ORAL/POSTER REFERENCE: ICF100770OR GROWTH OF CRACKS IN STEEL UNDER REPEATED THERMAL SHOCK IN A CHEMICALLY CONTROLLED ENVIRONMENT B. Kerezsi, J.W.H. Price and R. Ibrahim Department of Mechanical Engineering, Monash University, Caulfield Campus East Caulfield, 3145, Victoria, Australia ABSTRACT Repeated thermal shock loading is common in many industrial situations including the operation of pressure equipment found in thermal power stations. Thermal shock can produce a very high stress level near the exposed surface that eventually may lead to crack nucleation. Further crack growth under the influence of repeated thermal shock is a very complex phenomenon due to both the transient nature of the highly nonlinear thermal stresses and the strong influence of the environment. This paper describes an experimental analysis of crack growth in heated carbon steel specimens exposed to repeated thermal shocks using cold water. Analysis of the effect of steady state primary loads on the growth of the cracks is isolated using a unique test rig design. Environmental effects due to the aqueous nature of the testing environment are found to be a major contributor to the crack growth kinetics. KEYWORDS Crack growth, environmental effects, fatigue, pressure equipment, primary load, thermal shock. INTRODUCTION The growth and arrest of cracks due to repeated thermal shock loading is of interest in industrial applications where predictions can allow decisions to be made on the necessity of planned inspections and component replacements. Current methods for predicting repeated thermal shock (RTS) crack initiation lifetime and growth rates rely on standards and codes of practice such as the ASME Boiler and Pressure Vessel Code [1,2], and British Standard BS7910 [3], both of which use models based on isothermal fatigue tests and simplified stress profiles. The conservatism of these codes when analyzing RTS cracking is of concern, particularly when predicting crack growth rates after initiation has been observed. An over-estimation of this growth rate can lead to premature replacement of components that otherwise may have been left in service. A particular reference to the conservatism of the ASME code can be found in work by Czuck et al [4], where growth at the tip of a crack exposed to cyclic thermal shock loading was found to be an order of magnitude less than that predicted by using the code. Cracking due to repeated thermal shock (RTS) is a particular problem in thermal power stations. Thermal shocks in boiler equipment are an inevitable side effect of normal operation with start-up and shut-down procedures thought to be especially damaging. Cyclic operation of traditionally base-loaded units only
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