Marine Vessels and Shore Facilities" for more detailed information regarding the procedure and methods of determining line fullness. The effect of pipeline fullness is one of the more difficult aspects to determine, after the fact. While terminals are required to verify the effectiveness of the pipeline fullness method used, in practice this is almost never done. The following are points to be considered when evaluating the impact of pipeline fullness to a loss or gain situation:
7.5 Determination of Line Fullness
The pipelines that connect marine vessels to shore tanks can hold significant amount of product. Considerable lengths are made to accurately measure the quantity of product in a shore tank before and after transfer. However, if the fill condition of these pipelines is not determined it is not possible to accurately account for the custody transfer quantity, by an amount equal to the volume of the pipeline. The fill conditions of shorelines before and after loading and discharge should be correctly determined and documented. Partially filled (slack) lines can result in a discrepancy in the Bill of Lading or Discharge outturn. The preference would be for lines to be either full or empty, and to be in the same condition before and after the movement, which should be verified. The fill condition of vessel lines should also be documented to verify that there is no unmeasured cargo on the vessel. The effect of any reported differences in line fill can usually be calculated.
• A loss or gain due to a slack pipeline cannot exceed the capacity of the pipeline.
• The high point bleed method will only be effective if there are bleed valves on every high point on the line. • The displacement method can only be used at the beginning of the cargo operation, necessitating a different method to determine fullness at the end of cargo operations. • Displacement and circulation methods do not guarantee that voids will not remain in a line, especially if the transfer rate was slow. • Line packing will not entirely eliminate entrained air in a line, although it will typically reduce it to a very small quantity. In the event of a discrepancy the shore pipeline configuration should be verified to ensure that pipelines were correctly aligned.
Issues that can contribute to differences on Floating Roof tanks are as follows: • When a measurement is made and the roof is thought to be floating, but is not, an incorrect quantity will be measured.
• In older tanks sediment build up can extend the critical zone.
• Movement of the roof or gauge tape due to wind.
• Change in tank roof orientation i.e. tilting or canting, sinking etc.
• A change in the weight of the floating roof, i.e. water, snow load, product on roof.
Refer to “API MPMS Ch. 17.6 Guidelines for Determining the Fullness of Pipelines Between
• Absence of a fixed reference height.
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