CONSUMERS ENERGY CO

Incident Narrative

ON FEBRUARY 10, 2016 AT APPROXIMATELY 04:49 CONSUMERS ENERGY GAS CONTROL RECEIVED A SCADA ALARM IDENTIFYING A POSSIBLE OVER PRESSURE EVENT ON THE ADAMS RD. OUTLET AT THE COOLIDGE CITY GATE. THE COOLIDGE CITY GATE IS LOCATED AT 4600 COOLIDGE HWY., (OAKLAND COUNTY) ROYAL OAK, MICHIGAN. AN INSTRUMENT MECHANIC (IM) WAS DISPATCHED AT APPROXIMATELY 04:52 AND ARRIVED ON LOCATION AT APPROXIMATELY 05:53 TO DISCOVER A FAILURE OF THE PRIMARY REGULATOR (P2). THE REGULATOR FAILURE CAUSED THE RELIEF VALVE (RV- 6) SERVING THE ADAMS RD., OUTLET TO ACTIVATE AND REMAIN OPEN UNTIL APPROXIMATELY 06:18. THE RESPONDING IM PERFORMED A VALVING OPERATION TO ISOLATE THE FAILED REGULATOR ALLOWING THE STANDBY REGULATOR (S2) TO FEED. THE PRESSURE ON THE ADAMS RD. OUTLET INCREASED TO A MAXIMUM OF 318.37 PSIG AND APPROXIMATELY 4.2 MMCF OF NATURAL GAS WAS VENTED TO THE ATMOSPHERE AS A RESULT OF THE INCIDENT. THE INITIAL INVESTIGATION OF THE FAILURE SUGGESTED THE INLET SCREEN ON THE ADAMS RD. OUTLET MAIN RUN REGULATOR (P2) WAS PARTIALLY DISINTEGRATED CAUSING METAL DEBRIS TO CONTAMINATE THE REGULATORS INTERNAL COMPONENTS CAUSING IT TO FAIL OPEN. THE P2 REGULATOR WAS CLEANED OF DEBRIS AND THE INLET SCREEN AND REGULATOR DIAPHRAGM WERE REPLACED. THE EQUIPMENT WAS TESTED AND RETURN TO SERVICE. THE IMPACTED RELIEF VALVE WAS ALSO DISASSEMBLE AND CHECKED FOR DAMAGE AND DEBRIS WITH NEGATIVE RESULTS. AT APPROXIMATELY 04:42 THE FOLLOWING DAY THE P2 REGULATOR EXPERIENCED ANOTHER FAILURE. THE RELIEF VALVE OPERATED AS A RESULT OF THE EXCEEDANCE. HOWEVER, HYDRATES ENTRAINED IN THE GAS STREAM WERE FOUND TO HAVE PRECIPITATED OUT AND FROZE IN THE RELIEF VALVE'S PILOT RESULTING IN DELAYED ACTIVATION. THE PRESSURE ON THE ADAMS RD. OUTLET INCREASED TO A MAXIMUM OF 338 PSIG FOR APPROXIMATELY TWO MINUTES BEFORE RETURNING TO A STEADY RELIEF PRESSURE BELOW 110% OF MAOP. THE RELIEF VALVE WAS CLEANED, REBUILT, INSPECTED AND RETURN TO SERVICE. REGULATOR P2 HAS BEEN REMOVED FROM SERVICE UNTIL FURTHER INVESTIGATION AND LAB ANALYSIS IS COMPLETE AND APPROPRIATE REMEDIATION ACTIONS IDENTIFIED. A SAFETY RELATED CONDITION REPORT DETAILING THE FAILURE THAT OCCURRED ON FEBRUARY 11TH WAS REPORTED TO PHMSA ON FEBRUARY 18, 2016 (SCRC 20160022). A MOBILE AND WALKING SURVEY WAS PERFORMED ON APPROXIMATELY 1.5 MILES OF 12"" STEEL HIGH PRESSURE DISTRIBUTION PIPING (300 PSIG MAOP) OPERATING AT > 20% SMYS AND ASSOCIATED SERVICE LINES BETWEEN THE COOLIDGE CITY GATE AND MAPLE RD., TROY, MICHIGAN AND NO LEAKS WERE DETECTED. THE REGULATION EQUIPMENT (REGULATOR P2) REMOVED FROM SERVICE ON FEBRUARY 11, 2016 WAS REPLACED WITH A MOONEY FLOWGRID REGULATOR ON AUGUST 8, 2016 AND RETURNED TO NORMAL OPERATIONS. THE REGULATOR, DIAPHRAGM AND CAGE WERE EXAMINED BY CONSUMERS ENERGY LABORATORY SERVICES, IN SEPTEMBER 2016. THE INVESTIGATION FOUND THE DIAPHRAGM DIMENSIONS WERE INCONSISTENT WITH THE DIMENSIONS OF THE CAGE, PREVENTING A SECURE FIT DURING ASSEMBLY. IN ADDITION, MEASUREMENT DATA INDICATED THE O-RING ASSEMBLED ON THE BONNET WAS NOT SUBJECT TO COMPRESSION DURING ASSEMBLY. THE INVESTIGATION WAS INCONCLUSIVE AS TO WHY THE DIAPHRAGM WAS OUT OF POSITION, AND NO FAILURE CAUSE WAS IDENTIFIED. A SAFETY-RELATED CONDITION REPORT ""RETURN TO SERVICE"" NOTICE DETAILING REMEDIATION ACTIVITIES WAS SUBMITTED ON FEBRUARY 28, 2017.