And that’s how you weigh a platform topside!

When a platform has been built, you often hear how big it is – and how much it weighs. You might have thought the weight was just calculated based on the amount of steel, piping and equipment installed? Well, platforms are actually weighed physically. Find out how it’s done!

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Johan Sverdrup P2. All photos: Aibel/Øyvind Sætre

Platforms are enormous constructions that take years to build. The topside for P2, Equinor’s second processing platform for the Johan Sverdrup field, is the biggest ever designed and constructed by Aibel. But how much does it weigh?

Knowing the platform’s and each module’s exact weight is important. Marine Operations Manager at Aibel, Anne Kindlihagen explains:

“We need to know the weight for several reasons. When the platform or module is going to be moved by trailers, lifted by a crane, or placed on a barge or vessel, we need to know what it weighs and where the centre of gravity lies to verify the use of right equipment. It is a matter of safety.”

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Marine Operations Manager, Anne Kindlihagen.

Avoiding overload and strain

At the start of a project, Aibel’s weight estimators use input from all disciplines to estimate the weight of an object. The estimate works as a basis during the design phase, and modules are usually weighed one or two times during the construction period to ensure that the weight is within the calculated limits.

If a topside or module is too heavy or the centre of gravity is misplaced, it can lead to overload and strain in parts of the topside. In turn, this discovery would demand adjustments to the structure, affect the choice of equipment for marine operations, and cause project delays.

It is also important to verify the weight before installing the topside on a jacket offshore.

“The jacket has a limit to what it can carry. Knowing the exact weight of the topside and the components it is made of, makes it easier to modify the platform and install more equipment at a later stage, if that should become necessary,” Kindlihagen says.

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From the day of weighing Dogger Bank A (in the middle). Penguins FPSO to the left.

Weighing – step by step

Kjersti Strømsvold is Senior Estimator at Aibel and has a long track-record for weighing platforms.

“We follow an ISO standard that describes the requirements for different weighings. All equipment over one tonne is weighed before installation to remove any uncertainty and ensure that the estimate is accurate,” Strømsvold explains.

The verified weight of all the installed equipment and items forms a database that is used to estimate the total weight and centre of gravity.

The weight estimators take physical tours on the module or platform to confirm that everything reported as installed is actually there.

“In addition, we log anything that is temporarily on board, like pallets, trash cans, cables and lighting. This must be deducted from the total weight of the platform. Before the day of weighing, we issue a prediction report with our estimate of weight and centre of gravity,” Strømsvold says.

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Senior Estimator Kjersti Strømsvold.

Weight cells and displacement weighing

Two different methods are used for weighing large modules or entire platforms: weight cells, also known as load cells, and displacement weighing. For Johan Sverdrup P2 a combination was used. P2 was constructed with three modules, a flare tower and a bridge, each of which was weighed with weight cells from a specialist supplier.

The weight cells are placed into spaces in the grillage upon which the module is resting. To weigh the object, up to 50 – 60 weight cells simultaneously lift it from the grillage.

“This provides us with both the weight and centre of gravity. The process is done three times to get an accurate result,” Strømsvold explains.

When the Dogger Bank A topside was weighed before load-out from Aibel’s yard in Thailand in May 2022, it almost matched the estimated weight on the kilo. This is considered an impressive result and illustrates a successful cooperation between the engineering and fabrication disciplines.

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It is important to check that there is space between the platform and the grillage, to ensure that the entire platform is lifted up by the weight cells.

Weight estimator Kjersti Strømsvold confirms that there is space between the platform and the grillage and that the weight cell is doing the lifting.

A total of 36 weight cells were used to weigh the entire Dogger Bank A offshore wind platform.

Weighing according to Archimedes’ principle

The three modules for Johan Sverdrup P2 were assembled on a barge and displacement weighing was used to find the total weight of the topside. Using Archimedes’ principle, the weight is measured indirectly, by calculating the volume of water displaced by the barge before and after loading the topside.

Displacement weighing will also be used for Dolwin epsilon, which Aibel is currently constructing in collaboration with Keppel FELS. Dolwin epsilon is an HVDC platform for the DolWin 5 project, an offshore wind cluster on the German sector of the North Sea.

“This is a gravity-based semi-submersible platform, so for this one we will also perform an inclining test to find the total weight and vertical and horizontal centre of gravity. This is done by tilting the platform two degrees,” explains Marine Operation Manager Anne Kindlihagen.

Bets and glory

Finding the actual weight is an exciting process for everyone involved. It is the moment of truth for the weight estimators, and any surprises could lead to expensive delays. To add to the excitement, project members with access to the prediction reports usually have betting contests about the actual weight. So, what does the contestant with the closest bet get?

“Mostly honour and glory – and sometimes a small prize,” says estimator Kjersti Strømsvold.

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Weighing days are exciting for estimators Kjersti Strømsvold (left), Roger Ågnes Ødegård and Elena Kartseva.

This is the weight of Aibel’s projects

Here are some of Aibel’s projects over the years. The tonnes have been rounded.
For comparison – the The Eiffel Tower weighs 9 000 tonnes.






14 400

Visund Gas


1 000

Sleipner B


2 000



10 500

Dolwin Beta


22 000

Johan Sverdrup DP


22 000

Johan Sverdrup P2


24 000