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

-75-SizeIFSPressureServiceLbs304, 316 and2S Nickel - 20 ChromeStainless Steel$/Each3S6-T6Alum~ruunAlloy$/Each3ItFlgd4“ Flgd6“ Flgd81’Flgd3“ Flgd4“ Flgd6“ Flgd1so150150150150150150GateGateGateGateGlobeGlobeGlobe263.00376.00610.0040; .00h78 .00809.00268.00389.00622.00809.00273.00512.00891.00Cast stainless steel, 25 Nickel, 20 Chrome valves are recommended.However, as stated above, special approval to use materials other thanthose listed in the Regulations will have to be obtained from the AmericanBureau of Shipping and the U.S. Coast Guard.- The ballast system for the steel CHAIJXNGER consistsof fcRw- mch reams through the tanks, one each in the port and starboardupper wing tanks and double-bottom tanks, with 8 inch branches to eachtank. The necessary piping connections are provided in the engine room tofill and empty the tanks. In addition, the upper wing tanks are fittedwith 6 inch shell valves to permit rapid deballasting directly overboard bygravity. All pipe within the tanks is Schedule 80 galvanized steel.Several different materials may be used in the ballast system forthe aluminum hull ship, with the ultimate choice being based on the balanceof installed cost versus compatibility with aluminum and reliability andmaintenance cost. The different piping materials considered are aluminum,black steel, galvanized steel, fiberglass reinforced plastic, PVC coatedsbeel pipe, 90-10 copper nickel alloy and stainless steel pipe. Each ofthese materials have advantages and disadvantages which will be discussed.An aluminum pipe system with aluminum valves has the basic advantageof being completely compatible with the surrounding hull structure. IL isweldable and bendable and there is extensive experience in its use andinstallation. Because of its corrosion resistance Schedule 40 thicknesscan be used for ballast piping service. Its major disadvantage is its highinitial cost.A black steel pipe system with black steel or nodular iron valves hasthe advantages of low material cost and is easily fabricated, bent andwelded. However, it is not compatible with the aluminum hull structure,therefore, many measures have to be taken to protect the structure asfollows:(a)(b)(c)(d)Each bulkhead penetration has to be a thick aluminum spool piece.On each side of this bulkhead spool piece another thick aluminumspool piece has to be fitted to act as a waster piece to protectthe bulkhead fitting.Cathodic protection using expendable aluminum anodes must befitted within the tanks to protect the aluminum structure.Pipe supports must be carefully insulated.