12.12.2010.
NavyTimes.com
Jedva godinu dana nakon što je američka mornarica potrošila 40 miliona dolara za saniranje štete nastale nasukivanjem krstarice USS Port Royal, isti brod se ponovo nalazi van stroja - ovaj put ne zbog oštećenja trupa. Sada je problem u otvaranju pukotina u nadgradju broda...
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Cela vest...
The Port Royal was operating in the Pacific Northwest in September when sailors discovered new cracks in the superstructure, including an eight-foot-crack on the 06 level, one of the highest decks in the ship. Most of the cracks that appear on the Ticonderoga-class cruisers are being repaired during regular overhauls, but in this case the damage was enough to send the ship home to Pearl Harbor for yet another extended repair period.
So far, the Navy has awarded $14 million to BAE Systems in Pearl to fix the Port Royal. The work package will include repairs to the bulkheads and deck around two gas turbine intakes; fuel oil storage tank top repairs; superstructure crack repairs; and removal and replacement of aluminum decking and plating. The work is expected to be finished in February.
“We are dealing with a class-wide issue of superstructure structural issues,” said Cmdr. Jason Salata, a spokesman for Naval Surface Forces in San Diego. “These are things we’re seeing on other ships of this class.”
The Port Royal situation might be the worst case to date.
“Most of the issues are being dealt with when the ships come in for a regular availability,” or overhaul, said one source familiar with the situation. “This is the first one I know of where we specifically went in for repairs.” The work is necessary, the source added, “to restore structural integrity of the ship.”
The problem, according to the Naval Sea Systems Command, is the aluminum alloy used in the superstructure of the cruisers, which have steel hulls.
“There have been various degrees of crack repair on every CG [guided-missile cruiser] in the past year,” said Chris Johnson, a NAVSEA spokesman in Washington. “The decking is the most prevalent cracking area due to exposure to elevated temperatures caused by solar absorption and exhaust temperatures.”
More than 3,000 cracks have been found so far across the entire Ticonderoga class, which originally numbered 27 ships. Twenty-two of the ships remain in service, and Port Royal, commissioned in 1994, is the newest.
Their superstructures are made of aluminum alloy 5456, a material used on numerous U.S. warships since 1958. The alloy, according to NAVSEA, relies on approximately 5 percent magnesium as an alloying element to develop strength. Over time, the magnesium leaches out of the material and forms a film, susceptible to stress-corrosion cracking in a marine environment.
NAVSEA has developed more than 17 alterations to deal with the cracks. In late 2008, the service began evaluating a different welding technique called Ultrasonic Impact Treatment. The Port Royal was one of the test ships for the new technique, Johnson said, and the UIT procedure was applied to specific areas of the ship in 2009.
“With the current state of the technology, it is only practical to use UIT in small areas,” Johnson said in a written statement. “We believe it has potential, and are evaluating it as part of CG Aluminum Superstructure Task Force for future use.”
The task force was set up this year by NAVSEA — at the fleet’s request — to develop and assess technically viable options, Johnson said. Results from the group’s work are expected to appear next spring.
Many sailors who have served on a Ticonderoga-class cruiser have stories to tell about the cracks, ranging from descriptions of cracked masts to leaking fuel tanks next to high-wattage electrical equipment. Solving the issue is a key element in making sure the ships remain effective and safe to operate to the end of their planned 35- to 40-year service lives.
NAVSEA noted that the aluminum alloys used on the cruisers are not on the new littoral combat ships, which are built with commercial alloys 5083 and 6082.
“While the Navy has no current experience with this alloy, it is in wide use on commercial craft,” Johnson said.
The Port Royal has seen little service since returning from its last deployment in June 2008. On Feb. 5, 2009, just after completing a three-month overhaul, the ship ran up on a reef just off the Honolulu airport, in clear sight of every aircraft taking off and landing at the airport, and visible from the beaches at Waikiki. The cruiser was refloated after three-and-a-half days on the reef and towed back to Pearl Harbor, where the commanding officer was relieved of his duties.
The Port Royal’s hull, propellers and sonar dome received severe damage, and shipyard repairs continued into this year. After visiting Seattle in early August for Seafair, the cruiser caused a public relations stir when its wake washed up oysters on shore while operating near the Hood Canal.
Despite these problems, the ship apparently has not missed a deployment.
“Port Royal has not missed a scheduled deployment as a result of these repairs,” Salata said. “She will continue her training and deploy in 2011.”
