NORTHERN BORDER PIPELINE COMPANY

Incident Narrative

ON MAY 19, 2013, A COMPONENT IN ONE OF THE TWO 24VDC BATTERY CHARGERS/INVERTERS SUPPLYING POWER TO THE STATION PROGRAMMABLE LOGIC CONTROLLER (PLC) FAILED AND THE CHARGER BEGAN DELIVERING HIGH AND LOW VOLTAGE SPIKES. THE 24VDC BATTERY CHARGERS / INVERTERS AND ARE CONFIGURED TO SHARE THE LOAD UNDER NORMAL CONDITIONS. THE CHARGER THAT SENSES THE LARGEST VOLTAGE REQUIREMENT WILL TAKE OVER TO SUPPLY THE LOAD CONDITIONS. THE BATTERY CHARGER THAT WAS SPIKING HIGH TOOK OVER THE LOAD AND THEN FAULTED LOW RESULTING IN A LOW 24VDC SUPPLY TO THE CONTROL PANEL. THE LOW VOLTAGE AT THE CONTROL PANEL RESULTED IN VARIOUS DIGITAL INPUT AND OUTPUT CARDS TO FAIL WHICH RESULTED IN THE ESD EVENT. ALTHOUGH THE STATION SUCTION AND DISCHARGE VALVES INDICATED CLOSED, THE DISCHARGE VALVE DID NOT FULLY CLOSE AND HAD TO BE MANUALLY ACTUATED TO FULLY CLOSE. THE CLOSED STATUS, WHICH DROPS THE OUTPUT TO THE VALVE, WAS AN INACCURATE INDICATION CREATED DUE TO THE LOW VOLTAGE SUPPLYING THAT DIGITAL INPUT CARD. GAS CONTROL DISPATCHED FIELD PERSONNEL TO INVESTIGATE THE STATION SHUTDOWN AND WHEN PERSONNEL ARRIVED AT THE SITE, THEY DISCOVERED THAT GAS WAS STILL VENTING FROM THE STATION VENT VALVE. TECHNICIANS MANUALLY CLOSED THE STATION DISCHARGE VALVE TO ISOLATE THE STATION FROM THE MAINLINE AND THE STATION THEN VENTED DOWN TO ATMOSPHERIC PRESSURE. AFTER SHUTTING IN THE STATION, THE FIELD TECHNICIANS DETERMINED WHAT CAUSED THE ESD AND WHY THE STATION DISCHARGE VALVE DID NOT FULLY CLOSE. NUMEROUS FAULTY STATUS, ALARM, AND SHUTDOWN INDICATIONS WERE ALL CORRECTED WHEN THE FAULTY BATTERY CHARGER WAS REMOVED FROM SERVICE. THE BATTERY CHARGER WAS REPAIRED AND RETURNED TO SERVICE AND A FUNCTIONAL ESD TEST WAS PERFORMED WITHOUT ANY ISSUES. THE FOLLOWING IS A TIMELINE OF EVENTS WHEN THIS 24-VOLT CHARGER/INVERTER SYSTEM BEGAN TO EXPERIENCE PROBLEMS. ALL TIMES SHOWN ARE CENTRAL DAYLIGHT TIME (CDT): TIME DESCRIPTION 4:47 UNIT SHUTDOWN AND BEGIN STATION ESD 4:48 STATION SUCTION VALVE CLOSED STATION DISCHARGE VALVE CLOSED STATION VENT VALVE OPEN 4:50 GAS CONTROL CONTACTED THE FIELD ON-CALL TECHNICIAN TO INVESTIGATE THE STATION SHUTDOWN 4:54 STATION BYPASS VALVE OPENED 5:00 FIELD ON-CALL EMPLOYEE TECHNICIAN CONTACTED OTHER FIELD TECHNICIANS THAT WERE CLOSER TO STATION 5 FOR ASSISTANCE 5:30 FIRST EMPLOYEES ARRIVED AT STATION 5 5:55 ONSITE EMPLOYEES MANUALLY CLOSED THE STATION DISCHARGE VALVE AFTER DETERMINING THAT IT HAD NOT FULLY CLOSED DURING THE ESD EVENT. 5:57 STATION WAS NOW BLOWDOWN AND FULLY ISOLATED FROM THE PIPELINE.