A variety of solutions exist for countering corrosion in the marine environment.
Choosing a solution requires first a thorough understanding of the corrosion issues facing a particular facility, structure, or vessel. Assessing corrosion normally is accomplished by conducting a comprehensive on-site inspection, which generally includes:
- Carefully examining the facility, structure, or vessel
- Reviewing any available construction blueprints or prior inspections reports
- Evaluating the local environmental conditions
- Checking current and tidal data
- Analyzing the water to determine electrical conductivity (Conductivity is affected by salinity, mineral and impurity content, and temperature.)
A thorough inspection will be followed by a detailed report encompassing inspection data, digital photographs, digital video, and test instrument readings (as relevant). Based upon the inspection findings, detailed recommendations for the corrosion-control of the facility will be provided.
Galvanic corrosion often warrants cathodic protection (CP). CP in the marine environment is accomplished by two widely used methods:
- A sacrificial-anode system involves coupling a structure or vessel with a more-active metal, such as zinc, aluminum, or magnesium. This produces a galvanic cell in which the active metal (e.g., the zinc, aluminum, or magnesium) is the anode and the structure is the cathode. The active-metal anode provides a flux of electrons to the structure (cathode), protecting the structure, while the anode is sacrificed (progressively consumed).
- With an impressed-current system, a low-voltage, powered direct current (DC) is impressed between an anode and the structure (cathode). Electrons flow from the inert anode to the structure, protecting it from degradation.
Sacrificial-Anode Systems vs. Impressed-Current Systems
Sacrificial-anode systems are simpler than impressed current systems, requiring only direct contact between the anode and the structure. However, sacrificial systems require greater quantities of anodes placed at disperse locations. These simple systems cannot be tuned, meaning that inevitable (and intended) consumption of anodes significantly reduces the system's output over time.
Impressed-current systems, while more complex, are generally more effective since they allow for fewer anodes to be more widely distributed. Higher voltages found in impressed-current systems also are useful in low-conductive environments, such as freshwater and brackish water, where sacrificial anodes have reduced driving electrical current.
Marine Coatings and Encapsulations
Corrosion in a marine environment is most severe in the tidal zone or “splash zone” (the air/water interface), and special attention must be paid to this area. Cathodic protection systems are only effective when this area is immersed. Consequently, in the splash zone protective coatings or encapsulations – in addition to cathodic protection system – are warranted.
Substructure has researched, developed, field-tested, and installed hundreds of different types of corrosion control products and techniques, enabling us to provide corrosion assessment and solution advice based on knowledge and field experience.
Don’t Wait to Install a Corrosion-Control System
Effectively designed and installed corrosion-control systems can prevent corrosion of a new structure or can stop corrosion of an existing structure. Replacement of structural metal already lost to corrosion is incredibly expensive. Permitting a corrosion problem to continue unchecked can have very costly results.