API TR 2579

This document provides guidelines for the calculation of uncertainty for field stored and transported hydrocarbon liquids. Special emphasis is placed on the measurement uncertainty of crude oils measured at tanks, by lease automatic custody transfer (LACT), and alternative measurement systems.

This document provides a methodology for calculating the uncertainty in the measurement of liquid hydrocarbons by flow measurement systems. Specifically, uncertainty performance expressions are developed for positive displacement and Coriolis meter types under API Manual of Petroleum Measurement Standards (MPMS) Chapter 5 for measuring hydrocarbons by volume. This includes ancillary devices, processes, and measurements used to calculate a net standard volume (NSV) such as pressure, temperature, density, and sediment and water (S&W).

This document was written to determine if the performance of a given measurement device is in compliance with an acceptable level of uncertainty, either pre-installation or after the installation is in service. If this is not the case, the measurement device, its installation, or maintenance practices, etc. can be upgraded to meet the desired uncertainty performance criterion.

Techniques are described to assess the uncertainty contribution of individual components of measurement systems and the overall measurement facility's measurement uncertainty. By following the guidance and calculation procedures of this document, cost-effective measurements of appropriate quality can be achieved. In most cases, the rigorous requirements of industry standards intended for allocation and custody transfer quality measurements can be reduced and still achieve the desired measurement uncertainty required.

For this document, a measurement system is comprised of meters, provers, and the associated devices to calculate a NSV.