18" x 12' 16 Gauge Steel Culvert. Corrugated metal pipe has been the drainage pipe of choice for engineers and project specifiers for over 100 years. With its various coatings, corrugation patterns, and steel thicknesses CMP provides the predictable strength, durability, and value that todays projects require. No other pipe material on the market today can match CMPs versatility and value. Galvanized: Hot rolled steel that is coated in zinc to form a 2oz/sq. ft. protective coating. The oldest and most economical form of protection, galvanized pipe provides a service life up to 50 years. Polymer: Galvanized steel that has a 10mil polymeric film laminated to both sides of the steel. This is the premier protective coating for CMP that offers multiple layers of protection, supreme abrasion resistance, and the ability to withstand the widest range of soil and water environments. Polymer coated CMP provides a service life up to 100 years. To read the National Corrugated Steel Pipe Associations studies and reports on the durability and performance of polymer coated steel pipe click on the following.