Seiji Ioka

An Inverse Method for Determining Thermal Load History Which Reduces Transient Thermal Stress

When high temperature fluid flows into a pipe, a temperature distribution in the pipe induces a thermal stress. It is important to reduce the thermal stress for managing and extending the lives of plants. In this problem heat conduction, elastic deformation, heat transfer, liquid flow should be considered, and therefore the problem is of multidisciplinary nature. In this paper an inverse method is proposed for determining the optimum thermal load history which reduces transient thermal stress considering the multidisciplinary physics. As a typical problem, transient thermal stress in a thin pipe during start-up was treated. It was assumed that the inner surface was heated by liquid flow and the outer surface was insulated for simplicity. The multidisciplinary complex problem was decomposed into a heat conduction problem with given internal wall temperature history, thermal stress problem with given temperature distribution, and heat transfer problem with given heat flux on an inner surface. An analytical solution of the temperature distribution of the radial thickness and the thermal hoop stress distribution was obtained. The maximum inner hoop tensile stress was minimized for the case where inner surface temperature Ts (t) was expressed in terms of the 3rd order polynomial function of time t. Finally, from the temperature distributions, the optimum fluid temperature history was obtained for reducing the transient thermal tensile stress.Copyright

Multiphysics Inverse Analysis Method for Reducing Transient Thermal Stress in a Thick-Walled Pipe

When high temperature fluid flows into a pipe, a temperature distribution in the pipe induces a thermal stress. It is important to reduce the thermal stress for managing and extending the lives of plants. In this problem heat conduction, elastic deformation, heat transfer, liquid flow should be considered, and therefore the problem is of multidisciplinary nature. In a previous paper the present authors proposed an inverse method for determining the optimum thermal load history which reduces the transient thermal stress considering the multidisciplinary physics. The optimum temperature history of inlet fluid may be useful for designing and operating plants. Analytical solutions of the temperature and stress distributions for a thin-walled pipe were used in the analysis. In the present study the reduction of transient thermal stress in a thick-walled pipe is considered. The finite element techniques are employed in the optimization for obtaining the temperature distribution and the thermal stress in the thick-walled pipe. The maximum hoop tensile stress is minimized for the case where inner surface temperature is expressed in terms of a polynomial function of time. The effect of the ratio of inner radius to outer radius on the optimum temperature history is examined. It is found that when the ratio of inner radius to outer radius is larger than 0.8 the optimum temperature history for the thin-walled pipe gives a good estimate. For thicker pipes the optimum temperature history for the thin-walled pipe can be an initial guess for searching the optimum temperature history.Copyright

Development and Validation of Inverse Analysis of Heat Conduction and Thermal Stress for Elbow: Part II

A heat conduction inverse method for piping elbow was developed to estimate the temperature and stress distribution on the inner surface by measuring the outer surface temperature. In the Part I paper, the derivation and verification of the heat conduction inverse method were described. In the Part II paper, the accuracy for the thermal stress calculation was confirmed by assuming several thermal stratification patters and comparing with the reference results from normal FE heat conduction and thermal stress analyses. As a result, in the case of the measured-basis fluid temperature input from a high temperature-pressure test, the inverse method estimated the maximum stress change by 7% conservative comparing the normal FE analyses. For the assumed temperature change pattern the estimation accuracy was conservatively improved by attaching the additional thermocouples on the outer surface adjacent to the thermal stratification phase. The developed method is practically useful because of short calculate time of 1–2 seconds for 500 time data points after providing the transfer functions.Copyright

Inverse analysis of inner surface temperature history from outer surface temperature measurement of a pipe

When slug flow runs through a pipe, nonuniform and time-varying thermal stresses develop and there is a possibility that thermal fatigue occurs. Therefore it is necessary to know the temperature distributions and the stress distributions in the pipe for the integrity assessment of the pipe. It is, however, difficult to measure the inner surface temperature directly. Therefore establishment of the estimation method of the temperature history on inner surface of pipe is needed. As a basic study on the estimation method of the temperature history on the inner surface of a pipe with slug flow, this paper presents an estimation method of the temperature on the inner surface of a plate from the temperature on the outer surface. The relationship between the temperature history on the outer surface and the inner surface is obtained analytically. Using the results of the mathematical analysis, the inverse analysis method of the inner surface temperature history estimation from the outer surface temperature history is proposed. It is found that the inner surface temperature history can be estimated from the outer surface temperature history by applying the inverse analysis method, even when it is expressed by the multiple frequency components.

Passive electric potential CT method using piezoelectric film for identification of defects

The present authors proposed the electric potential computed tomography (CT) method for identifying defects in electric-conductive bodies from electric potential distributions observed on their surfaces under electric current application. When the piezoelectric material is pasted on a cracked body subjected to mechanical load, the electric potential distribution can be obtained due to the direct piezoelectric effect without applying the electric current. The passive electric potential CT method proposed by the present authors uses this distribution. This paper describes the fundamentals of the passive electric potential CT method, inverse analysis schemes and its applications for identification of a through-thickness crack, a surface crack, plural cracks and delamination in a layered composite material. The usefulness of the method is demonstrated.

Development of Inverse Analysis of Heat Conduction and Thermal Stress for Elbow: Part I

Thermal fatigue may develop in piping elbow with high temperature stratified flow. To prevent the fatigue damage by stratified flow, it is important to know the distribution of thermal stress and temperature history in a pipe. In this study, heat conduction inverse analysis method for piping elbow was developed to estimate the temperature history and thermal stress distribution on the inner surface from the outer surface temperature history. In the inverse analysis method, the inner surface temperature was estimated by using the transfer function database which interrelates the inner surface temperature with the outer surface temperature. Transfer function database was calculated by FE analysis in advance. For some patterns of the temperature history, inverse analysis simulations were made. It was found that the inner surface temperature history was estimated with high accuracy.Copyright

Multi-electrodes active and passive electric potential CT methods for crack identification using a smart layer

The present authors proposed the passive electric potential CT method using an electric potential distribution appear- ing due to the direct piezoelectric effect on a piezoelectric film pasted on a structure subjected to mechanical load. By applying an electric pulse on the film for emitting pulse-echo due to the inverse piezoelectric effect, the active pulse-echo method was proposed. In this paper a simultaneous application of the passive and the active methods using the piezoelectric film with multi- electrodes was made for the quantitative identification of through-cracks. The electric potential was measured on the film of a cracked specimen subjected to a varying load. The electric pulse was applied to an electrode on the piezoelectric film and reflection waves were received at several electrodes on the piezoelectric film. Inverse analysis was made to identify the cracks from the observed electric potential distributions and the reflected waves. It was found that the active/passive method was useful for the estimation of the crack depth, for which the passive method was not efficient. The effectiveness of the active/passive method was shown.

An Inverse Analysis Method for Estimation of Heat Flux and Temperature-Dependence of Heat Transfer Coefficient

Transient thermal stresses develop in pipes during start-up and shut-down. In previous papers the present authors [1–4] proposed an inverse method for determining the optimum thermal inlet liquid temperature history which reduced the maximum transient thermal stress in pipes. The papers considered multiphysics including heat conduction, heat transfer, and elastic deformation. The inverse method used the relationship between inner surface temperature history, transient temperature distribution and transient thermal stresses. The coefficient of heat transfer plays an important role in the evaluation of thermal stress. In this study an inverse method was developed for estimating heat flux and temperature-dependence of the coefficient of heat transfer from the history of the outer surface temperature and the liquid temperature. The method used the relationship between the outer surface temperature and the inner surface temperature. For the regularization of solution the function expansion method was applied in expressing the history of flux on the inner surface. Numerical simulations demonstrated the usefulness of the proposed inverse analysis method. By examining the effect of measurement errors of temperature on the estimation, the robustness of the method was shown.Copyright

Determination of the optimum temperature history of inlet water for minimizing thermal stresses in a pipe by the multiphysics inverse analysis

It is important to reduce the thermal stresses for managing and extending the lives of pipes in plants. In this problem, heat conduction, elastic deformation, heat transfer, liquid flow should be considered, and therefore the problem is of a multidisciplinary nature. An inverse method was proposed by the present authors for determining the optimum thermal load history which reduced transient thermal stress considering the multidisciplinary physics. But the obtained solution had a problem that the temperature increasing rate of inner surface of the pipe was discontinuous at the end time of heat up. In this study we introduce temperature history functions that ensure the continuity of the temperature increasing rate. The multidisciplinary complex problem is decomposed into a heat conduction problem, a heat transfer problem, and a thermal stress problem. An analytical solution of the temperature distribution of radial thickness and thermal hoop stress distribution is obtained. The maximum tensile and compressive hoop stresses are minimized for the case where inner surface temperature Ts(t) is expressed in terms of the 4th order polynomial function of time t. Finally, from the temperature distributions, the optimum fluid temperature history is obtained for reducing the thermal stresses.

Free-Edge Stress Singularity of Bonded Dissimilar Materials with an Interlayer

Free-edge stress singularity usually prevails at the edge of the interface of the bonded dissimilar materials. When two materials are bonded by using an adhesive, an interlayer develops between two materials. An interlayer may inserted between two materials to defuse the residual stress due to the difference in the coefficients of thermal expansion. In this study, to investigate the effect of the interlayer on the free-edge stress singularity of the bonded dissimilar materials with an interlayer, the stress distributions on the interface were examined numerically and theoretically. Relation between the free-edge stress singularity of the bonded dissimilar materials with and without an interlayer was investigated by using the boundary element method. It was found that the effect of the interlayer on the stress distribution was limited within a small area of the order of the interlayer thickness. Stress distributions near the edge of the interface were controlled by the free-edge stress singularity of the bonded dissimilar materials without an interlayer.