Incident details
Operator, cause, commodity and consequences with raw source fields.
GTG incident on 2020-09-16 — SD
Operator
Northwestern Corporation
Cause
Corrosion Failure
Commodity
Natural Gas
Program
GTG
Damage and Injuries
0 fatalities
0 injuries
Property damage (nominal)
$650,000
Incident datetime
2020-09-16 14:30
Report number
Location
SD
Narrative
This is a supplemental final report for incident report 20200107-34393 submitted on 10/16/20. Please refer to that incident report for the initial narrative. The cause of the incident has been changed in part g from external corrosion to internal corrosion. This change has occurred because of data that was gathered from running a high resolution vertalog, which can differentiate between internal and external corrosion. The internal corrosion was also verified with a caliper log that was run down the casing with the vertalog tool. As noted in the initial report, the well was killed and then a composite plug was placed at 4479' just above the perforations. A production casing was installed from surface to 4431'. The production casing was cemented in place. Cement was run down the inside of the inner casing and there were returns to surface through the annular space between the new production casing and the outer casing. This sealed the leak in the outer casing and provides a mitigation against additional leaks. A cement bond log was run for the cementing work of the inner casing and no deficiencies were noted in the log. A pressure test was completed on the new installation and no issues were noted during the test. Following the integrity testing, the composite plug was drilled out. The well was then re-commissioned on 12/01/20. The well has been operating for two weeks with no identified issues. As an additional mitigation, leak surveys have been completed around the well and along the previous incident plume boundary. The plume from the incident has dissipated significantly. Readings within the plume area are under a percent gas in bar holes. Nwe is continuing to monitor the plume and will do so until it has dissipated. There are no safety or public safety concerns. This will be the final report for this incident.
Detailed record list
Report Received Date
2020-10-16 00:00:00
Iyear
2020
Report Number
20200107
Supplemental Number
34628
Report Type
Supplemental Final
Operator Id
31632
Name
Northwestern Corporation
Operator Street Address
3010 W. 69th St.
Operator City Name
Sioux Falls
Operator State Abbreviation
SD
Operator Postal Code
57108
Local Datetime
2020-09-18 12:00:00
Time Zone
Mountain
Daylight Savings Ind
Yes
Location Latitude
45.25191
Location Longitude
-109.116451
Nrc Rpt Num
1287711
Nrc Rpt Datetime
2020-09-18 12:48:00
Additional Nrc Report Numbers
1287832
Commodity Released Type
Natural Gas
Unintentional Release
333186
Intentional Release
0
Accompanying Liquid
0
Fatality Ind
No
Fatal
0
Injury Ind
No
Injure
0
Status When Identified
Normal Operation, Includes Pauses During Maintenance
Shutdown Due Accident Ind
Yes
Shutdown Datetime
2020-09-21 17:00:00
Restart Datetime
2020-12-01 12:04:00
Communication State Fed Ind
Yes
Party Initiated Communication
Operator
Initial Responder Com Datetime
2020-09-18 20:37:00
Ignite Ind
No
Num Pub Evacuated
0
Incident Identified Datetime
2020-09-16 14:30:00
On Site Datetime
2020-09-16 07:00:00
On Off Shore
Onshore
Onshore State Abbreviation
Mt
Onshore Postal Code
59014
Onshore City Name
Not Within A Municipality
Onshore County Name
Carbon
Designated Location
Not Applicable
Pipe Fac Name
Dry Creek Storage
Segment Name
Storage Well Bn 8-3
Federal
No
Location Type
Operator-Controlled Property
Incident Area Type
Belowground Storage Or Aboveground Storage Vessel, Including Attached Appurtenance
Crossing
No
Pipe Facility Type
Intrastate
System Part Involved
Belowground Storage, Including Associated Equipment And Piping
Item Involved
Underground Gas Storage Or Cavern
Installation Year
1983
Manufactured Year
Unknown
Material Involved
Carbon Steel
Release Type
Leak
Leak Type
Other
Leak Type Other
Unknown
Class Location Type
Class 1 Location
Could Be Hca
No
Pir Radius
266
Heat Damage Ind
No
Non Heat Damage Ind
No
Est Cost Oper Paid
0
Est Cost Unintentional Release
565283
Est Cost Intentional Release
0
Est Cost Prop Damage
650000
Est Cost Emergency
150000
Est Cost Other
0
Gas Cost In Mcf
1.6966
Prpty
1365283
Num Persons Hosp Not Ovnght
0
Num Injured Treated By Emt
0
Num Resident Building Affctd
0
Num Business Building Affctd
0
Wildlife Impact Ind
No
Accident Psig
1140
Gas Flow In Pipe In Mcf
7872
Mop Psig
1600
Mop Cfr Section
Other
Mop Cfr Section Details
Well Casing Maop Believed To Be Equal To Or Exceed The Maop Of The Field
Maop Established Date
1983-08-16 00:00:00
Maop Reversal Flow Ind
Bi-Directional
Accident Pressure
Pressure Did Not Exceed Maop
Pressure Restriction Ind
No
Gas Required Odorized Ind
No
Pipeline Function
Transmission In Storage Field
Scada In Place Ind
Yes
Scada Operating Ind
Yes
Scada Functional Ind
Yes
Scada Detection Ind
Yes
Scada Conf Ind
No
Accident Identifier
Scada-Based Information (Such As Alarm(S), Alert(S), Event(S), And/or Volume Or Pack Calculations)
Investigation Status
No, the operator did not find that an investigation of the controller(s) actions or control room issues was necessary due to: (provide an explanation for why the operator did not investigate)
Investigation Status Details
There were no actions that the gas controllers could have done that caused this issue.
Employee Drug Test Ind
No
Contractor Drug Test Ind
No
Cause
Corrosion Failure
Cause Details
Internal Corrosion
Internal External
Internal Corrosion
Int Visual Exam Results
Other
Int Visual Exam Details
Nwe Is Changing To Internal Corrosion Because Of Data That Was Gathered From Running A High Resolution Vertalog, Which Can Differentiate Between Internal And External Corrosion. The Internal Corrosion Was Also Verified With A Caliper Log That Was Run Down The Casing With The Vertalog Tool.
Int Other Corrosion Ind
Yes
Int Corrosion Type Details
It Is Believed That A Water Interface Occurred At This Location Based On Nwe Cathodic Nace Smes. This Could Not Be Verified. Microbiological Testing Was Not Completed Because The Well Had Had Biocide Added And Foreign Water Added To Kill The Well.
Int Other Basis Ind
Yes
Int Corrosion Basis Details
Internal Corrosion Was Selected Because Of Data That Was Gathered From Running A High Resolution Vertalog, Which Can Differentiate Between Internal And External Corrosion. The Internal Corrosion Was Also Verified With A Caliper Log That Was Run Down The Casing With The Vertalog Tool.
Int Other Loc Ind
Yes
Corrosion Location Details
Well Casing At ~1900' Below Surface.
Corrosion Inhibitors
Yes
Corrosion Lining
No
Cleaning Dewatering
Not Applicable - Not Mainline Pipe
Corrosion Coupons
Not Applicable - Not Mainline Pipe
Preparer Name
K**** M*****
Preparer Title
Manager Of Gas Transmission Compliance
Preparer Email
K***********@n***********.com
Preparer Telephone
406-461-1211
Authorizer Name
K**** M*****
Authorizer Title
Manager Of Gas Transmission Compliance
Authorizer Telephone
406-497-1211
Authorizer Email
K***********@n***********.com
Narrative
This is a supplemental final report for incident report 20200107-34393 submitted on 10/16/20. Please refer to that incident report for the initial narrative. The cause of the incident has been changed in part g from external corrosion to internal corrosion. This change has occurred because of data that was gathered from running a high resolution vertalog, which can differentiate between internal and external corrosion. The internal corrosion was also verified with a caliper log that was run down the casing with the vertalog tool. As noted in the initial report, the well was killed and then a composite plug was placed at 4479' just above the perforations. A production casing was installed from surface to 4431'. The production casing was cemented in place. Cement was run down the inside of the inner casing and there were returns to surface through the annular space between the new production casing and the outer casing. This sealed the leak in the outer casing and provides a mitigation against additional leaks. A cement bond log was run for the cementing work of the inner casing and no deficiencies were noted in the log. A pressure test was completed on the new installation and no issues were noted during the test. Following the integrity testing, the composite plug was drilled out. The well was then re-commissioned on 12/01/20. The well has been operating for two weeks with no identified issues. As an additional mitigation, leak surveys have been completed around the well and along the previous incident plume boundary. The plume from the incident has dissipated significantly. Readings within the plume area are under a percent gas in bar holes. Nwe is continuing to monitor the plume and will do so until it has dissipated. There are no safety or public safety concerns. This will be the final report for this incident.
| Report Received Date | 2020-10-16 00:00:00 |
|---|---|
| Iyear | 2020 |
| Report Number | 20200107 |
| Supplemental Number | 34628 |
| Report Type | Supplemental Final |
| Operator Id | 31632 PHMSA Enforcement |
| Name | Northwestern Corporation |
| Operator Street Address | 3010 W. 69th St. |
| Operator City Name | Sioux Falls |
| Operator State Abbreviation | SD |
| Operator Postal Code | 57108 |
| Local Datetime | 2020-09-18 12:00:00 |
| Time Zone | Mountain |
| Daylight Savings Ind | Yes |
| Location Latitude | 45.25191 Google Maps OpenStreetMap |
| Location Longitude | -109.116451 Google Maps OpenStreetMap |
| Nrc Rpt Num | 1287711 NRC Report How to search |
| Nrc Rpt Datetime | 2020-09-18 12:48:00 |
| Additional Nrc Report Numbers | 1287832 |
| Commodity Released Type | Natural Gas |
| Unintentional Release | 333186 |
| Intentional Release | 0 |
| Accompanying Liquid | 0 |
| Fatality Ind | No |
| Fatal | 0 |
| Injury Ind | No |
| Injure | 0 |
| Status When Identified | Normal Operation, Includes Pauses During Maintenance |
| Shutdown Due Accident Ind | Yes |
| Shutdown Datetime | 2020-09-21 17:00:00 |
| Restart Datetime | 2020-12-01 12:04:00 |
| Communication State Fed Ind | Yes |
| Party Initiated Communication | Operator |
| Initial Responder Com Datetime | 2020-09-18 20:37:00 |
| Ignite Ind | No |
| Num Pub Evacuated | 0 |
| Incident Identified Datetime | 2020-09-16 14:30:00 |
| On Site Datetime | 2020-09-16 07:00:00 |
| On Off Shore | Onshore |
| Onshore State Abbreviation | Mt |
| Onshore Postal Code | 59014 |
| Onshore City Name | Not Within A Municipality |
| Onshore County Name | Carbon |
| Designated Location | Not Applicable |
| Pipe Fac Name | Dry Creek Storage |
| Segment Name | Storage Well Bn 8-3 |
| Federal | No |
| Location Type | Operator-Controlled Property |
| Incident Area Type | Belowground Storage Or Aboveground Storage Vessel, Including Attached Appurtenance |
| Crossing | No |
| Pipe Facility Type | Intrastate |
| System Part Involved | Belowground Storage, Including Associated Equipment And Piping |
| Item Involved | Underground Gas Storage Or Cavern |
| Installation Year | 1983 |
| Manufactured Year | Unknown |
| Material Involved | Carbon Steel |
| Release Type | Leak |
| Leak Type | Other |
| Leak Type Other | Unknown |
| Class Location Type | Class 1 Location |
| Could Be Hca | No |
| Pir Radius | 266 |
| Heat Damage Ind | No |
| Non Heat Damage Ind | No |
| Est Cost Oper Paid | 0 |
| Est Cost Unintentional Release | 565283 |
| Est Cost Intentional Release | 0 |
| Est Cost Prop Damage | 650000 |
| Est Cost Emergency | 150000 |
| Est Cost Other | 0 |
| Gas Cost In Mcf | 1.6966 |
| Prpty | 1365283 |
| Num Persons Hosp Not Ovnght | 0 |
| Num Injured Treated By Emt | 0 |
| Num Resident Building Affctd | 0 |
| Num Business Building Affctd | 0 |
| Wildlife Impact Ind | No |
| Accident Psig | 1140 |
| Gas Flow In Pipe In Mcf | 7872 |
| Mop Psig | 1600 |
| Mop Cfr Section | Other View CFR 49 §192 |
| Mop Cfr Section Details | Well Casing Maop Believed To Be Equal To Or Exceed The Maop Of The Field |
| Maop Established Date | 1983-08-16 00:00:00 |
| Maop Reversal Flow Ind | Bi-Directional |
| Accident Pressure | Pressure Did Not Exceed Maop |
| Pressure Restriction Ind | No |
| Gas Required Odorized Ind | No |
| Pipeline Function | Transmission In Storage Field |
| Scada In Place Ind | Yes |
| Scada Operating Ind | Yes |
| Scada Functional Ind | Yes |
| Scada Detection Ind | Yes |
| Scada Conf Ind | No |
| Accident Identifier | Scada-Based Information (Such As Alarm(S), Alert(S), Event(S), And/or Volume Or Pack Calculations) |
| Investigation Status | No, the operator did not find that an investigation of the controller(s) actions or control room issues was necessary due to: (provide an explanation for why the operator did not investigate) |
| Investigation Status Details | There were no actions that the gas controllers could have done that caused this issue. |
| Employee Drug Test Ind | No |
| Contractor Drug Test Ind | No |
| Cause | Corrosion Failure |
| Cause Details | Internal Corrosion |
| Internal External | Internal Corrosion |
| Int Visual Exam Results | Other |
| Int Visual Exam Details | Nwe Is Changing To Internal Corrosion Because Of Data That Was Gathered From Running A High Resolution Vertalog, Which Can Differentiate Between Internal And External Corrosion. The Internal Corrosion Was Also Verified With A Caliper Log That Was Run Down The Casing With The Vertalog Tool. |
| Int Other Corrosion Ind | Yes |
| Int Corrosion Type Details | It Is Believed That A Water Interface Occurred At This Location Based On Nwe Cathodic Nace Smes. This Could Not Be Verified. Microbiological Testing Was Not Completed Because The Well Had Had Biocide Added And Foreign Water Added To Kill The Well. |
| Int Other Basis Ind | Yes |
| Int Corrosion Basis Details | Internal Corrosion Was Selected Because Of Data That Was Gathered From Running A High Resolution Vertalog, Which Can Differentiate Between Internal And External Corrosion. The Internal Corrosion Was Also Verified With A Caliper Log That Was Run Down The Casing With The Vertalog Tool. |
| Int Other Loc Ind | Yes |
| Corrosion Location Details | Well Casing At ~1900' Below Surface. |
| Corrosion Inhibitors | Yes |
| Corrosion Lining | No |
| Cleaning Dewatering | Not Applicable - Not Mainline Pipe |
| Corrosion Coupons | Not Applicable - Not Mainline Pipe |
| Preparer Name | K**** M***** |
| Preparer Title | Manager Of Gas Transmission Compliance |
| Preparer Email | K***********@n***********.com |
| Preparer Telephone | 406-461-1211 |
| Authorizer Name | K**** M***** |
| Authorizer Title | Manager Of Gas Transmission Compliance |
| Authorizer Telephone | 406-497-1211 |
| Authorizer Email | K***********@n***********.com |
| Narrative | This is a supplemental final report for incident report 20200107-34393 submitted on 10/16/20. Please refer to that incident report for the initial narrative. The cause of the incident has been changed in part g from external corrosion to internal corrosion. This change has occurred because of data that was gathered from running a high resolution vertalog, which can differentiate between internal and external corrosion. The internal corrosion was also verified with a caliper log that was run down the casing with the vertalog tool. As noted in the initial report, the well was killed and then a composite plug was placed at 4479' just above the perforations. A production casing was installed from surface to 4431'. The production casing was cemented in place. Cement was run down the inside of the inner casing and there were returns to surface through the annular space between the new production casing and the outer casing. This sealed the leak in the outer casing and provides a mitigation against additional leaks. A cement bond log was run for the cementing work of the inner casing and no deficiencies were noted in the log. A pressure test was completed on the new installation and no issues were noted during the test. Following the integrity testing, the composite plug was drilled out. The well was then re-commissioned on 12/01/20. The well has been operating for two weeks with no identified issues. As an additional mitigation, leak surveys have been completed around the well and along the previous incident plume boundary. The plume from the incident has dissipated significantly. Readings within the plume area are under a percent gas in bar holes. Nwe is continuing to monitor the plume and will do so until it has dissipated. There are no safety or public safety concerns. This will be the final report for this incident. |
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