Ship Shape
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Smaller crews mean corrosion-resistant materials are needed to reduce the maintenance of the
topsides of navy ships
Nickel magazine, Sep. 01 -- For the first time, designers and engineers are making an
all-out assault on corrosion and maintenance on the topsides of U.S. navy ships during the intial detailed
design stage. Twelve LPD 17 ships, designed to carry amphibious troop landing craft, will make extensive use
of nickel-containing stainless steel. The material will be used for outfitting items ranging from light
fixtures to the foundations to which equipment is bolted.
Alloy types used include:
S30400 (used primarily in piping),
S30403,
S31600 (used mainly for outfitting items), and
S31603. For applications requiring extra strength, nickel alloys
N05500,
N06625,
N04400 and
N07718 are used.
"One of the major tenets of the LPD program is total ownership cost," says Robert Fitch, a topsides engineer with the Supervisor of Shipbuilding, C&R, USN in Bath, Maine. "The navy has taken the philosophy of reducing manning on ships and decreasing maintenance-type activities. One of the major ways this can happen is by reducing corrosion on ships." At times, nearly half of the U.S. fleet's maintenance budget is allocated to corrosion prevention.
Although navy ships have long used copper-nickel alloys in piping systems (each LPD 17 will use 32,000 metres of C70600 and 17,000 metres of C71500), the Navy has discovered that there are many other areas where improved materials is cost-effective. "A tremendous number of problems have been found throughout ships, not only exterior, but interior also," says Fitch.
"There are two truths that the Navy came to realize," explains Fitch. "One is that if stainless steel is used instead of high-performance coatings, it costs less and requires less maintenance. The other is that, although making acquisitions in stainless steel is an up-front cost increase, there will be savings in the long run. A lot of these items have edges, where coatings tend to wear. What is new to the LPD 17 is a lot of stainless steel outfitting items -- items that, in the past, were carbon steel and consequently bled all over the ship."
Some 60 tonnes of stainless steel are being installed on each ship. Among the stainless steel items that were previously made of carbon steel are: topside lockers; hose reels; watertight doors; lights and electronic receptacles; ammunition lockers; life rails; ladders; electrical conduit; conduit and cable hangers; flag supports and masts; stowage racks; grating support structures, such as catwalks around the flight deck; and boat stowage and cradles.
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