CONSUMERS ENERGY CO

Incident Narrative

ON DECEMBER 5, 2020 AT APPROXIMATELY 07:20 HOURS CONSUMERS ENERGY GAS CONTROL RECEIVED AN ALARM NOTIFICATION WHICH INDICATED A POSSIBLE FIRE AT THE ST. CLAIR COMPRESSOR STATION (PLANT 4 - DEHYDRATION SYSTEM BUILDING). THE CONSUMERS ENERGY ST. CLAIR COMPRESSOR STATION IS LOCATED IN IRA, MICHIGAN (ST. CLAIR COUNTY). A STATION MECHANIC AT THE SITE WAS NOTIFIED AND CONFIRMED ACTIVATION OF THE PLANT FIREGATE SYSTEM OCCURRED DUE TO THE FIRE DETECTION ALARM. FOLLOWING THE EVENT, THE PLANT WAS REMOVED FROM SERVICE AND THE SCENE WAS MADE SAFE. ADDITIONAL PERSONNEL WERE DISPATCHED TO THE STATION TO DETERMINE THE POTENTIAL CAUSE OF THE ACTIVATION. DURING THE INCIDENT INVESTIGATION, SCORCH MARKS WERE DISCOVERED ON INSULATION ON THE REBOILER VENT STACK. THE PLANT SAFETY SYSTEM IDENTIFIED A HIGH HEAT SIGNATURE ON THE THERMAL OXIDIZER WHICH INITIATED THE FIREGATE ACTIVATION. THE EQUIPMENT WAS TAKEN OFF-LINE AND PHYSICALLY INSPECTED. SEVERAL CRACKED WELDS WERE IDENTIFIED ON THE EXHAUST LINE OF THE THERMAL OXIDIZER. THE INCIDENT WAS REPORTED TO MICHIGAN PUBLIC SERVICE COMMISSION ON DECEMBER 5, 2020 BECAUSE THE EMERGENCY SHUT-DOWN SYSTEM WAS ACTIVATED, AND GAS RELEASED. HOWEVER, A MORE IN-DEPTH VISUAL INSPECTION CONFIRMED ADDITIONAL EQUIPMENT DAMAGE ANTICIPATED TO EXCEED PHMSA REPORTING CRITERIA OF $50,000. ONCE THIS WAS DISCOVERED, ON DECEMBER 10, 2020 A NOTIFICATION WAS MADE TO THE NATIONAL RESPONSE CENTER. ADDITIONAL INVESTIGATION SUBSEQUENT TO THE EVENT HAS IDENTIFIED A CONCERN RELATIVE TO DESIGN/ACTUAL UNIT OPERATING TEMPERATURE, MATERIAL TEMPERATURE LIMITS OF THE EXHAUST SYSTEM COMPONENTS, AND EXCESSIVE THERMAL CYCLING CAUSED BY SYSTEM PROGRAMMING. FURTHER PROBLEM SOLVING IS REQUIRED TO DETERMINE THE ROOT CAUSE OF THE FAILURE. HOWEVER WITH THE CONCERNS DEFINED, CONSUMERS ENERGY HAS TAKEN ACTION TO REMEDIATE EACH CONCERN THROUGH A DECREASE IN THE OPERATING TEMPERATURE OF THE SYSTEM AND A REDUCTION IN THERMAL CYCLING OF THE EQUIPMENT. ALL DAMAGED MATERIALS HAVE BEEN REPLACED AND WELDS HAVE BEEN IMPROVED IN THE RESTORATION PROCESS. FURTHER ANALYSIS CONFIRMED THE SYSTEM DESIGN AND MATERIAL SUPPLY OF THE THERMAL OXIDIZER SUPERHEATER TO THE EXHAUST STACK INADEQUATELY ACCOUNTED FOR THE STRESS LEVELS PRESENT ON THE SYSTEM DUE TO THE OPERATING TEMPERATURE RANGE OF THE SYSTEM. IN ADDITION TO THE INITIAL REMEDIAL ACTIONS TAKEN, THE EQUIPMENT WAS ANALYZED TO DETERMINE FATIGUE AND STRESS. THE EVALUATION RESULTED IN EQUIPMENT DESIGN MODIFICATIONS TO (1) REDUCE THE STRESS PRESENT IN THE SYSTEM AND (2) PROVIDE ACCESS FOR INSPECTIONS AND REPAIRS. ADDITIONALLY, THERMAL CYCLES WILL BE MONITORED AND INSPECTED AT A PREDETERMINED CYCLE COUNT TO CONFIRM SYSTEM INTEGRITY.