Crawler assesses condition of deepwater Aasta Hansteen spar pull tubes

Offshore staff

STANSTED, UK – Optical Metrology Services (OMS) has completed remote measurement and inspection of various 230-m (754-ft) long pull tubes for Statoil’s Aasta Hansteen spar project in 1,300 m (4,265 ft) water depth in the Norwegian Sea.

Hyundai Heavy Industries is constructing the cylindrical 195-m (640-ft) high, 70,000-ton topsides facility at its Ulsan shipyard in South Korea. This will be capable of producing 23 MMcm/d of oil and gas and of storing 160,000 bbl of condensate.

It is due to go online next year, 300 km (186 mi) offshore western Norway and connected to the Shell-operated Nyhamna gas processing plant via the 480-km (298-mi) Polarled pipeline.

The location in the Arctic Circle, and the fact that this will be the world’s largest spar platform to date, introduced numerous considerations concerning the steel catenary risers connecting the subsea pipelines to the topsides of the platform.

According to OMS, this necessitated detailed and accurate inspection and assessment to determine the internal bore of the pull tubes used to connect the production risers, product export lines and pump caissons via a “pull head” to the topsides cellar deck.

Another consideration was the minimal clearance within the pull tubes. OMS deployed an 8LV crawler with visual and 3D laser modules to inspect 16, 230-m (755-ft) long pull tubes and eight caissons to assess:

  • Pipe ovality
  • HiLo misalignment
  • Weld root penetration.

Defects or obstructions within the pull tubes as a result of pipe welds or fluctuations in pipe geometry were a possibility, and of concern to Statoil due to potentially serious costly consequences once the platform was positioned at sea, where they could not be remedied.

OMS operator Tim Green said: “Much of the pipework to be inspected was in the horizontal position, but in many areas the tool had to handle inclines of up to 20°.

“The tool performed excellently in the vertical position, proving the versatility of the technology…Being able to produce standard MS Excel reports with the weld images embedded in the report - linked with the weld profile - is a very useful method of reviewing weld condition. Also having a permanent visual inspection record of the root pass of a weld is a valuable asset.”


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