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Definitions - Petroleum Measurement Standards - Marine Measurement

Observed Reference Height is the distance actually measured from the tank bottom or datum plate to the established reference point.

Reference Height is the distance from the tank bottom to the established reference point or mark.

Reference Point is the point from which the reference height is determined and from which the ullages / innages are taken.

Remaining On Board (ROB)  (Go to Volumes)

Sediment and Water (S&W) is the non-hydrocarbon solid material and water in suspension in petroleum liquid.  Sediment and water is measured by the techniques described in MPMS Chapters 10.1 ~ 10.8 of Appendix A.

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Slops are oil, oil/water/sediment, and emulsions contained in the slop tanks or designated cargo tanks.  The mixture usually results from tank stripping, tank washing, or dirty ballast phase separation.

Stop Gauge is a pre-transfer determination of a specific volume of cargo represented by a specific tank level, which, when reached, results in cargo completion of the transfer.  This determination may be done by either shore or vessel personnel.

Tank Washing is divided into two types of activities:

     Water Washing involves the use of high-pressure water stream to dislodge clingage and sediment from the bulkheads, bottom and internal tank structures of a vessel.

     Crude Oil Washing (COW) involves the use of a high-pressure stream of the crude oil cargo to dislodge or dissolve the clingage and sediment from the bulkheads, bottom and internal tank structures of a vessel during the discharge operation.

It must be noted that regulatory agencies (including most ship / facility internal documented procedures require the tanks to be inerted during tank cleaning.

Total Calculated Volume (TCV)  (Go to Volumes)

Total Observed Volume (TOV)  (Go to Volumes)

Trim is the condition of a vessel with reference to its longitudinal position in the water.  It is the difference between the forward and aft drafts and expressed "by the head" if the forward draft is deeper than the aft draft or "by the stern".

Trim Correction  is the correction applied to the observed gauge or observed volume when a vessel is not on an even keel (equal forward and aft drafts), provided that the liquid is in contact with all bulkheads in the tank.  Correction for trim may be made by referencing trim tables for each individual tank or by mathematical calculation.

Ullage Gauge (Outage) is the measured distance from the cargo liquid surface to the reference point.

Vessel Experience Factor (VEF) is a compilation of the history of the total calculated volume (TCV) vessel measurements, adjusted for on-board quantity (OBQ) or remaining on board (ROB), compared with the TCV shore measurements.  Separate VEFs should be developed for loadings and discharges.  The information used to calculate VEF should preferably be based on documents that follow accepted industry standards and practices, such as inspection company reports.

It may be noted that for the purpose of calculating a load or discharge vessel ratio, the TCV on board the vessel includes all petroleum liquids, sediment and water, free water and slops found after loading (TCV sailing volume) or before discharge (TCV arrival volumes).  However, if in the completion of the Sequential Voyage Log, a TCV ratio (vessel - shore) appears to be in gross error, the ratio may be deleted with the agreement of both parties.  If all qualified voyages are based on load/discharge data from the same terminal, the applicability of those VEF data to the loads/discharges at other terminals should be evaluated.

Vessel Load Ration (VLR) is the total calculated volume (TCV) by the vessel measurement upon sailing, less on-board quantity (OBQ), divided by the TCV by shore measurement at loading -

     VLR = (TCV on sailing - OBQ) / TCV received from shore at loading

Vessel Discharge Ration (VDR) is the total calculated volume (TCV) by the vessel measurement on arrival, less remaining on-board (ROB), divided by the TCV by shore measurement at discharge -

     VDR = (TCV on arrival - ROB) / TCV received from shore at discharge

Volume Correction Factor (VCF) is the numerical value determined by laboratory analysis or by standardized computer arithmetic that when multiplied by the Gross Observed Volume at tank temperature results in the volume of the product at its standard temperature (15oC or 60oF).  The factors applicable for bands of API (relative density) and temperature are available in standard tables booklets or may be computed using a standardized format.  If the VCF is below 1 it is shown accurate to 5 places of decimal otherwise it is shown in 4 places of decimal.

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