Two New York subway tunnels heavily damaged by Hurricane Sandy will be closed for long-term repairs this summer, the Metropolitan Transportation Authority announced.

The Greenpoint Tube, which carries the G train under Newtown Creek between Brooklyn and Queens, will be closed for 12 weekends this summer and fall starting July 6. The Montague Tube, an almost mile-long pair of tunnels that carries the R train under the East River between Brooklyn and Manhattan, will be closed for up to 14 months starting the first week in August.

Sandy inundated the tubes with millions of gallons of seawater, which corroded, degraded, or ruined almost everything from tracks and switches, to signals and controls, to power and communications cables. Temporary fixes brought those tunnels back into service, but the damage has led to increased failures of components, a growing number of delayed trains and a pressing need to make permanent repairs.

In the Greenpoint Tube, power cables that were immersed in salt water are corroding from the inside, while corrosion on the outside of rails and fasteners raises the potential for short circuits. The controls for ventilation, lighting and communication systems were destroyed and have not been restored to their pre-Sandy condition.

The Montague Tube is in far worse condition and will require much more extensive repairs. It was flooded for a length of 4,025 feet to a depth of 20 feet with corrosive salt water sitting stagnant in the tube for 10 days. More than 27 million gallons of water were eventually pumped from the tube before work began to make it useable again for train service. While the work was enough to restore R service between Brooklyn Heights and Lower Manhattan, it was never intended to be a permanent repair.

VIDEO: Check out video of MTA officials inspecting the Montague Tube.