DEFECT CHARACTERISATION IN SA-213-T22 TUBE STEEL R. Rodríguez1, I. Ocaña1, A. Martín-Meizoso1, J.M. Martínez-Esnaola1, M. Fuentes1, L. Tauroni2, A.S. Pérez3 and J. Izquierdo3 1 Centro de Estudios e Investigaciones Técnicas de Gipuzkoa (CEIT), Paseo de Manuel Lardizábal, 15, 20018 San Sebastián, Spain and Escuela Superior de Ingenieros, Universidad de Navarra Apartado 1674, 20080 San Sebastián, Spain 2 Tecnatom, S. A., Avda. Montes de Oca, 1, 28709 San Sebastián de los Reyes, Madrid, Spain 3 Iberdrola, S. A., Paseo Virgen del Puerto, 53, 28005 Madrid, Spain ABSTRACT To correctly predict the life of a component, it is necessary to start from a right description of its defects (in the as manufactured condition and of those that service will induce) and its service conditions (temperature, stress, time, ambient...). The population of defects in SA-213-T22 tube steel, used as heat exchangers in boilers of fossil power plants, has been characterised. The population of internal defects was measured by conventional metallography procedures. Oxidation induced defects were generated on a laboratory facility using Ar saturated with water vapour at different times and temperatures, representative of those expected in service. It is concluded that defect populations fit reasonably well to Log-Normal distribution functions. T22 is usually a very clean steel (with small internal defects) and oxidation produces a morphologically very stable interface, comparable with the initial surface roughness of the as manufactured tubes. INTRODUCTION It is actually accepted that the life of a component is dictated by its initial defects (inclusions, pores, surface roughness, etc.) and its operating conditions [1-4]. The component service conditions will generate new surface defects due to oxidation, corrosion, erosion, etc. Both types of defects (as manufactured and service induced) will compete, and even may co-operate, for the component destruction. Operating condition rules the growing of all these defects, but in very different ways for the different kinds of defects. The growth of a surface defects is very largely affected by oxidation, and oxidation is very sensible to temperature and ambient. On the other hand, interior defects will not be so largely affected by temperature. Life prediction should start from the quantification of initial defects (as manufactured) and the generation of defects due to oxidation, corrosion and erosion. A computer code can then be used to follow the evolution of the different kinds of defects under given operating conditions. Spanish Power Generation companies will have to renew their power stations in the medium term. This renewal may result in new operating condition for components already in use. A computer program has been produced to cope with the life assessment of these components under changing operating conditions. The model details have been described elsewhere [5]. Within this frame, it is clear that fatigue-oxidation interaction is a major issue, especially for surface defects. Oxidation on one hand creates a brittle oxide layer at the crack tip, so enhancing fatigue crack growth; on the
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