Anodized pipe is pipe which has been subjected to the anodizing process. Anodizing is use of electric current to create a layer of oxide of the base metal on the surface of the object. Anodizing has many advantages including resistance to corrosion, improved performance with lubricants, improved adhesion for decorative or further protective coatings, and improved resistance to wear and cracking over other applied coatings. Metal that has been anodized has bonded on a molecular level with a layer of oxide. Aluminum is the most commonly anodized metal, and anodized pipe is usually made from this material.
Aluminum pipe is by far the most common type of anodized pipe and is really the only type produced commercially in any great quantity. It has numerous uses but is rarely used to carry liquids. It is more commonly used in architectural applications such as railings, shelving structures, bicycle frames, and even in very large structures like spacecraft launch towers. The hollow pipe is much lighter than solid bar or beam constructions and is much stronger for its weight than other common construction materials.
The process of anodizing an object is similar to electroplating, but the coating that is created is formed by the oxidation of the object itself rather than by depositing another metal on the surface. The term anodizing comes from the fact that the object being treated is used as an anode in an electric circuit. That means that electrons flow out from the object which is submerged in a bath of weakly acidic liquid that is is capable of conducting electric current. A cathode is attached to the inside of the container holding the bath and accepts the current flow. This flow of electrons causes oxygen ions to bond with atoms of the object being anodized, forming a layer of oxide on the surface.
The coating created by the anodizing process is attractive, durable, and provides many benefits. It prevents corrosion, damage from wear, and it is very hard. It provides a superior base for the application of other coatings such as paint, dye, and other protective materials. The layer of oxide is porous, allowing for the absorption of coatings that is impossible on materials with a smooth finish. These properties make it suitable for any number of uses in situations where pipe is desirable for aesthetic reasons or for structural efficiency.