CONSUMERS ENERGY CO

Incident Narrative

ON DECEMBER 8, 2018 AT APPROXIMATELY 20:50 HOURS CONSUMERS ENERGY GAS CONTROL RECEIVED A NOTIFICATION OF A POSSIBLE GAS RELEASE FROM A CONTRACTOR WORKING ONSITE AT CONSUMERS ENERGY FREEDOM COMPRESSOR STATION. FREEDOM COMPRESSOR STATION IS LOCATED IN MANCHESTER, MICHIGAN (WASHTENAW COUNTY) A STATION MECHANIC ARRIVED ONSITE AT APPROXIMATELY 21:30 HOURS AND IDENTIFIED A RELEASE AT RELIEF VALVE #171 (UNIT 3-1). THE MECHANIC CLOSED VALVE 171 TO ISOLATE THE GAS FROM ENGINE 3-1 WHICH STOPPED GAS FROM BLOWING. UPON FURTHER INVESTIGATION A CRACK (LEAK) ON THE RELIEF VALVE PILOT LINE WAS DISCOVERED. THE PILOT LINE LEAK CAUSED PRESSURE TO BLEED OFF WHICH ALLOWED THE RELIEF VALVE TO OPEN AND RELEASE GAS TO THE ATMOSPHERE. NEW PILOT LINE TUBING WAS INSTALLED AND A RELIEF VALVE INSPECTION PERFORMED TO VERIFY NO CHANGE IN SET PRESSURE OCCURRED AS A RESULT OF THE FAILURE. ADDITIONAL VALVE INSPECTIONS AND LEAK TESTS WERE PERFORMED ON THREE ADDITIONAL RELIEF VALVES LOCATED IN PLANT 3 AS A PRECAUTIONARY MEASURE. NO ADDITIONAL LEAKS WERE DISCOVERED. THE FAILED EQUIPMENT WAS SENT TO CONSUMERS ENERGY'S LABORATORY SERVICES FOR FURTHER ANALYSIS. A SUMMARY OF THE FINDINGS ARE DETAILED BELOW: THE LONGER LEG OF THE TUB FRACTURED IN HIGH CYCLE FATIGUE INITIATING AT MULTIPLE LOCATIONS ON THE TUB OD UNDER THE FERRULE, APPROXIMATELY 3/8"" FROM THE END OF THE TUBE. THE FATIGUE CRACK HAD PROPAGATED APPROXIMATELY 300 DEGREES AROUND THE TUBE PRIOR TO THE TUBE BEING TAKEN OUT OF SERVICE. THE FRACTURE SURFACE EXHIBITED A TRANSITION AFTER APPROXIMATELY 150 DEGREES OF PROPAGATION INDICATING THE STATE OF STRESS CHANGED OR THE PROPAGATION RATE INCREASED. THE FERRULE AT THIS LOCATION WAS NOT SQUARE WITH THE TUBE ABOVE IT, INDICATING A SIDE LOAD MAY HAVE BEEN APPLIED AT SOME POINT. THERE WAS NO APPARENT DEFECTS AT THE CRACK ORIGIN LOCATION. THE TUBE, FERRULE AND NUT FROM THE FAILURE LOCATION WERE ALL MADE OF TYPE 316 STAINLESS STEEL. ALTHOUGH NO RELATED TO THE FAILURE, THE ID OF THE TUBING HAD AN INTER-GRANULAR TEXTURE CONSISTENT WITH HAVING BEEN IN CONTACT WITH A CORROSIVE MEDIA. THE CAUSE OF THIS IS NOT UNDERSTOOD, AND THIS CONDITION MAY HAVE BEEN PRESENT AS-RECEIVED FROM THE MANUFACTURER.