Corrosion Screening of Greenhouse Structural Steel Pipes Using Cold Infrared Thermography

Greenhouse structural steel pipes are susceptible to internal and external corrosion under hot and humid service conditions, leading to cross-sectional loss and reduced structural strength. This study proposes a cold infrared thermography method for screening corroded pipes and identifies effective indicators for different cooling-affected regions. Experiments were performed using three non-corroded and five salt-spray-corroded SPVHS-grade specimens and three field-corroded specimens. After a cooling stimulus was applied using an ice pack, time-series mean surface-temperature data were acquired using an infrared camera. For the direct cooling region, the recovery phase was fitted with an exponential model to estimate the time constant (τ). For the indirect cooling region, located approximately 50 mm from the direct cooling region, the cooling phase was fitted with a linear model to obtain R2 and the root mean square error (RMSE). Mean τ was consistently higher in the non-corroded group than in the combined corroded group across all four environmental conditions. The linearity indices in the indirect cooling region showed only exploratory, condition-dependent group differences. These findings suggest that the recovery time constant may support corrosion screening under controlled conditions.