Corrosion is a severe problem for marine vessels and offshore structures built in steel working in sea water and harsh environmental conditions. Corrosion of hull steel causes billion-dollar losses every year.
Serious corrosion can lead to ship damage and accidents. To prevent corrosion of steel surfaces, it is important to have a good surface preparation prior to the application of marine coatings. The paint films build up a barrier to prevent corrosive seawater from directly contacting with the steel surface of a hull. The quality of paint is a significant factor that affects the protection performance. The painting processes and the associated pre-painting works also play important roles in preventing corrosion. In particular, pre-painting works, commonly surface cleaning of steel plates, are necessary steps for the painting work with considerable impact on protection performance.
Surface cleaning methods for shipbuilding and ship repair are well established. The most popular cleaning method is dry blasting which is often conducted by ejecting abrasives, such as grit, from copper slag or similar abrasive and reusable steel shots against steel work pieces to achieve blasting standard of at least SA2.5 as required by the ISO standard 8501. The normal air pressure required for blasting is at least 7 bars. The strong impingement of abrasives with the surface removes millscale, rust, paints and other organic coatings to give a clean surface. But dry blasting processes often produce air pollution and secondary wastes where copper slag or similar abrasives have been used. The use of copper slag or equivalent abrasive materials and their disposal annually cost million dollars for shipyards. The dirty environment arising from dusts of various particle sizes resulting from blasting work also exposes health risks to operators and the general public. In order to solve these problems, alternative cleaning methods, such as hydro-blasting and hydro-jetting have been developed and used in ship repairs. But these methods have not gained universal acceptance by ship owners as these cleaning processes require the use of more expensive waterbased epoxy coating systems.
Surface cleaning using a laser has been studied and successfully implemented in semiconductor manufacturing industries. Laser cleaning for the removal of coatings and contaminants are widely used for the aerospace industry.Laser cleaning also provides the possibility to meet the surface cleaning requirements of shipbuilding and ship repairs with economic and ecological benefits. The cleaning quality of the laser processed samples can meet the requirements of shipbuilding and ship repairs.
MRJ Laser made a comparison of several kinds of popular cleaning method.
We can see from the picture above that laser cleaning can overcome the downsides of these traditional methods and even improve the production process in general.
The cleaning or removal is based on locally confined interaction of pulsed or continuous laser radiation with the surface layer. Depending on the laser wavelength, the intensity and the interaction time of the laser radiation with the surface layer, as well as the material properties, a thermal decomposition (e.g. evaporation, sublimation) or chemical reaction occurs.
● High-precision removal of layers with thicknesses in the range from sub-µm to mm
● Selectivity of removal e.g. for cleaning sensitive surfaces or multilayer systems
● Contactless process without mechanical impact, no damage of the surface of cleaned object.
● Low thermal and chemical load of the base material
● Ideal for automation,easy to integrate in a production line
● Abrasive and chemical free,Lower sensitivity to corrosion after cleaning
● Environmentally friendly, disposal of the removed material is all that is required
● Simple operation, realized automated cleaning by hand-held or cooperate with manipulator;
● Stable laser cleaning system, high cleaning efficiency, saving time.