API MPMS 18.1:1997(R2007) pdf download.Manual of Petroleum Measurement Standards Chapter 18—Custody Transfer
1 Scope and Field of Application
These procedures are organized into a recommended sequence of steps for manually determining the quantity and quality of crude oil being transferred under Þeld conditions. These measurements and tests are performed by crude oil truck drivers (COTDs) and other parties who are responsible for the custody transfer and for recording the results of the measurements and tests on run tickets. Since the ownership of the crude oil being gathered may change and the custody is always passed from the storage tank to the transporting truck as the crude oil passes the tankÕs last Þxed outlet ßange, accurate custody transfer is extremely important to both the shipper and the carrier. Therefore, all measurements shall be taken carefully and completed to the full satisfaction of all parties or their authorized representatives.
4 The Custody Transfer Concept Used
The Manual of Petroleum Measurement Standards covers individual procedures for sampling, temperature taking, gauging, and quality testing. This publication integrates these procedures into a sequence that can be applied during custody transfer of crude oil from small tanks to a tank truck (see Section 6). With the column-of-oil concept used as the basis for the sequence, the sequence requires the COTD to start sampling and temperature taking from the top of the crude oil volume and to work systematically down through the crude oil layer until the free water and sediment level has been located; ini- tial merchantability is then assessed. This practice offers the best known method for manually obtaining the most repre- sentative quality samples of the crude oil being gathered. After these quality samples have been obtained for testing, the quantity measurements may be taken without concern for possible contamination of the quality samples.
5 General Responsibilities and Cautions for the COTD
5.1 CONTROL OF MEASUREMENT ERRORS
Losses or gains may occur if preventive measures are not taken against spills, tank overruns, inaccurate measurements, or recording of incorrect measurements on run tickets. Proper truck and tank prepumping checks and alert monitoring dur- ing pumping are two measures that help to prevent losses or gains. Operating the measurement and testing equipment skillfully and keeping it clean and in top operating condition are two more preventive measures that help the COTD avoid losses or gains. A vital link in controlling crude oil losses or gains, the COTD is also responsible for detecting and report- ing defective or inadequate control conditions such as internal encrustation of the tank, dents, settling, or leaks.