Purpose – This study aims to study the effect of Sn on the corrosion behavior of weathering steel (WS) in a simulated tropical marine atmosphere. Design/methodology/approach – Indoor alternate immersion tests, electrochemical measurements and real-time current-monitoring technology based on the galvanic corrosion principle were used and the scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy and electron probe microanalyzer were used to analyze the morphology and component of the rust layer. Findings – The results indicated that Sn has a positive influence on the corrosion process. Sn participated in the composition of the rust layer in the form of SnO2 and is enriched in the inner rust layer. SnO2 participated in the coprecipitation process with iron oxides and oxyhydroxides, which promoted further transformation of g-FeOOH to a-FeOOH. As a result, the rust layer of Sn-containing steel was continuous, compact and effectively blocked the invasion of aggressive Cl
. Therefore, the additive of Sn enhanced the corrosion resistance of WS in a simulated tropical marine atmosphere. Originality/value – The corrosion behaviors of WS were researched by the real-time current-monitoring technology which was rarely used.