By G. Basile, C. Clienti, G.A. Fargione, A.L. Geraci, A. Risitano
Through a study of the current state-of-the-art techniques used to find hidden defects in steel elements (as well as in other metals including pipes made of titanium, inox steel, etc.) and on the basis of the application procedures of the different methodologies existing in literature for plane geometry, this experiment attempted to create a new methodology, simple and practicable on the field, for risk assessment, monitoring, and planning control of interconnected piping in oil refineries with the use of thermal infrared imagery. This methodology adds to the array of non-destructive testing methods, traditionally indicated as appropriate by rules of good technique and praxis and by sector-specific guidelines. The methodology, developed in the laboratory, elaborates on a technique used for safety verification of pipe in industrial plants. These pipes are subjected to corrosion phenomena with the subsequent risk of a break that could result in a spill of highly inflammable and polluting products. The technique allows an accurate scan of the critical pipe components, in spite of what the traditional thickness measurements do by sampling. Additionally, the proposed methodology enables checking warm pipe, while the traditional ones require the pipe to be at room temperature or within a certain range. This is based on the fact that heat deposited on a surface by a thermal impulse, very brief and of the order of few milliseconds, will disperse mostly along the plate thickness. Several trials, performed in order to find the most appropriate method to uniformly heat the pipe surface, pointed out the possibility of using thermography to locate defects artificially created on the pipe's internal surface. The proposed technique consists of the generation of a warm or cold flux, inside or outside the pipe, and in the observation of the thermal pattern development on the external surface. The methodology leads to a quick diagnosis, highlighting areas that need to be controlled more accurately, once the critical points have been located.