1.1 本规范涵盖主要用于环境温度较低地区的石油和天然气管道的锻造碳钢和合金钢法兰。包括规定尺寸或尺寸标准（如MSS、ASME和API规范）的法兰，这些规范在第节中引用 2. . 1.2 当需要额外要求时，提供了补充要求。仅当买方在订单中单独规定时，才适用。 1.3 包括八个等级、四个屈服强度等级和三个不同的缺口韧性等级。 1.4 特定等级和类别的特定尺寸法兰的可用性仅受成分满足规定机械性能要求的能力的限制。然而，目前的做法通常会限制以下方面: （a） 等级L1至1级和2级， （b） L2至1、2和3级， （c） 1、2和3级L3， （d） L4至1、2和3级， （e） L7至1级和2级，以及 （f） L5、L6和L8级通常适用于任何类别。 1.5 本规范以英寸-磅单位和国际单位制表示。但是，除非订单规定了适用的“M”规格名称（国际单位制），否则材料应以英寸-磅为单位提供。 1.6 以英寸-磅单位或国际单位表示的数值应单独视为标准值。在文本中，国际单位显示在括号中。每个系统中规定的值不是精确的等价物；因此，每个系统必须相互独立使用。合并两个系统的值可能会导致不符合规范。 1.7 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）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》中确立的国际公认标准化原则制定的。

1.1 This specification covers forged carbon and alloy steel flanges intended primarily for petroleum and gas pipelines in areas subject to low ambient temperatures. Included are flanges to specified dimensions or to dimensional standards such as those MSS, ASME, and API specifications that are referenced in Section 2 . 1.2 Supplementary requirements are provided for use when additional requirements are desired. These shall apply only when specified individually by the purchaser in the order. 1.3 Eight grades, four yield-strength classes, and three different notch toughness levels are included. 1.4 The availability of a particular size of flange of a specific grade and class is limited only by the capability of the composition to meet the specified mechanical property requirements. However, current practice normally limits the following: (a) Grade L1 to Classes 1 and 2, (b) Grade L2 to Classes 1, 2, and 3, (c) Grade L3 to Classes 1, 2, and 3, (d) Grade L4 to Classes 1, 2, and 3, (e) Grade L7 to Classes 1 and 2, and (f) Grades L5, L6, and L8 are generally available in any class. 1.5 This specification is expressed in both inch-pound units and in SI units. However, unless the order specifies the applicable “M” specification designation (SI units), the material shall be furnished to inch-pound units. 1.6 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification. 1.7 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.