Weathering steels (WS) have been widely used due to the protective rust formed on the surface of the bare metal exposed to the atmosphere. They have been studied attending to specifications and characteristics in engineering, but in cultural heritage the use of this material does not follow the same criteria and has different needs which must be addressed. Among them, the design and the location of the sculpture may have an impact on the rust formed and may not be as protective as it was supposed to be. This work presents the study of the weathering steel sculpture Once Módulo which shows areas with different exposure to rainwater and different surface heterogeneities. The results obtained by Electrochemical Impedance Spectroscopy (EIS) have shown that the protective ability of the rust depends on the previous differences and that design and location of the artwork play an important role for its conservation.