10. Steel Material Preparation

Any fabrication activity is preceded by the steel material preparation activity. Steel plates and sections are received from the steel mills in as rolled condition. The very process of production in steel mills leads to formation of residual stress and a hard layer of oxides over the steel surface. Both this locked-in stress and the oxide layer, known as mill scale, needs to be removed before taking the plates and sections for further production operation. The handling of materials from steel mill to shipyard steel stockyard may also lead to surface deformation, hence straightening is required. Thus steel material preparation involves, straightening, stress relieving and mill scale removal. The plates are fed from the steel stockyard to the straightening machine and from there to the surface dressing station. Surface dressing is necessary to remove mill scale present on the plate surfaces. Mill scale is a layer of ferric and ferrous oxides formed on the plate surface during the hot rolling operation of the steel plates in steel rolling mills. There are various methods of surface dressing, however shot blasting and chemical pickling processes are the most efficient ones.