By: T. J. Kwee, G. X. Chen, N. R. Lei, K. P. Tan, Y. S. Choo, M. H. Hong

Centre of Innovation (Marine & Offshore Technology)
Faculty of Engineering, National University of Singapore

Ships play a significant role in our life by carrying about 90% of the world’s intercontinental cargo. But the service condition of ships in the seawater is severely corrosive. It often costs billions of dollars on maintenance, repair, and corrosion-related down time of ships. Ships require the best possible paint protection to extend their operating life and to save money.

Surface preparation is an important step for building a new ship. The condition of surface preparation determines the quality of paint coating, which could further affect the occurrence of corrosion and fouling. Removal of millscales from raw steel plates using abrasive blasting method is often a significant process of surface preparation for shipbuilding work. It is a standard and effective procedure used by worldwide shipyards. But abrasive blasting always causes environmental problems by producing heavy air pollution and a huge volume of processing wastes. It also exposes health risks to operators. The operation cost is usually very high. It is necessary to develop an alternative method to replace conventional abrasive blasting technique.

The increasingly widespread use of lasers on surface treatment provides a potential solution for surface preparation in shipbuilding industry. Laser cleaning method has the advantages of the capabilities of automation, precisely and selectively cleaning, and clean-processing without pollution. The volume of processing waste is extremely reduced. The system used in this study is a pulsed high-power fibre laser. It has the benefits of low operation cost, almost maintenance free, and compact system.

Current study shows that the scanning speed of laser beam, laser pulse energy and laser output power/power density is important factors for removing millscales. The cleanliness and surface profile of processed samples can meet the requirements of shipbuilding standards. Laser as a tool has been well-established for welding and cutting in shipbuilding industry. So it’s not difficult to extend its application to surface preparation. Laser cleaning can provide a green manufacturing solution for shipbuilding industry.