Case Study - Elf-Petroland Offshore Platforms


A subsidiary of Elf-Aquitaine, Elf-Petroland operates 17 platforms in the Dutch offshore waters of the North Sea. The un-manned platforms collect, pre-treat and compress natural gas for transport to onshore facilities. The platforms had been previously treated with sodium hypochlorite and the anti-fouling product, Toxion. These treatments resulted in recurring problems of mussel build-up on the steel grid used to block water flow, corrosion on the fire protection pumps and up to one-centimeter accumulation of an extremely dense hard scale on piping surfaces. The reduction in the pipe diameter threatened the entire fire protection system with no way to replace the piping. Mexel was employed to reduce the build-up and preventing future corrosion and deposition.


The platforms employ permanently submerged risers 30-40” in diameter that allow for entrance of seawater. Each riser has a steel grid at the bottom and contains one, 50 gpm submerged pump (alongside with an installed spare pump) that supplies the heat exchangers. A similar 1750 gpm system serves the fire protection system. All pumps are 316L stainless steel. Mexel treatment began in 1995 with daily dosage of 10 ppm for two hours into the riser. The fire protection system was treated at a rate of 10 ppm for 15 minutes once every two weeks when the system was inspected and run for two hours.


The bottom grid was inspected and no mussel accumulations were discovered. In addition, there was no longer any corrosion in the fire protection pumps. The Mexel treatment was beginning to disperse the hard scale, which resulted in full use of the piping being restored. By the end of 1996, Elf Petroland decided to standardize on Mexel 432. During the next two years, all remaining platforms were retrofitted.