ISO 91 Petroleum measurement tables - Part 2: Tables based on a reference temperature of 20°C
1 Scope
This part of ISO 91 refers to Computer implementation procedures for the correction of densities and volumes to the reference temperature of 20°C (see note 1). The implementation procedures referred to do not cover the full range of tables referred to in patt 1 of this International Standard, but provide for those tables designated in part 1 as being for primary use. In addition, reference is made to implementation procedures for use with lubricating oils that are not included in ISO 91-1:1982 (see note 2).
This part of ISO 91 provides for the reference temperature of 20°C, using the Same expansion data as used for the tables referred to in ISO 91-1.
NOTES
1 Although the Standard reference temperature for petroleum measurement adopted in ISO 5024 is 15°C and should be used in international trade, it is recognized that its use is not yet universally accepted and that the reference temperature of 20°C is still widely used.
2 Tables relating to lubricating oils and the reference temperatures of 15°C and 60°F are proposed for adoption in a revision of ISO 91-1 in course of preparation.
2 Normative reference
The following Standard contains provisions which, through reference in this text, constitute provisions of this part of ISO 91. At the time of publication, the edition indicated was valid. All Standards are subject to revision, and Parties to agreements based on this part of ISO 91 are encouraged to investigate the possibility of applying the most recent edition of the Standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 91-1:1982, Petroleum measurement tables - Part 1: Tables based on reference temperatures of 15°C and 60 degrees F.
3 Source of computer implementation procedures
3.1 The Computer implementation procedures have been published by the Institute of Petroleum as Petroleum measurement Paper No.3: Computer implernentation procedures for correc fing densities and volumes to 20°C, October 1988. The six implementation procedures are designated by table numbers for continuity with the tables referred to in part 1 of this International Standard and are as follows:
Table 59A - Implementation procedure for sub-routine TAB59A - Generalized crude oils - Correction of observed density to density at 20°C
Table 60A - lmplementation procedure for sub-routine TAB60A - Generalized crude oils - Correction of volume to 20°C against density at 20°C
Table 59B - Implementation procedure for sub-routine TAB59B - Generalized products - Correction of observed density to density at 20°C
Table 60B - Implementation procedure for sub-routine TAB60B - Generalized products - Correction of volume to 20°C against density at 20°C
Table 59D - Implementation procedure for sub-routine TAB59D - Generalized lubricating oils - Correction of observed density to density at 20°C
Table 60D - lmplementation procedure for sub-routine TAB60D - Generalized lubricating oils - Correction of volume to 20°C against density at 20°C
Such publications are reprinted from time to time. If corrections are included in such reprints, the IP 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.
A list of errata was published by the IP in January 1989 and supplied with all copies of Petroleum measurement paper No.3. Users of this part of ISO 91 shall ensure that the corrections in the errata slip are used.
3.2 Of the tables referred to above, the series of tables 59A, 59B and 59D shall be used to convert from observed hydrometer readings, or observed densities, at an observed temperature, to density at a temperature of 20°C. If the input variable is observed density rather than an observed hydrometer reading, Steps 3 and 4 shall be omitted. The series of tables 60A, 60B and 60D shall be used to calculate the volume correction factor for the correction of a volume at an observed temperature entering with the density at 20°C. The procedures in these tables make use of the procedures for tables 53A and 53B, as referred to in ISO 91-1, to which reference shall also be made.
NOTE 3 In the implementation procedures 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 differente in coefficient is not significant for most temperature differentes found in practice. It may be corrected for by subtracting 0.000002R'(θ - 20) from the hydrometer reading, before entering tables 59A, 59B and 59D with readings made using hydrometers complying with ISO 649-1 , where R' is the hydrometer reading and θ the observed temperature, if it is agreed between the interested parties that the temperature differente (θ - 20) is sufficient for the error to be otherwise significant.
