The National Park Service’s (NPS) Submerged Resources Center (SRC) received a FY03 Legacy Grant (Project No. 03-170) for research directed to understanding the nature and rate of natural processes affecting deterioration of USS Arizona in Pearl Harbor, Hawaii. The USS Arizona Long-Term Management Strategies Research Project, conducted in partnership with the USS Arizona Memorial (USAR), is designed to be multi-year, interdisciplinary and cumulative, with each element contributing to developing an overall management strategy designed to: 1) minimize environmental hazard from fuel oil release; and 2) provide basic research necessary to make informed management decisions for long-term preservation. This project has been designed to serve as a model because it will have direct application to preservation and management of other iron and steel historical vessels and to intervention actions for other leaking vessels. The first application of the lessons learned from the work being conducted under this research program is most likely to be applied to Utah, the only other vessel in Pearl Harbor remaining from the 1941 attack.

USS Arizona, a National Historic Landmark (NHL)—the highest level of national historic significance—is among the most recognized and visited war memorials in the nation. USS Arizona became a NPS unit in 1980. Currently, more than 1.5 million people annually visit the USS Arizona Memorial, tomb of more than 900 US sailors and the most visible warship lost in World War II (Figure 1). This ship, a national shrine and Naval memorial that remains deeply ingrained in the American consciousness, still commands an honor guard from the many capital ships that ply Pearl Harbor today, as it did during the war when it served as inspiration to Navy personnel going into battle.

Figure 1. The USS Arizona Memorial, Pearl Harbor, Hawaii.

The Arizona Legacy Project builds upon pioneering site documentation and environmental research conducted by the NPSSRC in the 1980s. The early SRC investigations initiated in situ documentation and study of large, submerged steel warships both here and internationally.

The current project is designed to provide the scientific foundation for long-term preservation and management decisions for this immensely significant site. This Legacy project, which we consider a NPS/Department of Defense partnership, builds upon the research design and fieldwork begun by SRC in 1999. Legacy Grant funding was initially provided in FY02 for what was originally designed as a three-year research project. Because funding was at a level less than requested for FY03, fieldwork and research being reported here for FY03 represents only a portion of the second year in this projected funding cycle.

To make the most cost-effective use of FY03 Legacy funds, SRC provided project principals who have been involved in Arizona research from its beginning, and contributed equivalent matching funds to maximize project results, in effect doubling available funds. We are also accruing significant project savings, as we did in 2002, by partnering with US Naval commands, academic institutions, commercial companies, research laboratories, professional societies and individuals willing to contribute to the research addressing the many multifaceted questions that confront managers responsible for USS Arizona preservation.

The primary project focus is toward developing requisite data for understanding the complex corrosion processes affecting Arizona’s hull, both internally and externally, and modeling and predicting the nature and rate of structural changes. Developing reasonable and effectual management alternatives and determining the most desirable actions, particularly those regarding intervention or rehabilitation, cannot be done without this scientific information.

The current project addresses another critical issue besides preservation of an important national shrine. USS Arizona apparently contains several hundred thousand gallons of Bunker C fuel oil, which has been slowly escaping since its loss in 1941. This oil, a potentially serious environmental hazard, is contained within the corroding hull. Catastrophic oil release, although by all indications not imminent, is ultimately inevitable. Understanding the complex and varied hull corrosion process and modeling structural changes and oil release patterns offers the best method of developing an appropriate, sound management solution to this potential hazard. Because of the particular national importance of Arizona, any solution must incorporate a minimum-impact approach, or long-term site preservation can be seriously compromised. Unnecessary impairment of Arizona’s hull is likely to be seen by many as ultimately more problematic than oil release. Addressing the oil release problem within a site-preservation framework as incorporated within this project provides the best balance of competing social values, and it has the highest probability of success for arriving at the best and most defensible solution for both environmental and preservation issues.

Based on our experience of more than two decades of federal submerged cultural resource management research, this project, as part of a cumulative progression of multidisciplinary steps, will provide the most cost-efficient approach initially, and will provide significant cost savings in future management decisions. Dividends of this approach should also accrue to the many legacy vessels worldwide facing similar combined problems of environmental hazard and site preservation. Successful completion of the Arizona research and its incorporation into action with the most desirable management alternative will provide a model with global application.

Research domains pursued in 2003 continue and expand the original course of research proposed at the outset of this research program. Data from these initiatives are providing a comprehensive picture of Arizona’s current state, and are beginning to project that understanding into the future. A major field project was conducted by NPS-SRC and USAR for three weeks in November 2003, which resulted in new data sets to be incorporated in ongoing research domains.

CORROSION ANALYSIS
Hull Sample (Coupon) Analysis In August 2002, NPS-SRC and USAR partnered with the Naval Facilities Engineering Service Center-Ocean Construction Division, the Navy’s Mobile Diving and Salvage Unit One and Titan Maritime Industries, Inc. to collect external hull plate samples ("coupons") from USS Arizona for electrochemical, microbiological, metallurgical and metallographic analyses. A total of eight samples were collected, four from the port side and four from the starboard side, in vertical transects from just below the upper deck to below the mudline. After removing samples, the holes were plugged, and each area but one was sealed with a pH-neutral epoxy to inhibit corrosion cell formation. The single area not completely sealed with anti-corrosion epoxy covered the surrounding metal but left the plug accessible so interior water samples could be removed should they be necessary for future analyses.

Coupons were initially sent to Rail Sciences, Inc. (RSI) Materials Engineering in Omaha, Nebraska, where Dr. Don Johnson and Dr. John Makinson made detailed thickness measurements around the circumference of each coupon under laboratory conditions. They removed a small "chord" from each sample for optical measurement of plate thickness and metallographic examination (Figure 2). This precise thickness measurement was compared to original hull thickness in each location, and a corrosion rate for that location determined. Assuming a consistent corrosion rate since Arizona’s loss, the corrosion rates varied from 1.1 to 6.0 mils per year (1 mil = one thousandth of an inch). The fastest corrosion rates were obtained from the top of the hull near the surface where there is the highest level of dissolved oxygen and water movement. These hull corrosion rates can be compared to the laboratory-determined corrosion rate of unprotected mild steel, which is 4.5 mils per year. A combination of environmental variables and concretion formation are believed to account for the observed variation, a hypothesis under investigation.

Figure 2. Hull "coupon" with interior and exterior concretion. Note the "chord" cut from the steel sample on left.

After completing analysis at RSI, coupons were transferred to Dr. Tim Foecke at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, for additional metallographic and metallurgical testing. This analysis is on-going and will continue in FY04.

Concretion Resistivity and Density Measurements
During FY03, experimental work continued at University of Nebraska—Lincoln using concretion samples from USS Arizona provided by NPS. In addition to Legacy funds, a University of Nebraska Foundation grant supported this research. Dr. Brent Wilson and Mr. Matthew Dick conducted experiments measuring electrical resistivity and resistance of concretion to determine whether a correlation exists between those parameters and corrosion rate of in situ hull steel. In addition, experiments were made to measure concretion density and to determine its affect on observed hull corrosion rates. In November 2003, Dr. Don Johnson conducted more accurate field density measurements at the USS Arizona Memorial on concretion samples as they came out of the water. Analysis is on-going to establish a relationship between these parameters and steel corrosion rates on Arizona. These data will be compared with those of other researchers, including those at the Western Australian Maritime Museum.

In Situ Hull Corrosion Measurments
Immediately prior to removing hull coupons in August 2002, NPS archeologists measured corrosion potential (Ecorr) and pH in each coupon sample location. Using the same procedure as in past field operations, SRC archeologists drilled through the concretion in proximity to the sample area measuring pH and Ecorr at various concretion-depths. Hole depths were controlled by several depth jigs to provide uniform data. Ecorr and pH instruments were connected to the surface by cables; the topside recorder had voice communication with the diver (Figure 3). We have found this method to produce the most consistent, reproducible results for these measurements. Immediate review by topside researchers allows anomalies or errors to be discovered and measurements retaken to ensure accuracy.

The 2002 sample locations were revisited in November 2003 to once again collect Ecorr and pH data. This replication allows researchers to gauge the impact to the ship of removing the hull coupons and surrounding encrustation. Data collected were comparable to 2002 data from the same locations, indicating no negative impact to the ship resulted from coupon removal, and that the epoxy sealing had succeeded in preventing formation of local areas of increased corrosion during the year since coupon collection.

Ultrasonic Thickness Testing
One goal of November 2003 fieldwork was to test nondestructive hull thickness measurement techniques. Because precise hull thickness is known in the location of each of the eight hull coupons, those locations were selected for ultrasonic thickness (UST) instrument testing. In December 2001, NPS-SRC tested a diver-deployed Cygnus 1 Underwater Multiple Echo Ultrasonic Digital Thickness Gauge on Arizona’s hull. This instrument proved to be unreliable (consistent, reproducible readings were unobtainable), even with significant surface preparation. For 2003 fieldwork, another instrument was tested. Dr. Art Leach from Krautkramer Ultrasonic Systems recommended their DMS 2 A-Scan Digital Thickness Gauge, and arranged for Mr. Jay Schraan from Inspection Technologies of Pomona, California, a Krautkramer dealer, to demonstrate their technology on Arizona. In October 2003, before beginning fieldwork in Hawaii, Dr. Leach visited NIST in  Gaithersburg, Maryland, to calibrate the  instrument on the hull coupons collected from Arizona in August 2002. This direct calibration with Arizona plate material allowed precise speed-of-sound measurements to be made from actual hull steel taken from the in situ locations to be tested. During field operations in November 2003, Jay Schraan arrived on site with the Krautkramer instrument. Our methodology was to revisit the sites of the six above-mudline hull coupons collected in August 2002. Because we know the exact hull thickness at each of these locations based on measurements made by Dr. Don Johnson and Dr. John Makinson, these locations made ideal test sites for the UST instrument.

During UST operations, NPS researchers worked underwater to prepare the hull’s surface and deploy the probe, while Dr. Johnson and Mr. Schraan worked topside with the instrument’s user interface (Figures 4 and 5). Surface preparation on the ship involved removing the outer encrustation and using a pneumatic grinding wheel to flatten the surface. We could not get reliable readings on the unprepared hull surface, which is mildly pitted from corrosion. Even on locations where we employed significant surface preparation, grinding the hull steel until it was shiny and smooth, the readings were not always consistent—sometimes they were accurate and other times not. For future operations in areas where the hull thickness is not already known, there would be too much doubt in the final results to be useable.

Figure 4. November 2003 topside ultrasonic thickness operations.

Figure 5. Deploying the ultrasonic thickness probe on Arizona’s hull.

Dr. Leach and Mr. Schraan have expressed interest in working with NPS to experiment with ways to refine their instrument to make it more reliable on Arizona’s hull. If this instrument can be refined, it would find more wide-spread application in shallow sites and, when deployed on a ROV, in difficult access or deep sites. In addition to this opportunity, NPS-SRC and USAR will pursue other potential avenues of nondestructive thickness measurements using different technologies. Nondestructive testing is a key component of future research, necessary to determine if hull corrosion rates observed at the locations of hull coupons removed in August 2002 are consistent across the exposed, outer surfaces of the hull. Ideally, the appropriate technology will be deployable on a small ROV so internal measurements can be obtained.

Summary
Corrosion potential, pH and hull thickness data from in situ measurements were analyzed to determine the average annual corrosion rate of the submerged hull at selected sites, port and starboard, from the hull top to beneath the mudline. Based on preliminary data, corrosion rates are highest near the hull top (near the current waterline) and decrease to the lowest rates just below the mudline. Limited data at about 1½ meters below the mudline indicate that the Tafel constant is higher below the mudline than above it, indicating that oxygen availability is lower into the mud. Assuming limiting current, oxygen diffusivity in the concretion is somewhat higher than that reported for oxygen in sea water.  Attenuation of the corrosion rate as a result of reduced oxygen availability across the concretion is confirmed based on voltage drop and knowledge of concretion resistivity from literature sources. X-Ray diffraction analysis of the concretion reveals that the major species is siderite (FeCO₃) with lower amounts of magnetite (Fe3O4) and calcite (CaCO3). Presence of siderite and magnetite are consistent with corrosion potential/pH data superimposed on stability fields in the H2O, Fe and CO2 Pourbaix diagram. Chemistry and structural observations using scanning electron microscope imaging and electron dispersive spectroscopy element identification yield variable iron and calcium gradients across the concretion. Based on these analyses, the iron content of the concretion does not account for all of the iron lost from the hull. The balance may be lost to open sea water during the initial stages of corrosion and concretion formation. In addition, direct in situ observations confirm that iron may remain trapped in low pH solution in gaps between the hull plate and concretion. Assessment of corrosion and bacterial activity below the mudline and interior spaces continues, and they will be a focus in FY04 (Makinson et al. 2002; Johnson et al. 2003).

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