Development of a Rational Method for Predicting Corrosion Rates of Metals in Soils and Waters

摘要

Methods used by the Florida Department of Transportation for predicting corrosion rates of metallic piling, anchors, and metallic drainage pipe used in highway construction were examined and updates were proposed as needed. Pile and anchor procedures were found to be generally adequate, with caution on the possibility of enhanced underground corrosion and new modalities of microbiologically induced corrosion. Special attention was given to the case of aluminized steel drainage pipe due to recent cases of extensive premature corrosion of spiral-ribbed pipes made of that material. That corrosion, affecting in particular the formed pipe ribs and associated with manufacturing deficiencies, took place under nominally mild environmental conditions. Laboratory tests sought to establish whether a corrosion prediction method based on scaling tendency of the soil water was a better predictor of corrosion than the presently used method based on environmental resistivity and pH values. The results were supportive of the scaling tendency method under relatively aggressive accelerated test conditions. However, tests with a less nominally aggressive water indicated that under those conditions the aluminized layer may fail to provide cathodic protection to base steel exposed at highly strained areas of the material such as those that may exist at formed ribs. Microbial influenced corrosion (MIC) was found to be a potentially important component of field corrosion of the metallic components studied, and a recommendation for inclusion of MIC in future design guidelines was made. FDOT analysis methods for chloride, sulfate pH and resistivity were assessed and potential improvements were tested. Revised test procedures were formulated and proposed for adoption.