In some instances, these two terms can be used interchangeably. However, the primary distinction between them lies in dimensional tolerances and intended application. Tubes are primarily used for structural and mechanical purposes; consequently, their outside diameter (OD) is critical, and manufacturing precision focuses more on the OD than the inner diameter. In contrast, pipes are typically used to transport gases and liquids, making their flow capacity—which depends on the inner diameter (ID)—the key factor. Pipes feature a circular cross-section, which provides good internal pressure resistance. Tubes, however, are manufactured with square and rectangular cross-sections in addition to circular ones. Pipes are generally classified using Nominal Pipe Size (NPS), nominal diameter, and Schedule number; a specific Schedule number may apply to different pipe sizes, yet the resulting wall thicknesses will vary.

Tubes are typically ordered by specifying the outside diameter and wall thickness, although combinations such as outside diameter with inner diameter, or inner diameter with wall thickness, are sometimes used. Generally speaking, pipes cover a broader dimensional range than tubes.

Key Points:

• Pipes are primarily used for fluid transport, whereas tubes generally serve mechanical purposes.

• Pipes are identified by NPS, nominal diameter, and Schedule number, whereas for tubes, the outside diameter and wall thickness are the critical specifications.

  Compiled by: Engineering and R&D Department