-temperature tube materials in power plants, the long-time($10^4$~105h) creep life prediction by ISM for 2.25Cr1Mo steel was studied. It was clarified experimentally and quantitatively that the newly developed long-time creep life prediction equation was very coincident with the actual experimental data with high confidence, and the model was $t_r=\alpha\varepsilon_0^{\beta}\sigma^{-1}$.

• Journal of the Korean Society of Safety
• /
• v.21 no.1 s.73
• /
• pp.28-34
• /
• 2006

A procedure of estimating failure probability is demonstrated for a pressurized pipe of CrMo steel used at $538^{\circ}C$. Probabilistic fracture mechanics were employed considering variations of pressure loading, material properties and geometry. Probability density functions of major material variables were determined by statistical analyses of implemented data obtained by previous experiments. Distributions of the major variables were reflected in Monte Carlo simulation and failure probability as a function of operating time was determined. The creep crack growth life assessed by conventional deterministic approach was shown to be conservative compared with those obtained by probabilistic one. Sensitivity analysis for each input variable was also conducted to understand the most influencing variables to the residual life analysis. Internal pressure, creep crack growth coefficient and creep coefficient were more sensitive to failure probability than other variables.

• Journal of the Korean Society of Safety
• /
• v.28 no.3
• /
• pp.6-10
• /
• 2013

The Heat Recovery Steam Generator(HRSG) is a device recycling the exhaust gas of gas turbine in combined power and chemical plants. Since service temperatures was very high, the damage of HRSG tubes intensively occurred in superheater and reheater. The aim of this paper is to determine life and hardness relationship that addresses creep-rupture test and creep-interrupt test in modified 9Cr-1Mo steel. The measured life that consists of function of hardness was found to constant tendency.

• Journal of the Korean Society for Precision Engineering
• /
• v.21 no.2
• /
• pp.168-176
• /
• 2004

Interrupted creep tests were carried out on the Mod.9Cr-1Mo steel in order to investigate the structural degradation during creep. The ranges of creep stress and temperature were from 71 to 167MPa and 873 to 923k, respectively. The change of hardness and tempered martensitic lath width were measured in the grip and gauge parts of interrupted specimens. The lath structure was thermally stable in static conditions, but was not stable during creep, and the structural evolution was enhanced by creep strain. The relation between the change in lath width and strain was described in the from, $\delta$W= a ($W_s-W_o$)$cdot;varepsilon$, where $\varepsilon$ is the strain, $W_o$is the initial lath width, $W_s$ is the final lath width depending solely on stress, and a is the constant of the magnitude of 0.67 $\mu$m /strain. The change in Victors hardness was expressed by a one-valued function of creep life consumption ratio. Based on the empirical relation between strain and lath width, a model was proposed to explain the relation between change in hardness and creep life consumption ratio. The model revealed that about 65$%$ of dislocations in lath structures were eliminated by the migration of subboundaries.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.2
• /
• pp.296-303
• /
• 2001

Kachanov-Rabotnov(K-R) creep damage theory was reviewed, and applied to design a creep curve for type 316LN stainless steel. Seven coefficients used in the theory, i.e., A, B, k, m, λ, r, and q were determined, and their physical meanings were analyzed clearly. In order to quantify a damage parameter ($\omega$), cavity amount was measured in the crept specimen taken from interrupted creep test with time variation, and then the amount was reflected into K-R damage equations. Coefficient λ, which is regarded as a creep tolerance feature of a material, increased with creep strain. Mater curve with λ=2.8 was well coincided with an experimental one to the full lifetime. The relationship between damage parameter and life fraction was matched with the theory at exponent ${\gamma}$=24 value. It is concluded that K-R damage equation was reliable as the modelling equation for type 316LN stainless steel. Coefficient data obtained from type 316LN stainless steel can be utilized for life prediction of operating material.