In August 2006, the USS Abraham Lincoln aircraft carrier cruised into Puget Sound in Bremerton, WA, and docked in preparation for a massive tank blasting and coating project that was expected to take several months to complete. Thanks in part to a sophisticated air distribution system and custom built, innovative desiccant dehumidification systems from Munters, it quickly became anchors aweigh: the Puget Sound Naval Shipyard and Intermediate Maintenance Facility (PSNS & IMF) completed ship tank maintenance in less than half the scheduled time -- a major and unexpected accomplishment that allowed the U.S. Navy vessel a speedy return to service.
At 1,092 ft in length and with a flight deck area of 4 1/2 acres, the USS Abraham Lincoln, nicknamed “Abe,” and based in Everett, WA, is the fifth Nimitz-class supercarrier in the U.S. Navy. It is powered by two nuclear power plants, includes four engines, and has a displacement of 97,500 tons.
Abe boasts all the amenities found in any American city with a comparable population (5,500+): a post office with its own ZIP code, television and radio stations, newspaper, fire department, library, hospital, general store, barbershops, and more. The ship has enough generating power to supply electricity to 100,000 homes, food and supplies to operate for 90 days, and the capability of distilling more than 400,000 gallons of fresh water from the sea each day.
Drinking Water Tanks Require Maintenance
Therein lay the problem -- the aircraft carrier’s 16 drinking water tanks required blasting and coating due to accumulated corrosion from the salt in the seawater. The assignment was to abrasive blast the inside surfaces of the tanks, clean out the abrasive and debris, and prepare a clean, dry surface for application of the paint coating.
The project’s sophisticated design incorporated abrasive handling equipment to facilitate high pressure blasting to remove the corrosion, dust collection systems to remove airborne dust and debris from the blast work, humidity control to create a dry atmosphere inside the tanks to speed paint drying during application, and blowers to remove volatile fumes.
The Pacific Northwest’s largest naval shore facility for ship maintenance for the U.S. Navy provided the tank maintenance portion of the work.
J.T. Systems, Inc, based in Liverpool, NY, was awarded the contract to assist with the design, development, and delivery of the air distribution, vacuum recovery, dust collection, and abrasive handling equipment. The designer and manufacturer of customized dust collectors, abrasive vacuum recovery units, centrifugal fans, and other industrial air pollution control equipment for the industrial sector had partnered with the Navy on previous preservation projects.
Humidity Control a Key Element
Shipyard personnel asked Jit Turakhia, president of J.T. Systems, to contact Munters about supplying the desiccant dehumidification units for the project. Munters specializes in building systems that control humidity in a variety of work environments.
“The Navy typically seeks innovative equipment for projects and, based on our previous experience with Munters, we knew they could provide the specialized dehumidification systems that were needed to complete the tank work,” said Turakhia.
PSNS & IMF personnel outlined their requirements for the air flows and air supply. David Simkins, national sales manager-industrial with the Munters Moisture Control Services division, proceeded with the system’s mechanical design and engineering the unit to fit into a specific footprint.
To meet project requirements, Munters developed a desiccant system that incorporates both chilled water and steam heat packaged together with the dehumidifier. All of the components were specified to fit on a compact skid.
“We engineered a packaged system that had both cooling and heating integrated with the dehumidification,” said Simkins. “This unique system was configured and designed specifically for the Navy.”
Innovative System Deployed
A few weeks after arriving in its homeport, Naval Station Everett, the USS Abraham Lincoln was moved to Puget Sound Naval Shipyard so the tank work and other maintenance projects could begin.
The ship sailed into one of the largest graving docks on the West Coast, and was set onto a dry dock. In early September ‘06, 26 trucks delivered all of the equipment from J.T. Systems and Munters to the dry dock.
The project required 36 pieces of equipment: Munters provided 16 5,000-12,000 cfm desiccant dehumidification units; J.T. Systems provided the remaining 20 items, including the dust collection and abrasive handling systems, and packaged all of the equipment for the job.
Concurrently, PSNS & IMF personnel used pressure treated, marine grade plywood to build four temporary containment quadrants underneath the ship. Enclosures were built around tank openings that had been cut to gain access to the work. Temporary, rigid ductwork that snaps together was connected to the dehumidification and ventilation equipment and then fed into the containment areas. From the hard vent, PSNS & IMF personnel also placed ductwork into the tank enclosures.
The project design called for simultaneous servicing of each quadrant. Four Munters dehumidifiers were placed in each quadrant, with two units running constantly and two connected and ready to go in case of emergency.
Port and starboard were looped together with a ventilation and dehumidification system and then balanced to support all the tanks on that particular quadrant. Emergency cross connects were utilized so if any part of the system on a particular quadrant was lost, the team could take a cap off and run flex ductwork to interconnect to keep both sides operational.
PSNS & IMF personnel also built prefabricated, smooth bore aluminum piping and ran the line all the way around the ship. Off these lines, small ports with valves enabled personnel to pump air and exhaust into each tank individually.
Dehumidifiers Working Round the Clock
All setup work was completed in early October. The sophisticated air distribution system supplied cool, dry air to both the blasting and coating containment and also directly into the tanks where the work was being performed. The large enclosed areas underneath the ship provided the return air.
A complete closed loop system was made from the dust collection equipment and dehumidification units so that although they were on completely separate legs, they still could feed every tank. This also provided personnel with the ability to cross over from port to starboard so they could balance and adjust air flow to lower the dewpoint inside the tanks.
Throughout the project, PSNS & IMF personnel monitored the conditions on site, including temperature volume and moisture levels entering and exiting the containment areas.
The Munters dehumidifiers featured a touch panel display so personnel could confirm that all of the critical performance parameters of the system were met, including reactivation temperatures, leaving air dewpoint, amp draw, and the leaving air temperature.
The project required maintaining humidity levels at 50% or less. Using Munters equipment, the levels were maintained 24 hours a day.
PSNS & IMF personnel worked around the clock for 89 days to complete the project.
Anchors Aweigh After Successful Project Completed
On December 18, Abe left dry dock at the shipyard ahead of schedule and under budget, with the previous industry standard of completing six tanks in 101 days shattered -- an accomplishment unheard of in the ship maintenance industry. The 18 tanks, to be completed in early 2007, were finished ahead of schedule, saving the Navy hundreds of thousands of dollars in manpower and maintenance expenses.