GB/T 1995-1998 Petroleum products — Calculation of viscosity index

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1. Method number / full title / English name / replacement relationship

• Standard number: GB/T 1995—1998
• Chinese title: Petroleum products — Calculation of viscosity index
• English title: Petroleum products—Calculation of viscosity index
• Replacement relationship: replaces GB/T 1995—88
• Adoption relationship: equivalent adoption of ASTM D2270—93 "Calculation of viscosity index from kinematic viscosity using 40°C and 100°C"
• Method number: Method A (Chapter 5), Method B (Chapter 6)
• Publication/implementation: published on 1998-08-20, implemented on 1999-01-01
• Issuing body: State Bureau of Quality and Technical Supervision

2. Scope of application and non-applicability

• 1.1 This standard specifies the method for calculating the viscosity index of lubricating oils and related substances from the kinematic viscosities at 40°C and 100°C.
• 1.1.1 Method A—— is applicable to petroleum products with a viscosity index less than 100 and equal to 100.
• 1.1.2 Method B—— is applicable to petroleum products with a viscosity index greater than 100 and equal to 100.
• 1.2 Table 1 of this standard is applicable to petroleum products with a kinematic viscosity at 100°C in the range 2~70 mm²/s. For petroleum products with a kinematic viscosity at 100°C greater than 70 mm²/s, the viscosity index may be calculated according to the formula.
• 1.3 The kinematic viscosity of 20°C distilled water at 1.0038 mm²/s is used as the reference value for determining kinematic viscosity. The determination of the kinematic viscosity of petroleum products shall be carried out in accordance with GB/T 265.
• 5.1.1 / 6.1.1: If the kinematic viscosity of the sample at 100°C is less than 2 mm²/s, its viscosity index may be left unspecified or not reported.
• Appendix A (informative appendix): Calculation of viscosity index using kinematic viscosity at non-standard temperatures is for appropriate information only and cannot be used as a result report for specification requirements.
• Non-applicability: no explicit "non-applicability" clause is provided in the available source.

3. Method principle

• 3.1 Viscosity index: a conventional value representing the characteristic of the change in kinematic viscosity of petroleum products with temperature. Note: For oils with similar kinematic viscosity, the higher the viscosity index, the smaller the effect of temperature on kinematic viscosity.
• 4.1 The viscosity index is a widely used and generally accepted measure of the change in kinematic viscosity of petroleum products caused by a change in temperature between 40°C and 100°C.
• 4.2 A higher viscosity index of a lubricating oil indicates that the decrease in kinematic viscosity of the oil with increasing temperature is smaller.
• 4.3 In practice, the viscosity index is a numerical value indicating the relationship between kinematic viscosity and temperature.
• Calculation principle: From the kinematic viscosities at 40°C and 100°C, obtain the values of L and H by means of Table 1 or formulas, and then calculate the viscosity index according to Method A (Equation 3) or Method B (Equation 5, Equation 6).

4. Reagents and materials (purity / preparation)

not provided in the available source.

5. Instruments and equipment

not provided in the available source (the standard is a calculation method; the determination of kinematic viscosity is carried out in accordance with GB/T 265).

6. Recommended operating conditions

• Temperature conditions: 40°C and 100°C (standard temperatures).
• Appendix A: When the conditions cannot meet the standard temperatures 40°C and 100°C, the kinematic viscosities at 40°C and 100°C may be estimated from kinematic viscosities at other temperatures by means of appropriate equations in GB/T 8023; the two non-standard temperatures used for determining kinematic viscosity should be as close as possible to the standard temperatures, and the difference between them should be as large as possible.
• Other operating conditions: not provided in the available source.

7. Sampling and sample preparation

not provided in the available source.

8. Analytical procedure

Method A (Chapter 5, applicable to VI ≤ 100)

• 5.1.1 If the kinematic viscosity of the sample at 100°C is less than or equal to 70 mm²/s, select appropriate values of L and H according to Table 1. If the measured value is not listed and is within the range of Table 1, it may be obtained from Table 1 by linear interpolation. If the kinematic viscosity of the sample at 100°C is less than 2 mm²/s, its viscosity index may be left unspecified or not reported.
• 5.1.2 If the kinematic viscosity of the sample at 100°C is greater than 70 mm²/s, the values of L and H may be calculated according to Equation (1) and Equation (2):
  • L = 0.8353Y² + 14.67Y − 216 … (1)
  • H = 0.1684Y² + 11.85Y − 97 … (2)
  • Where: L— is the kinematic viscosity at 40°C of an oil having the same kinematic viscosity at 100°C as the sample and a viscosity index of 0, mm²/s; Y— is the kinematic viscosity of the sample at 100°C, mm²/s; H— is the kinematic viscosity at 40°C of an oil having the same kinematic viscosity at 100°C as the sample and a viscosity index of 100, mm²/s.
• 5.1.3 The viscosity index VI of the sample may be calculated according to Equation (3):
  • VI = [(L − U) / (L − H)] × 100 … (3)
  • Where: U— is the kinematic viscosity of the sample at 40°C, mm²/s.
• 5.1.4 Calculation example: The measured kinematic viscosity of the sample at 40°C is 73.30 mm²/s, and at 100°C is 8.86 mm²/s. Using Table 1 (by interpolation), L=119.94 and H=69.48 are obtained. Substituting into Equation (3) and rounding to an integer: VI=[(119.94−73.30)/(119.94−69.48)]×100=92.43, VI=92.

Method B (Chapter 6, applicable to VI ≥ 100)

• 6.1.1 If the kinematic viscosity of the sample at 100°C is less than or equal to 70 mm²/s, select an appropriate value of H according to Table 1. If the measured value is not listed but is within the range of Table 1, it may be obtained from Table 1 by linear interpolation. If the kinematic viscosity of the sample at 100°C is less than 2 mm²/s, its viscosity index may be left unspecified or not reported.
• 6.1.2 If the kinematic viscosity of the sample at 100°C is greater than 70 mm²/s, the value of H may be obtained by Equation (4):
  • H = 0.1684Y² + 11.85Y − 97 … (4)
  • Where: Y— is the kinematic viscosity of the sample at 100°C, mm²/s; H— is the kinematic viscosity at 40°C of an oil having the same kinematic viscosity at 100°C as the sample and a viscosity index of 100, mm²/s.
• 6.1.3 The viscosity index VI of the sample may be obtained according to Equation (5) and Equation (6):
  • VI = {[(antilogN) − 1] / 0.00715} + 100 … (5)
  • N = (logH − logU) / logY … (6)
  • Where: U— is the kinematic viscosity of the sample at 40°C, mm²/s. Note: antilogN denotes inverse logN (the same below).
• 6.1.4 Calculation example:
  • (1) The kinematic viscosity of the sample at 40°C is 22.83 mm²/s, and at 100°C is 5.05 mm²/s. Using Table 1 (by interpolation), H=28.97 is obtained. Substituting into Equation (6): N=[(log28.97−log22.83)/log5.05]=0.147 08. Substituting into Equation (5) and rounding to an integer: VI={[(antilog0.147 08)−1]/0.00715}+100=[(1.403 07−1)/0.007 15]+100=156.37=156.
  • (2) The kinematic viscosity of the sample at 40°C is 53.47 mm²/s, and at 100°C is 7.80 mm²/s. Using Table 1, H=57.31 is obtained. Substituting into Equation (6): N=[(log57.31−log53.47)/log7.80]=0.033 76. Substituting into Equation (5) and rounding to an integer: VI={[(antilog0.033 76)−1]/0.00715}+100=[(1.080 84−1)/0.007 15]+100=111.

Appendix B (informative appendix) Other calculation methods

• B1 Chapters 5 and 6 have given the precise methods for calculating the viscosity index; calculation of the viscosity index by computer or programmable calculator is also required. This appendix describes three calculation methods.
• B2 The calculation of the viscosity index requires the following conditions: B2.1 input the kinematic viscosities at 40°C and 100°C; B2.2 calculate the values of L and H corresponding to the kinematic viscosity at 100°C; B2.3 the calculation of the viscosity index should use the formulas in Chapters 5 and 6.
• B3 The values of L and H are determined using the following three cases:
  • B3.1 Store the complete L and H value tables in a computer; the L and H values will be accurately obtained by linear interpolation in the same way as the calculation method of this standard.
  • B3.2 Input the finite number of entries in Table 1 into the computer memory, and use the given Y value of the kinematic viscosity of the sample 100°C to calculate the corresponding L value. From Table B1, select a set of data closest to the given kinematic viscosity, and similarly select a pair of data sets above and below this set; using these three sets of data, calculate the coefficients a, b, and c by formula (B1): L = aY² + bY + c … (B1); calculate the coefficients d, e, and f by formula (B2): H = dY² + eY + f … (B2). The 32 sets of data in Table B1 are selected from Table 1.
  • B3.3 The data in Table 1 can also be applied to a series of other quadratic equations; the range of each equation must be consistent with the acceptable accuracy of all values within the ranges of the L and H values. Table B2 gives a data table composed of 16 sets of data, so that the error of the individual values of L and H calculated in this way will not exceed 0.1%.
• B4 Using the given Y and U values, find the corresponding Y value from Table B2, and from the calculated L and H values, the viscosity index can be directly calculated by B4.1 or B4.2. B4.1 formula (3) (when VI ≤ 100); B4.2 formula (5) and formula (6) (when VI ≥ 100), which has already been described in Chapter 6 of this standard.
• B5 Calculation example: sample 40°C kinematic viscosity 73.50 mm²/s, 100°C kinematic viscosity 8.86 mm²/s.
  • B5.1 Using the description of B3.1, "look up" the L and H value tables stored in the computer memory: 100°C kinematic viscosity 8.8 mm²/s corresponds to L=118.5, H=68.79; 8.9 mm²/s corresponds to L=120.9, H=69.94. The sample L and H values are obtained by linear interpolation calculation: L=119.94, H=69.48.
  • B5.2 According to the description in B3.2, using Table B1, select three sets of data from the computer memory: 8.4 mm²/s (L=109.2, H=64.18), 9.0 mm²/s (L=123.3, H=71.10), 10.5 mm²/s (L=160.6, H=88.95). According to formulas (B1) and (B2), the following are calculated: L=0.65079Y²+12.1762Y−39.00; H=0.17460Y²+8.4952Y−19.50. For Y=8.86, the Y value lies between the ranges of 8.4 and 9.0, and the sample L and H values are obtained: L=119.9681, H=69.4741.
  • B5.3 According to the description in B3.3, the memory contains Ymin=7.7 and Ymax=9.0 of Y=8.86, and the formulas obtained are: L=0.41858Y²+16.1558Y−56.040; H=0.05794Y²+10.5156Y−28.240. According to the given Y=8.86 mm²/s, the L and H values are calculated: L=119.9588, H=69.4765.
  • B5.4 According to the above calculation, since VI ≤ 100, calculate the viscosity index VI by formula (3). The viscosity index VI of the sample obtained by the three calculation methods respectively is as follows:
    • B5.4.1 For the L and H values obtained from B5.1: VI=(119.94−73.50)/(119.94−69.48)×100=92.033=92
    • B5.4.2 For the L and H values obtained from B5.2: VI=(119.9681−73.50)/(119.9681−69.4741)×100=92.027=92
    • B5.4.3 For the L and H values obtained from B5.3: VI=(119.9588−73.50)/(119.9588−69.4765)×100=92.030=92

9. Qualitative and Quantitative and Calculation Formulas

• Method A (VI ≤ 100):
  • L = 0.8353Y² + 14.67Y − 216 … (1) (when Y > 70 mm²/s)
  • H = 0.1684Y² + 11.85Y − 97 … (2) (when Y > 70 mm²/s)
  • VI = [(L − U) / (L − H)] × 100 … (3)
• Method B (VI ≥ 100):
  • H = 0.1684Y² + 11.85Y − 97 … (4) (when Y > 70 mm²/s)
  • VI = {[(antilogN) − 1] / 0.00715} + 100 … (5)
  • N = (logH − logU) / logY … (6)
• Symbols: L— the kinematic viscosity at 40°C of an oil having the same kinematic viscosity as the sample 100°C and a viscosity index of 0, mm²/s; H— the kinematic viscosity at 40°C of an oil having the same kinematic viscosity as the sample 100°C and a viscosity index of 100, mm²/s; Y— the kinematic viscosity of the sample at 100°C, mm²/s; U— the kinematic viscosity of the sample at 40°C, mm²/s.
• Table 1: Reference values of L and H for kinematic viscosity classified by 40°C, 100°C (100°C kinematic viscosity 2.00~70.0 mm²/s).
• Table B1: Quadratic interpolation data sets of L and H values (32 sets of data selected from Table 1).
• Table B2: Coefficients of the quadratic equations (formula B1 and formula B2) (16 sets of data, Ymin/Ymax range 2.0~>70).
• Rounding: Report to an integer; when this number is midway between two integers, report the even number (Chapter 7).

10. Precision

• 8.1 Precision: The precision of the viscosity index depends on the precision of the two independent kinematic viscosities used for calculation. The kinematic viscosities used to calculate the viscosity index shall conform to the precision specified in GB/T 265.
• Adoption note 1]: The precision of this standard is only associated with GB/T 265.
• 8.2 Bias: The calculation of the viscosity index using the kinematic viscosities of 40°C and 100°C is accurate, and this calculation method will not cause bias.
• Foreword: The 8.2, 8.3 and related partial appendix contents in Chapter 8 Precision and Bias of ASTM D2270—93 have not been adopted.
• Adoption note 1.: The X1.3 "Discussion of Viscosity Index Precision" in the original text X1 has not been adopted.

11. Report

• Chapter 7 Report: Report the viscosity index of the sample to an integer. When this number is midway between two integers, report the even number.
• 5.1.1 / 6.1.1: If the kinematic viscosity of the sample 100°C is less than 2 mm²/s, its viscosity index may be left unspecified or not reported.
• Appendix A A2: The viscosity index of a sample calculated using kinematic viscosities at non-standard temperatures can only be used as appropriate information and shall not be reported as a result for specification requirements.

12. Referenced Documents

• GB/T 265 Petroleum products — Determination of kinematic viscosity and calculation of dynamic viscosity
• GB/T 8023 Viscosity-temperature calculation charts for liquid petroleum products
• Note: The provisions of the following standards, through reference, constitute a part of this standard. Unless otherwise expressly specified in the standard, the following referenced standards shall all be currently effective standards.