7305.31 - Longitudinally welded:

This HTS category, 7305.31, encompasses longitudinally welded tubes and pipes made from iron or steel. A critical defining characteristic is their circular cross-section with an external diameter exceeding 406.4 mm. The "longitudinally welded" designation specifically refers to the method of joining the edges of the metal to form the tube, where the weld seam runs parallel to the length of the pipe. This distinguishes them from other welding methods that might form a spiral seam.

In contrast to its sibling category, 7305.39 (Other, welded, not longitudinally welded), this classification is exclusively for pipes and tubes where the weld is applied along the length of the cylinder. The parent category, 7305, broadly covers "Other tubes and pipes," but this subcategory drills down into the specific construction and diameter for longitudinally welded steel pipes.

Underneath this category, further distinctions are made to refine classification. Subcategory 7305.31.20.00 addresses tapered pipes and tubes of steel that are primarily utilized as components in illuminating articles, indicating a specific end-use application. The remaining "Other" subcategory is a residual provision for longitudinally welded pipes and tubes that do not meet the specific criteria of the tapered illuminating article pipes.