API MPMS 6.2:2004 pdf download.Manual of Petroleum Measurement Standards Chapter 6—Metering Assemblies
1 Introduction
This standard serves as a guide in the selection, installation and operation of loading rack metering systems for petroleum products, including liquefied petroleum gas. This standard does not endorse or advocate the preferential use of any spe- cific type of metering system or meter. In general, metering system installations must meet certain fundamental requirements, including those that ensure proper meter type, size, installation and adequate protective and read- out devices (such as presets, registers [counters], strainers, relief valves, pressure and flow control valves, and air elimi- nators, where required). Descriptions of these and other sys- tem components are covered elsewhere in this standard or other API standards. Also, to ensure compliance with state laws and regulations the latest editions of NIST Handbook 44, Handbook 12, as well as specific local weights and measures requirements, should be considered.
4 Loading Rack Metering Systems
The loading rack metering systems described in this stan- dard are those that apply to transport-type truck facilities. The rack may be of a single-product/single-meter, single- product/multi-meter, or multi-product/multi-meter design. The design of the rack should allow one meter to be proved without interfering with the other meters involved in the loading operations.
4.1 LOADING RACK METERING SYSTEM INSTALLATION
Loading rack metering systems are designed to deliver accurate quantities of products into transport trucks for the subsequent delivery to remote locations. The metering config- urations may consist of single tally meters, single product meters, blend meters and additive meters. Since rack delivery meter volumes are considered in the terminal loss/gain deter- mination, the design, installation and operation of the meters is extremely important. It must be noted that the loading rack is usually the final opportunity to measure accurately, i.e., after the product leaves the loading rack, measurement errors are difficult to correct. Each meter must be proved under conditions as close to normal as possible. This would encompass the usual delivery flow rate into a tank prover. Another acceptable consideration is to prove via a pipe prover, with the prover return line deliv- ering to the transport truck. Some designs now include termi- nal return lines where, following the proving, the fluid is delivered back to the originating tank. When return lines are utilized, ensure that tank head pressure or pump inadequacy doesn’t cause an unacceptable decrease in flow rate. Caution should also be exercised to ensure adequate tank pump deliv- ery flow rate so that multiple product activity doesn’t cause a drop in flow delivery.