Using seawater in raw water networks exposes the system to three distinct types of damage:
3 SCALE
Corrosion is a result of electrolysis; an electrolytic process that occurs when dissimilar metals are in direct contact, or metals are exposed to oxygen with water present at the surface to serve as electrolyte.
If the water is salty (i.e. “Offshore” seawater), then the electrolytic process is enhanced. A solution of saltwater contains sodium chloride (NaCl), which has more dissolved ions than does a freshwater solution. This allows electrons to move more easily within the solution. In effect, the salt accelerates the electrolytic process by lowering the electrical resistance of water.
Corrosion is the deterioration of the metal alloy through the oxidation in which metal atoms lose electrons, forming ions. The more easily the electrons flow from metallic alloys to the oxygen (in H2O), the quicker the metal deteriorates. Certain metals that spend a lot of time submerged in saltwater (such as those found on marine systems) will deteriorate more quickly than those only exposed to air.
In the maritime industry, metal alloys used in engines, pumps, exhaust systems, and more are constantly submerged in a solution of water, which unavoidably results in electrolysis. Corrosion of the metals in these systems is indicated by the formation of rust on iron and steel or oxidation and pitting of softer alloys such as aluminum or copper.
Compounding the electrolysis issue, biological bacteria found in ocean water also consumes iron, and their excretions turn to rust.
For manufacturers of systems that use seawater for cooling, electrolysis and corrosion are generally accepted as normal, and drive many of the “costs of ownership” for engine systems, climate control systems, and more. For example, on vessels that have a marine “wet exhaust” system, manufacturers recommended replacing mixing elbows, zincs, and pumps and plumbing at routine intervals to maintain proper function. This significantly increases operating costs over the life of a particular engine system.
There are two distinct types of biofouling that occur within raw water networks:
Biofilm is the organic biological material buildup caused by bacteria and algae in seawater in both inshore and offshore waters. This is common occurrence in a vessel’s raw water cooling/circulating networks and is usually a soft growth that can easily be removed at the early onset. It is pervasive and resilient enough to affect the entire raw water network in its early stages but does not impede the operation of the system.
Bio-scale often appears as a buildup of mineral deposits but can also be a buildup of biological material that occurs if biofilm is left unchecked over time. Calcareous algae, Bryozoans and bunch of other reef-building algae build scaley, calcium-containing “exoskeletons” around themselves for protection. They form single-layered sheets which encrust over surfaces. This encrustation provides an ideal substrate for the attachment of barnacles, mussels, and other such nuisances that love to settle and grow in raw water networks. Biofilm and scaling, once started, can compound their growth very rapidly because raw water systems are constantly flowing fresh nutrient and oxygen-rich water over these organisms, promoting perfect conditions for growth.
Over time, the buildup of bio-scale will both restrict water flow and prevent the heat exchanger from being able to pass heat from the combustion into the water, which will cause the engine to run hotter.
Some parts of a vessel’s raw water system are too hot (e.g., heat exchangers) to allow growth and accumulation of biofilm and scale and, as such, are less vulnerable to biofouling. These hot zones are prone to another type of fouling called mineral scale. Seawater is very salty, which includes a high concentration of calcium… mostly in the forms of calcium carbonate and calcium sulfate.
Both of these minerals precipitate from seawater when it is heated to temperatures that exist in heat exchangers. When they precipitate, they form crystals that settle onto and adhere to the interior surfaces of heat exchanger plumbing. Over time, these crystalline colonizers expand to form mineral scale, which can lead to reduced water flow and heat transfer, and higher operating temperatures.
For example, when an engine is turned off and the flow of raw coolant water ceases, the water that is trapped inside the heat exchangers will absorb the remaining heat that is still inside the engine block. As the water absorbs the heat and the temperature rises, the minerals inside the water will precipitate out and adhere to the walls of the heat exchanger as hard deposits. Over time, this buildup will both restrict water flow and prevent the heat exchanger from being able to pass heat from the combustion process into the water. Manufacturers recommend regular service intervals to remove this scale buildup, typically between 500-1000 hours of operation, and specialized technicians, tooling, and parts replacement is typically required
Common practices for flushing raw water networks include chemicals like bleach, vinegar, or acids; however, these do have consequences:
The active ingredient in bleach is a chemical compound called sodium hypochlorite which is a strong base. It acts as an oxidizing agent, ionizing other materials by removing electrons from them. The oxidizing properties of bleach accelerate corrosion on metal alloys, as they lose electrons more readily in the presence of bleach than in plain water. This enhances the electrolytic process and degrades metal components at a more rapid rate.
Vinegar is a dilute form of acetic acid. The positive hydrogen ions in the acid remove electrons from alloy metals, ionizing them and making them more susceptible to corrosion. Vinegar in water also conducts electricity better than water alone, facilitating the movement of electrons and ions during the electrolytic process.
While usually diluted and formulated specifically for use in marine systems, they still degrade softer metal alloys found in mechanical systems… notably aluminum and zinc, which are commonly used throughout many engines.
The use of caustic chemicals to remove scale requires a significant investment of time and effort to perform the task effectively, and it often inflicts damage to the surfaces within the raw water networks through chemical etching. Ironically, with repeated use, it can enhance the potential for and accumulation rate of biofilm, bio-scale, and mineral scale as the surfaces become porous and rough due to the etching. Additionally, the materials used in gaskets, impellers and other components do not tolerate chemical baths very well.
The case can be made that routine flushing with chemical solutions actually INCREASES the frequency and the pain of maintaining raw water networks, and the final result is the same as if no flushing was ever done… with professional technical services and replacement of critical parts.
Surprisingly, chemicals are often not necessary to mitigate scale buildup. A routine PHIBER FWF ensures that any potential for marine growth or scale within systems is thwarted at the earliest stage. Marine organisms in seawater are eliminated at the larval stage thereby preventing attachment and maturation into the destructive adult stage, and if the formation of the biofilm (earliest stage of system biofouling and scale) is prevented, the bio-scale buildup can’t even get started.
The absolute best practice for the maintenance and care of a raw water circuit is regular flushing with fresh water at the end of every run cycle…
Professionally installed PHIBER Systems guarantee a correct Freshwater Flush, proactively preserving critical system components by “pickling” them with fresh water.
PHIBER Systems are engineered to prevent biofouling and mineral scale, and mitigate damage from electrolysis and corrosion.
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