May 22 (Reuters) - U.S. natural gas pipeline venture

Mountain Valley Pipeline pushed back the target in-service date

of its long-delayed pipe from West Virginia to Virginia to early

June from the prior target of "prior to June 1".

The company told federal energy regulators in a filing late

Tuesday that the small delay was "due to the extended

construction duration to achieve weld-out, which has been

associated with weather and environmental protection."

The $7.85 billion Mountain Valley project 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

President Joe Biden and help from the Supreme Court before it

could restart construction.

On April 22, Mountain Valley sought authorization from the

U.S. Federal Energy Regulatory Commission (FERC) to put the

project in service by May 23 to meet the "prior to June 1" in

service target.

Since then, Mountain Valley said in the FERC filing that the

project is nearly "welded out," with fewer than ten welds

remaining to allow testing for mechanical completion out of more

than 51,000 welds project-wide.

Hydro testing has been successfully completed on

approximately 99% of the project facilities, with the final

hydrotest to be completed shortly after weld-out, the company

said.

Earlier in May, the company said it repaired a segment of

pipe that failed a water test.

Commissioning is complete for all project compressor

stations and facilities are packed with gas between the northern

terminus of the project and milepost 186.1, the company also

said.

When Mountain Valley started construction in February 2018,

U.S. energy company Equitrans Midstream ( ETRN ) with a roughly

49% interest, the lead partner building the project, 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-kilometre) Mountain Valley project is

owned by units of Equitrans, NextEra Energy,

Consolidated Edison ( ED ), AltaGas ( ATGFF ) and RGC Resources ( RGCO )

. Equitrans will operate the pipeline.