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

Marine and offshore industry often treats with complicated and huge underwater constructions, such as deepwater drilling facilities, undersea oil pipelines, and submersed towers of offshore platforms. These kind of underwater structures often need on-site building, maintenance and repair works. The quality of underwater work is affected by surface contaminants such as oil, rust, fouling material, biofilm and deteriorated paint. Most of the conventional cleaning techniques are limited by the critical conditions of the underwater environment. Especially, there is not an effective cleaning method for removing underwater oil contaminants. It is important to develop a promising cleaning method for underwater works.

Oil spill frequently takes place and endangers the sea ecological system. Pollution of the sea by persistent oil such as crude oil is a severe environmental problem that can last over a long time. It has attracted much effort to control the oil pollution in the sea. The spill of crude oil requires a lot of financial support and labors to clean up. New environment-friendly cleaning methods are under extensive research and development.

Laser cleaning method can be a suitable approach for removing oil contaminants with significant advantages such as localized treatment, noncontact working mode, and the flexibility for processing complicated geometries. The use of a pulsed high-power fibre laser has additional benefits such as low operation and maintenance cost. This research work focuses on laser removal of the crude oil from steel plates in an underwater condition. Water depth (underwater optical path), laser power, and pulse energy affect the cleaning quality. Underwater laser cleaning is a complicated process involving laser-heating induced oil breakdown/decomposition and vapor-bubble initialized cavitation cleaning. Laser underwater cleaning is a promising method for underwater surface preparation and controlling oil pollution.