Supplementing the metallic coating on galvanized and aluminized type 2 steel, the following coatings can be used to develop the desired durability required to meet a variety of service conditions.
1. PARTIAL ASPHALT COATED: A hot-dip coating of bituminous material that coats the lower 20% of the pipe. It has an approximate thickness of .05 inch on the crest of the corrugations, inside and out, and .03 inch for perforated pipe.
Asphalt provides extended service life where abrasion at the lower end of the pipe is concerned.
2. FULL ASPHALT-COATED: A hot-dip coating of bituminous material that coats the entire pipe. It has an approximate thickness of .05 inch on the crest of corrugations, inside and out, and .03 inch for perforated pipe.
Asphalt provides extended service life where soil side corrosion is a concern.
3. POLYMERIC PRE-COATED SHEETS: Pre-coated polymer coatings, such as Dow Trenchcoat protective film, are factory applied to galvanized steel sheet prior to forming the pipe.
Polymer pre-coated steel provides a higher level of protection where interior AND exterior corrosion in mildly corrosive and/or abrasive conditions exist.
4. SPECIAL INVERT TREATMENTS: A variety of specialized invert treatments can be used to provide protection from truly abrasive or highly corrosive flows of when a higher degree of assurance is needed. Materials commonly used for invert lining include high strength concrete, steel bars are placed and polyethylene sheet. These can be field or factory applied.
Where abrasive or corrosive flows are most severe, special invert designs are needed to provide the highest level of protections. These systems are generally renewable and with proper maintenance can provide indefinite service life.