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What happened?
While troubleshooting the process on hydrocarbon recovery unit (HRU) Train 3 (see diagram), a shutdown valve automatically closed, creating a section of stagnant produced water in the piping.
The shutdown valve was not manually reopened when Train 3 was returned to production mode 10 hours later.
A flammable hydrocarbon release (>30% LEL) triggered a plant emergency shut down.
The water line was found to have a 3-line split which released 750kg of flammable hydrocarbons.
The heaters were not manually shut down until 14 minutes after the general alarm triggered.
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Why did it happen?
Low winter temperatures - the stagnant section could freeze.
Improper temperature sensor placement the electric heat trace (EHT) circuit was not active as the temperature set point was met.
The boot level instrumentation was unreliable.
Lack of procedures to trigger EHT review of any stagnant lines (created either as part of normal operations or manual isolations).
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What did they learn?
Create a programme, including procedures and training, for stagnant/dead leg detection and the management of freezing risks.
Review placement of temperature sensors in EHT circuits, prioritising lines which could be stagnant or lead to a flammable release.
Ensure reliability of level indication instrumentation (LSIT, LIC and LG). Raise work notifications when instrumentation deviation alarm is triggered.
When alarms are triggered, heaters should be manually turned off immediately.
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Ask yourself or your crew
How can something like this happen here?
How visible is stagnant/dead leg piping, formed either as part of normal operation or isolation?
What assessments can be done on known stagnant/dead leg piping to ensure EHT is in good operating condition?
How do we know that the instrumentation is reliable for the complete operating range?
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What happened?
While troubleshooting the process on hydrocarbon recovery unit (HRU) Train 3 (see diagram), a shutdown valve automatically closed, creating a section of stagnant produced water in the piping.
The shutdown valve was not manually reopened when Train 3 was returned to production mode 10 hours later.
A flammable hydrocarbon release (>30% LEL) triggered a plant emergency shut down.
The water line was found to have a 3-line split which released 750kg of flammable hydrocarbons.
The heaters were not manually shut down until 14 minutes after the general alarm triggered.
Why did it happen?
Low winter temperatures - the stagnant section could freeze.
Improper temperature sensor placement the electric heat trace (EHT) circuit was not active as the temperature set point was met.
The boot level instrumentation was unreliable.
Lack of procedures to trigger EHT review of any stagnant lines (created either as part of normal operations or manual isolations).
What did they learn?
Create a programme, including procedures and training, for stagnant/dead leg detection and the management of freezing risks.
Review placement of temperature sensors in EHT circuits, prioritising lines which could be stagnant or lead to a flammable release.
Ensure reliability of level indication instrumentation (LSIT, LIC and LG). Raise work notifications when instrumentation deviation alarm is triggered.
When alarms are triggered, heaters should be manually turned off immediately.
Ask yourself or your crew
How can something like this happen here?
How visible is stagnant/dead leg piping, formed either as part of normal operation or isolation?
What assessments can be done on known stagnant/dead leg piping to ensure EHT is in good operating condition?
How do we know that the instrumentation is reliable for the complete operating range?
The automatic closing of a shutdown valve triggered a water influx in a stagnant piping section of a hydrocarbon recovery unit (HRU). Because this was not noted and equipment that should have triggered alarms failed, it caused a split in the water line, which released 750kg of flammable hydrocarbons.
