1.1 本试验方法包括测定石油产品、润滑剂、生物柴油和生物柴油混合物中酸性成分的程序。 1.1.1 试验方法A-- 开发用于石油产品和润滑剂，可溶于或几乎可溶于甲苯和丙-2-醇的混合物。适用于水中离解常数大于10的酸的测定 –9 ; 离解常数小于10的极弱酸 –9 不要干涉。 如果盐的水解常数大于10，盐就会反应 –9 .精度声明中包含的酸值范围为0.5 mg KOH/g至90 mg KOH/g。精度仅针对精度部分所示的材料和酸值范围进行了测定。 1.1.2 试验方法B-- 专门为低酸度、溶解度略有不同的生物柴油和生物柴油混合物开发。该测试方法要求使用具有自动终点查找功能的自动滴定仪。 注1: 在新的和使用过的油中，可以被认为具有酸性特征的成分包括有机酸和无机酸、酯、酚类化合物、内酯、树脂、重金属盐、氨和其他弱碱的盐、多元酸的酸盐以及添加剂，如抑制剂和清洁剂。 1.2 用于测定原油和石油产品中酸性成分的酸值，包括蜡、沥青、基础油和可溶于二甲苯和丙烷混合物的沥青- 2-ol使用试验方法试验方法 D8045 .该方法的精度尚未对试验方法所涵盖的任何产品进行测定 D8045 . 1.3 该试验方法可用于指示在氧化条件下使用期间油中发生的相对变化，而与所得油的颜色或其他特性无关。尽管滴定是在确定的平衡条件下进行的，但该测试方法并不旨在测量可用于预测油在使用条件下性能的绝对酸性。 酸值和油对金属的腐蚀倾向之间没有一般的关系。 注2: 通过本标准获得的酸值可能与根据试验方法获得的酸值在数值上相同，也可能不同 D974 和 D3339 没有任何尝试将该方法与其他非滴定方法相关联。 注3: 一些实验室已经观察到试验方法存在差异 D664 当使用水性与非水性缓冲液时的结果。 1.4 以国际单位制表示的数值应视为标准。本标准不包括其他计量单位。 1.5 本标准并不旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.6 本国际标准是根据世界贸易组织技术性贸易壁垒委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认的标准化原则制定的。 ====意义和用途====== 5.1 新的和使用过的石油产品、生物柴油和生物柴油混合物可能含有酸性成分，这些成分作为添加剂或在使用过程中形成的降解产物（如氧化产物）存在。这些物质的相对量可以通过用碱滴定来确定。酸值是在试验条件下油中酸性物质含量的量度。酸值被用作润滑油配方质量控制的指南。 它有时也被用作润滑剂在使用中退化的衡量标准。任何谴责限度都必须根据经验确定。 5.2 由于各种氧化产物对酸值有贡献，而有机酸的腐蚀性能差异很大，因此该测试方法不能用于预测油或生物柴油及其混合物在使用条件下的腐蚀性。酸值与生物柴油、混合物或油对金属的腐蚀倾向之间没有普遍的相关性。

1.1 This test method covers procedures for the determination of acidic constituents in petroleum products, lubricants, biodiesel, and blends of biodiesel. 1.1.1 Test Method A— Developed for use with petroleum products and lubricants soluble or nearly soluble in mixtures of toluene and propan-2-ol. It is applicable for the determination of acids whose dissociation constants in water are larger than 10 –9 ; extremely weak acids whose dissociation constants are smaller than 10 –9 do not interfere. Salts react if their hydrolysis constants are larger than 10 –9 . The range of acid numbers included in the precision statement is 0.5 mg KOH/g to 90 mg KOH/g. The precision has only been determined for those materials and acid number ranges as shown in the precision section. 1.1.2 Test Method B— Developed specifically for biodiesel and biodiesel blends with low acidity and slightly different solubility. This test method requires the use of an automatic titrator with automatic endpoint-seeking capability. Note 1: In new and used oils, the constituents that may be considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, salts of ammonia and other weak bases, acid salts of polybasic acids, and addition agents such as inhibitors and detergents. 1.2 For acid number determination of acidic components in crude oil and petroleum products including waxes, bitumen, base stocks, and asphalts that are soluble in mixtures of xylenes and propan-2-ol use test method Test Method D8045 . The precision for this method has not been determined for any products covered by Test Method D8045 . 1.3 The test method may be used to indicate relative changes that occur in oil during use under oxidizing conditions regardless of the color or other properties of the resulting oil. Although the titration is made under definite equilibrium conditions, the test method is not intended to measure an absolute acidic property that can be used to predict performance of oil under service conditions. No general relationship between acid number and the corrosive tendency of oils towards metals is known. Note 2: The acid number obtained by this standard may or may not be numerically the same as that obtained in accordance with Test Methods D974 and D3339 . There has not been any attempt to correlate this method with other non-titration methods. Note 3: A few laboratories have made the observation that there is a difference in Test Method D664 results when aqueous versus nonaqueous buffers are used. 1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 New and used petroleum products, biodiesel, and blends of biodiesel may contain acidic constituents that are present as additives or as degradation products formed during service, such as oxidation products. The relative amount of these materials can be determined by titrating with bases. The acid number is a measure of this amount of acidic substance in the oil, always under the conditions of the test. The acid number is used as a guide in the quality control of lubricating oil formulations. It is also sometimes used as a measure of lubricant degradation in service. Any condemning limits must be empirically established. 5.2 Since a variety of oxidation products contribute to the acid number and the organic acids vary widely in corrosion properties, the test method cannot be used to predict corrosiveness of oil or biodiesel and blends under service conditions. No general correlation is known between acid number and the corrosive tendency of biodiesel and blends or oils toward metals.