A hot-dip galvanized steel pipe is a carbon steel pipe coated with a layer of zinc by immersing it in molten zinc at about 450°C (840°F). This forms a metallurgically bonded zinc-iron alloy coating that provides both barrier protection and sacrificial (cathodic) protection, preventing rust even if the coating is scratched.

Key properties include excellent corrosion resistance, a typical coating thickness of 45 to 200 micrometres (average 80-100 µm), and a long service life of 25 years or more in most environments. The coating mass is typically 460 to 800 g/m². The pipe retains the mechanical strength of the base steel, with common yield strengths of 205-240 MPa (Grade A/B) and tensile strengths of 330-415 MPa.

Common Standards:

- ASTM A53 (American) – Grades A and B, welded and seamless.

- ASTM A123 / A153 – Coating specifications.

- EN 10255 (European) – Threadable tubes.

- JIS G 3444 (Japanese) – Structural tubes.

- BS 1387 (British).

Typical Dimensions: outer diameter from 10 mm to 750 mm (1/8 to 30 inches), wall thickness from 0.5 mm to 25 mm, lengths of 3 m, 6 m, or custom.

Surface Finishes: standard bright spangled, minimised/zero spangle, or passivated (chromated or chromate-free) to reduce white rust.

Applications: water supply, plumbing, fire protection systems (NFPA 13), gas transmission, scaffolding, fencing, handrails, structural frameworks, agricultural greenhouses, irrigation, and industrial low-pressure fluid lines.

Connection Methods: threaded (threads cut before galvanizing), flanged (for larger diameters), or grooved (Victaulic-style). Welding is generally not recommended because it destroys the zinc coating; if necessary, the welded area must be repaired with zinc-rich paint.

Selection Note: Galvanized pipe is ideal for outdoor or wet environments. Black steel pipe is cheaper and easier to weld but lacks corrosion resistance. For most water and outdoor applications, hot-dip galvanized pipe provides the best balance of durability and cost over its service life.