PORT MAINTENANCE
One of the most common misconceptions about corrosion protection is that a single solution works for every marine structure.
Why system selection matters Selecting the wrong cathodic protec- tion system can leave vulnerable areas unprotected. For example, many cathodic protec- tion systems rely on seawater as the electrical pathway between the system and the steel reinforced concrete it is trying to protect. During extreme low tides, portions of the structure may no longer be submerged, interrupting the electrolytic path required for current to pass to the steel. Ironically, this often leaves the tidal zone — the area experiencing the greatest oxygen exposure and highest corrosion risk — with reduced protec- tion precisely where it is needed most. A properly engineered system accounts for these environmental con- ditions to provide continuous protec- tion where corrosion is most aggressive. Understanding the four marine exposure zones Concrete piles and marine structures are typically exposed to four distinct environmental zones; each presenting different corrosion risks. Zone 1 – Submerged — The under- water portion of the structure generally corrodes more slowly because dissolved oxygen levels are relatively low. Since oxygen is necessary for the cathodic reaction, corrosion progresses at a reduced rate. Zone 2 – Tidal — This section is alternately submerged and exposed as tides rise and fall. Constant wetting and drying cycles along with high chloride concentrations make this one of the most aggressively corroding areas. Zone 3 – Splash Zone — Frequently regarded as a very vulnerable region of a marine structure, the splash zone experiences intermittent wetting, abundant oxygen, and heavy chloride deposition. These conditions often produce high corrosion rates.
dramatically accelerating the deteriora- tion process. What begins as minor corrosion can quickly become a cycle of increasing structural damage. Breaking the corrosion cycle Producing steel from iron ore requires a significant amount of energy. Corrosion is essentially nature’s way of returning steel to its original, lower- energy state. As steel corrodes, electrons leave the metal. Where those electrons are lost, the steel experiences section loss. Cathodic protection works by sup- plying electrons back to the reinforcing steel, preventing it from sacrificing itself. There are two primary methods: Impressed Current Cathodic Protection (ICCP) This system uses an external power source to deliver protective current to the reinforcing steel or structural steel. Impressed Current Cathodic Protection systems (if maintained properly) can last 50 years or more. The trade-off, however, is that suc- cess depends on diligent maintenance and continuous monitoring. To ensure the ICCP system is performing prop- erly and maintaining protection stan- dards, the enlistment of a NACE (now AMPP) qualified professional is typ- ically required. Galvanic (Sacrificial) Cathodic Protection This approach uses a more active metal anode (such as zinc) that is directly connected to the steel. As the sacrificial anode corrodes, it nat- urally generates the small electrical current needed to protect the steel in the structure. One of the greatest
benefits of this system is its simplicity. Designed as a true “set it and forget it” solution, it requires little — if any — ongoing maintenance and can be monitored from a simple junc- tion box. The trade-off, however, is its finite lifespan. While dependable throughout its service life, the sys- tem is designed to protect the steel for 20-30 years before necessary replace- ment of the anodes. Both ICCP and Galvanic protection systems have proven effective when properly engineered for the application. Every marine environment is different One of the most common miscon- ceptions about corrosion protection is that a single solution works for every marine structure. In reality, no single system is appro- priate for every application. Every port, harbor, and coastal facil- ity presents unique environmental chal- lenges that influence system design. For example: • Alaska may experience tidal ranges exceeding 30-40 feet , creating extensive exposure zones. • Hawaii typically has tidal ranges of only about 1-3 feet . • South Pacific installations must contend with high temperatures and humidity. • Northern Pacific ports may face brackish water, flow-accelerated corrosion, and colder water that contains higher concentrations of dissolved oxygen. These variables significantly affect corrosion rates and determine which protection strategy will provide the best long-term performance.
36 — PACIFIC PORTS — July 2026
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