Special hang-off frames
Replacing riser plates on FPSO
Scope of work
Serve as an offshore feeding and wet-storage hub in DP mode with one Riser Protection Frame during the Egina FPSO repair/replacement. Lift the RPF into a hang-off frame, double-bank with Maersk Inventor (DP) to hand over the damaged unit and receive the replacement, then return the damaged RPF to port for decommissioning.
Methods
Executed with AutoCAD and OrcaFlex to support drawings, method development and motion analysis.
Engineering scope
Define offshore procedures for upending and laying down the RPFs; design a tugger-winch arrangement that does not interfere with deck operations; run OrcaFlex motion studies on RPF pendulum behaviour during upend/lay-down and on hang-off frame motions for OCV operations.
A unique all-round heavy lift project
No heavy lift project is ever the same – and that is exactly what makes our work so exciting. Recently, we had the opportunity to handle one of those true “all-rounders” that challenged every aspect of our expertise: logistics supply, engineering, heavy lifting, and offshore operations.
In late summer last year, MV Svenja demonstrated her offshore capabilities in the Egina oilfield, supporting operations on the EGINA FPSO.
The mission: Replace a 190-tonne riser protector
Under the FPSO’s hull, risers connect the vessel to 44 subsea wells. To protect these risers from external impact, massive steel protection grids are mounted along the waterline.
Each riser protector measures 24.8 × 31.5 metres and weighs 190 tonnes.
One of these protectors had been damaged and needed replacement. SAL was contracted to:
- Transport the replacement riser protector from Lagos to the oilfield
- Receive the damaged unit from MV Maersk Inventor, the offshore construction vessel responsible for installation and removal operations
Engineering solutions for an offshore exchange
Our team was faced with several major challenges throughout the project. First, our Engineering department had to determine how to safely transfer and handle the oversized protectors between two floating vessels offshore.
We designed four hang-off frames specifically to secure both riser protectors during the exchange and installed them on the side shell of MV Svenja.
Precision heavy lifting on a moving sea
For transport, the grid was safely lashed to the deck in a horizontal position.
However, before the offshore operation, it needed to be:
1. Uplifted; 2. Upended and 3. Positioned vertically on two of the hang-off frames
This was completed using MV Svenja’s two 1,000-tonne cranes in tandem.
Our Engineering team ran high-accuracy motion and stability simulations in AutoCAD and OrcaFlex to incorporate vessel movement. Motion studies ensured safe pendulum behavior during lifting, while a custom tugger-winch arrangement was developed to prevent any interference with deck operations.
The most critical challenge was designing a safe procedure for the joint cargo operation with MV Maersk Inventor. MV Svenja held position using her DP system, matching the DP3-class performance of her counterpart – demonstrating her strong offshore station-keeping capabilities.
Safe transfer and a successful departure
With extreme precision and coordination, MV Maersk Inventor approached MV Svenja and carefully lowered the damaged riser protector onto two of the hang-off frames. Afterward, she collected the new protector positioned on the remaining frames.
Once the damaged unit had been safely laid down and secured on deck, MV Svenja departed the Egina oilfield, adding yet another powerful offshore operation – and valuable engineering experience – to her vessel résumé.