This incident occurred in the compressor house, which forms part of the methanol plant and contains equipment for compressing synthesis gas (a blend of hydrogen, carbon dioxide and carbon monoxide) as well as a steam turbine generator with associated support systems.
The incident
During work to adjust the parameters of the regulator which controls steam admission to the turbine generator, a process shutdown (PSD) had to be initiated manually owing to an unexpected response from the control system.
When PSD is initiated, the generator must be disconnected from the power grid and the turbine isolated from the steam network. In this case, isolation from the steam network failed and the backflow of steam at the intermediate pressure level increased turbine rotation.
This faster speed caused turbine blades to come lose from the rotor, which then became wedged and stopped abruptly. That caused the shaft to snap between turbine and gear.
One result of this breakdown was that components from the turbine shaft and a flexible coupling on the shaft where flung about with great force.
Objects struck included piping for the turbine’s lube oil system, which broke. That caused a lube oil leak, which ignited.
The investigation
The PSA quickly decided to launch its own investigation of the incident.
This has found that the incident at Tjeldbergodden on 2 December 2020 had a major accident potential and could have caused serious personal injury or death as well as substantial financial loss.
Actual consequences
The actual consequences of the turbine breakdown were that turbine components came loose and caused damage to equipment and the building. Objects struck by components included piping for the turbine’s lube oil system.
The leaking lube oil ignited and caused a fire which lasted about an hour, but which did not spread to other systems in the compressor house. About 1 000 litres of lube oil are estimated to have leaked out.
No physical injuries were sustained as a result of the incident.
Because of the incident, production from the methanol plant was down for about 12 weeks. The plant came back on line in week 7 without the damaged turbine.
Potential consequences
In the event of a turbine trip, plant operators are supposed to make a physical check of the turbine generator. Had they or other personnel been in the compressor house when the breakdown occurred, they could have been struck by flying components. The latter have also been hurled with great force through the walls of the compressor house and could have hit people outside the building.
Flying components have also hit the synthesis gas plant located in the same building. Had this caused a synthesis gas leak, the outcome could have been an explosion and/or a large fire.
On that basis, the PSA’s assessment is that the incident had a major accident potential and could have caused serious personal injury or death as well as substantial financial loss.
Direct cause
The direct cause of the turbine breakdown with subsequent fire was that isolation from the steam network at the intermediate pressure level failed to function as intended during an PSD of the system.
Underlying causes
The investigation has identified several elements which have or could have been significant for the incident occurring. These comprise:
- information used as a basis for classification
- failure to handle an impaired barrier function
- maintenance
- failure of a system review to pick up design weaknesses
- technical documentation.
Observations
Four nonconformities have been identified by the investigation, related to:
- identifying safety functions and barrier follow-up
- follow-up of the system
- documentation
- safe distance from the fire scene.
Two improvement points have also been identified in relation to:
- unclear how the Tjeldbergodden fire appliance was used
- unclear performance standard for personnel check (POB) in the plant.
Order
The PSA’s investigation has identified serious breaches of the regulations and Equinor has now been given the following order.
Pursuant to section 69 of the framework regulations on administrative decisions, Equinor Tjeldbergodden is ordered to do the following.
Identify, initiate and follow up measures to ensure that equipment with a safety function is identified and classified to ensure correct follow-up of its function and proper handling of impairments in order to secure safe operation. See sections 5 and 21 of the management regulations on barriers and follow-up respectively, see sections 58 and 59 of the technical and operational regulations on maintenance and classification respectively. See sections 10.1.1 and 10.1.2 of the report.
The deadline for compliance with the order is 31 December 2021. The plan for complying with the order must be submitted to us by 15 September 2021.