TENNESSEE GAS PIPELINE COMPANY — Gas transmission and gathering — incident on 2019-11-18

Gas transmission and gathering incident in MADDOX, HARDIN County, TN. Reported cause: NATURAL FORCE DAMAGE. Reported consequences: 0 fatalities, 0 injuries, 116172 NATURAL GAS released, $0 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: 20190132.

Operator ID: 19160.

Reported incident date: 11/18/2019 13:14.

Location detail: VENT VALVE

Cause detail: TEMPERATURE

Cause detail: DAY OF DISCOVERY: ON 11/18/19, A KM MEASUREMENT TECH ARRIVED AT THE UNMANNED TGP STATION 856 FOR THE PURPOSE OF READING FUEL METER INDEXES. HE NOTICED A GAS RELEASE SOUND UPON EXITING HIS VEHICLE NEAR THE COMPRESSOR BUILDING. THE TECH REPORTED THE ISSUE TO THE OPERATIONS SUPERVISOR AND WAS INSTRUCTED TO TRY TO IDENTIFY THE LEAK. HE IDENTIFIED IT WAS COMING FROM THE BLOWDOWN SILENCER AS THE TECH COULD VISUALLY SEE THE GAS VENTING AND ALSO OBSERVED FROSTING ON THE SILENCER. THE TECH THEN PROCEEDED TO THE CONTROL ROOM AND ULTIMATELY IDENTIFIED THAT THE NORMALLY CLOSED REMOTED OPERATED 4IN COMPRESSOR LOADING VALVE WAS OPEN ON THE UNIT #2 LOAD LINE ALLOWING GAS TO VENT THROUGH THE NORMALLY OPEN COMPRESSOR VENT VALVE. THE TECH PROCEEDED TO CLOSE THE MANUAL BLOCK VALVE ON THE LOAD LINE ASSEMBLY AT 1:36PM TO STOP THE LEAK. THE LEAK STOPPAGE WAS REPORTED TO KM MANAGEMENT AT 1:40PM. AT THE TIME OF THE INCIDENT, IT WAS UNKNOWN THE QUANTITY OF GAS RELEASED BUT ON THE 2:35PM ERL CALL IT WAS DETERMINED TO REPORT TO THE NRC AS A PRECAUTION. IT WAS REPORTED TO THE NRC AT 2:46PM LOCAL TIME WITH THE UNKNOWN AMOUNT. THE REPORT NUMBER WAS 1264245. 48 HOUR UPDATE: DURING INVESTIGATION, IT WAS DETERMINED THAT THE GAS HAD BEEN VENTING THROUGH THE BLOWDOWN SILENCER FOR ABOUT 6 DAYS. THIS WAS REPORTED TO THE NRC (#1264366) ON THE 48 HR UPDATE AT 4:54PM LOCAL TIME ON 11/19/19. INVESTIGATION: DURING INVESTIGATION, IT WAS IDENTIFIED THAT THE UNIT #2 LOAD LINE VALVE OPENED ON 11/12/19 AT 11:43PM. THE LOAD LINE VALVE OPENED AS A RESULT OF FREEZING UP OF MOISTURE IN THE SOLENOID CONTROL BOX. AT STA 856, THE TEMPERATURE ON 11/12/19 WENT BELOW FREEZING AT 4PM AND WAS APPROXIMATELY 22 �F AT THE TIME OF THE EVENT. THIS AREA DOES HAVE WINTERIZATION PROCEDURES AND PLANS IN PLACE AND IS SCHEDULED IN MAXIMO TO BE PERFORMED MONTHLY NOVEMBER THROUGH MARCH. HOWEVER, SINCE THIS OCCURRED MID-MONTH, THE PLAN WAS NOT COMPLETED AT THE TIME OF THE INCIDENT. THE TIMING OF THE EVENT IS VALIDATED BY THE VALVE EVENT LOGS, THE ALARMS, AND THE PRESSURE RISE IN THE UNIT #2 PIPING AT THAT TIME OF THE EVENT. THE PRESSURE ON THE DISCHARGE OF UNIT #2 WHERE THE VENT VALVE IS LOCATED AVERAGED 135 PSI. THIS BACKPRESSURE FLUCTUATED WITH THE MAINLINE LINE PRESSURE AND WAS CREATED BY THE RESTRICTION OF AN ORIFICE PLATE ON THE INLET TO THE SILENCER. THE ORIFICE PLATE ON THE SILENCER IS A DESIGNED PLATE WITH 4 X 1.25" HOLES FOR CUTTING THE PRESSURE GOING INTO THE SILENCER. WHEN CALCULATING GAS LOSS IT WAS ASSUMED THAT THE ORIFICE PLATE ACTED AS 4 INDEPENDENT HOLES. THE TOTAL GAS LOSS CALCULATED WAS 116,172 MCF. THE GAS THAT PRESSURIZED THE UNIT #2 COMPRESSOR CASE ALSO PRESSURIZED THE UNIT #1 CASE. WHEN THE PLC SAW THE CASE PRESSURE ELEVATED ON UNIT #2, IT TRIGGERED THE UNIT TO TRY TO MAINTAIN SEAL OIL PRESSURE TRIGGERING ALARMS AND EVENT STATUSES. OVER THE COURSE OF THE EVENT THERE WERE 3 STATION WARNING CALLOUTS THAT WERE TRIGGERED THROUGH ALARMS ORIGINATING FROM THE LOAD LINE VALVE OPERATING. THESE ALARMS INDICATED ISSUES WITH UNIT 1 AND UNIT 2 IN RELATION TO THE SEAL OIL SYSTEMS. THE TECH RESPONDING TO THE CALLOUTS LOGGED IN REMOTELY TO ASSESS THE SCADA ALARMS. THE TECH VIEWED ONLY THE STATION LEVEL ALARM SCREEN AND UNIT 1A ALARM SCREEN, AND EITHER DIDN'T LOOK AT OR DIDN'T RECOGNIZE THE SIGNIFICANCE OF THE EVENTS. THE TECH ALSO DIDN'T LOG INTO THE UNIT 2A LEVEL MACHINES TO VIEW THE UNIT SPECIFIC ALARM SCREEN. IN ADDITION TO THE 2 EVENTS ON THE NIGHT THE INCIDENT ORIGINATED THERE WAS ALSO A CALLOUT 3 DAYS LATER AGAIN AS A RESULT OF A UNIT 2A ALARM THAT WAS NOT FOLLOWED UP ON. FOLLOW-UP ACTION ITEMS: OPERATIONS HAS CHANGED THE MAXIMO WORK ORDER TO BEGIN WINTERIZATION PLANS IN OCTOBER INSTEAD OF NOVEMBER. ALSO, THE TECH WAS PREVIOUSLY TRAINED ON SCADA AND HOW TO MANAGE ALARMS; HOWEVER AFTER THIS INCIDENT, OPERATIONS HELD RE-TRAINING FOCUSING ON ALARM LOG REVIEW AND ACKNOWLEDGEMENT RESPONSES. THE TECH IN QUESTION HAD OQ REVOKED AND WAS REQUIRED TO RETEST FOR THE OQ TASK.

PHMSA trend classification: significant incident, not serious.

PHMSA standardized cause: NATURAL FORCE DAMAGE — TEMPERATURE.

PHMSA indexed costs: $234,425 reported total cost, $242,186.753 in 1984 dollars, $298,236.429 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.