NORTHERN NATURAL GAS CO — Gas transmission and gathering — incident on 2018-03-20

Gas transmission and gathering incident in Not Within a Municipality, YOAKUM County, TX. Reported cause: EQUIPMENT FAILURE. Reported consequences: 0 fatalities, 0 injuries, 3900 NATURAL GAS released, $100 reported property damage. Operator-reported incident data submitted to PHMSA, generally within 30 days. Records may be supplemented or corrected and do not represent final agency causal findings.

Report number: 20180043.

Operator ID: 13750.

Reported incident date: 3/20/2018 0:01.

Location detail: MP 38.63

Cause detail: MALFUNCTION OF CONTROL/RELIEF EQUIPMENT

Cause detail: ON MARCH 20, 2018, THE RELIEF VALVE ON THE 30 INCH DIAMETER M840B IN THE PLAINS STATION YARD FAILED AND VENTED GAS TO THE ATMOSPHERE. A RELEASE OF 39 MILLION CUBIC FEET WAS REPORTED TO THE NATIONAL RESPONSE CENTER. THE LAST INSPECTION WAS PERFORMED ON MARCH 19, 2018. ROOT CAUSE: INTERNAL CORROSION IN MAIN VALVE BODY, PISTON AND SEAT, PILOT SEAT WAS HARD AND CRUSHED AND PILOT SPRING WOULD NOT HOLD A STEADY SET PRESSURE. THESE ISSUE CAUSED RELIEF VALVE TX-193 ' 2000 END OF 30-INCH-DIAMETER METER HEAD TO FAIL.

PHMSA trend classification: significant incident, not serious.

PHMSA standardized cause: EQUIPMENT FAILURE — MALFUNCTION OF CONTROL/RELIEF EQUIPMENT.

PHMSA indexed costs: $106,100 reported total cost, $98,118.986 in 1984 dollars, $121,713.941 in current-year dollars.

PHMSA trend flags, standardized causes, and indexed costs are analytical fields added to operator-reported incident data. They do not represent final agency causal findings.