Galvanized pipes are not used for underground lines. It is relatively better to use for hot water lines, however, it also works good for cold water lines. Avoid using galvanized pipe fittings for gas supply lines as natural gas can cause the zinc to come off and cause blockages in the system.
Outdoor applications are a more common use of galvanized steel pipe in the modern age. It is most likely to be seen on chain link fences or handrails. It is highly resistant to corrosion, which makes it a perfect choice for goods or materials that will be exposed to the elements on a regular basis.