Manufacturers galvanize steel pipes by hot-dipping them by submerging the pipes in a bath of liquid zinc. This method is used because it gives a thicker layer of zinc over the base metal of the pipe. 

The hot-dip method is the most common method used for pipes, though there are other methods that can be used if a thinner coating of the zinc is needed, like electro-galvanization.

The zinc protects the steel that is underneath it by acting as a sacrificial layer, which is also referred to as a sacrificial anode.

If the zinc gets damaged and exposes the steel underneath it, then the rest of the zinc still draws the corrosion away from the steel to the zinc.

These types of pipes are preferred for water applications because of the zinc's ability to protect the steel from rust.

Galvanized pipes come in a variety of sizes and diameters to meet each customer's individual needs. The majority of these types of pipes are used for indoor applications though they can be used outdoors. 

If used outdoors, they will need to be replaced more often due to exposure to the elements. 

Costs can vary depending on the size of the pipe and the amount needed for a given project, but many find it more cost-effective in the end because of the less frequent need to replace the material due to damage.