What causes Galvanic corrosion?
Electrolysis is a naturally occurring phenomenon resulting in the corrosion of metal surfaces.
Electrochemical corrosion (electrolysis) is brought about by the flow of ions from negatively charged metals to positively charged metals when they are connected in the same environment. The resulting electromotive force appears as voltage. This voltage is proportional to the flow of the aforementioned ions and its increase directly affects the intensity of the electrolysis phenomenon.
The naturally occurring phenomenon of electrolysis manifests itself in metal structures, bridges, storage tanks and generally in plumbing installations, machinery, engines etc.
What is Cathodic protection?
The various methods of preventing electrolysis are called methods of cathodic protection.
In order to avoid sustaining damages to the installations it is imperative that we apply cathodic protection, which is achieved by placing a mass of active metal in the same environment where corrosion takes place. The primary and most cost effective active metals are zinc, aluminum and magnesium.
One of the most widespread methods involves the immersion in liquid or the insertion in soil of a sacrificial anode, through which certain active metals are placed in the same environment of an electrolytic cell where the phenomenon of electrolysis occurs.
These metallic items made of active metals are called anodes.
The anodes are sacrificed releasing their mass in the form of ions which are transferred towards the less active metallic mass, i.e. the various installations or constructions.
This is the reason why this particular method is called cathodic protection through sacrificial anode.
Its applications include the shipping industry and in general plumbing installations with pipelines containing water.
As far as the shipping industry is concerned, the most common approach is the placement of zinc or aluminum mass on the sides of the ship as well as on any surfaces which come in direct contact with water.
As regards the rest of the cases, a single mass of magnesium is inserted in the soil after being connected to the installation through a cable.
The main disadvantage of this method is the fact that it requires multiple insertion points because of the limited range of cathodic protection it can offer. Another drawback is the residue materials of the sacrificial anode, which are created and subsequently diffused into the pipelines causing damage to the fitting plumbing components. Also the intensity or efficiency of the cathodic protection offered by conventional anodes is not consistent throughout their lifespan. As a matter of fact, it is declining due to the gradual reduction in their mass. Insertion in the soil is not applicable in most installations which remain unprotected.
The other method of cathodic protection uses impressed current current, essentially imposing electrical current on the metals which are subjected to electrolysis, a process which requires an external power source.
This method of impressed current current is more efficient compared to the previous one but it requires network installation and fitting, as well as prior planning and electrochemical field study by specialized personnel. Moreover, the high cost is rather prohibitive for small or medium sized installations. Lastly, constant monitoring by a specially trained technician is required.
What is the solution? STOPCOR Method
The proposed STOPCOR method thereby provides cathodic protection through impressed current current by the sacrificial anode in the self-contained device.
The impressed current current covers and protects wide metal surfaces with much less sacrificed mass of active metal (anode).
The impressed current current is the result of the transfer of ions due to the difference in voltage reference between the magnesium mass and the second electrolytic pole (copper coating).
The current is direct (DC) and compatible with other metals since it is naturally generated.
The negative charging of the protected metals is completely satisfactory, resulting in the surface which used to be anode of galvanic element (i.e. negative oxidizing pole) becoming cathode of electrolytic cell (i.e. negative reducing pole).
The protected surface remains negatively charged but its action is reversed and is now inclined to undergo reduction instead of oxidation.
The impressed current current must be over 0,8 volt but it must not exceed 10mA.
There are several advantages of this device compared to other methods. Here are some of them:
- The device is totally self-contained and does not require an external power source to function.
- It does not require monitoring, maintenance or repair because when the anode mass is exhausted, it simply stops being effective and is discarded.
- It does not pollute the environment.
- It is completely safe.
- It is not affected by weather conditions or any other circumstances.
- It does not come into contact with liquids and if connected to any water supply it does not come into direct contact with drinking water.
- It provides consistent voltage and amperage throughout its lifespan.
- It provides long term protection.
- It is affordable due to low manufacturing costs.
- Fitting it does not require any technical skills whatsoever.
- Any modification, intervention or alteration in the installations where the device is fitted in unnecessary.
- Its cathodic protection is completely compatible with other metals since magnesium is a very active metal whose naturally generated voltage is imposed on all of the other metals.
- It protects extended surfaces compared to other methods available.
It has been observed that several installations present specific challenges as a result of their technical specifications, the nature of the materials inside the pipelines or the composition of the soil in their location. Given these conditions STOPCOR Heater PRO 1&2 and STOPCOR MAX POWER are the ideal solution!
Using this particular method the anodes are capable of providing current density of up to 100 mA per device, thereby increasing the amperage of the impressed current current and providing protection of metal surfaces on a much wider scale. Moreover, the protective action is powerful even in cases of metal surfaces coming in contact with acid fluids.
Depending on the composition of the soil, installations in some areas have been known to absorb part of the impressed current current of anodes. As a result, the voltage of the impressed current current falls below 1 volt.
In order to increase the impressed current current to the appropriate levels we rearrange the configuration of the device sequentially, thereby achieving the desired effect.
As for metal constructions surrounded by water, (i.e. ships) the grounding rod must be immersed in the water. This is achieved by a bar of copper underneath the ship. Although constantly immersed in the water, it is insulated so that there is no conducting contact with the ship’s hull. This bar is the grounding surface of the ship on which all the electrical grounding is attached. Finally, constructions equipped with a closed cooling circuit, (i.e. vehicle engines) grounding is achieved by an electrode component which is fitted on a point of the circuit constantly run by water. This electrode comes with en external pin which is connected to the cathodic protection device on the upper side using a clamping bolt.
This pin goes through the electrode and is inserted in the material while being insulated so as to keep it fixed and ensure the sealing of the closed circuit.
The metal used in the pin is either titanium or niobium in order to avoid oxidation.