Alternately, the shore pipeline could be slack before and after the transfer which could affect the quantity either way.
5.3 API MPMS Chapter 17.6 The API standard that defines how pipeline verification can be achieved is MPMS Chapter 17.6 and this standard states that terminals may verify line fill condition in one of the following five ways:
5.1 Introduction 12
The pipelines that connect marine vessels to shore tanks can hold significant amounts of product. We go to considerable lengths to accurately measure the quantity of product in a shore tank before and after transfer. If we cannot confirm the fill condition of these pipelines at the time shore tank measurements are taken, we cannot accurately account for the custody transfer quantity, by an amount equal to the volume of the pipeline. If the shore pipeline is empty or slack before loading and full after, the marine vessel will receive less cargo than was determined by the shore tank measurement. If the shore pipeline is full before loading and empty or slack after, the marine vessel will receive more cargo than was determined by the shore tank measurement. If the shore pipeline is empty or slack before discharge and full after, the shore tank will receive less cargo than was delivered by the marine vessel. If the shore pipeline is full before discharge and empty or slack after, the shore tank will receive more cargo than was delivered by the marine vessel.
5.2 Where do voids come from?
1.Line Displacement 2.Internal Circulation 3.Line Press 4.Use of Hi-Point Bleed Valves 5.Pigging
Terminals usually consider their lines always remain full, based upon the premise that they do not do anything with their lines when they are not in use. However, a drop in temperature of the liquid in the pipeline will cause a reduction in the TOV (total observed volume) of that liquid and the line will no longer be full. Alternately, most ships and many barges use vacuum assisted stripping pumps. These systems can pump a considerable amount of air into the pipeline, especially if the vessel takes a long time to strip out its cargo. Shore pumping systems can also put air into a pipeline. A fast- loading rate may produce a vortex effect at the tank suction which will draw air into the line.
It is up to the terminal to determine the method; however, terminal staff are responsible to show that whatever method they choose is effective in verifying the fill condition of the pipeline. The chapter states: "Terminal personnel should designate a tank, a pipeline system (including meters, if used), and the method that will allow the most accurate determination of the quantity received or delivered.” However, there are still commercial considerations to be considered and certain clients may have specific preferences regarding the method used.
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