This suction cup corrosion testing cell is designed for on-site electrochemical corrosion measurements on large ferromagnetic structures, such as ship hulls and outdoor industrial equipment. The transparent organic glass body incorporates a strong built-in magnet, allowing secure attachment to iron surfaces without additional fixtures. It features a three-electrode configuration with a graphite or stainless steel rod as the auxiliary electrode and a silver-chloride reference electrode, suitable for standard corrosion potential and polarization tests. The cell has a capacity of 20 ml and defines a reaction area of 30 mm in diameter, enabling reproducible local corrosion assessments. This compact, portable setup is intended for laboratory and field use in materials degradation studies, corrosion monitoring, and protective coating evaluation.