Title: Fatigue Studies of Stainless Steel Pipes Subject to High Cycle Domain Sinusoidal Thermal Loads
Authors: PAFFUMI ElenaRADU VasileNILSSON Karl-FredrikTAYLOR Nigel
Citation: ASME PVP 2009 Pressure Vessel and Piping Conference, ISBN 978-0-7918-3854-9 vol. Design and Analysis 2009, Thermal Stresses in Vessels, Piping and Components p. PVP2009-77643 (9 pp)
Publisher: ASME
Publication Year: 2009
JRC N°: JRC48706
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC48706
Type: Articles in periodicals and books
Abstract: To contribute to the development of improved methods for assessing possible thermal fatigue damage in nuclear plant piping systems, a combined experimental and numerical investigation has been conducted on cylindrical components of 316L stainless steel subject to cyclic thermal shocks of varying intensity. Slightly different experimental conditions were applied in each test to explore the effect of different DT values of increasing severity, the effect of a superimposed static axial load and a reduced test piece wall thickness. It was established that conservative estimates of the thermal fatigue crack growth could be obtained using the engineering model in conjunction with an upper bound fatigue crack growth law. To investigate further the problem an analytical approach has been considered too. The assessment of fatigue crack growth due to turbulent mixing of hot and cold coolants presents significant challenges, in particular to determine the thermal loading spectrum. A simplified approach in which the entire spectrum is replaced by a sine-wave variation of the temperature at the inner pipe surface has been applied in this study. The amplitude can be conservatively estimated from the nominal temperature difference between the two flows, which are mixing. In this work the effect of sinusoidal load of different frequencies and amplitudes on the crack growth will be addressed. Particular attention is given to the evaluation of the maximum allowable surface temperature variation before the growth of a given defect occurs in relation to different frequencies of loading. A critical frequency defined as that which gives the shortest crack initiation and growth life has been investigated for different semi-elliptical crack shape. Such estimates are intended to be conservative but not un-realistic. The application of the method is described for the pipe geometry and loadings conditions reported for the Civaux 1 case. Thermal elastic finite element analyses and analytical solutions were used to calculate the stress intensity factors derived from the sinusoidal load model. The present approach combining detailed models and experimental data may establish a simplified route for assessing thermal fatigue damage evolution.
JRC Institute:Institute for Energy and Transport

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