Tank Sounding - Offshore Jack Up Rig

Sounding of Tanks
The process of quantifying the quantity of liquid present inside a tank is called “sounding”. We all are aware of storing water in head/gravity tank in our house. Frequently we ensure the level of water is maintained by checking the level in the tank. We fill up the water to the required level and stop filling. We can also say that we “sound” the tank level. In the same way, a ship’s fuel oil (bunker) tank or cargo oil tank has to be checked for its increase/decrease of its level during the operation of the rig/operations carried out on the rig.

So what is a “sounding pipe?”
A rig's preload tank must have a pipe extending from bottom of the tank to a level which is safe to “sound” the contents of the tank. A sounding pipe is a simple steel pipe, which is open at the bottom so that the liquid in the tank gets filled up to the same level as in the tank. As the level in the tank rises, the liquid level in the sounding pipe also increases, thus upon taking sounding, the quantity of liquid can be known.

Why to “sound” the tanks?
During watertight integrity test, the rig is at half of her floating draft to ensure no water ingress into preload tank. A modern rig built with at least 25 preload tank and each of them having dump valve which is expose to the sea directly. Although each dump valve installed with non-return valve/check valve, there is potential for sea water to leak through the valve. Thus, the roustabout will take sounding to ensure no water ingress into preload tank during watertight integrity test.

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