The valves will not be required if it can be shown that, even with the progressively flooded spaces taken into consideration, the vessel still complies with the applicable damage stability criteria.
7.5.5 Ballast Pipes Passing Through Fuel Oil Tanks
To minimize cross-contamination, where passing through fuel oil tanks, unless being led through pipe tunnel, ballast lines are to be of steel or equivalent [see 4-6-4/5.3.4(c)] having a thickness at least as required by column D of 4-6-2/Table 4. The number of joints in these lines is to be kept to a minimum. Pipe joints are to be welded or heavy flanged (e.g., one pressure rating higher). The line within the tank is to be installed with expansion bends. Slip joints are not permitted.