Sep 22, 2026Buying Guides
Galvanized Steel Pipe: Types, Sizes (DN15-DN200), Zinc Coating and Applications
Galvanized steel pipe comes in hot dipped and pre-galvanized types from DN15 to DN200. Compare zinc coating weights, wall thickness, standards and applications before ordering.
Galvanized steel pipe is a carbon steel pipe with a zinc coating, and two pipes with the same outside diameter can still be different products: a hot dipped pipe at 275 g/m2 and a pre-galvanized pipe at 60 g/m2 share a name and have very different service lives. This guide covers the types, the size range, zinc coating weights, the standards buyers specify and where each type belongs.
What Is Galvanized Steel Pipe?
Galvanized steel pipe is made from carbon steel pipe - usually ERW welded tube, sometimes seamless - coated with zinc to keep the steel from corroding. The zinc protects in two ways: it seals the surface from moisture and oxygen, and it sacrifices itself at scratches and cut ends, which is why a galvanized steel pipe keeps working long after the coating is damaged.
The base pipe still carries the load, so grade, wall thickness and standard are specified first. The zinc coating is specified on top of that, and it is the number most often left out of an inquiry.
Hot Dipped Galvanized Steel Pipe vs Pre-Galvanized Steel Pipe
| Hot dipped galvanized | Pre-galvanized |
|---|---|---|
When zinc is applied | After the pipe is made | On the coil, before the pipe is formed |
Typical coating weight | 200 - 275 g/m2 | 40 - 80 g/m2 |
Coating on cut ends | Zinc covers the pipe inside and out | Cut ends are bare steel |
Forming after coating | Not recommended | Light bending and cutting are normal |
Best for | Outdoor, wet, fire fighting and water service | Frames, ducting, light structures and formed parts |
Choose hot dipped galvanized steel pipe when the pipe stays outdoors, stays wet, or forms part of a fire fighting or water system. Choose pre-galvanized steel pipe when the pipe will be cut, bent or formed after coating, or when a lighter and more uniform coating is acceptable.
Galvanized Steel Pipe Sizes and Wall Thickness
Item | Common range |
|---|---|
Nominal size | DN15 - DN200 (1/2 inch - 8 inch) |
Outside diameter | 21.3 mm - 219.1 mm |
Wall thickness | 0.8 mm - 12 mm (SCH 40 and SCH 80 available) |
Length | 6 m standard, cut to length on request |
Ends | Plain, threaded, grooved or beveled |
Type | ERW welded, seamless, square and rectangular |
Nominal size and outside diameter are not the same number. DN50 refers to a nominal bore of about 50 mm, while the outside diameter of that pipe is 60.3 mm. When you order, give the outside diameter and wall thickness, or give the nominal size together with the standard, so both sides are describing the same pipe.
Schedule 40 and Schedule 80
The schedule system fixes the wall thickness for a given outside diameter. Schedule 40 galvanized steel pipe is the common medium wall, and SCH 80 is the heavier wall for higher pressure and mechanical service. Threading has to suit the wall thickness, so name the schedule, not only the diameter.
Welded, Seamless, Square and Scaffolding Pipe
- ERW galvanized steel pipe - electric resistance welded, the standard choice for water, gas and general service
- Seamless galvanized steel pipe - no weld seam, for higher pressure and critical service
- Galvanized steel pipe for construction - structural and general building use
- Galvanized scaffolding pipe - sized and coated for scaffold systems
- Square and rectangular galvanized tube - frames, gates and architectural work
Zinc Coating Weight and How Long the Pipe Lasts
Zinc coating weight is quoted in g/m2 and is the number that decides how long a galvanized steel pipe lasts outdoors.
Coating weight | Typical product | Where it holds up |
|---|---|---|
40 - 80 g/m2 | Pre-galvanized pipe | Indoor, dry and protected parts |
100 - 180 g/m2 | Light hot dipped | Sheltered outdoor and general fabrication |
200 - 275 g/m2 | Standard hot dipped | Outdoor, humid and water service |
300 g/m2 and above | Heavy coating on request | Coastal, industrial and aggressive atmospheres |
In a coastal, humid or industrial environment, always specify the coating weight instead of assuming that galvanized means the same thing everywhere. Two galvanized pipes with the same diameter and different coating weights are not substitutes.
Galvanized Steel Pipe Standards
- ASTM A53 galvanized steel pipe - welded and seamless pipe for water, gas and general service
- ASTM A500 - cold formed welded structural tubing
- BS 1387 galvanized pipe - galvanized steel pipe for water and general service
- EN 10255 - non-alloy steel tubes for welding and threading
- GB/T 3091 - welded steel pipe for low pressure liquid service
- JIS G3444 - general structural carbon steel tubes
The standard fixes dimensions, wall thickness, test pressure and coating requirements, so the same diameter under two standards is not automatically the same pipe. Ordering to the wrong standard is one of the most common reasons a container fails inspection on arrival.
Where Galvanized Steel Pipe Is Used
- Water supply, fire fighting and drainage lines
- Gas and compressed air lines
- Scaffolding and formwork support
- Greenhouse frames and agricultural structures
- Guardrails, fencing and handrails
- Steel structure, trusses and general fabrication
Common Mistakes When Buying Galvanized Steel Pipe
- Treating galvanized as a single specification instead of a coating weight.
- Comparing pipes of the same diameter that are quoted to different standards.
- Specifying a heavy hot dip coating and then bending the pipe, which cracks the coating.
- Leaving the pipe ends unspecified. Threading, grooving and beveling change the price and the lead time.
- Forgetting that cut ends and welds are the first places to rust on a pre-galvanized pipe.
FAQ
What is the difference between hot dipped and pre-galvanized steel pipe?
Hot dipped galvanized pipe is coated after forming, with a heavier coating and protection inside and out. Pre-galvanized pipe is coated on the coil before forming, with a thinner, more uniform coating and bare cut ends. Hot dipped suits outdoor and wet service; pre-galvanized suits pipe that is formed after coating.
What does DN50 galvanized steel pipe mean?
DN50 is a nominal bore of about 50 mm, not the outside diameter. DN50 pipe normally has an outside diameter of 60.3 mm, so specify the outside diameter and wall thickness, or the nominal size together with the standard.
How much zinc coating should a galvanized steel pipe have?
For indoor or protected use, 40 - 80 g/m2 (pre-galvanized) is normal. For outdoor, humid or water service, use 200 - 275 g/m2 hot dipped. Coastal and industrial environments call for 300 g/m2 and above.
Can galvanized steel pipe be welded?
It can be welded, but welding burns the zinc away at the joint and the zinc fume has to be controlled. In practice galvanized pipe is usually threaded, grooved or coupled, and the damaged coating is repaired after fabrication.
Is galvanized steel pipe available in cut lengths?
Yes. 6 m is the standard length, and cut-to-length supply is normal for projects. State the length and the pipe ends (plain, threaded or grooved) with the quantity, because both change the price and the lead time.
Related Guides
Request a Price for Galvanized Steel Pipe
Send the nominal size or outside diameter, wall thickness, standard, zinc coating weight, length, pipe ends and quantity, plus the destination port. Browse our hot dipped galvanized steel pipe, pre-galvanized steel pipe, seamless galvanized steel pipe, ERW galvanized steel pipe, ASTM A53 galvanized steel pipe and BS 1387 galvanized pipe product pages, or send your specification for a quotation.
