ISO 91 Petroleum measurement tables - Part 1: Tables based on reference temperatures of 15°C and 60°F
1 Scope
This part of ISO 91 refers to petroleum measurement tables based on reference temperatures of 15°C and 60°F.

The standard reference temperature for petroleum measurement adopted in ISO 5024 is 15 °C, and should be used for international trade. However, it is recognized that its use is not yet universally accepted and references to tables based on 60 °F have therefore been included in this part of ISO 91 and tables based on 20 °C are covered in ISO 91-2.

2 Normative references
The tables that form the basis of this part of ISO 91 contain printing errors which are identified in other documents listed below. These subsidiary documents constitute, through reference in the text, an integral part of this part of ISO 91.

API Standard 2540, Manual of petroleum measurement standards, Chapter 11.1 - Volume correction factors:
Volumes I to X, 1980;
Volumes XIII and XIV, 1982.
API Document, Editorial amplification of volume X - Background, development, and computer documentation, American Petroleum Institute, Washington DC, 1980.
API Document, Errata sheet to tables 23B and 53B, American Petroleum Institute, Washington DC, 1981.
API Document, The use of the petroleum measurement tables - API STD. 2540 (CH.11.1), ASTM D1250 and IP 200 (1980), American Petroleum Institute, Washington DC, 1984 (revised June 1987).
ASTM D1250, Petroleum measurement tables:
Volumes I to X, 1980;
Volume Xl/XII, 1982.
ASTM-IP-API, Petroleum measurement tables for light hydrocarbon liquids, density range 0.500 to 0.653 kg/litre at 15°C, published for the Institute of Petroleum by John Wiley and Sons, 1986.
IP Petroleum Measurement Paper No.2, Guidelines for users of the petroleum measurement tables (API STD. 2540; IP 200; ANSI(ASTM D1250), the Institute of Petroleum, London, 1984.

3 Sources of tables
3.1 For the purpose of custody transfer in accordance with this part of ISO 91, reference shall be made to the API-ASTM-IP Petroleum measurement tables, which were developed jointly by
a) the American Petroleum Institute (API) - USA,
b) the American Society for Testing and Materials (ASTM) - USA, and
c) the Institute of Petroleum (IP) - United Kingdom,
and have been adopted by these organizations under the following designations:
API STD. 2540-1980
ANSI/ASTM D1250-80
IP 200/80

See also 3.6.

3.2 The tables have been published by the American Petroleum Institute under the title Manual of petroleum measurement standards, chapter 11.1 - Volume correction factors, and by the American Society for Testing and Materials, which published two of the volumes, Volumes Xl/XII, as a combined document. The complete set of tables consists of 14 volumes, and the table numbers and titles are related to the volume numbers given in annex A to this part of ISO 91. Such publications are reprinted from time to time. If corrections are included in such reprints, the API has agreed to advise ISO of them, and an amendment will be issued to this part of ISO 91 referring to the corrections and to the date of the reprint. Users should then ensure that they have the most recent reprint.

No amendments or reprints have been published since the previous edition of this part of ISO 91, but corrections are listed in the following publications and the corrected values shall be used in connection with this part of ISO 91:
a) Editorial amplification of volume X - Background, development, and computer documentation;
b) Errata sheet to tables 23B and 53B;
c) The use of the petroleum measurement tables - API STD.2540 (CH.11.1), ASTM D1250 and IP 200 (1980);
d) Guidelines for users of the petroleum measurement tables (API STD.2540; IP 200; ANSl/ASTM D1250).

NOTE 1 Copies of items a), b) and c) are usually supplied with the appropriate volumes of the tables; they are also reproduced within item d), with other corrections.

3.3 Of the tables referred to in annex A, the three series of tables
5A, 5B, 5D, 6A, 6B, 6C, 6D
23A, 23B, 24A, 248, 24C
53A, 53B, 53D, 54A, 54B, 54C, 54D
are of primary use. They shall be used to convert from hydrometer readings of API gravity or relative density or density and volume measurements, first to obtain API gravity at 60°F, or relative density 60/60°F, or density at 15°C, respectively, and then to find the volume corrected to the corresponding reference temperature. The other tables, which are reproduced in volume XI/XII, permit accurate conversion of measurements from one system of units to another and conversions between apparent mass in air, mass and volume.

3.4 The tables referred to in annex A relate to the following ranges of density and relative density:
tables 5A and 6A: 100° to 0° API
tables 5B and 6B: 85° to 0° API
tables 5D and 6D: 10° to 45° API
tables 23A and 24A: 0.612 to 1.076 (60°F/60°F)
tables 23B and 24B: 0.654 to 1.075 (60°F/60°F)
tables 53A and 54A: 612 to 1074 kg/m3 at 15°C
tables 538 and 54B: 654 to 1075 kg/m3 at 15°C
tables 53D and 54D: 800 to 1164 kg/m3 at 15°C

3.5 For values below the ranges in 3.4 and down to 500 kg/m3 (0.500 kg/l) at 15 °C, reference shall be made to ASTM-IP-API Petroleum measurement tables for light hydrocarbon liquids, in which the tables are identical with the corresponding tables in the 1953 metric edition of API 2540, ASTM D1250 and IP 200 and referred to in ISO/R 91:1970. For values in terms of relative density in the equivalent range, reference shall be made to tables 33 and 34 of ASTM D1250.

The tables relating to values down to the equivalent of 500 kg/m3 are designated in annex A by reference to footnotes 3 and 4 to that annex.

3.6 Computer sub-routines in ANSI FORTRAN and the required program documentation are available for each of the tables in volumes I to IX. This documentation and information on the background and development of the tables have been published in volume X entitled "Background, development, and program documentation" (see notes 2 and 3).

Computer sub-routines in ANSI FORTRAN are included in volumes XIII and XIV for the tables in these volumes, but without implementation procedures.

The program documentation in volume X includes implementation procedures that are the primary standard. These procedures may be used to develop computer sub-routines in any computer language. Such a sub-routine that exactly follows one of the procedures (including the rounding and truncation operations specified) is a valid application of this part of ISO 91.

No implementation procedures are included in volumes XIII and XIV, but a procedure for table 54D has been included in IP Petroleum Measurement Paper No.2 as "Standard for volume correction of lubricating oils" and is a valid application of this part of ISO 91.

No implementation procedures or computer sub-routines have been published for the tables referred to in 3.5 that provide a completely valid application of this part of ISO 91 (see note 4).

NOTES
2 The computer sub-routines for tables 5, 23 and 53 contain an optional provision to bypass the hydrometer correction so that the values for API gravity, or relative density or density, may be introduced directly.

3 In the printed tables relating to the conversion of hydrometer readings, the coefficient of thermal cubic expansion for glass of 23 x 10(-6)°C(-1) has been used. This value is marginally below the conventional value quoted in ISO 1768, i.e. 25 x 10(-6)°C(-1). This difference in coefficient is not significant for most temperature differences found in practice. When using metric units, it may be corrected for, before entering tables 53A and 53B with readings made using hydrometers complying with ISO 649-1, by subtracting 2 x 10(-6)R'(0 - 15) from the hydrometer reading, where R' is the hydrometer reading and θ the observed temperature, if it is agreed between the interested parties that the temperature difference (θ - 15) is sufficient for the error to be significant.

4 In appendix A to the Petroleum measurement tables for light hydrocarbon liquids (see 3.5), calculation procedures have been provided for which sub-routines can be developed that will reproduce most of the tabulated values. The limitations of each procedure are indicated. Sub-routines developed from these procedures may be used by agreement between the parties concerned.