包覆層下腐蝕問題調查和影響因素探討

Investigation on the Corrosion Behavior of Materials under Insulation

本文調查國內塔槽包覆層下腐蝕（CUI）的損傷案例及腐蝕的成因，同時對影響腐蝕的因素進行探討，最後提出預防改善方案。研究結果顯示塔槽包覆層下腐蝕主要發生在支撐環上方殼體附近，呈現局部腐蝕型態，腐蝕往垂直高度方向呈現山形狀發展；腐蝕速率主要受溫度、天候條件和包覆形式的影響，且國內和國外工業經驗數據有差異，在高於室溫，CUI腐蝕速率隨著溫度增高而增加，在70 ~ 90℃溫度附近有最高的腐蝕速率，超過此溫度，腐蝕速率急劇下降，包覆材和腐蝕因子扮演催化腐蝕的角色；CUI的預防方案包括正確包覆材鋁皮的設計和安裝、應用高品質之有機或無機塗層以及藉由風險檢查基準評估技術來鑑別出CUI高風險的設備，同時運用多種檢測技術來提高檢查有效性。

This paper investigated corrosion under insulation (CUI) of tower structures and its root cause. Parameters affecting CUI were studied, and a mitigation program was accordingly proposed. The results revealed that CUI of a tower structure mainly occurred at the shell above the support ring, and its mode was localized corrosion. Corrosion propagated along the vertical direction of the tower structure in a continuous triangular morphology. Temperature, weather condition, and type of insulation were primary factors affecting CUI. The corrosion rate in a tower structure for a domestic case was different from the empirical data reported by the foreign industry. The corrosion rate increased with increasing temperature above ambient temperature. The highest corrosion rate occurred at the temperature range of 70 ~ 90 ℃, but it decreased dramatically at temperatures greater than 70 ~ 90 ℃. Insulation and corrosive agents played catalytic roles in terms of corrosion rate. For the mitigation of CUI in a tower structure, proposed approaches are as follows. Proper design and installation of Al-foil wrap for insulation should be conducted. High-quality organic and inorganic coatings should be applied. Equipments with the potential of inducing CUI should be identified by adopting risk-based inspections. Finally, multiple inspection techniques should be employed for high inspection reliability.