Metals (including alloys) can be arranged in a galvanic series that represents the potential they develop in a given electrolyte against a reference standard electrode. The relative position of the two metals in this series gives a good indication of which metal of the pair is most likely to corrode most rapidly. However, other factors such as aeration and water flow can significantly influence the process.

Galvanic corrosion is of great interest to the marine industry. Tables with galvanic series of metals in seawater are very common, due to the wide use of metal in shipbuilding. It is possible that corrosion of the silver solder in a saltwater pipe could have caused a failure that led to the sinking of the USS Thresher and the death of all its crew.

The common technique of cleaning silver by immersing it and a piece of aluminum foil in a bath of salt water (usually baking soda) is another example of galvanic corrosion. Care must be taken, as using this technique will clean the silver oxide that could be there as decoration. It is also not advisable to clean gold-plated silver objects in this way as it can introduce unwanted galvanic corrosion into the base metal.

There are several ways to reduce and prevent this type of corrosion.[2]​.

This is common in water heaters and boiler hot water tanks. Lack of regularity in replacing sacrificial anodes in water heaters severely decreases tank life. Substances to correct water hardness (water softeners) tend to degrade sacrificial anodes and tanks more quickly.

For example, let's consider a system composed of 316 stainless steel (a 300 series stainless steel, it is a very noble alloy which means it is quite resistant to corrosion and has a high potential), and a mild steel (a very active metal with lower potential). Mild steel") will corrode in the presence of an electrolyte, such as salt water. If a sacrificial anode is used (such as a zinc alloy, aluminum or magnesium alloy), these anodes will corrode, protecting the other metals. This is a common practice in the maritime industry to protect ship equipment. Ships and ships that are in contact with salt water use either zinc or aluminum alloys. If the ships are only in fresh water, a magnesium alloy. Magnesium has one of the highest galvanic potentials of all metals. If used in an installation exposed to salt water, such as on a steel or aluminum boat hull, hydrogen bubbles forming under the paint will cause blistering and peeling.

Metal boats connected to a shore power line typically have to have their hulls grounded for safety reasons. However, the end of the ground connection is likely to be a copper rod buried in the marina, resulting in a steel-copper "battery" of around 1.1 V. In such cases, the use of a galvanic isolator is essential - typically 2 diodes in series, to prevent any current flow, as long as the applied voltage is less than 1.4 V (i.e. 0.7 V per diode), but allowing full flow in the event of a ground fault. It has been noted that there will still be very little leakage through the diodes which may result in slightly faster corrosion than normal.

A "lasagna battery" or "lasagna stack" occurs accidentally when salty foods, such as lasagna, are stored in a steel baking container and covered with aluminum foil, or in any case when different metals touch each other and the salty medium (for example, when leaving a spoon in a pot). After a few hours, small holes develop in the paper at the points of contact with the lasagna, and the surface of the food is covered with small dots composed of corroded aluminum (oxide), which is neurotoxic.[6]​.

This metallic corrosion is due to the fact that every time two sheets of different metals come into contact with an electrolyte, the two metals act as electrodes, and an electrochemical cell, cell or battery is formed. In this case, the two battery terminals are connected to each other. Because the aluminum sheet touches the steel, this battery is short-circuited, a significant electrical current appears, and rapid chemical reactions take place on the surface of the metal in contact with the electrolyte. Thus, in this steel/salt/aluminum stack, as the aluminum is higher in the electrochemical series (higher potential), the solid aluminum oxidizes and dissolves forming dissolved ions, and the metal undergoes galvanic corrosion.

Contenido

La compatibilidad de dos metales distintos puede predecirse por medio del "índice anódico")". Este parámetro mide el voltaje electroquímico que se desarrolla entre el metal y el oro, tomado como electrodo de referencia. Para tener el voltaje relativo entre dos metales, basta con hacer la diferencia de sus índices anódicos.[7]​.

Para ambientes normales, tales como almacenes u otros ambientes interiores sin control de temperatura y humedad, la diferencia de los índices anódicos no debería ser superior a 0,25 V. En ambientes interiores con temperatura y humedad controladas, puede tolerarse hasta 0,50 V. Para ambientes más duros, tales como intemperie, alta humedad, y ambientes salinos, la diferencia no debería superar 0,15 V. Así, por ejemplo, los índices del oro y la plata difieren en 0,15 V, y por tanto serían compatibles para este tipo de ambientes.[8]​.

A menudo, cuando el diseño requiere que metales diferentes estén en contacto, se gestiona la compatibilidad galvánica entre ellos mediante los acabados y el revestimiento. El acabado y el recubrimiento seleccionado facilitan que los materiales disímiles estén en contacto y protegen así a los materiales de base de la corrosión.[8]​.

Compatibility between galvanized steel and aluminum

Can galvanized steel and aluminum come into contact or are they subject to galvanic corrosion? By theory, experiments and practice, these two materials are definitely compatible.

Theory predicts that aluminum and galvanized steel are compatible. Zinc (steel coating) and aluminum are adjacent to each other on the galvanizing scale.[9]​ The presence of aluminum coupled with galvanized steel increases the current density (corrosion rate) of zinc by only 0.1% to 1% (aluminum is the cathode, or protected side of the pair)[10]​ This increase in the corrosion rate of zinc is negligible, and therefore, contact between aluminum and galvanized steel It does not significantly accelerate the corrosion of either material.

Experimental tests confirm the theory. For example, Doyle and Wright[11]​ show that the degree of corrosion of aluminum does not increase when in contact with galvanized steel. Therefore, they conclude that zinc is very compatible with aluminum in all environments, and in several cases even showing that the aluminum was being cathodically protected by the zinc.

The regulations have incorporated these results. For example, the Aluminum Association, in its structural code, states that there is no need to separate or paint galvanized steel surfaces that are in contact with aluminum.[12]​.

Furthermore, many structures and components in the last half century attest to the above. Aluminum siding is frequently attached to galvanized steel structures and zinc-coated screws are often used. Most stadium grandstand exterior structures in North America are made of a galvanized structure to which aluminum floors or seats are attached. And also countless number of connection system connectors in service around the world have been manufactured by successfully and permanently joining galvanized steel pipes.

How does this type of corrosion affect galvanized steel?

Generally, galvanized steel behaves well in contact with the most common metals in construction when they are exposed to the atmosphere, as long as the surface ratio between the galvanized steel and the other metal is high. On the contrary, under immersion conditions the risk of attack by bimetallic corrosion increases significantly, so it is normally necessary to use some type of insulation between both metals.

Galvanized coatings are more resistant to atmospheric corrosion and corrosion caused by water, because the zinc corrosion products that form in such media, normally hydrated basic zinc carbonates, are insoluble, adherent and poorly porous, and constitute a passivation layer that effectively isolates the galvanized coating from contact with the aggressive environment.

Behavior of galvanized steel in contact with:.

Copper. Given the large potential difference between galvanized steel and copper or its alloys, electrical insulation of the two metals is always recommended, even under conditions of exposure to the atmosphere. Where possible, the design should also prevent water or moisture condensation from draining from the copper onto the galvanized items, as ionic dissolved copper could deposit on the galvanized surfaces and cause corrosion of the zinc.

For this same reason, sections of copper and galvanized steel pipes should not be mixed in water pipes (even if electrical insulation elements are used at the joints of both types of pipes), especially if the copper sections are placed in front of the galvanized steel sections and, therefore, the flow of water passes mainly through the copper pipes.

Aluminum. The risk of bimetallic corrosion due to contact between galvanized steel and aluminum in the atmosphere is relatively low.

It is worth remembering that a frequent application in which these two metals are used together are cladding with aluminum panels mounted on a substructure of galvanized steel profiles. In these cases it is advisable, although not essential, to isolate both metals, due to the large surface area of ​​the aluminum panels in relation to that of the profiles in contact.

Lead. The possibility of bimetallic corrosion with lead is low upon exposure to the atmosphere. No problems have been detected in applications such as the use of lead flashing with zinc products or coatings, or in the use of lead to secure posts or galvanized structural elements.

Stainless steel. The most common use of stainless steel in contact with galvanized steel is in the form of screws and nuts under conditions of exposure to the atmosphere (Fig. 4). This type of joints are not usually very problematic, due to the low galvanic torque established between both metals and the high surface ratio between the anodic metal (galvanized steel) and the cathodic metal (stainless steel). However, in high conductivity media (high humidity or immersion in water) it is advisable to provide insulation between the contact surfaces of both metals (e.g. plastic or neoprene washers and bushings or insulating tapes).

Techniques * NACE TM 0497 - Measurement related to the criteria for Cathodic Protection in underground or submerged metal pipe systems.

Metals (including alloys) can be arranged in a galvanic series that represents the potential they develop in a given electrolyte against a reference standard electrode. The relative position of the two metals in this series gives a good indication of which metal of the pair is most likely to corrode most rapidly. However, other factors such as aeration and water flow can significantly influence the process.

Galvanic corrosion is of great interest to the marine industry. Tables with galvanic series of metals in seawater are very common, due to the wide use of metal in shipbuilding. It is possible that corrosion of the silver solder in a saltwater pipe could have caused a failure that led to the sinking of the USS Thresher and the death of all its crew.

The common technique of cleaning silver by immersing it and a piece of aluminum foil in a bath of salt water (usually baking soda) is another example of galvanic corrosion. Care must be taken, as using this technique will clean the silver oxide that could be there as decoration. It is also not advisable to clean gold-plated silver objects in this way as it can introduce unwanted galvanic corrosion into the base metal.

There are several ways to reduce and prevent this type of corrosion.[2]​.

This is common in water heaters and boiler hot water tanks. Lack of regularity in replacing sacrificial anodes in water heaters severely decreases tank life. Substances to correct water hardness (water softeners) tend to degrade sacrificial anodes and tanks more quickly.

For example, let's consider a system composed of 316 stainless steel (a 300 series stainless steel, it is a very noble alloy which means it is quite resistant to corrosion and has a high potential), and a mild steel (a very active metal with lower potential). Mild steel") will corrode in the presence of an electrolyte, such as salt water. If a sacrificial anode is used (such as a zinc alloy, aluminum or magnesium alloy), these anodes will corrode, protecting the other metals. This is a common practice in the maritime industry to protect ship equipment. Ships and ships that are in contact with salt water use either zinc or aluminum alloys. If the ships are only in fresh water, a magnesium alloy. Magnesium has one of the highest galvanic potentials of all metals. If used in an installation exposed to salt water, such as on a steel or aluminum boat hull, hydrogen bubbles forming under the paint will cause blistering and peeling.

Metal boats connected to a shore power line typically have to have their hulls grounded for safety reasons. However, the end of the ground connection is likely to be a copper rod buried in the marina, resulting in a steel-copper "battery" of around 1.1 V. In such cases, the use of a galvanic isolator is essential - typically 2 diodes in series, to prevent any current flow, as long as the applied voltage is less than 1.4 V (i.e. 0.7 V per diode), but allowing full flow in the event of a ground fault. It has been noted that there will still be very little leakage through the diodes which may result in slightly faster corrosion than normal.

A "lasagna battery" or "lasagna stack" occurs accidentally when salty foods, such as lasagna, are stored in a steel baking container and covered with aluminum foil, or in any case when different metals touch each other and the salty medium (for example, when leaving a spoon in a pot). After a few hours, small holes develop in the paper at the points of contact with the lasagna, and the surface of the food is covered with small dots composed of corroded aluminum (oxide), which is neurotoxic.[6]​.

This metallic corrosion is due to the fact that every time two sheets of different metals come into contact with an electrolyte, the two metals act as electrodes, and an electrochemical cell, cell or battery is formed. In this case, the two battery terminals are connected to each other. Because the aluminum sheet touches the steel, this battery is short-circuited, a significant electrical current appears, and rapid chemical reactions take place on the surface of the metal in contact with the electrolyte. Thus, in this steel/salt/aluminum stack, as the aluminum is higher in the electrochemical series (higher potential), the solid aluminum oxidizes and dissolves forming dissolved ions, and the metal undergoes galvanic corrosion.

Contenido

La compatibilidad de dos metales distintos puede predecirse por medio del "índice anódico")". Este parámetro mide el voltaje electroquímico que se desarrolla entre el metal y el oro, tomado como electrodo de referencia. Para tener el voltaje relativo entre dos metales, basta con hacer la diferencia de sus índices anódicos.[7]​.

Para ambientes normales, tales como almacenes u otros ambientes interiores sin control de temperatura y humedad, la diferencia de los índices anódicos no debería ser superior a 0,25 V. En ambientes interiores con temperatura y humedad controladas, puede tolerarse hasta 0,50 V. Para ambientes más duros, tales como intemperie, alta humedad, y ambientes salinos, la diferencia no debería superar 0,15 V. Así, por ejemplo, los índices del oro y la plata difieren en 0,15 V, y por tanto serían compatibles para este tipo de ambientes.[8]​.

A menudo, cuando el diseño requiere que metales diferentes estén en contacto, se gestiona la compatibilidad galvánica entre ellos mediante los acabados y el revestimiento. El acabado y el recubrimiento seleccionado facilitan que los materiales disímiles estén en contacto y protegen así a los materiales de base de la corrosión.[8]​.

Compatibility between galvanized steel and aluminum

Can galvanized steel and aluminum come into contact or are they subject to galvanic corrosion? By theory, experiments and practice, these two materials are definitely compatible.

Theory predicts that aluminum and galvanized steel are compatible. Zinc (steel coating) and aluminum are adjacent to each other on the galvanizing scale.[9]​ The presence of aluminum coupled with galvanized steel increases the current density (corrosion rate) of zinc by only 0.1% to 1% (aluminum is the cathode, or protected side of the pair)[10]​ This increase in the corrosion rate of zinc is negligible, and therefore, contact between aluminum and galvanized steel It does not significantly accelerate the corrosion of either material.

Experimental tests confirm the theory. For example, Doyle and Wright[11]​ show that the degree of corrosion of aluminum does not increase when in contact with galvanized steel. Therefore, they conclude that zinc is very compatible with aluminum in all environments, and in several cases even showing that the aluminum was being cathodically protected by the zinc.

The regulations have incorporated these results. For example, the Aluminum Association, in its structural code, states that there is no need to separate or paint galvanized steel surfaces that are in contact with aluminum.[12]​.

Furthermore, many structures and components in the last half century attest to the above. Aluminum siding is frequently attached to galvanized steel structures and zinc-coated screws are often used. Most stadium grandstand exterior structures in North America are made of a galvanized structure to which aluminum floors or seats are attached. And also countless number of connection system connectors in service around the world have been manufactured by successfully and permanently joining galvanized steel pipes.

How does this type of corrosion affect galvanized steel?

Generally, galvanized steel behaves well in contact with the most common metals in construction when they are exposed to the atmosphere, as long as the surface ratio between the galvanized steel and the other metal is high. On the contrary, under immersion conditions the risk of attack by bimetallic corrosion increases significantly, so it is normally necessary to use some type of insulation between both metals.

Galvanized coatings are more resistant to atmospheric corrosion and corrosion caused by water, because the zinc corrosion products that form in such media, normally hydrated basic zinc carbonates, are insoluble, adherent and poorly porous, and constitute a passivation layer that effectively isolates the galvanized coating from contact with the aggressive environment.

Behavior of galvanized steel in contact with:.

Copper. Given the large potential difference between galvanized steel and copper or its alloys, electrical insulation of the two metals is always recommended, even under conditions of exposure to the atmosphere. Where possible, the design should also prevent water or moisture condensation from draining from the copper onto the galvanized items, as ionic dissolved copper could deposit on the galvanized surfaces and cause corrosion of the zinc.

For this same reason, sections of copper and galvanized steel pipes should not be mixed in water pipes (even if electrical insulation elements are used at the joints of both types of pipes), especially if the copper sections are placed in front of the galvanized steel sections and, therefore, the flow of water passes mainly through the copper pipes.

Aluminum. The risk of bimetallic corrosion due to contact between galvanized steel and aluminum in the atmosphere is relatively low.

It is worth remembering that a frequent application in which these two metals are used together are cladding with aluminum panels mounted on a substructure of galvanized steel profiles. In these cases it is advisable, although not essential, to isolate both metals, due to the large surface area of ​​the aluminum panels in relation to that of the profiles in contact.

Lead. The possibility of bimetallic corrosion with lead is low upon exposure to the atmosphere. No problems have been detected in applications such as the use of lead flashing with zinc products or coatings, or in the use of lead to secure posts or galvanized structural elements.

Stainless steel. The most common use of stainless steel in contact with galvanized steel is in the form of screws and nuts under conditions of exposure to the atmosphere (Fig. 4). This type of joints are not usually very problematic, due to the low galvanic torque established between both metals and the high surface ratio between the anodic metal (galvanized steel) and the cathodic metal (stainless steel). However, in high conductivity media (high humidity or immersion in water) it is advisable to provide insulation between the contact surfaces of both metals (e.g. plastic or neoprene washers and bushings or insulating tapes).

Techniques * NACE TM 0497 - Measurement related to the criteria for Cathodic Protection in underground or submerged metal pipe systems.