Choosing the Right CMP Material: A Guide to Service Life and Site Fit
Choosing the Right CMP Coating for Long-Term Stormwater System Performance
When it comes to underground stormwater systems, longevity depends heavily on material selection. While all corrugated metal pipe (CMP) systems offer structural integrity, the right coating ensures they perform for decades in the specific environmental conditions of your site. This article breaks down the main CMP coating types, their performance in different soil and water conditions, and when to use each.
Aluminized Type 2: The Workhorse Material
Aluminized Type 2 (ALT2) CMP features a steel base coated in Type 2 aluminum, which oxidizes to form a corrosion-resistant layer. It’s suitable for most native soils in the U.S., particularly where the pH ranges from 5–9 and resistivity is above 1,500 ohm-cm. This material provides a service life of 75+ years in most applications and is widely accepted by transportation and regulatory agencies.
Polymer-Coated CMP: Built for the Harshest Sites
Polymer coatings provide additional abrasion and chemical resistance. This makes polymer-coated CMP ideal for environments with acidic soils, high chloride content, or contaminated runoff, common in industrial areas, brownfield redevelopments, and landfill projects. Properly installed, this system can last over 100 years.
Galvanized CMP: A Limited Role Today
Galvanized steel, though still used, has declined in popularity due to its lower resistance to corrosion. While acceptable in neutral soils (pH ~7) with high resistivity, its service life is shorter, and agencies are increasingly limiting its use. It’s best suited for low-risk, temporary, or isolated applications.
Backed by Research
Multiple studies, including by the FHWA, NCSPA, and U.S. Army Corps of Engineers, confirm that when matched to appropriate site conditions, ALT2 and polymer-coated CMP can far exceed 50- to 100-year design lives. For example, Florida DOT concluded ALT2 has nearly three times the service life of galvanized steel in the same environments.
Material selection is the foundation of stormwater system durability. Conducting soil testing for pH and resistivity early in design, and selecting coatings accordingly ensures long-term performance and protects your project from future failures and liabilities.