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What happened?
A crew was hydrotesting a newly constructed pipeline when an incident occurred.
During pigging operations, hydrotest fluid and the pig became lodged. While the crew dewatered and depressured the equipment, a large volume of air inadvertently escaped into the adjacent 400-barrel production tank. High pressure in the tank blew off the tank lid and vent lines.
No one was injured in the incident, but it could have resulted in severe or fatal injuries to workers in the surrounding area.
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Why did it happen?
- Hydrotest fluid froze during the dewatering process.
- A non-pressurized production tank was used.
- The hydro-testing plan did not include a process that recognized appropriate risk associated with the change in process, including evaluation, risk controls and equipment operating limits.
-
What did they learn?
- Work with a professional engineer to develop the appropriate engineering controls i.e., equipment selection, use and configuration.
- Revise project specific hydro-testing plans, appropriate management of change processes and authorizations.
-
Ask yourself or your crew
- How can something like this happen here (e.g. on our site)?
- What safety measures (i.e. procedures, controls/barriers) do we have in place to mitigate the risk?
- How do we know the risk controls/barriers are working?
- What improvements or changes should we make to the procedures, controls/barriers or the way we work?
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
What happened?
A crew was hydrotesting a newly constructed pipeline when an incident occurred.
During pigging operations, hydrotest fluid and the pig became lodged. While the crew dewatered and depressured the equipment, a large volume of air inadvertently escaped into the adjacent 400-barrel production tank. High pressure in the tank blew off the tank lid and vent lines.
No one was injured in the incident, but it could have resulted in severe or fatal injuries to workers in the surrounding area.


Why did it happen?
- Hydrotest fluid froze during the dewatering process.
- A non-pressurized production tank was used.
- The hydro-testing plan did not include a process that recognized appropriate risk associated with the change in process, including evaluation, risk controls and equipment operating limits.

What did they learn?
- Work with a professional engineer to develop the appropriate engineering controls i.e., equipment selection, use and configuration.
- Revise project specific hydro-testing plans, appropriate management of change processes and authorizations.

Ask yourself or your crew
- How can something like this happen here (e.g. on our site)?
- What safety measures (i.e. procedures, controls/barriers) do we have in place to mitigate the risk?
- How do we know the risk controls/barriers are working?
- What improvements or changes should we make to the procedures, controls/barriers or the way we work?
Published on 09/04/23
1139 Views
A crew was hydrotesting a newly constructed pipeline. During pigging operations, hydrotest fluid and the pig became lodged. While the crew dewatered and depressurized the equipment, a large volume of air inadvertently escaped into the adjacent production tank. High pressure in the tank blew off the tank lid and vent lines. No one was injured in the incident, but it could have resulted in severe or fatal injuries to workers in the surrounding area.
Original material courtesy of Energy Safety Canada
Other resources:
Process Safety Fundamentals
CSA Store Z662 O&G Pipeline Systems
Supervisor Competency Guideline