Patent Application
20080105562
1. Field of the Invention
This invention relates to underwater impressed current cathodic protection system systems and methods. More particularly, it relates to placing components underwater which are now placed above the water surface.
2. Description of Related Art
Existing underwater impressed current cathodic protection systems (ICCPS) utilize an above water transformer rectifier to power the underwater anode(s). The transformer rectifier is typically powered with facility high-voltage alternating current (AC) which is converted to low voltage, high amperage direct current (DC) at the transformer rectifier. One leg of the transformer rectifier DC output is normally grounded to the structure being protected via the ICCPS and the other leg is connected to a power cable which is connected to the underwater anode(s).
Because low voltage/high amperage is transmitted through the power cable to the anode(s) the power cable diameter is large. Further, the facility structure must be capable of handling the power cable weight and accommodate the transformer rectifier weight and footprint. The facility structure must also bear the weight of an I-tube to protect the cable(s) through the splash zone of the facility.
The topside engineering costs of the existing systems and methods is high. The new methods and systems should eliminate a majority of these costs by placing the transformer or transformer rectifier underwater. They will also reduce the structural load to the platform by moving the transformer or transformer rectifier underwater. Additionally, the heavy low voltage/high amperage cable can be replaced by a lighter high voltage/low amperage cable which will also reduce the weight imposed on the facility. Because the cable is smaller, the associated I-tube is also smaller, and imposes less weight on the facility.
Placing the transformer or transformer rectifier underwater also eliminates the need for specific gravity sleds for the anodes. Instead, the anodes can be mounted directly onto the underwater transformer or transformer rectifier encasement which will function as the gravity sled for the anode.
Additionally, because the transformer or transformer rectifier is located underwater, the effective output of the transformer or transformer rectifier is greater, as current requirements are reduced because of the shorter distance from the transformer or transformer rectifier to the anode, and the structure ground or grounded structure. Cooling constraints are also reduced as the transformer or transformer rectifier uses water as a heat sink rather than air.
According to the invention, an ICCP system for use with a facility, such as an oil drilling or production platform, and having a portion, e.g., a platform, above water, comprises one or more waterproof transformers or transformer rectifiers adapted for placement on or near the floor of the body of water, one or more AC power cables for connecting these waterproof transformers/transformer rectifiers to a generator or other high voltage AC source above the surface of the water, a waterproof DC ground for underwater connection between the waterproof transformers or transformer rectifiers and the facility, and optionally, an I-tube for the cables.
Alternatively, an ICCP system for use with such facilities comprises one or more waterproof transformers or transformer rectifiers adapted for placement on or near the floor of a body of water, one or more high voltage/low amperage power cables for connecting these waterproof transformers/transformer rectifiers to a high voltage/low amperage DC current source. The high voltage/low amperage DC current source may be the output from a rectifier that converts AC power to high voltage/low amperage DC current.
The ICCP methods comprise connecting a source of high voltage power, above the surface of the sea, e.g., on the platform of a facility such as an oil drilling or production platform, to a waterproof transformer or transformer rectifier placed below the surface of the water, e.g., on or near the floor of the body of water, delivering high voltage power on one or more power cables from the power source to the waterproof transformer or transformer rectifier, converting the high voltage/low amperage power to low voltage/high amperage power in the transformer or transformer rectifier, and delivering the high amperage power to an underwater anode. Grounding of the underwater transformer or transformer rectifier is made underwater to the facility.
Waterproof transformers and transformer/rectifiers may be housed in oil filled containers. These containers are preferably sealed from the environment and substantially watertight because of the housing and oil within the housing.
The housing may be made of a waterproof material, e.g., fiberglass. The oil in the container acts as a coolant, and is equalized to hydrostatic pressure when the container is placed in deep water.
These systems and methods have several benefits:
The methods and systems of this invention are illustrated in the appended, exemplary drawing.
In the drawing, generator 1 is placed on the platform 10 of facility 9. Facility 9 is an oil drilling rig with a portion 11 located above the surface 8 of a body of water, e.g., sea 13, and a portion 12 located below water surface 8. Atop platform 10 is generator or other land-based high voltage AC source 1. Source 1 is connected, through high voltage AC lines 2, to underwater waterproof transformers or transformer rectifiers 6, which are connected to underwater anodes 5 through anode power cables 7. I-tube 2 protects AC lines 2 from environmental forces in the splash zone around facility 9. DC ground 4 is connected to facility 9 underwater.
