design considerations for aluminum hull structures - Ship Structure ...

-79-service, transfer and purifying systems should also be of all steel construetion.Special precautions are necessary where the steel piping penetratesthe aluminum structure.. .Diesel Engine Fresh Water Systems - The steel hull ore carrier hasthe diesel engine fresh water systems made of Schedule LO galvanized steelpipe. For the aluminum hull ship it is recommended that the same materialbe used for these systems, with special precaution to insulate the systemfrom the aluminum hull structure.Sea Water Systems Within the Machineq Spaces - The systems under considerationare sea water cooling service systems for all heat exchangers,clean ballast system, oily ballast system and bilge system.The steel hull ore carrier has the sea mater service systems withinthe machine~ spaces composed of 90-10 copper nickel alloy with bronzevalves and fittings. Because of U. S. Coast Guard Regulations, it isrecommended that these materials be retained for the sea -waterservicesystems in the aluminum hull ship. However, insulation of the entiresystem is required, particularly at the connections between the piping andthe sea valves. If the U. S. Coast Guard would approve the use ofaluminum for this service, it should be considered. However, it will bevery costly in comparison to the 90-10 copper nickel alloy system, primarilydue to the high cost of valves and fittings.The steel hull ore carrier ballast system within the machineqy spacesis of Schedule 80 galvanized steel pipe. For the aluminum hull ship it isrecommended that the ballast system within the sea water ballast tanks be offiberglass reinforced plastic. However, there is some question as towhether the U. S. Coast Guard will accept this material within themachine~ spaces. If the U. S. Coast Guard accepts the use of fiberglassreinforced plastic, tihiswill permit the use of standard materials forp~s and valves ard reduce maintenance costs. The second choice wouldbe aluminum pipe and valves. Since large capacity centrifugal pumps ofaluminum are not available, special pump connections with replaceablewaster pieces must be provided.The steel hull ore carrier bilge system within the machineqy spacesis of Schedule LO galvanized steel pipe. For the aluminum hull ship it isrecommended that the bilge system in the machinery spaces be of aluminum.This presents the same problem as noted above, namely, the requirement ofheavy waster pieces at the pump connections. However, in this case theywill be comparatively small (~ inch or 6 inch IPS) and their replacementis not too expensive. For this reason an all aluminum Schedule 40 pipingsystem is recommefied.The weather deck ard sanita~ drainage systems for the steel hull orecarrier are all made of galvanized steel Schedule 80 pipe. It is recommendedthat all aluminum construction be used for these systems in thealuminum hull ship, using Schedule LO aluminum piping to simplify the maqycorulectionsati structural penetrations.The tank venting system and sounding tubes for the steel hull orecarrier are all made of galvanized steel, Schedule 80 in way of the upperwing ballast tanks and Schedule LO for the remainder of the piping.Beciuse of the maw connections to structure and structure penetrationsof these s~stems, it is recommended that they be made of all aluminum con-