Seawater Treatment Offshore

For offshore oil platforms and drilling rigs sea water is taken direct from the ocean. Seawater is the major source of water offshore. Depending on the location where the rig is operating, the seawater might contain large amounts of salt and/or calcium carbonate. Both substances harm pipes and technical devices. Therefore sea water treatment is an urgent topic in this environment.

Sea water is used direct without desalination for cooling processes or for the drilling itself. It is treated and clarified in several steps to get drinking water, potable water or feeding water for steam boilers or other sensitive equipment. Even though reverse osmosis or water softener are used, limescale, corrosion, fouling and biological growth are still causing problems in the systems.

The consequence? Frequent shutdowns and high maintenance costs – always linked to production loss.

The project – Offshore sea water treatment in China

CNOOC before the installation

One of our largest customers facing these problems is CNOOC (Chinese Offshore Oil Company). They are drilling for oil and gas and produce oil in the Chinese Sea. Lately they have expanded their activitiy to the Gulf of Mexico, the North of Indonesia and the North Sea. Today they operate more than 20 manned offshore platforms.

Despite their size, they were not spared of the problems caused by seawater described above. A seawater desalination of all the water they need, is no option offshore. There is just not enough space for even a small desalination plant offshore.
Our task was not the desalination, but to prevent further fouling and to remove the existing limescale, corrosion and biofilm.

We started with installing some Merus Rings at a few especially critical applications to show the possible results. Only after some weeks the maintenance crew confirmed the significant reduction of deposits in the system. We could measure the stabilized cooling and heating efficiency, which had been a constant decline before the installation of the Merus Rings.

If you are interested in how this works please have a look at our explanation of the function.

As a consequence the maintenance was done less frequent. And the cooperation was enhanced.

To treat the water in the entire system we installed several Merus Rings at the pipes. We started with one Merus Ring at the main suction header to reach every spot in the piping system. Furthermore Merus Rings were added ahead of critical machinery and process steps. This was necessary as we assumed the whole system to be affected by deposits.
Please see the block diagramms of a few of the offshore platforms below.

The results

Three months after the installation the technical devices (boilers, heat exchangers, machinery,…) was opened for visual inspection. Have a look on the pictures, rust and visible corrosion was gone or reduced significantly. The small amount of limescale still existing in some of the machinery is flushed out of the cooling loop by the water itself without further effort. A positive side effect, there was no brown water coming anymore at showers for the crew.

After these excellent results we equipped the other platforms of this customer.

The results were confirmed by a technical revision in the end of the following year. Pipes and machinery still were in a good condition or even had improved. No shutdowns due to water problems were reported since the installation of our Merus Rings.

Roughly calculation the ROI for the sea water treatment in this case shows that the investment had paid off in less than 6 months.

Costs & Benefits

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