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Special hang-off frames: Replacing riser plates on FPSO

The entire team have proved that if there is a will to succeed, they can make it happen. It also goes to show what proper planning, coordination and teamwork can achieve without compromising safety.

Bashir Abduallahi, Egina Close-out Leader at TOTAL

Egina FPSO Riser Plate Protection Cover Replacement
ClientMarine Platforms Ltd. for Samsung Heavy Industries Nigeria
Scope of work
  • Serve as offshore feeding and wet storage facility in DP mode with one Riser Protection Frame during the repair and replacement work on the Egina FPSO
  • Lift on RPF into hang-off frame and double bank with Maersk Inventor OCV in DP which hands over damaged RPF onto special hang-off frame and picks up new RPF for replacement
  • Ship damaged RPF to port for decommissioning
Engineering scope
  • Find procedures for upending and laying down of the RPFs while offshore
  • Develop a tugger winch arrangement that is not interfering with the on deck operations
  • Motion studies to check the pendulum motions of the RPFs during the upending and laying down procedure
  • Motion studies to check the hang-off frame motions for OCV operations
Methods / Software
  • AutoCAD
  • OrcaFlex

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Precise calculations for Egina

No heavy lift project is like the other – and that is what makes our job so exciting. Recently, we had the chance to conduct one of these “all-rounders” that touches every aspect of our business: logistics supply, engineering, heavy lifting and offshore operations.

In late summer of last year, we sent MV Svenja to show off her offshore abilities with the big boys in the Egina oilfield and the EGINA FPSO.

Under its hull, risers connect the vessel to 44 subsea wells. To protect these risers from any external impact, massive steel grids are attached to the outside hull of the FPSO along the waterline. These riser protectors measure 24.8 by 31.5 metres, with a total weight of 190 tonnes. One of these riser protectors was damaged and had to be replaced. SAL was hired to transport a new riser protector from Lagos to the field, and to take on the damaged one from MV Maersk Inventor, an offshore construction vessel, which was responsible for the installation on the FPSO.

Our team had to find solutions to different challenges over the course of the project. At first, our Engineering team had to figure out how to safely handle the large grids between two floating vessels to complete the exchange in the field. We designed four hang-off frames for this purpose that were specially fitted to hold the two riser protectors, and then installed them on the side hull of MV Svenja.

While the protector grid was safely lashed on deck in a laying position for transport, it needed to be uplifted, upended and vertically positioned on two of the outside hang-off frames using the two 1,000 tonnes cranes of MV Svenja in tandem operation. Our Engineering team precisely calculated this manoeuvre using AutoCAD and Orcaflex software, taking the motion of the sea into account. They conducted motion studies to check the pendulum motions of the frames during the lift operations, and also derived safe cargo procedures. One of these involved developing a tugger winch arrangement to prevent any interference with on-deck operations.

Probably the most challenging task for our engineers was to find a safe procedure for the joint cargo operation with MV Maersk Investor. During the most critical part of the entire operation, our MV Svenja used her DP system to maintain her exact position – proving her offshore abilities alongside the DP3-operated Maersk Investor. Our engineers painstakingly analysed further motion studies to incorporate the motion of the hang-off frames.

With great caution, MV Maersk Investor approached MV Svenja in order to carefully place the damaged riser protector onto two of MV Svenja’s hang-off frames. After the successful delivery, MV Maersk picked up the new riser protector that was positioned on the remaining two frames. Once the taken-on protector was safely laid down and lashed on deck, MV Svenja left the Egina oilfield, having added some valuable engineering and offshore experience to her ship’s résumé.

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