Hidden Corrosion in Hollow Section Members on Dreco Jack-Up Derricks
During periodic inspection, DSL identified through-thickness internal corrosion in hollow section members on Dreco derricks on jack-up rigs, with one structure found to retain only 40% of its original design capacity.
Métricas clave
- Remaining design capacity
- 40%
- Build era of affected derricks
- Early 1980s
- Age at which thickness checks are recommended
- 10+ years
Certain Dreco derricks installed on jack-up rigs, mostly 1.2 to 1.3m hook load or GNC derricks built in the early 1980s, were suffering advanced internal corrosion of load bearing hollow section members. In places the corrosion had gone completely through the thickness of the base material, affecting the performance and load bearing capacity of the derrick.
In the worst cases this created the potential for member failure, which could overload other members and lead to a significant structural failure or dropped object incident. Because the corrosion develops from the inside out, previous inspections had not identified it, or its criticality, until holes appeared in the members. The rig owner was unaware of either the corrosion or the risk to their operations.
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