1. Different coating.
Black pipe is made of steel as is galvanized pipe. The difference is that galvanized pipe is coated with zinc, while black pipe is not.
2. Different Corrosion resistance
The black pipe is a light coating and provides only the barest protection. Black pipe will rust outdoors. The galvanized pipe will barely rust at all.
3. Different costs.
Black pipe is cheaper than galvanized pipe because of the zinc that is added to galvanized pipe.
4. Different application
Black pipe is best used for gas lines, not for water lines because it rusts easily, while galvanized cannot be used for gas lines because the zinc can clog the lines when it begins to flake, galvanized pipe is the safer pipe to use in water lines.
