1. Principle of ship cathodic protection system
Sacrificial anode cathodic protection is generally used on ships, and applied current cathodic protection is generally not used. Installing more anode blocks will increase the ship’s sailing resistance and cause over-protection, while less protection is insufficient and the ship’s hull still suffers from corrosion. Therefore, an appropriate amount of anodes must be installed, which requires a reasonable design.
According to the principle of cathodic protection, when implementing cathodic protection for metals, in order to achieve the best protection effect, it is necessary to pay attention to the minimum protection potential and minimum protection current density of cathodic protection two main parameters. In practice, taking into account the influence of other factors, the maximum protection potential and maximum protection current density should be selected.
2. Illustration of the principle of ship cathodic protection system
Each part of the ship is in a different corrosive environment and suffers from different external effects, so the performance requirements of the coating are different and very elaborate.
Ship bottom area: The ship bottom area is immersed in seawater for a long time and is subject to electrochemical corrosion and seawater scouring by seawater.
In addition, the ship usually adopts sacrificial anode or applied current for cathodic protection, and the whole underwater area of the ship will become cathode, which will be alkaline due to excessive hydroxide ions.
Therefore, the coating used in the ship bottom area must have good water resistance, alkali resistance and abrasion resistance, and its outer coating should also have anti-fouling property to prevent sea creatures from attaching.
Waterline area: The waterline area is often in the alternate dry and wet state of seawater immersion, washing and sunlight exposure, i.e. in the splash zone, which is a special corrosive environment, so the coating used in the waterline area must have good water resistance, weather resistance, dry and wet alternation resistance, and the coating should have good mechanical strength, friction resistance and impact resistance, and when the ship adopts cathodic protection, the coating is also required to have good alkali resistance.
Atmosphere exposure area: The dry side, superstructure exterior, open deck and deck outfitting etc. of the ship are in the marine atmosphere exposure area, these parts are in the wet marine atmosphere containing salt for years and years, and are often exposed to sunlight and sometimes wave impact, so the coating is required to have excellent rust resistance, weather resistance, impact resistance and friction performance.
Since the above-mentioned parts are the main parts of the ship’s appearance, its top coating also needs good color and light retention.
The coating below the waterline of warships is more often painted with iron-red anti-rust paint, such as chlorinated rubber bottom anti-rust paint; when epoxy asphalt bottom anti-rust paint is used, it appears black or brown; the waterline part can be painted with the same paint as the bottom of the ship, and phenolic, chlorinated rubber, epoxy asphalt and other types of waterline paint can be used alone, the former two appearing red, the latter appearing black or brown. The exterior painting above the waterline of warships, more consideration to stealth, visually as far as possible and the background color of the navigation area blend, electronic stealth is mixed with radar absorbing components, but generally do not change the visual effect
3. Hull cathodic protection device
The cathodic protection method of sacrificial anode, where the anode refers to the anode of the oxidizer, not the anode of the electrolytic cell.
The principle is that the material as the anode is more likely to lose electrons than the cathode, and the reduction reaction occurs, so that the reaction of the anode can protect the cathode from chemical reaction, which is generally used in the protection of ship hull in seawater for a long time. Hope it can help you
4. Principle of cathodic protection for ships with applied current
The purpose of cathodic protection is to reduce the potential difference between cathode and anode as much as possible to a negligible value.
This potential difference reduction is mainly due to the polarization of the cathode, according to Ohm’s law, using this method, the corrosion current can be well mitigated.
Cathodic protection can be achieved by applying an applied current to the surface of the corroded metal structure.
5. The principle of cathodic protection by applying current to the ship
Lightning storm protection to avoid breakdown of pipelines due to lightning storm weather.
6. What are the uses of cathodic protection devices on board ships
Epoxy zinc-rich primer and epoxy primer are both commonly used primers for industrial corrosion prevention, but there are still many differences between the two in application.
Epoxy zinc-rich primer takes epoxy resin and zinc powder as the main raw materials, where zinc powder is the main source of its characteristics and strong rust prevention performance
Epoxy primer is mainly made of epoxy resin and anti-rust pigment, which is less rust-proof than zinc-rich primer.
The difference of rust prevention mechanism:
Zinc powder in epoxy zinc-rich primer has cathodic protection, electrochemical anticorrosion and stronger rust prevention performance
Epoxy primer mainly uses the shielding effect of antirust pigment to achieve the rust prevention effect
Difference of functional types:
Epoxy zinc-rich primer is mainly distinguished by zinc powder content, with different prices for different zinc content and different anticorrosive properties, generally at 60%, 70%, 80%
Epoxy primer has more functions and types, and more room for performance improvement
Difference in application areas:
Epoxy zinc-rich primer is mainly used in harsh corrosive environments, such as industrial, marine, coastal, etc., for bridges, steel structures, buildings, machinery and other large projects, and is more often used in long-term protection over 15 years
Epoxy primer is mainly used in general to medium corrosive environment, a small part can be used in harsh corrosive environment, but the application range is wider, in all kinds of anti-corrosion coating can be used
Matching system difference:
Epoxy zinc-rich primer is generally a three-layer system: epoxy zinc-rich primer + epoxy cloud iron intermediate paint + fluorocarbon paint / acrylic polyurethane top coat
Epoxy primer is generally a two-layer system: epoxy primer + fluorocarbon paint / acrylic polyurethane paint / epoxy top coat
7. The principle of cathodic protection of sacrificial anodes for ships
Metal – electrolyte dissolution corrosion system by cathodic polarization, the potential negative shift, metal anodic oxidation reaction overpotential ηa decrease, the reaction rate is reduced, and therefore the metal corrosion rate is reduced, known as the cathodic protection effect. The use of cathodic protection effect to reduce the corrosion of metal equipment protection method is called cathodic protection . The metal oxidation reaction (electron loss reaction) is inhibited by the passage of electrons from an external circuit to the metal for the depolarizer reduction reaction. When the rate of metal oxidation reaction is reduced to zero, only the depolarizer cathodic reaction occurs on the metal surface.
Two types of cathodic protection methods : applied current cathodic protection and sacrificial anodic protection.
Principle of anodic protection:
When a metal is immersed in an electrolyte solution, a potential is established between the metal surface and the solution, corrosion electrochemistry in this potential is called the natural corrosion potential. Different metals in a certain solution potential is not the same. The potential of the same metal due to the existence of electrochemical heterogeneity between its parts and cause a certain potential difference between different parts, it is this potential difference leads to the electrochemical corrosion of the metal in the electrolyte solution.
To the electrolyte solution immersed in the metal applied DC, the natural corrosion potential of the metal will change, this phenomenon is called polarization. When the current passed is positive current. Metal as the anode its potential change in the positive direction of the process is called anodic polarization; conversely, the current through the negative current, the metal as the anode its potential change in the negative direction of the process is called cathodic polarization. The corresponding relationship between potential and current density is drawn as a curve called the polarization curve. When anodizing a metal with a passivity tendency, if the current reaches a sufficient value, a passivation film with high corrosion resistance can be generated on the metal surface and the current is reduced, and the metal surface is passivated. Continue to apply a smaller current can maintain this passivation state, the passivated metal surface dissolution is very small to prevent the corrosion of the metal, this is the basic principle of anodic protection.
8. principle of cathodic protection device for ships
Cathodic protection ) protection principle: metal – electrolyte dissolution corrosion system by cathodic polarization, the potential negative shift, metal anodic oxidation reaction over potential ηa reduced, the reaction rate is reduced, and thus the metal corrosion rate is reduced, known as the cathodic protection effect. The use of cathodic protection effect to reduce the corrosion of metal equipment protection method is called cathodic protection. From the external circuit to the metal to pass electrons for depolarizing agent reduction reaction required, so that the metal oxidation reaction (electron loss reaction) is inhibited.
When the rate of metal oxidation reaction is reduced to zero, only the depolarizer cathodic reaction occurs on the metal surface. Two types of cathodic protection methods: applied current cathodic protection and sacrificial anode protection
9. Marine cathodic protection device
Marine electrode is divided into reference electrode and cathodic protection, and there is a large shaft grounding, cathode failure, does not play a protective role anymore, showing that there is a problem anode passivation, circuit failure
We introduce the marine cathodic protection method is titanium anode products.
In the steel use environment of ships, bridges, tanks, etc., the corrosion of these buildings is very serious due to the corrosion effect of impurities and micro cells in the steel, plus the wind and rain, which greatly threatens the safety production, so the use of titanium electrodes is an effective protection measure. In addition, titanium electrode can also be used as marine oil sewage treatment device, marine domestic sewage treatment device, etc.
Here are some pictures of titanium anode products, if you also need, please contact us