Introduction
This article explains pre-galvanized steel pipe, covering the process, coating and applications. Galvanized steel pipe is steel pipe coated with a zinc layer for corrosion protection, used for water supply, scaffolding, conduits, fencing and structural members. The coating is applied by hot-dip galvanizing or, for thinner coatings, by electro-galvanizing.
Coating Methods
Hot-dip galvanized pipe is produced by dipping the finished pipe in molten zinc, giving a thick, durable coating on the inside and outside surfaces. Pre-galvanized pipe is made from galvanized strip that is then formed and welded, which leaves the weld zone with less protection, and electro-galvanized pipe carries a thin smooth coating for indoor and lightly corrosive service.
Grades and Materials
The base pipe is usually low-carbon steel in grades such as the EN or ASTM designations for welded and seamless pipe, and the galvanized product is identified by the pipe standard together with the coating requirement. Common designations in trade include SGCC-based and hot-dip grades for structural and conduit service.
| Type | Coating | Typical Use |
|---|---|---|
| Hot-dip pipe | Thick, inside and out | Water, scaffolding |
| Pre-galvanized | Thin, weld exposed | Conduit, light frames |
| Electro-galvanized | Smooth thin layer | Indoor service |
Applications
Typical uses are water and air lines, scaffolding, handrails, fence posts, cable conduit, greenhouse frames and structural members in agricultural and industrial buildings. The coating protects the pipe against atmospheric corrosion, and the pipe is cut and threaded on site with the cut ends protected by zinc-rich paint or galvanizing repair compound.
Maintenance and Verification
Galvanized pipe needs little maintenance in most services, but cut threads and welds should be recoated. Verify the coating mass, the pipe dimensions and the pressure rating on the certificate, and check the coating uniformity on the delivered lot.
