石膏型防火被覆下鋼板腐蝕速度偵測

Corrosion Monitoring of Steel Under Fireproofing Coating

鋼骨結構在塗裝防火被覆後曝露在大氣中是否會受到大氣中之酸雨、濕氣的侵蝕而影響其安全性必需有實際腐蝕速度資料來研判。本研究使用電化學技術及特殊設計的腐蝕偵測探頭來測量防火被覆下之鋼板的腐蝕速度，以評估鋼板表面在塗佈防火被覆之前施以防蝕處理的效果。大氣的腐蝕環境，以每日噴灑純水和pH= 4 的稀硫酸溶液來模擬，經過二個月的試驗後發現鋼材在噴灑pH= 4的稀硫酸溶液環境下，腐蝕速度約0.82mm/yr。鋼板在塗佈防火被覆前若經無機鋅底漆處理，腐蝕速度可大為降低。鋅底漆在pH=4的稀硫酸環境下消耗速度約為9.5µm/yr。

Structural steel beam is required to apply fireproofing coating on the ground of straucture integrity in case of fire accident. However, in high humidity and acidic rain envoronment the corrosion rate of steel under fireproofing coating could be too high to be acceptable. In this study, a specially designed corrosion monitoring probe was used to measure the corroion rate of steel under fireproofing coating and to evaluate the effect of surface preparation before the application of fireproofing coating. Corrosion environment was simulated by daily spraying of pH=4 diluted sulfuric acid onto the fireproofing coating. After 2 months of exposure, the corrosion rate of steel under fireproofing coating was detected to be as high as 0.82 mm/yr. With the application of inorganic zinc rich primer on the steel surface below fireproofing coating could reduce the corrosion rate of steel substantially. The corrosion rate of zinc rich primer layer detected is around 9.5 µm/yr.