バラストタンク耐食鋼JFE-SIP~®-BT適用船の塗装劣化挙動と腐食挙動

摘要

バラストタンクの塗装劣化を抑制し，塗装寿命を延長するバラストタンク耐食鋼(JFE-SIP~®-BT)を開発した。本報では，開発鋼を実船（VLOC: Very large ore carrier)のバラストタンクに適用し，約5年経過後，塗装の劣化,ならびに鋼材の腐食挙動を調査した結果を報告する。適用部材は上甲板と上甲板ロンジである。上甲板では，鋼板サンプル(ダブリングプレート）を上甲板に溶接後，船体と同時塗装し，塗装スクラッチからの劣化挙動を観察した。5年経過後，開発鋼における塗装劣化面積，腐食深さ，腐食体積は，従来鋼に対し，それぞれ，75％,84％,58％であった。上甲板ロンジでは，エッジ部における塗装劣化長さ率を評価した。その結果，開発鋼の平均塗装劣化長さ率は従来鋼の約65％であった。開発鋼の塗装劣化進展抑制効果を実船で確認することができた。%The corrosion resistant steel for ballast tank "JFE-SIP~®-BT"， which prolongs coating life by preventing coating deterioration, has been developed. The developed steel has been applied to ballast tanks of a VLOC (Very large ore carrier). This paper reports evaluation results on coating deterioration and corrosion behavior of the developed steel after S-year use. The parts applied were upper deck plates and longitudinal members of upper deck of ballast tanks. Doubling plates were welded to upper deck plates of ballast tanks and were coated simultaneously with the upper deck plates. The coating deteriorated area, corrosion depth and corrosion volume of the developed steel were 75％， 84％, and 58％ of those of the conventional steel, respectively. The deteriorated length at the edge of longitudinal members in the developed steel was about 65％ of that in the conventional steel. The prevention effect of coating deterioration by the developed steel was confirmed under the actual ballast tank condition.