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Definitions - Petroleum Measurement Standards - Marine Measurement

API Gravity (relative density) is a means used by the petroleum industry to express the density of petroleum liquids.  API gravity is measured by a hydrometric instrument having a scale graduated in degrees API.  The relation between API gravity and relative density (formerly called specific gravity) is :

API Gravity 60oF = (141.5 / Relative Density 60oF/60oF) - 131.5

Automatic Sampler is a device used to extract a representative sample from the liquid flowing in a delivery pipe.  The automatic sampler generally consists of a probe, a sample extractor, a flow meter, a controller and a sample receiver (container).

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Ballast is the water that is taken on when a vessel is empty or partly loaded to increase draft to properly submerge the propeller and maintain stability, trim and list.

Clingage is the cargo that adheres to all surfaces of the emptied portion of the tank other than bottom surfaces.

Crude Oil Washing ( Go to Tank Washing)

Cargo Quantity Option Certificate is a certificate signed by the vessel and shore representatives acknowledging the amount of cargo intended to be loaded.  Generally, most product cargoes have a tolerance based on either supplier, receiver or vessel capabilities.  Each party involved with the loading shall agree to the quantity to be loaded.

Draft is the depth of a vessel below the water line measured from the surface of the water to the bottom of vessel's keel.  The draft can be taken at six positions (forward, amidships, aft - port and starboard side).  Deviations from measured and calculated figures usually relate to deviations in the known constant and hog/stress.

Free Water (FW) is the volume of sea water (or other water contamination) that is in a container that is not in suspension in the contained liquid (oil).  See also definitions for sediment and water.

Gross Observed Volume (GOV)  (Go to Volumes)

Gross Standard Volume (GSV)  (Go to Volumes)

Gross Observed Weight (GSW)  is the total weight of all petroleum liquids and sediment and water (if any), excluding free water, as determined by applying the appropriate weight conversion factors to the gross standard volume.

Indicated Volume  (Go to Volumes)

Inerting is a procedure used to reduce the oxygen content of a vessel's cargo spaces to 8 percent or less by volume by introducing an inert gas such as nitrogen, carbon dioxide or a mixture of gases such as boiler / inert gas generator flue gas.

Innage gauge (dip sounding) is the measured distance from the surface of the liquid to a fixed datum plate or to the bottom of the tank.

Letter of Protest (Notice of Apparent Discrepancy) is a letter issued by any participant in a custody transfer citing any or all the conditions of dispute.  This letter serves as a written record that the particular action or finding was questioned at the time of occurrence.  The letter usually has a paragraph reserving the issuer's right to refer to matter at a later date.

Liquid volume is the measurable amount of material that is free flowing at the time of measurement.

List (Heel) is the leaning or inclination of a vessel, expressed in degrees port or starboard.  If found to be other than zero, list correction tables are to be used to correct the measured ullage or sounding to compensate for the measured list.  See next paragraph.

List (Heel) correction is the correction applied to the observed gauge or observed volume when a vessel is listing, provided that the liquid is in contact with all the bulkheads in the tank.  Correction for list may be made by reference to the vessel's list correction tables for each individual tank or by mathematical calculations.

Load on Top is defined as both a procedure and a practice.

     Procedure: Load on top is the shipboard procedure of collecting the settling water and oil mixtures, resulting from ballasting and tank cleaning operations (usually in a special slop tank or tanks), and subsequently loading cargo on top of the slops and pumping the resultant mixture ashore at the discharge port.

     Practice: Load on top is the act of commingling onboard quantity with cargo being loaded.  The onboard quantity is the remnant of the previous cargo or part load into the tank.

Multipoint gauging is the activity of measuring cargo in a vessel tank through two or more openings in the top of the tank.

Net Standard Volume (NSV)  (Go to Volumes)

Net Standard Weight (NSW) is the total weight of all petroleum liquids, excluding sediment and water and free water, determined by deducting the S&W weight from the Gross Standard Weight (GSW).

Non-liquid volume is the measurable amount of material that is not free flowing at the time of measurement.  Non-liquid material may include anyone or a combination of hydrocarbon waxes, water/oil emulsions, sediment, or solidified cargo.

On-board quantity (OBQ)  (Go to Volumes)

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