In March 2012, Nautec worked with Sarawak Shell Sdn. Bhd. to undertake the inspection and structural reinstatement of conductors for a platform located offshore Sarawak. The conductor had corroded significantly and the inner casings were exposed to further corrosion, causing concern due to the increased well loads on the remaining casings.
Sarawak Shell Sdn. Bhd.
A series of vertical rebars were installed to reinstate bending moment capacity of the conductor and the inner casing. Shear studs were installed to provide enough shear transfer between the casings and the repair material. The entire repair area was encased in an especially designed mould that could be installed over the conductor from the bottom of the spider deck down to -4m from MSL without the need for divers. Prior to installation of mould, marine growth on the conductor was removed using ultra-high pressure water jet so that the UHPC material and vertical rebars would have sufficient bond with the steel conductor. The structures were repaired and reinforced with steel bars and grouted together using UHPC material.
Extensive corrosion of the 26 inch conductor in the splash and tidal zones had caused it to become partially parted. The 18 5/8 inch inner casing was also suspected to be heavily corroded. In this condition additional loads are transferred onto the remaining intact casings, which can lead to overstressing and failure.
The conductor had corroded significantly and the inner casings were exposed to further corrosion, causing concern due to the increased well loads on the remaining casings. The conductor and casing were encapsulated in a combination of steel rebars and UHPC material to reinstate full design structural capacity.
The small footprint of the grout equipment spread allowed all operations to be carried out from the platforms main deck. After mould installation, the UHPC material was injected into the mould to completely encapsulate the conductor and inner casing. Due to the high strength development of the UHPC material, the mould was removed after 24 hours from casting.
Nautec’s engineering team designed the repair method and counterchecked using FEM analysis.
Click here to read the case history.