Splash zone protection of offshore structure requires special consideration. The common method of using a heavy duty coating and corrosion allowance raises questions regarding corrosion rate and duration of the coating. Furthermore, possible repair must be considered. Among our platforms operating in the North Sea there are eight with steel jackets, five steel floaters and two concrete structures. The corrosion protection is designed for the lifetime, which varies from 20 to 40 years. The "splash zone" that area immediately above and below the mean water level, has long been of major concern to design and corrosion engineers of offshore installations.
Tides cause the water level to rise and fall, alternately wetting and drying exposed metal surface, such as offshore oil and gas platform legs and risers.
The brackish water and exposure to oxygen is corrosive, the wave action is constantly eroding the metal members and debris and boats come in contact with the metal to cause damage. Most common areas affected are riser clamps, J-Tubes, bends, spools, (Vortex Included Vibration) VIV Suppression Strakes, and pipe field joint.
The metal which is constantly submerged can usually be protected by cathodic means, but that won't work in the "splash zone" because the water level is constantly changing. The areas well above coatings, but must be reapplied when necessary. But protecting the "splash zone"; with traditional above and below the "splash zone" solution have proven unsatisfactory. Monel jackets welded to the metal surface; special coatings and sprayed-on paint; and even making the metal components thicker, of course, are not effective in the "splash zone"
The criteria for successful "splash zone" protection consists of the following requirements :
Metal surface isolation - metal must be isolated and separated from the environment High electrical resistance-coating should inhibit electrolytic corrosion and resist electrical current flow. High impact resistance-protect against and resist buffeting from boats and floating debris Flexible-won't crack under the distortion of pipe bends or twists Bio-fouling resistant-isolate metal from sea life, fungus and scale attack Good thermal insulation-important in the case of flow lines Guaranteed for life-should last virtually the life of the installation.