Edge-Preparing Plasma Arc Cutting (EPPAC) systems have been developed. Top edges of kerfs generated by these systems have bevel angle θ >155°, which is equal to or larger than that of 3-path grinding edges. Cutting qualities except for melting of cut shoulder equivalent to or better than those of kerfs generated by conventional machines, and there is no slowdown on the cutting speed. The developed systems are tested under the practical condition in Japanese shipyards, and it has been demonstrated that there is no special problem in workplace safety, and kerfs which satisfy the requirements specification can be generated with high stability. The lower bound of 95% confidence interval of edge retention ratio (ERR) of kerfs generated by EPPAC systems is about the same as that of 3-path grinding edges. This means that the top edge shape of kerfs generated by developed EPPAC systems conforms to IMO/PSPC, and there is no need of additional hand grinding. We can cut the man-hours for edge treatment in half by using developed EPPAC systems.
On December 2006 the International Maritime Organization (IMO) has adopted a Performance Standard for Protective Coatings (PSPC). This new coating standard applies to ballast water tanks on newbuildings in all types of ships and is settled in the Resolution MSC.215(82). Hereafter, we call this new regulations IMO/PSPC. Ship structures often come with complex geometric configurations, having large surface and highly stressed areas, such as corners, edges, and weld seams areas. Coating defects such as insufficient film thickness are often observed, resulting early coating failure and corrosion in these areas. It is well known that secondary surface preparation (SSP) is effective in preventing these coating defects. It is mandated that edges to be treated to a rounded radius of min. 2mm, or subjected to 3 path grinding or at least equivalent process by IMO/PSPC.
