Experimental Study on Corrosion Performance of A588 Grade A Weathering Steel Material in Marine Environment

A588 Grade A weathering steel is a high strength, low alloy steel that exhibits excellent atmospheric corrosion resistance. It is widely used in various applications such as bridge construction, structural steel, and marine equipment due to its durability and corrosion resistance properties. This study focuses on investigating the corrosion performance of A588 Grade A steel material in a marine environment through experimental analysis.

Experimental Procedure

The experiment was conducted in a marine environment at the B.S. Marine Research Center, Texas A&M University. The test specimens were cut from A588 Grade A weathering steel plates and were exposed to seawater for a period of 12 months. The seawater was collected from Port Aransas near the Gulf of Mexico and had a salinity of approximately 32 parts per thousand.

The specimens were exposed in four different orientations: flat, upright, sloping, and upside down, to represent different exposure conditions. The specimens were also divided into two groups: with and without the presence of biofouling. Biofouling is the accumulation of marine organisms on the surface of the steel, which can accelerate the corrosion process.

The corrosion performance of the specimens was evaluated through the following methods:

1. Weight Loss Measurement

Weight loss measurement was performed at three-month intervals to determine the corrosion rate of the steel. The specimens were weighed before and after exposure to seawater, and the corrosion rate was calculated from the weight loss.

2. Electrochemical Analysis

Electrochemical measurements were carried out using a potentiostat/galvanostat with a three-electrode cell system. The steel specimens acted as the working electrode, a standard saturated calomel electrode (SCE) acted as the reference electrode, and a platinum electrode acted as the counter electrode. The electrochemical parameters measured were open circuit potential, polarization resistance, and corrosion current density. The electrochemical tests were performed at six-month intervals.

3. Surface Analysis

Surface analysis of the specimens was carried out before and after exposure to seawater to determine the morphological changes and extent of corrosion. The surface characterization was performed using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS).

Results and Discussion

The weight loss measurement indicated that the corrosion rate of the A588 Grade A steel in a marine environment ranged from 0.6 to 1.1 mils per year (mpy). The specimens with biofouling had a higher corrosion rate than those without biofouling. The corrosion rate of the specimens was also found to be higher for sloping and upright orientations compared to flat and upside down orientations.

The electrochemical analysis revealed that the open circuit potential of the steel specimens remained stable during the entire exposure period, indicating the presence of an oxide layer on the surface of the steel that provides protection against corrosion. The polarization resistance decreased with exposure time, indicating the formation of corrosion products and the degradation of the protective oxide layer. The corrosion current density increased with exposure time, indicating increased corrosion activity.

The surface analysis showed that the surface of the specimens became rough and pitted after exposure to seawater. The presence of biofouling was observed to accelerate the corrosion process, as it promotes the accumulation of moisture and dissolved oxygen on the surface of the steel. The morphological changes and extent of corrosion observed on the surface of the specimens were consistent with the electrochemical measurements.

Conclusion

The experimental results revealed that A588 Grade A weathering steel exhibits good corrosion resistance in a marine environment. The corrosion rate ranged from 0.6 to 1.1 mpy, which is within the acceptable limit for marine structures. However, the presence of biofouling and certain orientation angles can accelerate the corrosion process.

The results also indicate that electrochemical measurements and surface analysis are effective methods for evaluating the corrosion performance of steel in a marine environment. The combination of these methods provides valuable information on the corrosion mechanism and extent.

The findings of this study have practical implications for the use of A588 Grade A weathering steel in marine structures. The results suggest that the steel can be used with confidence in marine environments, provided that proper maintenance and cleaning protocols are followed to prevent biofouling.