<![CDATA[Corrosion is a major problem affecting the durability of steel materials, creating a need for effective and environmentally friendly corrosion-control methods. This study evaluated the effectiveness of pineapple peel extract as a corrosion inhibitor for ST 42 steel in rainwater at immersion durations of 7 and 20 days. The gravimetric weight-loss method was used to determine the corrosion rate based on the mass loss of the steel specimens. Six ST 42 steel specimens were used individually for the experimental conditions, with one specimen representing each condition. Uninhibited specimens were immersed in rainwater and seawater for comparison, while pineapple peel extract was evaluated as an inhibitor only in rainwater. The uninhibited ST 42 specimens immersed in rainwater showed corrosion rates of 0.0952 and 0.1000 g/(cm²·day) after 7 and 20 days, respectively. In contrast, the specimens treated with pineapple peel extract showed no measurable mass loss, resulting in a calculated corrosion rate of 0.0000 g/(cm²·day) at both immersion durations. The calculated inhibition efficiency of the pineapple peel extract was therefore 100% at both 7 and 20 days. The uninhibited specimens in seawater showed corrosion rates of 0.0952 and 0.1000 g/(cm²·day) after 7 and 20 days, respectively, which were identical to those observed in rainwater. These results indicate the potential of pineapple peel extract as a plant-based corrosion inhibitor for ST 42 steel in rainwater under the tested conditions. However, the results should be interpreted cautiously because each condition was represented by a single specimen and the resolution of the digital scale was not documented.]]>
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