Story highlights The U.S. Navy cites "unauthorized and undocumented weld repairs" made to steam pipe elbows

The USS John Warner, USS North Dakota and USS Minnesota face restrictions

(CNN) Less than a week after the U.S. Navy welcomed its newest submarine to the fleet, the USS John Warner and two sister fast-attack subs are facing operating restrictions after a contractor was found to have made unauthorized repairs to parts on the nuclear subs.

"As part of an ongoing investigation into a quality control issue with a supplier, General Dynamics Electric Boat determined that three steam pipe elbows supplied by the vendor in question required additional testing and repair due to unauthorized and undocumented weld repairs having been performed on these elbows," a Navy statement said.

The elbows help take steam from the subs' nuclear reactor plants to their propulsion systems, Defense News reported Wednesday . It quoted a senior Navy official as saying the concern was "long-term wear-and-tear" on the affected parts.

Besides the John Warner (SSN-785), the affected vessels are its predecessors in the Virginia class of subs, the USS North Dakota (SSN-784) and USS Minnesota (SSN-783).

General Dynamics and the other builder of the Virginia-class subs, Huntington Ingalls Industries -- Newport News Shipbuilding, were making additional checks on the problem, the Navy said. The unauthorized work was done by a subcontractor to the shipbuilding giants.

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