A third-party report has determined that a May rupture in the Mountain Valley Pipeline was caused by a manufacturer's defect in an elbow joint, rather than corrosion as environmental advocates had warned. The report from DNV GL USA highlighted a defective weld in a fitting installed in 2018, which failed during hydrostatic testing, but found no evidence of external or internal corrosion. This incident was the only failure among over 2,500 fittings tested, and the pipeline has been operational since June 2023, delivering natural gas from West Virginia. Environmental groups have expressed concern over potential corrosion due to delays in construction caused by legal challenges, but the report concluded that the failure resulted from exceeding the material's strength. The pipeline's builders, EQT, have faced fines for related environmental violations and have insisted on its safety. The project, costing nearly $8 billion, was pushed to completion by legislative measures from Senator Joe Manchin amid ongoing controversy.