Ullage Tape-and-Bob Procedure

Definition - What does Ullage Tape-and-Bob Procedure mean?

Ullage Tape-and-Bob Procedure is an established way of measuring petroleum in tanks. This procedure is carried out by measuring the leftover space between the reference point on the ullage hatch and the top level of the liquid inside the storage tank. Once this is recorded, the liquid level inside the tank is found by subtracting the outage measurement from the gauging height of the tank.

Petropedia explains Ullage Tape-and-Bob Procedure

Ullage tape-and-bob procedure is also known as outage tape and bob procedure. The ullage measurement using the ullage tape and bob procedure is as follows:

  • The approximate ullage value is obtained with the help of vessel ATG.
  • At the top of the tank, the ullage hatch is opened and once the tape is grounded safely, the ullage tape and bob is lowered inside the tank until they touch the liquid.
  • Once the bob stops swinging and becomes still, the tape is lowered until a small portion is in the liquid and an inch, centimeter, or hundredth of a foot graduation on the tape is at the reference gauge point.
  • The tape reading is then measured at the reference point.
  • The tape is withdrawn from the tank and the ullage bob scale is read at the liquid cut and the reading is recorded. During the withdrawal procedure the measurement operator needs to make sure that the tape and bob are not allowed to again enter the liquid, else it will give false reading.
  • The sum of the tape readings at the reference gauge point and the ullage bob reading at the cut is the ullage gauge.
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