API MPMS 17.2A:1995 pdf download.Manual of Petroleum Measurement Standards Chapter 17—Marine Measurement
Government and regulatory agencies worldwide have imposed safety and environmental regulations that prohibit tank vessel operations from releasing hydrocarbons into the atmo- sphere. This has resulted in the restriction and, in some cases, the prohibition of traditional methods of obtaining cargo measurements. Consequently, numerous measurement methods and technologies are now being used and developed that allow the necessary cargo measurements and samples to be taken while the vesselÕs cargo tanks remain closed to the atmosphere. Tank vessels are using closed and restricted measurement devices when operational, safety, and environmental consid- erations mandate all systems be closed to vapor releases to the atmosphere. These devices are used during various vessel operations including, but not limited to, tank-to-tank transfers, loading, discharging, crude oil washing, and ballasting. Closed and restricted devices are designed to provide liquid levels temperature measurement. Samples may be taken under closed or restricted conditions using specially designed equipment through vapor control valves (VCVs).
This standard covers the use of manual portable measure- ment units (PMUs) through deck-fitted VCVs and fixed auto- matic tank gauge (ATG) systems when a marine vesselÕs cargo tanks may not be opened to the atmosphere. It establishes the procedures for obtaining the level measurements of cargo, free water, and onboard quantity/remaining onboard (OBQ/ROB) as well as taking the temperatures and samples required for the marine custody transfer of bulk liquid petroleum cargoes under closed or restricted system measurement conditions. It does not address in detail the technologies of the equipment used. This standard is not intended for use with pressurized or refrigerated cargoes such as LPG and LNG.
For the purpose of this standard, the following definitions apply: An automatic tank gauge (ATG) is an instrument that automatically measures and displays liquid levels or ullages in one or more tanks continuously, periodically, or on demand. It also refers to the liquid level in a tank as measured using an ATG system. An automatic tank thermometer system (ATT) is a system that automatically measures and displays temperatures of liquids in one or more vessel tanks continuously, periodi- cally, or on demand. An automatic vessel tank gauge system is a system that automatically measures and displays liquid levels or ullage in one or more vessel tanks continuously, periodically, or on demand (see API MPMS Chapters 1 and 17.2). A closed system exists when a marine tank vessel does not permit the direct exposure and/or release of the tank contents into the atmosphere under normal operating conditions. (See definition of restricted system.) Closed system measurement (CSM) is the measurement of petroleum cargoes on a closed system marine tank vessel performed using closed measurement devices. (See defini- tion of restricted system measurement.)