CBP interprets 'similarly closed' to mean mechanical joining methods functionally analogous to riveting — such as lock-seaming or crimping — that create a longitudinal seam without fusion welding. Pipes joined by brazing, soldering, or adhesive bonding may fall outside this heading; a binding ruling is recommended when the closure method is non-standard.

Riveted and lock-seam steel pipe is most common in large-diameter drainage culverts, corrugated metal pipe, and certain ventilation duct applications where the mechanical seam provides adequate strength at lower cost than welding. For pressure-bearing or high-temperature service, welded or seamless alternatives are typically specified instead.