COLUMBIA GAS TRANSMISSION, LLC

Incident Narrative

ON OCTOBER 15, 2014, A CONTRACTOR EMPLOYED BY COLUMBIA GAS TRANSMISSION, LLC (COLUMBIA) WAS WORKING ON A NEAR-BY PROJECT, WHEN HE DETECTED THE ODOR OF NATURAL GAS. UPON FURTHER INVESTIGATIONS, A CASING VENT WAS TESTED FOR EVIDENCE OF A NON-HAZARDOUS NATURAL GAS LEAK INSIDE A CASING. OPERATIONS PERSONNEL WERE NOTIFIED TO ASSIST IN SECURING THE SITE PENDING FURTHER ASSESSMENT AND NECESSARY SAFETY MEASURES. THE SEGMENT WAS ISOLATED BY COLUMBIA PERSONNEL AND THE LINE WAS BLOWN DOWN. HENCE, THE SITE WAS SECURED. UPON FURTHER INVESTIGATION, A DECISION WAS MADE TO REPLACE THE CASING AND THE PIPE WITH A PIPE. UPON REMOVAL OF THE PIPE, AN EXTERNAL CORROSION PIT WITH 100 PERCENT WALL PENETRATION WAS DETERMINED TO BE THE CAUSE OF THE UNINTENDED NATURAL GAS RELEASE. THE CORROSION PIT WAS APPROXIMATELY 3.75 INCHES INSIDE OF THE NORTH END OF THE CASING AT THE 5 O'CLOCK POSITION WHEN FACING NORTH. THE PIT WAS AT A LOCATION OF DAMAGED OR MISSING COATING. THE DAMAGED COATING WAS LOCATED UNDER THE RUBBER CASING ISOLATOR. BOTH RUBBER ISOLATORS AND WOODEN CENTRALIZERS WERE OBSERVED TO BE IN USE UPON REMOVAL OF THE CASING. HOWEVER, THE CARRIER PIPE WAS NOT CENTERED THROUGH THE CASING. WATER MARKS WERE OBSERVED ON BOTH THE CARRIER PIPE AND ON THE CASING, INDICATING THAT THE CASING SEALS HAD BEEN COMPROMISED AND, AT TIMES, WATER HAD BEEN PRESENT IN THE ANNULAR SPACE. WATER FLOWED OUT OF THE SOUTH SIDE OF THE CASING WHEN THE SOUTH SIDE CASING SEAL WAS EXPOSED. NO KNOWN SOIL CONDITIONS OR MEASURED POTENTIAL READINGS COMMONLY ASSOCIATED WITH MICROBIOLOGICALLY INFLUENCED CORROSION OR CATHODIC PROTECTION INTERFERENCE WERE OBSERVED. 1. THE EXTERNAL CORROSION PIT OCCURRED AS A RESULT OF CORROSION AT THE SITE OF COATING DAMAGE UNDER THE RUBBER CASING ISOLATOR ON THE NORTH SIDE OF THE CASING. 2. THE COATING DAMAGE LIKELY OCCURRED DURING INSTALLATION OF THE CASING OR DURING A SUBSEQUENT EXCAVATION OF THE CASING ENDS. THE WOODEN CENTRALIZERS CAUSED AND/OR EXACERBATED THE COATING DAMAGE. 3. THE PLACEMENT OF THE CASING ISOLATOR OVER THE AREA OF DAMAGED COATING DID NOT ISOLATE THE EXPOSED STEEL FROM EVENTUAL ELECTROLYTE INTRUSION. WITH WATER BEING PRESENT BETWEEN THE CASING SEAL AND THE PIPE, ATMOSPHERIC AND CREVICE CORROSION PITTED THE PIPE TO CAUSE THE LEAK. 4. THE INTRODUCTION OF WATER AS AN ELECTROLYTE TO THE EXPOSED STEEL CREATED A LOCALIZED CORROSION CELL UNDER THE RUBBER CASING ISOLATOR. EXTERNAL CORROSION OCCURRED WHEN THE NON-LEVEL CASING FILLED WITH WATER COMPLETELY TO THE NORTH (HIGH) SIDE OF THE ROAD AND ATMOSPHERIC CORROSION OCCURRED WHEN THE CASING WAS NOT COMPLETELY FILLED. 5. DURING THE TIME WHEN THE CASING WAS COMPLETELY FILLED WITH WATER, THE RUBBER CASING ISOLATOR SHIELDED THE EXPOSED STEEL FROM CATHODIC PROTECTION CURRENT THAT COULD HAVE MITIGATED THE CORROSION CELL DURING THAT TIME. DURING THE TIME WHEN ATMOSPHERIC CORROSION WAS OCCURRING, ONLY RE-COATING THE EXPOSED STEEL OR MAINTAINING DRY CONDITIONS INSIDE THE CASING COULD HAVE MITIGATED THE CORROSION CELL. KEY LESSONS LEARNED/CORRECTIVE MEASURES: 1) THE NATURE AND LOCATION OF THE CORROSION PIT THAT CAUSED THE LEAK MAKES IT DIFFICULT, IF NOT IMPOSSIBLE, TO DETECT DURING TYPICAL, NON-EXCAVATION CASING POTENTIAL OR SHORT TESTS. BECAUSE THE CORROSION OCCURRED IN AN ELECTRICALLY SHIELDED AREA, THE ONLY RELIABLE METHOD FOR DETECTION IS THE USE OF IN-LINE INSPECTION TOOLS. LINE R-701-N IS IN THE PROCESS OF BEING RECONFIGURED FOR THE PURPOSE OF RUNNING IN-LINE INSPECTION TOOLS IN THE FUTURE. 2) THERE WERE NO INDICATORS FOR A LOW PIPE-TO-SOIL POTENTIAL MEASUREMENTS FOR THE PIPELINE IN THE AREA GOING BACK TO 2008. LIKEWISE, NO CASING-TO-SOIL POTENTIAL MEASUREMENTS INDICATED SHORT TESTING WAS NEEDED. 3) FILLING THE ANNULAR SPACE BETWEEN THE CARRIER PIPE AND THE CASING WITH A DIELECTRIC MATERIAL REMOVES THE CORROSIVE ENVIRONMENT AND CAN PREVENT CORROSION FROM OCCURRING. FILLING OF THIS CASING COULD HAVE PREVENTED THIS LEAK.