Closed gauging and measure Ullage of tank
“Closed gauging” is an old but new concept, oil tanker crews have more or less heard about making sealed goods a long time ago, but near the new wires applying mass in Southeast Asia and large tanks in Vietnam. Limit this article to the measurement of goods using oil gauges – a measure of the list of oil and water oil limits (also known as UTI or MMC rulers) rather than broadly discussing the process or closed cargo equipment.
Of course, making goods must measure goods, and making closed goods cannot measure open goods. Therefore, the measurement of goods requires an airtight oil gauge. The measurement by the oil gauge is slightly inverted compared to the usual Sounding ruler. Roughly, we will measure the void (Ullage) above the liquid surface to achieve the A result, then take the total height minus A as sounding level (Level).
The structural airtight oil gauge consists of a electrolytical combination ultrasonic measuring head, pt100, which can detect Air, Oil, water, and temperature simultaneously. The detection distance read on the tape through the glass hole reads the result on the ruler body. Fully enclosed ruler structure so that gasoline vapor or chemicals do not release into the atmosphere
Reading Index value aka Offset
Overall, measuring the Ullage gap is not too difficult. But the standards for bunker capacity are not yet fully the same among organizations that shoot the capacity of oil tankers. This confused the crew when summing up the results. Below I would like to introduce the basic principle, people can flexibly apply to their volume book to make accurate measurements.
Usually, any volume will have a leather height value (Hmax) or some ships can calculate Hmax themselves = Tank height + deck surface toning thickness + H1 + H2.
- Note: At the bottom of the measuring tube there is usually 1 millet, when calculating the Tank height, it is necessary to subtract the height of the spaced piece to match the point 0 (Zero) of the measuring tube.
Ullage Gap = Reading Index (e.g., With Marsen or Hermetic ruler, read value is 3500mm, Ullage Void = 3500 – 460 = 3040mm. This is the Ullage gap from the Hmax point)
Hmax – Ullage Space = Sounding (Level)
Problems with reading index (aka Offset)
- Different firms will have ruler designs with different Reading Index values
- The coupling head of the ruler is usually negative to the Deck valve, so the determination of the Reading Index should follow the manufacturer. Manual self-determination is confusing
Here are some rulers with the default Reading Index value as follows:
- Tank systems Hermetic GTEX and Marsen Korea UTL-200 UTI tape : Reading Index: 460mm
2. Shanghai Rongde UIT-200 Oil Gauge: Reading Index: 495mm
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