Dropped Angle Iron from Drill Floor Ducting Support

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Average: 4.7 (3 votes)
Alert ID: 
Description of Process: 

During plug & lubricate (P&L) operations, a four-man team was on the drill floor breaking down a wireline toolstring.

Description of Incident: 

A piece of angle iron weighing 7.75 kg, used to secure the draw-works exhaust ducting dropped from approximately 12m. The angle iron hit and smashed the re-enforced glass roof of the dog house, bounced 2m laterally (contacting one of the wireline team on their hard hat) and eventually landed a further 2m away on the drill floor.

Immediate Cause:

  • the angle iron fell from the draw-works motor discharge duct after primary fixing bolts had either failed or worked loose.

Underlying Causes:

  • Potential bi-metallic corrosion. Carbon steel bolts were used to secure the stainless steel angle iron section.

  • The failed / loose bolts were not identified during inspection. The ducting inspection work order only called for a general visual inspection from drill floor level.

  • Reliable securing practices were not utilised as evidenced by double nuts used on other parts of the structure.

  • The draw-works exhaust duct is not captured in the weekly derrick inspection as it is owned by the platform maintenance & operations team
Good Practice Guidance: 

Lessons learned

  • Carbon steel bolts must be adequately isolated from any stainless steel material to avoid the potential for bi-metallic corrosion.

  • To identify failed / loose bolts; incorporate inspection of bolts in the derrick inspection.

  • Clearly define responsibilities for maintaining / checking equipment.

  • Level of inspection detail for support structures must be adequate and clearly defined in the work orders.

  • Reliable securing practices should always be used.



  • Review the top side inspection scope for HVAC and exhaust ducting to ascertain whether support structures are included and that the level of inspection is a close visual inspection. If not, amend accordingly.

  • Inspect HVAC & exhaust support structures at height. Identify any deficiencies in the securing mechanism and rectify.

  • Identify high risk areas on all platforms with regards to dropped objects and develop a scheme to mitigate the risk.

  • Review dropped object picture books for all operating rigs. Ensure all items with a DROPS potential within the drilling package are included, regardless of maintenance responsibility. Rectify any omissions.

Causes and consequences of incident or accident: 
Moving, flying or falling object
Contributing factor: 
Change management
Control of work