• The salinity and pH of the surrounding soil
• The salinity and pH of the water in the culvert
• The velocity and size of particles passing through the culvert
• Freezing and thawing cycles within the surrounding soil
A. GALVANIZED COATINGS
Galvanizing is the process by which steel is coated with a thin layer of zinc. Zinc is widely used to protect corrugated steel pipe from corrosion. Zinc metal has excellent corrosion resistance in most all North Carolina environments. Zinc acts sacrificially to protect the base steel from the elements -- in other words, zinc gives itself up to corrosion, thus preventing corrosion from occurring to the base metal.
Corrugated steel pipe shall be fabricated from galvanized steel sheet meeting the requirements of AASHTO M 218. Materials and Tests technicians shall check for minimum coating thickness prior to installation of the pipe. Whether the pipe is used on contract construction projects, division design-construct projects, or on maintenance work (driveways, subdivision roads for future acceptance onto the state system, encroachment work within the right of way, etc.), please contact your local Section Materials Specialist for inspection.
B. ALUMINIZED COATINGS (TYPE 2)
Steel pipe can also be coated for corrosion resistance using aluminum. Aluminum acts as a barrier to corrosion and protects the base metal from the elements. The Type 2 designation for this coating requires that the aluminum be commercially pure.
Corrugated steel pipe shall be fabricated from aluminized steel sheet meeting the requirements of AASHTO M 274. Materials and Tests technicians shall check for minimum coating thickness prior to installation of the pipe.
NOTE: Do not use plain galvanized or aluminized corrugated steel pipe in the following counties:
Beaufort, Bertie, Bladen, Brunswick, Camden, Carteret, Chowan, Columbus, Craven, Currituck, Dare, Gates, Hertford, Hyde, Jones, Martin, New Hanover, Onslow, Pamlico, Pasquotank, Pender, Perquimans, Tyrrell, and Washington.
C. POLYMERIC COATINGS
Polymeric coatings provide both corrosion and abrasion resistance. The application process used for polymers allows the metal sheet to be precoated prior to fabrication of the pipe. Polymeric coatings must meet the minimum thickness requirements set forth in AASHTO M 246. Materials and Tests technicians will check polymeric coating thickness at the producer's facility. As provided in
Section 1032-4(A)(2) of the Standard Specifications: When shown in the plans or as approved by the Engineer, a polymeric coating meeting AASHTO M 246 for Type B coating may be substituted for aluminized coating.
