Grounding offshore

In a normally pressured reservoir, the pressure is transmitted through a continuous column of water from the surface down to the reservoir. At the datum level at surface the pressure is one atmosphere. The datum level for an offshore location is the mean sea level (msl), and for a onshore location, the ground water level. 

Chemical analyses should be provided for all anodes used in the offshore and harbor area, together with results for current content in A h kg and current output in amperes [2,3]. The geometric shape and the number of anodes required is determined by these parameters. Expensive calculations for design based on grounding resistances are made only in exceptional cases because in practice there are too many uncertainties and the number and mass of the anodes have to be quoted with a corresponding safety factor. 

Offshore, the equipment and system ground conductors are connected to the facility s metal deck, usually by welding. The metal deck serves the function of the ground loop and is connected to ground by virtue of solid metal-to-metal contact with the platform jacket. 

Height is the vertical distance from ground or water surface to the center of area. The shape coefficient C, for a derrick is assumed as 1.25. and were obtained from ABS, Rules for Building and Classing Offshore Drilling Units, 1968. ... 

The intensity of microwaves at ground level in the center of the beam is likely to be comparable to that used by mobile phones. The microwaves cannot be too intense in order to avoid injury to wildlife, especially birds. Experiments with microwaves at reasonable levels have failed to show any negative effects even over multiple generations. Some designs locate rectennas offshore, but this presents other problems. 

Offshore neritic formations in the Paleozoic rock sequence probably include, on faunal and lithologic grounds, the Lower Ordovician Beekmantown dolomites, Middle Ordovician limestones, and Devonian Marcellus and Burket black shales (Table III). The first two are characterized by 0.1-0.4% organic carbons, very low organic nitrogen, and about 20 p.p.m. hydrocarbons but no carbohydrate residues. The Devonian offshore neritic black shales by contrast... 

Direct current is arranged to flow ont from the impressed anodes into the surrounding electrolyte, which is the sea water for offshore structures or the damp ground for onshore structures. The current returns through the structure itself and then back to the negative terminal of the impressed current source. The direction of current as described prevents the loss of metal from the structure into the electrolyte. This is opposite in direction to the natural current present due to corrosion action. 

The most frequent type of macrocell in reinforced-concrete structures exposed to the atmosphere is that established between more superficial rebars that have been depassivated by carbonation or chloride penetration, and internal passive rebars. Another example may be walls where chloride penetrates from one side and oxygen penetrates from the other side, which may occur in hoUow structures Hke tunnels and offshore platform legs or with ground retaining walls. 

Ground cracking was observed 400 to 800 ft inland. Two large mud boils were reported approximately 1/2 and 11/2 miles offshore. 

Seawater supply is from an intake 20 m below the water surface, about 1.5 km offshore and 2.2 km from the RO plant. The supply tunnel is about 70 m below the ground surface. The pre-treatment train includes chlorination, polyelectrolyte and ferrous sulphate coagulation/flocculation, acid dosage, dual-media filtration, anti-sealant addition, acid, cartridge filtration and sodium metabisulphite (e.g. see Figures 3.31 and 3.32]. The RO system is a two-pass unit. Post-treatment includes CO2 and lime treatment and chlorination with sodium hypochlorite. The desalinated product water TDS is 220 mg/1 with maximum boron concentration of 1 mg/1. 

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