セルオートマトンによる塗膜下腐食シミュレーション手法に関する研究(第1報：スクライブ塗装鋼板の解析)

摘要

An underfilm corrosion simulation method for epoxy coated steel panels in ship's water ballast tanks (WBT) has been developed. The incubation and extension of coating failure are simulated by using 2-dimensional cellular automaton method, and the steel diminution is simulated by modifying the corrosion model proposed by Kawamura et al. (2015). Analysis parameters are determined by using the results of onboard exposure and cyclic corrosion tests performed by Shiotani et al. (2014). The change in corroded surface shape of epoxy coated and scribed steel panels made of conventional steel and corrosion resistant steel (CRS) exposed in an ore carrier's WBT for 4.8 years is simulated. The simulated coating deterioration (blister) area and the corroded surface profile agree well with those measured. This demonstrates the effectiveness of the developed simulation method and the determined parameters. The differences in analysis parameters between conventional steel and CRS suggest that CRS can reduce the harmful effect of the active corrosion region on the remaining coating life at the blister's frontline and the corrosion under the blister.%バラストタンク(以下でWBTとよぶ)上部の腐食はエッジ等の線状塗膜欠陥を起点とする塗膜下腐食の拡大と塗膜剥離後の全面腐食により生じる.Shiotaniet al.,塩谷らは新鋼材(WBT用耐食鋼Corrosion Resistant Steel，以下で耐食鋼またはCRSと呼ぶ)によりWBT内環境下の塗膜下腐食進行速度を抑制できると報告している.この耐食鋼をWBT内構材に使用すれば，塗装•鋼材切替え寿命延伸によるライフサイクルコスト低減と，腐食予備厚引下げによる船体軽量化•温室効果ガス削減の効果を期待できる.耐食鋼を使用したWBT防食技術の有効性を検証するには，塗装寿命•鋼材切替え寿命に相当する長期間にわたって，WBTパネル単位で塗膜下腐食•全面腐食一貫シミュレーションを実施し，鋼種の違いが塗膜残存面積•腐食深さの統計値に与える影響を定量的に評価する必要がある.