7306.19.51 - Of alloy steel

This HTS category, 7306.19.51, specifically classifies tubes, pipes, and hollow profiles of iron or steel that are used for oil or gas pipelines and are constructed from **alloy steel**. These articles are characterized by their application in transporting hydrocarbons, and the defining material is alloy steel, which implies the inclusion of elements beyond iron and carbon to enhance its properties.

The key distinction of this category from its sibling, 7306.19.10, lies in the material composition. While 7306.19.10 covers similar pipeline articles made of "iron or nonalloy steel," this category is exclusively for those fabricated from **alloy steel**. This differentiation is crucial for accurate tariff application as alloy steels often possess superior strength, corrosion resistance, or other specialized characteristics tailored for demanding pipeline environments.

Within this classification, further subdivisions exist based on the physical dimensions of the pipe. Category 7306.19.51.10 pertains to alloy steel line pipe with an outside diameter not exceeding 114.3 millimeters, whereas category 7306.19.51.50 encompasses those with an outside diameter exceeding 114.3 millimeters. This granular classification by diameter is a standard practice in HTS to address variations in manufacturing, application, and often, in the associated duties or regulations.