Maintaining Electronic Connections and Eliminating Corrosion in Marine Applications
How Metals Rust
Not all metals rust. For example, aluminum doesn’t rust because it has a protective layer of aluminum oxide on its surface. This stops the metal coming into direct contact with water (or moisture in the air) and oxygen. On the other hand, iron rusts because it forms hydrated iron oxide when it comes into contact with water (or moisture in the air) and oxygen.
Rusting cannot occur without both water and oxygen. Water helps iron react with oxygen by breaking up the oxygen molecule. During the initial stages of rusting, iron loses electrons and oxygen gains electrons. Ferrous and ferric ions then react with water to form ferrous hydroxide, ferric hydroxide and hydrogen. The hydroxides lose their water to make even more iron compounds. The sum of all these chemical reactions makes the rust flake, so it falls off the iron and exposes new iron, which can then also begin to rust.
Iron oxide, a reddish-brown compound, is normally referred to as rust. It forms when iron and oxygen react in water or in moisture in the air. The reaction of iron and chloride underwater is also referred to as rust. Certain factors speed up the rusting process, such as salt in the water.
Rusting is a common form of corrosion, which occurs when metal atoms react with their environment. Salt water does not make a metal rust, but it accelerates the rusting process because electrons move more easily in salt water than they do in pure water.
Salt Water vs. Fresh Water
Current flows more easily in salt water than it does in fresh water. This is because salt water, an electrolyte solution, contains more dissolved ions than fresh water, meaning electrons can move more easily. Since rusting is all about the movement of electrons, iron rusts more quickly in salt water than it does in fresh water. Certain metal objects that spend a lot of time submerged in salt water, such as boat engines, rust quickly. However, objects do not have to be completely submerged in salt water for this to happen because increased moisture in the air and salt spray can provide the electrolyte’s cation (positive ions) and anions (negative ions).
Fundamentals of Corrosion
This is what is needed for corrosion to grow. Corrosion triangle 1- Metal
2-An oxidizer (Oxygen In the air) 3-Moisture or some other chemical. Dissimilar metals create a current to grow the corrosion. Corrosion products have a greater volume than the base metal. This greater volume is what pushes the electrical connector pins apart causing intermittent electrical signals. At the microscopic level the contacts are not smooth with full area contact. Current flows mostly between the peaks. The oxide or salt corrosion products become like the ore from which the metal was made. To mitigate contact corrosion, one of the corrosion pillars would need to be eliminated.
Moisture forms a conductive circuit in pores through which electrons pass between the dissimilar metals causing corrosion. Generally, electroplated or hot dipped coatings that are completely free of pores and other discontinuities are not commercially feasible. Contact cleaners do not remove corrosion. They only remove, grease, oil and dirt. Most aircraft maintenance manuals say to use alcohol and a brush to clean connectors, but alcohol does not remove corrosion. Pits eventually form at coating flaws, and the coating is penetrated. Pits where corrosion starts are so small you need 20X power to see them.
All water treatment facilities, be it drinking water, waste water reclamation or desalinization plants, experience problems with electronics unique to the industry. All of the meters and sensors, data connections, and communication lines utilize low voltage to send their signals. When a connector, switch or relay becomes compromised, these signals are susceptible to becoming distorted with micro signal rate fluctuations that lead to excess heat, false data, cascade failures and the unneeded expense of replacing cables, connectors and other equipment.
These problems are the result of corrosion. Corrosion exists when three things are present: (i) metal; (ii) an oxidizer (oxygen in the air); and (iii) moisture or other chemicals. Dissimilar metals in connections create a current that actually helps to grow the corrosion. Treatment facilities have more of these contributing factors than most environments – water and/or water vapor, salts or other chemicals such as sulfur or methane involved, will deteriorate metals through corrosion.
Corrosion on surfaces increases the volume of the base metal. This extra volume can push electrical connector pins apart causing intermittencies in the signal. Likewise, at the microscopic level, metal contact surfaces are not smooth with full area contact. Rather, signals/current flow mainly between the peaks on the surface. Excess corrosion can prevent the needed contact between the metals and distort or eliminate connectivity.
For example, consider the supervisory control and data acquisition (SCADA) systems used to control and monitor the various processes locally and at remote locations throughout a plant. These systems are crucial to plant operation as they monitor, gather, and process real-time data and directly interact with sensors, valves, pumps, and more.
The key to maintaining and maximizing electronic connections is to ensure that it is clean and free from corrosion down to the microscopic level. Even if the metals look clean, corrosion may still be present and in a low voltage application, a little corrosion goes a long way. Most contact cleaners are comprised of a volatile chemical designed to evaporate quickly such as methanol, or ethyl- or isopropyl alcohol. Such cleaners simply evaporate too quickly to eliminate the corrosion at the microscopic roots where it is adhered to the metals.
The ideal solution is to use an oil-based contact cleaner that will remain on the part to eliminate even the slightest bit of corrosion. Be sure that it is not an alcohol based cleaner with a lubricant added as the cleaning properties will vanish quickly leaving only a lubricant. One such oil-based cleaner is the DeoxIT® D-Series from CAIG Laboratories. This product is generally safe on most materials and will eliminate oxidation down to the microscopic level. The DeoxIT will also lubricate and protect the metals insuring the highest possibly conductivity and signal rates.
Apply the DeoxIT or other oil-based contact cleaner wherever you are experiencing signal degradation. This includes edge connectors, DIMM sockets, A/V and RF connections, transducers, flow meters, door switches, and basically anywhere where a signal needs to travel through connectors. By taking this simple step, oxidation corrosion will be eliminated, connectivity will be increased, and equipment life will be extended.
Several treatment facilities are already using DeoxIT D Series products with excellent results. According to one engineer at a municipal treatment facility, it was the first time in his many years that all green lights appeared on the SCADA board. A little electronic maintenance will save headaches and money down the road.