Development of Corrosion Resistant Steel for Coal Carrier Cargo Hold

摘要

In the coal carrier cargo hold, severe corrosion of steel occurs, and has become the cause of serious accidents in the past. From the conventional knowledge and our results of corrosive environment survey including component analysis of rust and pH measurement in corroded part in actual cargo hold and laboratory corrosion test using coal, it was concluded that dilute sulfuric acid derived from sulfur in coal caused that severe corrosion. New corrosion resistant steel for the coal carrier cargo hold was developed and its performance was investigated. As the result of laboratory corrosion test, maximum corrosion depth reduced about 30% in developed steel compared to conventional steel. This corrosion resistance was confirmed in exposure test in actual cargo hold as well. Electron Probe Micro-Analysis (EPMA) of rust layer showed that concentration of sulfur in the vicinity of interface between rust and steel substrate was smaller in developed steel than conventional steel. Transmission Electron Microscopy (TEM) observation showed that rust particle size of developed steel was about one-tenth of that of conventional steel. These results indicate that dense protective rust layer was formed in developed steel and inhibited the permeation of sulfate derived from coal to steel substrate.