Duluth-Superior Harbor Corrosion

Updates

Randall E. Hicks, Professor Department of Biology 1035 Kirby Drive, SSB 207 University of Minnesota Duluth Duluth, MN 55812

Using a community DNA fingerprinting method called T-RFLP, we demonstrated that bacterial communities on corroded steel sheet pilings in the most affected part of this harbor are different from bacterial communities on these structures at a less affected area just outside the harbor. Siderooxidans lithoautotrophicus, a microaerophilic chemotrophic bacterium that oxidizes Fe2+ to Fe3+, was repeatedly isolated from the corroding structures (Fig. 1). Sequencing the 16S rDNA gene of bacterial clones indicated that the majority of bacteria on the surfaces of steel pilings at the corroded sites examined were from three bacterial phyla, the β- and α- Proteobacteria, and Cyanobacteria. This clonal analysis also indicated the presence of a bacterium most similar to an iron-reducing bacterium (Rhodoferax ferrireducens), which can grow well at the low temperatures (4°C) seasonally encountered in this harbor.

It is clear that corroding steel structures in the DSH are covered by complex microbial biofilms that contain bacteria of the type responsible for corrosion of steel in other environments (Fig. 2). While data from the field research lead us to suspect that MIC may be responsible for the accelerated corrosion seen in this harbor, they do not provide conclusive evidence that S. lithoautotrophicus nor any other bacterium isolated or found in the clone library so far are responsible for this corrosion. Thus, while we continue to examine microbial communities attached to corroded structures in this harbor, we are now also investigating the development of corrosion on experimental steel coupons in the laboratory and placed in the harbor (Fig. 3). We hope results from these new studies will conclusively demonstrate if the metabolism of microbial biofilms attached to these steel structures is accelerating the corrosion of the sheet steel material in the DSH.

We are collaborating with scientists and engineers from the Duluth Seaway Port Authority, AMI Consulting Engineers, the U.S. Naval Research Laboratory-Stennis Space Center, and the U.S. Army Corps of Engineers on this project. Research grants from the Duluth Seaway Port Authority, the UM Center for Urban and Regional Affairs, the Great Lakes Maritime Research Institute, and the Minnesota Sea Grant Program have supported our research.

Fig. 1. Iron-oxidizing bacteria. (A) FeS gradient culture tubes inoculated with corrosion materials from Hallett Dock 5 collected on Sept. 14, 2006. (B) Photomicrograph of Siderooxidans lithoautotrophicus isolated by Emerson and Moyer (1997). (C) Photomicrograph of bacterial cells in the tube 2 band in panel A, whose 16S rDNA is 96% similar to S. lithoautotrophicus.

Fig. 2. Light photomicrographs of corrosion tubercle materials from the Duluth-Superior harbor. Note filamentous algae (A) and bacteria (blue color) on the surface of orange corrosion products (B). [photomicrographs by R. E. Hicks/UMD]

Fig. 2. Light photomicrographs of corrosion tubercle materials from the Duluth-Superior harbor. Note filamentous algae (A) and bacteria (blue color) on the surface of orange corrosion products (B). [photomicrographs by R. E. Hicks/UMD]

2007 Project Field Investigations
The majority of field work completed in 2007 consisted of collecting existing coupons from the trays installed in 2006 and the installation of eight new trays. Several coupon samples were collected from the Hallet Dock coupon tray (installed in 2006), visually inspected and then sent to labs for further corrosion project analyses (see new “Project Photos”). In addition, eight new trays were installed in the fall of 2007, each which contained four uncoated and four coated coupons each. The work was completed by AMI Consulting and summarized in their project report “ACOE SAMPLE TRAY INSTALLATION”. This study is being completed to collect field data from both bare steel and coated steel samples. The bare steel samples will be evaluated for actual corrosion process information and the coated samples will investigate how several different types of protective coatings work under the actual harbor corrosion and ice conditions.

Project Databases
Updated project summary databases were prepared which included all data collected with respect to harbor water quality samples and existing structure details. Both databases are in Excel format and include both recent collected data as well as any historical data the project team has assembled which would be relevant to the harbor corrosion studies. Both databases are included in the “Documents” section of the project web pages.

Project Photos
New Duluth/Superior corrosion photos as well as photos of several other Great Lakes harbors and marinas with observed corrosion issues have also been added to the “Project Photos” web pages. The Duluth/Superior harbor corrosion photos where taken during the extremely low Lake Superior water levels and clearly show the extent of corrosion damage at several locations in the harbor. The photos of other Great lakes locations also show examples were steel corrosion has also been visually noted but not diver inspected. While the causes for these structure issues at other Great Lakes locations may or may not be directly related to the accelerated corrosion seen at the Duluth/Superior harbor, the pictures point out that our study results could be extremely useful for rehabilitation projects elsewhere throughout the Great Lakes region.

2008 Investigations To Begin
With $410,000 of new project funding from the state of Wisconsin and the federal Water Resources development Act, several new or continuation of existing tests are expected to begin starting June 2008. The following tasks are planned:

1. Additional Coupon Sample Collection
   Investigation will focus on the continued collection of coupons from several coupon trays already in place throughout the harbor. Both uncoated and coated coupons will be removed for inspection and additional lab tests.
2. Linear Polarization Tests
   Linear polarization testing (LPR) will be conducted for 12 to 14 locations (minimum of two cycles each) to estimate instantaneous corrosion rates at different locations throughout the harbor.
3. DC Current Tests
   A high voltage DC current test will be conducted with measurements taken at 8 locations in the harbor. This test will investigate the possible effects of the high voltage DC power line which terminates in the region.
4. Hydro Coating Tests
   This test will investigate a new technology using diver applied coatings to existing underwater steel structures. This technology could eliminate the need for the traditional cofferdams used to dewater the sheets before coatings could be applied in the dry.
5. In Place Coating Tests - Ice Zone Focus
   This small scale test would place one or more coated steel sheets to test how the coatings stand up to the severe ice action in the harbor.
6. In Place Coating Tests - Review of Existing Coatings In Place
   Study will document coating history and include diver inspections of the existing coated sheets already in place throughout the harbor. These coated steel structures were placed before the current corrosion study was initiated and evaluation of these locations will serve as companion tests to our new coating trials.
7. In Place Coating Tests - New Coated Sheets
   This study will include full scale testing of coating existing steel structures at Superior Entry and also at possible Harbor Assistance Grant locations. This work will test the applicability of the use of cofferdams as a base case method for cleaning and coating existing steel already in place but not damaged beyond repair.
8. Perforated Dock Repair Tests
   This investigation will test possible repair methods for structures that have corrosion so severe that it has already have perforated the steel.
9. Alternative technology Tests
   These investigations will explore many alternative corrosion control methods. Anticipated methods which will be tested include but not be limited to: wraps and jackets for pile structures, jackets and plates for sheet pile structures and anodes for both types of structures.
10. Additional Coupon Trays
    Additional coupon trays may be added at new harbor locations such as upstream in the Nemadji River and at the upstream dam in the St Louis River.
11. Continued Bulk Chemistry Tests
    Additional bulk water chemistry samples and associated testing may be added to compare changes of water chemistry with those samples collected in 2006.
12. Continued MIC Testing
    Microbiologically Influenced Corrosion (MIC) testing will continue to investigate the role MIC may have in the accelerated corrosion process.

The “Final Report – Duluth Corrosion Investigation – Duluth Harbor” report was prepared by Altech Environmental Services, INC and includes field data on the entire harbor water quality sampling results (a total of 27 Federal and 17 non-Federal locations) as well as data collected to document the existing conditions of 27 Federal monitoring locations throughout the harbor. The water quality data collected included sampling at several different depths and sampled parameters such as PH, dissolved oxygen, conductivity, temperature, alkalinity, chloride ions, sulfate ions, total suspended solids, hardness and total iron. The corrosion measurements were completed by non-destructive methods and typical details collected included overall plate thickness, corrosion pit depth and pit diameter measurements, a qualitative indication of corrosion rating and many photographs.

The “DSPA Corrosion Investigation Report” was prepared by AMI Consulting Engineers P.A. and focused on investigating the non-Federal structures. This portion of the total suite of 2006 field work collected corrosion condition data on a total of 22 non-Federal locations, including field data collected at Two Harbors, MN. In addition to the corrosion measurements similar to those completed for the Federal structures, this report also contains the results of several additional studies that were completed. These studies include additional water quality data collected using a Quanta Probe at each investigation location measuring depth, PH, dissolved oxygen, conductivity, turbidity, temperature, oxygen reduction potential and salinity (at a few selected sites). Also collected were linear polarization resistance (LPR) measurements and the installation of sample coupon trays. The LPR measurements were short term measurements which could be extrapolated to estimate longer term corrosion rates. The sample coupon tray installations were completed at six different locations and consisted of a coupon tray at each location each containing eight “coupons” or plates of new steel which were carefully weighed before placement and could then be collected at different intervals to measure corrosion product details and to collect biological samples for culturing and DNA testing.

Both reports contain detailed data summaries, structure condition photographs and the results of these first phases of the Duluth-Superior corrosion studies. These reports are also now being used to scope the additional field work planned for 2007 and beyond.

In addition to the three specific studies currently being scoped, with additional funding the steering committee will initiate a series of coating tests to evaluate the use of various types of protective coatings to protect the steel from corrosion.