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Definitions

A glossary of terms used in these procedures is provided in this pages. It incorporates terms for volumes which have been approved by ISO for use in connection with crude oil, but excludes those that do not apply to refined products.

Bill of Lading- A document issued by the cargo supplier which states the quantity of material delivered to the vessel.

Clingage- Oil residues which adhere to the surface of tank walls and structures on completion or discharge.

Note: This quantity, in practice, can only be estimated.

Critical zone- The volume close to the bottom or a floating roof tank in which there are complex interactions and buoyancy effects as the floating roof comes to rest on its legs. The zone is usually clearly marked on tank calibration tables and measurements for custody transfer should not be made within it.

Density- The ratio of the mass of a substance to its volume. Since density is dependent on temperature and pressure these should be stated.

In-transit loss- The difference between the Total Calculated Volume on board a vessel after loading and the Total Calculated Volume on board before discharge.

Note: In cases where measured quantity is greater before discharge than after loading, then the terms In- Transit Gain or In-Transit Difference can be used.

Load on top (LOT)- The procedure of commingling the recovered oil slops with the next cargo by loading the cargo on top of the slops.

Meter factor- The ratio of the actual volume of liquid passed through a meter to the volume indicated by the meter.

Meter K-factor- The number of pulses emitted by a meter whilst unit volume is delivered (usually expressed in pulses/m3).

On board quantity (OBQ)- All the oil, water, sludge and sediment in the cargo tanks and associated lines and pumps on a ship before loading a cargo commences. (This term may not apply to product movements.)

Outturn- The quantity of material discharged from a vessel, measured by a shore terminal.

Outturn Certificate- A statement issued by a receiving terminal and/or cargo surveyor certifying the outturn.

Outturn Loss- The difference in Net Standard Volume of oil between the quantity shown on the Bill of Lading and the quantity shown on the Outturn Certificate. The adjusted loss is the Outturn Loss corrected for the difference between the OBQ and the ROB. where applicable.

Quantity remaining on board (ROB)- AII the oil. water. sludge and sediment in the cargo tanks and associated lines and pumps on a ship after discharging a cargo has been completed. excluding vapour but including clingage. (This term may not apply to product movements.)

Sediment- Suspended Sediment: Non-hydrocarbon solids present within the oil but not in solution.

Bottom Sediment: Non-hydrocarbon solids present in a tank as a separate layer at the bottom.

Total Sediment: The sum of the suspended and bottom sediment.

Slops- Material collected after such operations as stripping. tank washing or dirty ballast separation. It may include oil, water, sediment and emulsions, and is usually contained in a tank or tanks permanently assigned to hold such material.

Vessel experience factor-loading (VEFL)- The mean value of the qualifying VLRs obtained after several voyages.

Vessel experience factor-discharge (VEFD) -The mean value of the qualifying VDRs obtained after several voyages.

Vessel load ratio (VLR)- The ratio of the quantity (TCV) or oil measured on board a vessel immediately after loading less the On Board Quantity (OBQ) to the quantity (TCV) measured by the loading terminal, i.e.

                VLR= Vessel's TCV after loading-OBQ

                                   Shore TCV loaded

 

Vessel discharge ratio (VDR)- The ratio or the quantity (TCV) or oil measured on board a vessel immediately before discharge less the Quantity Remaining on Board (ROB) to the quantity (TCV) measured by the receiving terminal, i.e.

VDR= Vessel's TCV before discharge-ROB

              Shore TCV received

 

Volumes correction factor- A factor dependent upon oil density and temperature which corrects volumes to the standard reference temperature. Such factors shall be obtained from the latest API-ASTM-IP Petroleum Measurement Tables.

Volumes for dynamic measurement calculations-

Indicated Volume: The change in meter reading that occurs  during transfer through a meter.

Gross Volume: The indicated volume multiplied by the appropriate meter factor nor the liquid and flow rate concerned, without correction for temperature and pressure.

Note: This includes all water and sediment transferred through the meter.

Gross Standard Volume: The gross volume corrected to the standard conditions. e.g. 15°C and 1.01325 bar.

Note: For refined products, dissolved water, suspended water and sediment are not usually deductible, as limits are commonly prescribed in the quality specification. For this reason the term NET is not used for products.

Volumes for static measurement calculations-

Total Observed Volume (TOV): The volume or oil including total water and total sediment, measured at the oil temperature and pressure prevailing. This may be either the volume in a tank or the difference between the volumes before .and after a transfer.

Gross Observed Volume (GOV): The volume or oil including dissolved water, suspended water and suspended sediment but excluding free water and bottom sediment, measured at the oil temperature and pressure prevailing. This may be either the volume in a tank or the difference between the volumes before and after a transfer.

Gross Standard Volume (GSV): The volume or oil including dissolved water, suspended water and suspended sediment but excluding free water and bottom sediment, calculated at standard conditions, e.g. 15 C .and 1.01325 bar. This may be either the volume in a tank or the difference between the volumes before and after a transfer.

Total Calculated Volume (TCV): The gross standard volume plus the free water measured at the temperature and pressure prevailing.

Note: For refined products, dissolved water, suspended water and sediment arc not usually deductible, as limits arc commonly prescribed in the quality specification. For this reason the term NET is not used for products.

Dissolved Water: The water contained within the oil forming a solution at the prevailing temperature.

Suspended Water: The water within the oil which is . finely dispersed as small droplets.

Note: It may, over a period or time, either collect as free water or become dissolved water depending on the conditions or temperature and pressure prevailing.

Free Water: The water that exists in a separate layer.

Note: It typically lies beneath the oil.

Total Water: The sum of all the dissolved, suspended and free water in a cargo or parcel of oil.

Water cut or dip:  The measured depth of free water.

Wedge formula: An equation relating the volume of liquid material in a ship's tank to the dip, ship's trim, dipping point location and the tank's dimensions when the ship's calibration tables cannot be applied. To derive the equation, assumptions have to be made. The major assumption in the derivation is that the material is free flowing and will  accumulate in the aft end of a tank when the ship is trimmed by the stern.

Weigh conversion factor- A factor dependent on the density for converting volume to weight-in-air. Such factors shall be obtained from the API-ASTM-IP Petroleum Measurement Tables.

Gross Weight-in-Air: The weight of oil including dissolved water, suspended water and suspended sediment but excluding free water and bottom sediment.

Net Weight-in-Air: The weight of oil excluding total water and total sediment.

Weight-in-Air: The weight or oil excluding free water.

Note: Under circumstances where gross or net terms are used, it may be necessary to use gross weight-in- .air and net weight-in-air.