API MPMS 11.2.5:2007 (R2012)

Foreword The purpose of this procedure is to provide a simplified means of estimating equilibrium vapor pressures of various natural gas liquids (NGLs) from a knowledge of the fluid's relative density (60°F/60°F) and process temperature. The intended application of this procedure is to provide the values of Pe (equilibrium vapor pressure) required to determine the pressure effect contributions to volume correction factors as specified in the American Petroleum Institute Manual of Petroleum Measurement Standards (MPMS) Chapter 11.1-2004 (which superseded Chapter 11.2.1-1984) and Chapter 11.2.2. It is realized that other equations of state are currently in use for specific custody transfer applications and that such methods will continue to be used as acceptable for both buyer and seller. This procedure is applicable to four major classifications of petroleum fluid mixtures: commercial propanes, commercial butanes, natural gasolines, and light end fluids.The latter consists of EP mixes and high ethane content fluids. It covers the relative density range of 0.350 to 0.675 over a temperature range of -50 °C through 140 °C. This procedure is an extension of GPA Technical Publication TP-15 (1988)/API MPMS Addendum to Chapter 11.2.2-1994 to include light end fluids in the relative density range of 0.350 to 0.490. Variations from the computed vapor pressures to the actual values are to be expected because of the infinite number of possible compositions that can result in the same relative density product. Representative and extreme compositions were selected to develop the correlations, but it is realized that additional streams with compositions from among the infinite potential may well behave differently. This potential for variation is especially true at relative densities in the neighborhood of 0.500. For example, at a relative density of 0.505 the fluid could be propane or Y-grade mix, each having significantly different compositions and vapor pressure behaviors. As is always the case in correlations published for custody transfer and settlement purposes, additional accuracy may be obtained by developing a modified correlation for certain specific applications if agreed to by all contracting parties. An equation to improve the accuracy of the generalized correlation at 100 °C is also included. It is important to note that the application of the correlations presented in this document to conditions or fluids not specified, will result in untested and unknown results which could contain significant errors. Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent. This document was produced under API standardization procedures that ensure appropriate notification and participation in the developmental process and is iii designated as an API standard. Questions concerning the interpretation of the content of this publication or comments and questions concerning the procedures under which this publication was developed should be directed in writing to the Director of Standards, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the director. Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least every five years. A one-time extension of up to two years may be added to this review cycle. Status of the publication can be ascertained from the API Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is published annually and updated quarterly by API, 1220 L Street, N.W., Washington, D.C. 20005. Suggested revisions are invited and should be submitted to the Standards and Publications Department, API, 1220 L Street, NW, Washington, D.C. 20005, standards@api.org.