Washing (COW) recovering Clingage from previous cargo, etc.
Calibration Error relates to the accuracy (calibration) of the measurement equipment. Only the base international standards are deemed to be exact. The possibility of introducing a fixed error or bias increases with every step in the calibration chain, moving from the base standard to the field device. Random error or uncertainty increases with each step. Furthermore, all measuring equipment is affected by use and handling, so regular field checks and verifications are necessary to ensure that equipment continues to provide accurate measurements Paper Loss / Gain is a term frequently used to include all Apparent Losses / Gains. It is the result of calculation errors which may occur when converting basic measurement data into cargo quantities. Computer programmes and calculators have reduced the risk of mathematical errors, but the cargo calculations should always be checked when a large discrepancy occurs.
Evaporative loss may occur during load / discharge operations and during transit. Daily temperature variations and movement of the cargo during voyage (sloshing) will increase evaporative losses. Cargoes with higher vapour pressure are likely to suffer greater evaporative losses. ROB (quantity remaining on board) is the liquid and non-liquid cargo left on board the vessel after discharge. ROB measurement can only include the cargo which is on the tank floor and can be measured from available gauge points. Cargo which remains as Clingage on the tank sides or other internal structure is not included in the ROB measurement and will result in a real loss when the outturn is considered. The amount of Clingage will be dependent upon cargo viscosity, pour point and temperature. Line fill losses result from transfer lines which contain more cargo after the movement than before, leading to reduced quantities being measured in the receiving tanks. This can occur during loading or discharge. Cargo diversion can occur inadvertently because of incorrectly set or leaking valves, or intentionally as theft. While physical gains are not common, some cargoes with the ability to absorb water or to blend with other components or additives may show physical gains. In addition, gains may be caused by physical operations and equipment errors or failures such as cargo diversion, Crude Oil
7.2 Meters Custody transfer measurement can be carried out using meters, which may be incorrectly installed, maintained, operated or have errors due to wear and tear of components.
Points for consideration include the following:
• Meter proving frequency (this should be in accordance with the manufacturer's recommendations, company or national legislation)
• Maintenance records.
• Control charts.
• Meter factor or K factor on the custody transfer document compared to the most recent prover report.
• Prover calibration records.
• Possible application of incorrect (out-of-limit or out-of-date) meter factors. The terminal should be able to provide meter factor control charts and the last prover calibration report with traceability to national/international standards. Custody transfer meters should be properly proven, certified, and operated to a recognized industry
7.1.2 Physical Loss/Gain
This is an actual loss or gain of cargo (sometimes referred to as "Real Loss or Gain").
Physical losses can be the result of evaporation, unmeasured ROB, line fill, cargo diversion, spillage or theft.
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