Special Topic on Offshore Drilling Rigs: Pressure Holding Systems

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In order, we will explain and elaborate on the systems listed in the previous article one by one. First, regarding the ballast system. Its function is to enable the platform to take on water relatively freely and maintain stability in deep waters. Simply put, it uses a pump to draw seawater from outside the ship’s hull into the tanks on the platform designed for storing seawater (ballast tanks), and it can also pump seawater out of these tanks and back into the sea. That’s roughly how this system works. The ballast system includes, 1, a sea chest, which is a dedicated area for pumping water out from outside the vessel (made of steel), located on the lowest level of the platform. 2. Ballast pumps – at least two, centrifugal pumps. 3. Piping and fittings. 4. Ballast tank: a compartment filled with seawater; in modern ship design, the ballast tanks are placed at the outermost part of the hull and are divided into separate small compartments. Even if something unexpected happens, even if one compartment is damaged and seawater floods in, it won’t cause water to enter all the compartments. I remember that on the Titanic, it seemed to be 6 compartments that took in water at the same time, yet the ship didn’t sink. The same principle applies. Here is its simplified schematic diagram: How to choose the displacement and head pressure of the ballast pump? First, we need to determine the total volume of our ballast tanks. Then, as required, we have to determine within how much time these ballast tanks can be filled with seawater. Obviously, displacement times time = volume; therefore, displacement = volume/time. Generally speaking, we live under atmospheric pressure, and we learn in middle school that one atmosphere can support a column of mercury 760 mm high. Converted to water, this is equivalent to a column of water about 10 meters high. The height of our ballast tanks determines the head pressure of our ballast pumps. If the head pressure is 5 bar, that means it can support a water column of 50 meters high; the pump can thus deliver water to a height of 50 meters. Note: 1 atmosphere is equal to 1 bar. In this way, we can easily determine the parameters of the pump. What about the pipelines? The size of the pipeline can be determined by the flow rate of seawater inside it. Pump displacement = Cross-sectional area of the pipe × Flow velocity. The flow rate of seawater in the pipes should not be too high, as seawater is corrosive; a high flow velocity can easily lead to corrosion of the pipes. To prevent corrosion of seawater pipes, glass fiber reinforced plastic pipes are widely used in ballast systems. The original text is from the Offshore Drilling Rigs blog