GPA 8117-20的目的是提供一种简化的方法，根据流体的相对密度（60°F/60°F）和工艺温度来估算各种天然气液体（NGL）的平衡蒸汽压。本程序的预期应用是提供确定压力效应对体积修正系数的贡献所需的Pe（平衡蒸汽压）值，如美国石油学会石油测量标准手册（MPMS）第11.1-2004[1]章（取代第11.2.1-1984[2]章）和第11.2.2[3]章所述。据了解，其他状态方程目前正在用于特定的监护权转移应用，此类方法将继续被买方和卖方接受。本程序适用于四大类石油流体混合物: 商用丙烷、商用丁烷、天然汽油和轻端液体。后者由EP混合物和高乙烷含量液体组成。该程序涵盖了-50°F至140°F温度范围内0.350至0.675的相对密度范围。该程序是GPA技术出版物TP-15（1988）[9]/API MPMS附录第11.2.2-1994[4]章的延伸，包括相对密度范围为0.350至0.490的轻端流体。由于可能产生相同相对密度积的成分数量无限，因此预计会出现从计算蒸汽压到实际值的变化。选择了代表性成分和极端成分来发展相关性，但人们意识到，具有无限电位成分的额外流可能表现出不同的行为。 当相对密度在0.500左右时，这种变化的可能性尤其明显。例如，在相对密度为0.505的情况下，流体可以是丙烷或Y级混合物，每种混合物的成分和蒸汽压特性显著不同。与为监护权转移和结算目的而发布的相关性的情况一样，如果所有缔约方同意，可以通过为某些特定应用开发修改的相关性来获得额外的准确性。还包括一个用于提高100°F下广义相关性精度的方程式。重要的是要注意，将本文件中给出的相关性应用于未指定的条件或流体，将导致未经测试和未知的结果，这些结果可能包含重大错误。

The purpose of GPA 8117-20 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in the American Petroleum Institute Manual of Petroleum Measurement Standards (MPMS) Chapter 11.1-2004[1] (which superseded Chapter 11.2.1-1984[2]) and Chapter 11.2.2[3]. 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°F through 140°F. This procedure is an extension of GPA Technical Publication TP-15 (1988)[9]/API MPMS Addendum to Chapter 11.2.2-1994[4] 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°F 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.