EVALUATING THE PRODUCTIVITY OF WATERJETTING FOR MARINE APPLICATIONS

Abstract

In 1996, the National Shipbuilding Research Program's Surface Preparation and Coatings Panel commissioned a study to assess the productivity of waterjetting when used for coating removal in representative areas of a ship. During the study, 10 visits were made to various ships undergoing repair pierside, in drydock, or in new construction; and one visit was made to an offshore pumping station. Three types of specifications for removing coatings by waterjetting were studied: selective stripping, spot and sweep blasting, and complete blasting to bare metal. During each visit, the coated surfaces were evaluated before waterjetting to determine coating type, thickness, contamination, adhesion, and overall condition. During the actual waterjetting, productivity data including downtime for the production run, were gathered. Information on equipment type, operating pressures, and flow rates was collected. After the blasting was done, the surface was again evaluated for adherence of remaining coatings, resultant surface contamination levels, and overall effectiveness of the blast. This article summarizes the type and results of data collected for the three types of waterjetting specifications observed. Of the three types of coating removal specifications observed, selective stripping was most common. It is concluded that for large-scale, quick turnaround coating removal on a ship's underwater hull or freeboard, the automated or semiautomated robotic machinery that contains all blasting water and effluent represents the most promise for the ship repair industry. The machines can efficiently remove coatings down to the original substrate without the fear of flash rusting and provide excellent surfaces for immediate recoating.