Nondestructive inspection for cracks detection in welded joints of clad steel by radio wave techniques

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The hard conditions for oil exploitation at Pre-salt region in Brazil created a challenging environment to turn production economically viable and safe. Corrosive environments and increasingly critical high pressures and temperatures raised the demand for special steels and alloys. One of the main materials being used in such conditions is the clad steel, which consists on the junction of a base material that provides mechanical strength and a corrosion resistant alloy, commonly called CRA (Corrosion Resistance Alloy). Several Pre-salt fields have used this material in the construction of different parts of equipments for the deep water exploitation system, among these, the pipes that conduct oil from the sea bed to the platforms or ships on the surface. Despite the excellent properties presented by clad steels, there are a few problems associated; the main one is the nucleation of corrosion fatigue cracks in the pipe weld root. For this reason, an inspection procedure of equipment manufactured with this type of steel is needed to ensure the production of a reliable offshore exploitation system. The bilateral collaboration between IKTS and LNDC will handle the problem of inspection methodologies in clad steels. The parties involved will share their experiences strategically in order to enhance the inspections success possibilities. The Laboratory of Nondestructive Testing, Corrosion and Welding (LNDC / UFRJ), will make its contribution with the expertise on implementing the development of nondestructive inspection methodologies for the petrochemical industry, and the Technische Universitaet Dresden together with Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) with the experience on nondestructive testing technologies. The following conjoined proposal should be understood as an initialization of a future long term collaboration between the partners. Within a completed pre study it turns out, that the high resolving Radio Frequency Eddy Current technique of Heuers group is a promising solution for crack detection and the characterization of strain and local impurities of clad steel samples. Based on preliminary work on algorithms for sub surface strain characterization of IN718 aero engine alloys, artificial cracks at the interface of differed prepared claddings provided by UFRJ were found. The experiments of this pre study needs to be repeated within a more extended experimental work combined with a basic concept for theoretical description of phenomenas of radio wave EC interaction within poor conductive layered materials and its distortions. Within this short term initialization project a more qualified base of data a will be acquired in order to evaluate the potential and relevance.