May 10 (Reuters) - U.S. natural gas pipeline venture Mountain Valley Pipeline said on Friday it repaired a segment of pipe that failed a water test earlier in the month and will continue to prepare the long-delayed West Virginia-Virginia pipe for service.

The venture was on track to complete the $7.85 billion project by the end of May, U.S. energy firm Equitrans Midstream , the lead partner in the Mountain Valley venture, said in late April.

"Mountain Valley continues to expect to complete construction and final commissioning activities on or about May 31, 2024," an Equitrans spokesperson said.

Mountain Valley made its latest comments about the pipe repair in a filing with the U.S. Federal Energy Regulatory Commission (FERC) on Friday.

Mountain Valley said that as of April 30, it had successfully completed hydrostatic testing for 269 miles of the project’s 303-mile route.

Hydrostatic testing involves the use of water to pressure test the pipe for a specified time period, exposing all pipeline components to a pressure that exceeds the maximum allowable operating pressure to ensure all components will operate safely prior to the introduction of gas into the pipe, Mountain Valley said in the FERC filing.

Mountain Valley said it notified federal and state agencies on May 1 of a hydrostatic testing failure at milepost 245.95.

Since then, the company said it "has successfully performed hydrostatic testing on additional segments, including the repaired segment where the disruption occurred, without incident."

Mountain Valley is the only big gas pipeline under construction in the U.S. Northeast. It has encountered numerous regulatory and court fights that have stopped work several times since construction began in 2018.

The pipe, which is key to unlocking gas supplies from Appalachia, the nation's biggest shale gas-producing region, needed a bill from the U.S. Congress that was signed into law by the president and help from the Supreme Court before it could restart construction.

Environmentalists have said that the project would harm soil and water quality in the forest, increase the use of natural gas, a leading fossil fuel and greenhouse gas emitter, and stymie efforts to address climate change threats.

When Mountain Valley started construction in February 2018, Equitrans estimated the 2.0-billion cubic feet per day project would cost about $3.5 billion and enter service by late 2018.

The 303-mile (488-kilometer) Mountain Valley project is owned by units of Equitrans, the lead partner building the pipe with a roughly 49% interest, NextEra Energy, Consolidated Edison, AltaGas and RGC Resources . Equitrans will operate the pipeline.

(Reporting by Scott DiSavino and Anjana Anil; Editing by Aurora Ellis)