Huayu Magnesium Industry, Brilliant With the rapid development of social economy and the continuous progress of social civilization, China has made great progress in shipbuilding and made important contributions to China's socialist modernization. But for now, many hulls are more or less corrosive. Various corrosion phenomena have seriously affected the normal use of the vessel. Therefore, timely understanding and mastering the corrosion status of the vessel and actively exploring and studying the ship's anti-corrosion and maintenance technology can better maintain the basic performance of the hull, thus greatly extending the service life of the hull. Temperature Controller,Pid Controller,Temperature Regulator,Temperature Controllers Wuxi Winsun Automation Instrument Co., Ltd , https://www.jswxwinsun.com
Key words: hull; corrosion; maintenance; maintenance; measures
For the time being, the hulls of many ships today are made of metal materials. In the seawater, due to the influence of seawater temperature, atmosphere and seawater salinity, it often causes corrosion of the hull and corrosion of the hull. The extent is also deep. After the hull is corroded, it often causes damage to the hull structure, and sometimes even threatens the lives of the people on board. Therefore, we must actively understand and master the relevant situation of hull corrosion and the necessary anti-corrosion and maintenance measures, in order to promote the development of hull anti-corrosion business, thus ensuring the structural integrity of the vessel and property safety.
First, several major influencing factors causing hull corrosion
Hull design factor
There are many factors that cause hull corrosion, and the design factor of the hull is one of the important aspects. And the degree of corrosion of the hull is closely related to the design of the hull. Therefore, the scientific and rational design of the hull and the adoption of some reasonable anti-corrosion measures have become the direction that the countries of the world are constantly striving for. However, for the time being, many hulls still have many defects in design, and most of these defects are related to the unscientific design. For example, when designing the cover layer of the hull, the maintainability of the cover layer is not fully considered, so that it is easy to cause a long time of water accumulation in a local position in the hull and it is difficult to discharge, which may cause corrosion of the hull structure. In the second aspect, some watertight devices of the hull do not have good reliability. Not only does the hull have no good corrosion resistance, but also the relevant watertight devices of some pipelines on the hull have no excellent corrosion resistance. This makes it easy to make the hull's three-leakage phenomenon more common, so that there are more water sources in the cabin of the ship, which further exacerbates the corrosive environment of the cabin inside the ship. In the third aspect, no precautions have been taken for the gaps in some hulls, resulting in more serious corrosion conditions. In addition, galvanic corrosion is also a case of this type. In the case of long-term existence of gaps and galvanic couples and without effective precautions, the hull has relatively many holes and perforations. In addition, the inner cabin of the hull does not have a highly targeted coating design, so some weak parts in the cabin of the hull may not be effectively protected, thereby damaging the cabin of the hull.
2. Environmental factors
There are many reasons for the corrosion of the hull. Usually, the materials of the hull are deteriorated or destroyed due to various environmental factors. Therefore, the corrosion resistance of the hull material is relative to environmental factors. Under normal circumstances, the main material of the hull is steel, which is divided into low alloy steel and carbon steel. If analyzed from the final results of the exposure test, the degree of corrosion of low-alloy steel and carbon steel in various sea areas of the world is not much different. However, if some ships are constructed of the same steel, the degree of corrosion caused by different parts of the hull is not the same, and the corrosion rate is also quite different. Then we can attribute the reason to the different protection conditions and environmental conditions of different vessels, and these so-called protection conditions and environmental conditions are closely related to the design of the hull itself. Some of the most important environments outside the hull are seawater immersion, and some are dry and wet alternate zones, and then the oceanic atmosphere. In general, the internal environment of the hull is mostly in the marine atmosphere. However, the local position of the hull can be further subdivided. For example, it can be divided into a humid water environment, a general atmospheric environment, and a water accumulation environment on the bottom of the ship. It is precisely because there is a large amount of water in the cabin, so that the cabin is in a humid water environment. As a result, the hull structure is subjected to severe electrochemical corrosion. Some hulls are poorly maintained, but rely on some simple coatings to protect the exterior of the hull in a severely corrosive environment. This can easily cause serious corrosion of the hull. In the case of water in the corroded hull, there is also a situation in which some water in the hull is not easily found. The accumulated water stays in the cabin for a long time, so that the accumulated water cannot be removed in time, causing the hull to be eroded by water for a long time.
Second, several types of hull corrosion and the main reasons
1. Corrosion on the water part of the hull structure
The parts of the hull that are on the water mainly include decks, superstructures and freeboards. The nautical parts of these hulls are mainly affected by rain, snow, seawater droplets and the ocean atmosphere, and these factors are important causes of severe corrosion on the hull. In the ocean atmosphere, there is a large amount of nitride, which makes the condensed water worsen the damage to the hull structure. On the other hand, the surface of the nacelle and the surface of the boiler are relatively high, which also exacerbates the degree of water damage in these areas to some extent. Some scientific experiments have shown that the firework correction part in the hull has a great change in its structure due to its metal structure, so its corrosion resistance is much lower than other parts of the hull. Therefore, there is no good coating film for the firework correction part in the hull, and it is more likely to be broken than other parts, and the corrosion rate of the hull is greatly accelerated.
2. Corrosion of the hull structure in the underwater part
The underwater part of the hull structure generally consists of four parts: the crotch, the crotch, the bottom of the ship and the side of the ship. The crotch of the hull has long been in the wavy zone and the foam has been rolling over for a long time. Seawater can generate powerful fluid dynamics to the vessel's casing, the first of which is the coating, which is often severely damaged. The outer shell of the ship's side is often severely damaged by the surface coating of the ship's side when the hull is docked. The stern in the hull structure is mainly made of copper alloy material, especially at the end of the hull, which is prone to severe anodic polarization, which can cause serious hull corrosion. The outer coating of the hull is extremely susceptible to severe damage. In addition, some floating objects in the ocean may also cause serious damage to the hull's coating. Moreover, if there is a large amount of petroleum products on the ocean surface where the hull is located, these petroleum products will also cause serious damage to the outer coating of the hull. This is because the coatings used in the hulls in the waterline area do not have stable properties, especially in petroleum products, coupled with constant changes in dry and wet conditions, which greatly increases the aggressiveness of certain corrosive media. In addition, the welded parts of the underwater part of the hull structure are also particularly prone to corrosion. The corrosion of the hull structure in the underwater part is often electrocorrosive.
3. Correlated corrosion in the internal structure of the hull
Due to the different conditions of use of the hull, there are also varying degrees of corrosion in the interior compartments of different hulls. For example, the corrosion level of the working cabin and the living cabin is generally lighter, and no obvious signs of corrosion are visible. However, there is a serious corrosion phenomenon in the sanitary compartment. Especially in the bathroom, toilet and washing room, the corrosion situation is more serious. In the cargo hold of the hull, the coating in the cargo hold structure is more susceptible to damage due to the frequent loading and unloading of cargo and the combined effect of accumulated water and condensed water. After the coating in the cargo hold is destroyed, it is easy to speed up the corrosion of the inner bottom and cargo bulkheads in the hull. In addition, the degree of corrosion of the tank in the hull is more serious. The ballast tank and the fresh water tank are cement-coated, but the cement coating is unstable and water-permeable, so it is difficult to suppress the corrosion of the hull water tank. There is also a kind of corrosion in the hull which is electric corrosion. In general, the electric corrosion is mainly caused by the hull being repaired in the floating or when the terminal is installed because the power supply line is not wired in the correct way. Therefore, stray currents are generated in the waters where the hull is docked. This forms a relatively serious electrical corrosion.
Third, how to carry out effective protection against the corrosion of the hull
1. Use corrosion-resistant hull material
To improve the corrosion resistance of the hull, a welding process with excellent performance and appropriate strength should be used in the construction of the hull, and different types of steels which are relatively matched in electrochemical performance should be selected. The construction materials used on the same vessel should have their corrosion potentials as close as possible, thus greatly reducing the hazards posed by galvanic corrosion to the hull.
Many power systems, fire pipes and related cooling water pipes on the hull often leak, leak, and leak oil due to vibration or corrosion, which is what we call the three-leakage phenomenon. In order to control the three-leakage phenomenon, a copper tube with a relatively slow flow rate should be selected on the hull, but in general, we often use a white copper tube. If the flow rate in the tube is relatively fast, we can use copper and iron anode combined technology. If the flow rate inside the tube is quite high and you need to withstand strong scouring and corrosion, then we can use duplex stainless steel "target=_blank> stainless steel tube or titanium tube. Although the performance of titanium tube is quite superior, but its price It is also extremely expensive. For the case where the flow rate in the pipe is not high and the corrosion resistance is not too high, we often use galvanized pipe or ordinary steel pipe.
2. Coating protection measures
The degree of protection of the hull and the degree of corrosion protection depend to some extent on the coating material of the hull. Therefore, if we use suitable marine coatings and can effectively cover certain parts of the ship with appropriate construction techniques, so that the steel surfaces of various parts of the ship are isolated from the external environment, then we can make The hull is effectively protected to reduce corrosion of the hull structure. For the average hull, the most common method is to choose the right coating, because the coating is the most effective and economical way for the hull. In fact, if the ship's surface coating can protect the ship reasonably, scientifically, economically and effectively, then this is also important for the protection of the hull. But the key to this is to choose a reasonable scientific coating system, but also to have the right construction technology and scientific management measures.
3. Electrochemical protection measures
The so-called electrochemical protection measures are to make the corresponding potential difference of the corrosion battery disappear or reduce, so as to reduce the corrosion of the hull. Electrochemical protection methods can be divided into two types: cathodic protection and anode protection. The so-called anode protection is to connect the external DC power supply anode to the protected metal, which can reduce the corrosion rate of the metal. This is a special passive protection method. But this method does not work for all metals because some metals do not have a so-called passive state. The cathodic protection method is to reduce the anodic corrosion rate and the dissolution rate of the protective structure by applying a cathode current to the protected structure, and even to minimize the corrosion rate or the dissolution rate. This method of protecting the hull is the cathodic anode protection method.
Fourth, the conclusion
With the rapid development of China's economy, China's ships have also developed faster and faster, and have made significant contributions to China's economic and social development. However, in real life, there are many phenomena of hull corrosion. These hull corrosion phenomena have seriously affected the service life of the ship and, to a certain extent, hindered the rapid development of China's shipbuilding industry. Therefore, we must actively explore and study the causes of hull corrosion and strive to find ways and measures to solve such problems, thus accelerating the development of China's shipbuilding industry.
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