GB/T 4945-2002 in English

《GB/T 4945-2002石油产品和润滑剂酸值和碱值测定法（颜色指示剂法）》由TC280（全国石油产品和润滑剂标准化技术委员会）归口，TC280SC1（全国石油产品和润滑剂标准化技术委员会石油燃料和润滑剂分会）执行，主管部门为国家标准化管理委员会。
本标准适用于测定能在甲苯和异丙醇混合溶剂中全溶或几乎全溶的石石油产品和润滑剂酸性或碱性组分，它适用于测定在水中离解常数大于10的-9次方的极弱酸或碱不影响测定，如果盐类水解常数大于10的-9次方，则有影响。本标准可用于表明使用中的油品在氧化条件下的相对变化。尽管滴定是在规定条件下进行的，但是本标准不能测定绝对酸性和碱性，以预测油品在使用条件下的性能。已经知道酸值或碱值与轴承腐蚀之间没有必然联系。

1 Scope

1.1 This standard covers the determination of acid or basic constituents in petroleum products and lubricants soluble or nearly soluble in mixtures of toluene and isopropyl alcohol. It is applicable for the determination of acids or bases whose dissociation constants in water are larger than 10−9; extremely weak acids or bases whose dissociation constants are smaller than 10−9do not interfere. Salts react if their hydrolysis constants are larger than 10−9.
Notes:
1 In new and used oils, the constituents considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, and addition agents such as inhibitors and detergents. Similarly, constituents considered to have basic properties include organic and inorganic bases, amino compounds, salts of weak acids (soaps), basic salts of poly acidic bases, salts of heavy metals, and addition agents such as inhibitors and detergents.
2 This test method is not suitable for measuring the basic constituents of many basic additive-type lubricating oils. Test method in SH/T 0688 may be used for this purpose.
1.2 This test method can be used to indicate relative changes that occur in an oil product during use under oxidizing conditions. Although the titration is made under specified conditions, the method is not able to measure an absolute acidic or basic property that may be used to predict performance of an oil product under service conditions. No general relationship between bearing corrosion and acid or base numbers is known.
Note: Oils, such as many cutting oils, rust proofing oils, and similar compounded oils, or dark-colored oils, that are not able to be analyzed for acid number by this test method due to obscurity of the color-indicator end point, may be analyzed by test method in GB/T 7304. The acid numbers obtained by this color-indicator test method need not be numerically the same as those obtained by test method in GB/T 7304, the base numbers obtained by this color indicator test method need not be numerically the same as those obtained by test method SH/T 0688, but their data is in a certain relation.

2 Normative References

The following standards contain provisions which, through reference in this text, constitute provisions of this standard. Unless otherwise specified in the standard, the standards below shall be valid and current.
GB/T 6682 Water for Analytical Laboratory Use - Specification and Test Methods
GB/T 7304 Petroleum Products and Lubricants; Determination of Neutralization Number; Potentiometric Titration Method
SH/T 0688 Petroleum Products and Lubricants-Determination of Base Number-Potentiometric Titration Method

3 Definitions

This standard adopts the definitions as follows.
3.1 Acid number
It refers to the quantity of base of sample that is required to titrate a sample of 1g to a specified end point, expressed in mgKOH/g.
3.2 Base number
It refers to the quantity of acid of sample that is required to titrate a sample of 1g to a specified end point, expressed in mgKOH/g.
3.3 Strong acid number
It refers to the quantity of base of sample that is required to titrate a hot water extract of 1g sample to a yellow end point using methyl orange solution, expressed in mgKOH/g.
3.4 Used oil
It refers to any oil that has been in a part of equipment (for example, an engine, gearbox, transformer, or turbine) whether operated or not.

4 Summary of Test Method
4.1 To determine the acid or base number, the sample shall be dissolved in a mixture of toluene and isopropyl alcohol containing a small amount of water, and the resulting single-phase solution shall be titrated at room temperature with standard alcoholic base or alcoholic acid solution, respectively, to the end point indicated by the color change of the added p-naphtholbenzein solution (orange in acid and dark green in base). To determine the strong acid number, a separate portion of the sample is extracted with hot water and the aqueous extract shall be titrated with potassium hydroxide solution, using methyl orange as an indicator.

Forward I
1 Scope
2 Normative References
3 Definitions
4 Summary of Test Method
5 Significance and Use
6 Apparatus
7 Reagents
8 Test Preparation
9 Procedure for Determining Acid Number
10 Procedure for Base Number
11 Procedure for Determining Strong Acid Number
12 Quality Control Checks
13 Calculation
14 Precision and Deviation
15 Report
Annex A (Normative) Specifications for P-naphtholbenzein