Some engineers are hesitant to use corrugated metal pipe (CMP) for stormwater applications because they have read or heard about CMP being used in culverts that have corroded. This shouldn’t be the case. Many decades ago, galvanized pipe was the coating of choice for culverts; that now has been replaced with Aluminized Type 2 (ALT2).  The primary reason for culvert failure is the galvanized coating is not properly designed to withstand a high flow and abrasion environment, which wears the galvanized coating off the invert of the pipe allowing for corrosion. The ALT2 is far more abrasive resistant for applications such as culverts and has a wider range for pH and resistivity. Additionally, a detention/infiltration application is not an abrasive environment, so these concerns are further mitigated.  Finally, a properly designed infiltration system includes pretreatment and flow control, as well as a stone envelope which prevents interaction with native soils further reducing the potential for abrasion and corrosion. Consider the following:

• CMP infiltration systems have a proven service life that may exceed 100-years when properly installed and meets all AASHTO and ASTM pipe specifications.
• CMP infiltration systems can be designed to meet HS-20 or greater load requirements with proper depths of cover.
• With no abrasion and low flows there is no reason for corrosion to occur inside the pipe that is holding stormwater runoff.
• Protective pipe coatings such as Aluminized Type 2, Galvanized, CORLIX® Aluminum, and polymeric are matched to the pH and resistivity of the surrounding soil.
• CMP infiltration systems need to be surrounded by clean crushed stone to provide increased capacity utilizing storage in the void space. The system is then wrapped with fabric on the sides and the top to prevent the native soil from having contact with CMP.  Thus, corrosive soils do not come into contact with the pipe, and the outside of the pipe is protected.

There may be instances where alternative materials are needed for subsurface infiltration due to site specific needs. For example, plastic chambers are best suited in shallow depth applications, and concrete structures and vaults are best suited for high loading applications such as railroads or airports. But for the majority of applications, CMP is the “go to” material for subsurface infiltration.