Many hot corrosions of marine engine have been experienced in C fuel oil operation. This oil has approximately 40-400 p.p.m. vanadium, 50 p.p.m. Na and 3 3.5 wt % sulphur.
This paper describes on “because of hot corrosions, how to prevent these troubles and how to assure proper corrosions controll”.
Controlling factors for its corrosive effect are deposits on metal surfaces (V2O5, Na2SO4, SO3), elevated temperature (500 to 700°C), pulsating combustion pressure and so on.
Corrosion experimental tests were carried on 2 austenitic steels (14Cr-14Ni-2W and 17-4PH), 3 ferritic steels (2Si-11Cr-1Mo, 1Cr-1Mo-1/4V and 1Cr-1/4Mo) and 3 facing alloys (45Co-33Cr-18W, 65Co-28Cr-4W and 29Cr-39Ni-15W-10Co). Corrosion tests results on various alloy at 600°C and V2O5 90 wt % and Na2SO4 10 wt % are as follows. 2 austenitic steels, 1 ferritic steel 2Si-11Cr-lMo and 1 facing alloy 29Cr-39Ni-15W-10Co are relatively protective to vanadium attack. 2 facing alloys (45Co-33Cr-18W and 65Co-28Cr-4W) are the most corrosive.
Aluminized process to develop Al-Fe alloy layer on each steel surfaces are experimentally confirmed to be protective to vanadium attack as well as to minimize oxidizing loss and strengthen fatigue resistance at elevated temperature, if proper materials to aluminized process are selected.
12 aluminized exhaust valves (6; 14Cr-14Ni-2W and 6; 2Si-11Cr-lMo) were used on actual marine service to assure corrosion controll.
Besides proper material selection to corrosion, creep and strength and aluminized process to develop Al-Fe alloy layer, a program of deposits cleaning and recoating on metal surfaces after a marine service are recommended to assure proper corrosion controll of marine engine.