The difference between black pipe and galvanised pipe is the coating: galvanised pipe is coated with hot-dip zinc, black pipe is uncoated. The body steel and the production method are largely the same.
That single difference decides in which environment the pipe can be used and how long it will last.
Comparison
| Coating | Black: none · Galvanised: hot-dip zinc |
|---|---|
| Corrosion resistance | Markedly higher on galvanised |
| Cost | Black is more economical |
| Use | Black: dry/enclosed · Galvanised: water, outdoors |
| Welding | Straightforward on black · Special precautions on galvanised |
| Diameter range | Black: 1/2" – 8" · Galvanised: 1/2" – 6" |
When black pipe
For structural, scaffolding and machine work that will stay in a dry, enclosed environment, black pipe is sufficient and more economical.
It is also preferred for work that will be painted or coated afterwards.
When galvanised pipe
Galvanised pipe should be chosen for any line in contact with water, staying outdoors or working in a damp environment.
Drinking water, fire lines, irrigation and outdoor railings are the typical fields of use.
How to compare cost
Looking only at the price per metre is misleading. The right comparison is made over the expected service life.
In a damp environment black pipe may have to be replaced within a few years while galvanised pipe lasts far longer; the initial price difference is more than closed over that period.