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Report Prepared by Report Prepared by: Alberto A. Sagüés Noreen D. Poor Leonardo Cáseres Mersedeh Akhoondan FINAL REPORT DEVELOPMENT OF A RATIONAL METHOD FOR PREDICTING CORROSION RATES OF METALS IN SOILS AND WATERS Contract No. BD497 Final Report to Florida Department of Transportation A. A. Sagüés Principal Investigator Department of Civil and Environmental Engineering University of South Florida Tampa, FL 33620 October 31, 2009 Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. BD497 4. Title and Subtitle 5. Report Date DEVELOPMENT OF A RATIONAL METHOD FOR PREDICTING October 31, 2009 CORROSION RATES OF METALS IN SOILS AND WATERS 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. A. A. Sagüés, N. D. Poor, L. Cáseres, M. Akhoondan 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Department of Civil and Environmental Engineering University of South Florida 11. Contract or Grant No. Tampa, FL 33620 BD497 12. Sponsoring Agency Name and Address 13. Type of Report and Period Florida Department of Transportation Covered 605 Suwannee St. MS 30 Final Report Tallahassee, Florida 32399 (850)414-4615 14. Sponsoring Agency Code 15. Supplementary Notes 16. Abstract 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. 17. Key Words 18. Distribution Statement This report is available to the public through the NTIS, Springfield, VA 22161 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of 22. Price Pages 294 DISCLAIMER The opinions, findings, and conclusions expressed in this publication are those of the authors and not necessarily those of the State of Florida Department of Transportation. ii iii EXECUTIVE SUMMARY The Florida Department of Transportation (FDOT) has a large inventory of metallic structural components in direct contact with soil and water, including metallic culvert pipe made of solid and clad aluminum alloy, galvanized steel, or aluminized steel; structural steel piling (both steel shapes and pipe), galvanized tie strips in mechanically stabilized earth (MSE) walls, and buried metals in a variety of additional engineering applications. Corrosion is the most important durability limitation factor in these components, which must operate for long design service lives ranging from decades to100 years and beyond. Premature replacement of buried metallic components damaged by corrosion is costly and reliable means are needed for predicting the corrosion rates of metals in soil and waters. The objective of this project is to develop a rational basis for predicting corrosion rates of structural metals in soil and water service. In addition, the work is intended to develop or confirm practical methods for forecasting, and for the supporting analysis to measure the environmental parameters used as input. Priority areas were selected by concentrating on components and materials with large impact on construction and not addressed by other recently completed investigations. The selected areas were metallic piling and anchors, and metallic drainage pipe. Because of unexpected severe deterioration of aluminized steel drainage pipe in several Florida locations observed in 2005, much of the project effort was focused on the performance of that material in culvert applications. Properties of soil and water that influence corrosion rates of buried metals include temperature, oxygen concentration, resistivity, pH, and scaling tendency; presence of acids, alkalis, and salts; soil particle size distribution, porosity, and water content; and microbial activity. The characteristics of the associated modes of deterioration and needs for improvement of analysis methods were evaluated at the onset of the project. Chloride and sulfate analysis were selected for development of alternative test methods. Resistivity and pH method refinements were addressed as well. Microbial activity was also selected as a new area of environmental characterization. A potentially important factor in corrosion in the field may be the presence of microbiologically-influenced corrosion (MIC). The above field observations and laboratory experiments were examined combined with results of a literature review. It was concluded that carbon steel, stainless steel, galvanized steel and aluminized steel buried in soil or immersed in natural waters are susceptible to localized corrosion due to MIC. Biofilms that develop from microbial activity on metal surfaces in natural waters can promote or inhibit corrosion, however, placement of metal structures or components in polluted or iv stagnant water tends to thicken biofilms and accelerate corrosion. Tests that define soil aggressiveness per this mechanism should include organic matter content and water content to capture the potential for MIC. A review of ca. 2008 FDOT and alternative design guidelines for steel pipe, H-pile, and sheet pilings, ground anchors (tie-backs), and wall anchor bars was conducted. Potential improvements for future versions of the FDOT Structure Design Guidelines include adopting depth-specific corrosion rates for steel pilings to a depth greater than 1 m (3 ft) below the water table; adoption of uniform and pitting corrosion guidelines for ground anchors (tie-backs), and design service life provisions for corrosion control measures in both pilings and anchors. Recent experiences outside Florida of accelerated corrosion in both freshwater and marine environments with high nutrient levels suggest that corrosion rates at the waterline could be in some instances as much as an order of magnitude greater than expected. The operating mechanism is not sufficiently known and awareness of this issue in inspection and monitoring is recommended. Examination of the current durability forecasting methods used by FDOT for galvanized and for clad aluminum pipe, and of alternatives to those methods, did not show compelling evidence for changing procedures at this time. Until recently, the FDOT method to project durability of aluminized steel type 2 was considered to be similarly adequate. However, unexpected corrosion failures of aluminized pipe recently took place in central Florida locations after only a few years of service, much less than the predicted service life. Environmental conditions fell under relatively mild regimes per conventional classifications. Corrosion damage took place mostly at the pipe ribs and seams, which were found to be frequently affected by cuts from manufacturing deficiencies. Under those conditions of large breaks that expose steel, the aluminized coating, which is intended primarily as a barrier, is not expected to produce strong galvanic protection. Field half cell potential measurement results were consistent with that expectation. The service life estimation methods in present use do not have provisions for consideration of the effect of substantial localized aluminized coating damage. The following items in this summary address those issues. A total alkalinity, hardness and CO2 environmental content corrosion prediction method associated with scaling tendency was examined as a possible alternative to the current FDOT pH- and resistivity- based method. The focus on these tests (three model solutions) was on stagnant water conditions and a 300 ppm chloride content, to create a relatively aggressive environment and reveal trends in moderately short test intervals. For unblemished aluminized steel the findings tended to support retaining the present FDOT guidelines for durability forecasting regardless of scaling tendency, at least for environments that approach the low end of the recommended resistivity application range and have neutral to mildly alkaline conditions. In contrast, for blemished surface conditions with significant amounts of exposed base steel and for the same environmental
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