Category Marine Engineering Tech

The Protection of Modern Metal


Cathodic Protection


While metals are always vulnerable to corrosion and degradation when left unprotected and exposed to the elements, they face particular risk when left exposed for long periods of time underwater. Companies making use of steel and other metals for applications that involve long-term submersion have developed techniques to fight off metal corrosion using a process known as Cathodic Protection (CP). This treatment of metals is most commonly seen in manufacturing processes that involve producing metals for applications that include piping, shipbuilding, production of concrete-embedded steel, and various marine applications.


Applying Cathodic Protection to any metal involves an electrochemical process. The metal surface of the product is altered by making the actual exposed surface the cathode of an electrochemical cell. The corrosion protection comes into play thanks to the creation of an added layer of protection that this process induces. The protective layer that is created is actually more susceptible to corrosion, allowing it to act as an anode or “sacrificial metal” that guards the primary metal surface of the product. While it may sound as if this complicated process would be reserved for advanced metals that are only involved in expansive construction projects, this technique is present in homes and small projects all over the world.


Galvanized steel is generally protected using this process. The steel is given a coating of sacrificial zinc that corrodes more easily in order to protect the structural integrity of the steel itself. The CP process is also commonly used to protect metals that are used to produce water heaters in homes and storage tanks on small properties that are used to contain petroleum or natural gases. Projects that require industrial-level production for this treatment in order to ensure the long-term safety of their applications include off-shore oil rigs and reinforced concrete in large-scale buildings and housing developments. Steel and other metals that are put under strain for extended periods of time while exposed to harsh elements have been known to suffer from stress corrosion cracking when this type of protection is not put into place.


The actual anodes and sacrificial metals that are used in the practice can vary based on the project, the conditions where the metal will be used, and the underlying metal that requires protection. Among the most common anodes are zinc, aluminum, platinum, and carbon. The anodes are also designed to increase the efficiency and performance of the metal based on the given application as well. For instance, galvanic anodes are the most common solution for fighting corrosion on ships thanks to its flexibility in regard to shape and production standards. It can be outfitted to provide corrosion protection while also minimizing the drag produced by its interaction with moving water.


Applying CP protection to metal surfaces is typically done after the metal itself has been shaped and fabricated. However, the process varies slightly when it comes to protecting steel that is embedded in concrete. In these instances, the protective technology is applied at the time of manufacturing, being embedded in the concrete along with the metal itself. It is also possible for cathodic protection to be applied to the interior of metal products as well. These strategies are most often used when constructing pipelines that transport hazardous materials or when constructing storage containers for water, including conventional water heaters.


The process was first refined using iron and copper sheathing on the bottom of boats and large vessels. However, the rudimentary technology first resulted in the increased growth of marine life, posing a completely different problem for engineers. The incorporation of an electric current and the allotment of outer corrosion soon proved to be effective on all fronts, quickly leading to the cathodic protection methods that we use today. Go to for more information on this indispensable technology used in modern metals.

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CAPAC Impressed Current System

It is somewhat disconcerting to think that the metallic structures produced through modern refining processes are not as indestructible as they appear to be. From behemoth ship propellors to giant wind turbines, the one thing these and many other submerged or buried metallic structures have in common is their susceptibility to the destructive effects of corrosion. CAPAC systems, or impressed cathodic protection systems, are what the Marine and Offshore Oil & Gas and Civil Industries rely on to preserve their multimillion dollar assets.


Using Energy to Save Energy

While industrial coatings are an absolute neccessity in the protection of structures that are exposed to the elements, cathodic protection (CP) is a secondary technique to control corrosion. Operating on the basis of how these substrates are manufactured, CP uses electrical DC current to stop the corrosion reaction from occurring. With very few exceptions, a great deal of energy goes into the refining of metals. The corrosion reaction is simply nature’s way of taking that energy back. This exchange is evidenced in the formation of rust or iron oxide.


Global Impact

Oxidation is responsible for more deterioration of unprotected surfaces on a scale that is estimated between 3-5 percent of the gross national product (GNP) of all industrialized nations as reflected here – In actual cost, that equates to an average of $300 billion annually. Applying the electrochemical process of Cathodic Protection is a way to save at least a third of this economic hit.


The Electrochemical Process

Creating an electrical current to flow from a rectifier through a cabling system to anodes, which may include junction boxes, the anodes will discharge the current as it is coming off the structures and the flow continues through the cabling system back to the rectifier. Structures that are buried or submerged are exposed to electrolytes. Soil, water and sea water all act as an electrolytic channel for this process of corrosion that occurs as energy is pulled from the substrates.

The Anode Systems

There are two basic anode systems:

  • Galvanic or sacrificial anodes
  • Impressed current anodes that use an external power supply


Sacrificial Anodes

Sacrificial Anodes




Impressed Current Anode

Impressed Current Anode



Designing CAPAC Systems calls for a thorough analysis of the geometric structures to be protected contemplating their bare surface area and the quality and type of coated areas as well as gaining an understanding of the metallurgy and determining the electrical continuity of the structure. Then the site and its environment are evaluated in order to calculate the current and density that will be required. After that, the anode selection can be made. The determining factors are anode length and electrolyte resistance. A full range of anodes are manufactured in strict accordance with NACE and ASTM standards.


Industrial Engineering Services

Whether building new projects, deploying to high seas, offshore or land-based industrial sites, for technical sales, new systems engineering or a host of other engineering services, turn to for Cathodic Protection (CP), Marine Growth Prevention Systems (MGPS) and their Engineering and Fabrication works.


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Cathodic Protection Systems

Within the realm of engineering, Cathodic Protection Systems are extremely important. These systems are specifically designed to protect underground storage tanks from corrosion. Such protection is essential because many of these tanks often contain harmful materials. There are two types of Cathodic Protection Systems that are allowed to be installed: Sacrificial Anodes and Impressed Current.

Impressed Current Cathodic Protection

Sacrificial anodes are metal attachments that contain a greater electric charge than the metal of the underground storage tank. This greater electrical charge allows the corrosive effect to be deposited onto the anodes and away from the underground storage tank. Once the sacrificial anodes are corroded they have to be replaced.

Impressed current systems are used as the preferred way to protect larger underground tanks that are too big to be protected using a sacrificial system. Impressed current systems work by connecting anodes to DC power from a nearby AC system using a rectifier. Impressed current systems work by directing the current into metal bars buried in the ground via an insulated wire. The current prevents the system from becoming corroded via the current.

Once installed Cathodic protection systems must be inspected by a qualified inspector. Additionally, systems have to be carefully maintained and inspections are conducted every few years. The proper maintenance of these systems guarantees that erosion does not occur (also see Advanced Water Treatment Systems for Large Boats).

All Underground tank systems are required to have one of the aforementioned anti-corrosion systems. Various engineering services can install this type of system. Environmental agencies are adamant that such systems greatly reduce pollution by preventing harmful materials from entering the air and the ground. The absence of such a system or the failure of an anti-corrosion system could prove disastrous.

Cathodic Systems play an important role in ensuring the safety of underground tank systems. In the years to come it is likely that new and innovative systems will be developed for cathodic systems. For additional information on these systems is an excellent and informative resource. Engineering Services Engineering Services


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