EVALUATION OF METAL DRAINAGE PIPE DURABILITY AFTER TEN YEARS

This study represents an investigation of the comparative performance of coated and uncoated, corrugated, galvanized steel and aluminum drainage pipe in Louisiana. The highly corosive environments in some areas of the state make durability requirements of metal pipe as critical as strength requirements. Department personnel installed 10 types of metal drainage pipes at each of 10 locations in 1973. The test sites were selected on the basis of the pH and electrical resistivity of the soil and the effluent. One pair of each type of culvert was installed at each site. Every 2 years one designated culvert of each of the pairs was removed and subjectively rated by a panel. The final (10-year) panel ratings reflect the condition of the undisturbed culverts in each pair. It was found that, in general, the 16-gauge asphalt-coated aluminum; the 14-gauge asbestos-bonded, asphalt-coated galvanized steel; and the 16-gauge galvanized steel with a 12-mil interior and a 5-mil exterior polyethylene coating were the test pipes with the most resistance to corrosion at the majority of the test sites. It was also found that, although all of the coatings provided added resistance to corrosion to some degree, the thicker coatings tested provided increased protection to the base metal. Comparisons of actual versus predicted years to perforation are made for galvanized steel in the harsher environments where test culverts actually experienced perforation.