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Home : Media : News
NEWS | Sept. 14, 2023

NSS-SY Spotlight: Engineering Pillar -- Isolating firemain piping on aircraft carriers with freeze seals helps accomplish work faster, safer

By Aime Lykins, PSNS & IMF Public Affairs

In direct alignment with the U.S. Navy’s “Get Real, Get Better,” initiative, the Naval Sustainment System-Shipyards’ (NSS-SY) Engineering Pillar is promoting ways to accomplish work faster, safer and with the highest quality. Recently, the NSS-SY Engineering Intervention Board (EIB) worked to improve the maintenance of firemain piping on aircraft carriers as one of its improvement initiatives.

The firemain system aboard aircraft carriers distributes pressurized seawater for firefighting, cooling and washdown services. It is one of the most mission-critical fluid distribution systems aboard naval ships and provides a cooling medium for key equipment. Because it is so vital to the entire ship’s water flow, the isolation valves in firemains are designed not only to enable routine maintenance but, more importantly, to continue support for the ship and its crew after a system incurs battle damage.

“A freeze seal creates a mass of ice within a pipe that prevents water movement– similar to a shut valve,” said Michael Tracy, NSS-SY Engineering Pillar lead, Puget Sound Naval Shipyard & Intermediate Maintenance Facility. “The freeze seals consist of two sections of coiled copper tubing, with eight coiled loops per section. Each eight-coil section is fed by an independent liquid nitrogen supply line.”

Norfolk Naval Shipyard, and PSNS & IMF, along with partner shipyards, have tested the use of freeze seals to replace 12-inch firemain isolation valves on nuclear-powered aircraft carriers. The first carrier to use freeze seals during maintenance is USS Harry S. Truman (CVN 75).

Prior to the use of freeze seals, mechanical firemain isolation was challenging and often required the closure of three or four valves in each direction to obtain the necessary isolation. Because there are a number of areas of the ship and pieces of essential equipment which also require water flow from these valves, the use of freeze seals was implemented to reduce the need to close multiple valves and to save mechanics valuable time and resources.

“The intent of freeze seals is to have a single location rather than the dual freeze seal set up that was successful in earlier tests,” said Floyd Beckwith, branch manager, Code 267, Surface Ship Non-Propulsion Piping Waterfront Support Branch at Norfolk Naval Shipyard.

Freeze seal testing aboard Truman began in July 2022. Testing of the single expanded freeze seal was successful on the mock-up assembly, with the freeze seal solidifying in approximately 23 hours.

Installation of freeze seals aboard Truman was successfully performed in March 2023 to support replacement of firemain second-deck header isolation valves. A freeze seal was established on the 12-inch second deck firemain header piping to isolate one side of the work area. The freeze seal was fully formed within 36 hours.

“The coordination and set-up time to create the freeze seal was significant, but the results were excellent,” said Beckwith.

Since March, PSNS & IMF has been coordinating with Norfolk Naval Shipyard’s Code 267 and 2310, Reactor Engineering Division, to document the procedures, results and lessons learned. Once data is analyzed, the routine use of freeze seals will be rolled out to all Navy public shipyards.

“At PSNS & IMF, we will begin training the workforce on using firemain freeze seals and developing standard work,” Tracy said. “This provides an opportunity for shipyard employees to expand their skill sets and push innovation forward.”

The development and use of freeze seals is just one example of how the shipyards are working together to help the Navy complete maintenance faster. The NSS-SY EIB is seeking to sponsor more great improvements like this one.

If you have an idea for improving a process, please contact PSNS & IMF’s NSS-SY team in Building 457, or by email at psns.nss-sy.

For more information on Get Real, Get Better, please visit: GRGB-Overview/About-GRGB/.