Abstract: Due to the long-term service of seawater valves in the marine environment, it is inevitable that the engineering materials will be damaged and corroded. As an important moving part in marine engineering/system, seawater valves face severe damage such as wear and corrosion. Therefore, this paper According to the analysis of the behavior and mechanism of seawater valve metal material wear and corrosion in seawater environment, and the comparison of series of anti-corrosion and wear integration technologies, the mechanism of wear and anti-corrosion performance of wear and anti-corrosion integrated materials is analyzed, which is the wear and corrosion protection of seawater valve. Provide a reference for solving the problem.
Key words: seawater valve; metal material; wear corrosion; integrated technology With the continuous development of marine equipment for marine engineering construction in China, offshore platforms, breeding platforms, diving equipment and other offshore facilities and equipment have become important for marine defense and economic construction. component. Since marine equipment needs to work long hours in the marine environment, the associated motion system is bound to suffer from wear and corrosion. Therefore, we fully understand the problems of wear and corrosion and interaction of seawater valve materials, and actively carry out research and development of effective anti-corrosion materials and integrated protection technologies, which become an important guarantee for reliable and safe operation of marine equipment.
1. Main factors causing corrosion and wear 1.1 Influence of medium The main factors affecting the corrosion performance of the material include the concentration of the medium, the pH value and its temperature, etc., and are also important factors affecting the wear and corrosion properties of the material. The corrosive medium not only has a corrosive effect, but also can generate a corrosive new material to corrode the wear material through the reaction.
1.2 Influence of materials The microstructure, chemical composition, plasticity, and roughness of hard surfaces of materials are important factors influencing the abrasive properties of materials. Therefore, the corrosion-resistant and wear-resistant material should have superior corrosion resistance and wear resistance. It is necessary to comprehensively optimize the microstructure and chemical composition of the material. The important factor determining the wear and corrosion of the material is the mechanical properties of the material itself. Organizational structure, etc. The material itself is resistant to corrosion and wear and can be used in abrasive and corrosive environments.
2 Influence of wear and corrosion factors of special metal materials 2.1 Influence of medium The damage behavior caused by wear corrosion of 304 stainless steel and its mechanism are affected by the influence of pH value and concentration of corrosive medium. It is found that the concentration of chloride ion increases significantly. Increase the sensitivity of local corrosion of Type 304 stainless steel, especially the sensitivity of pitting. Therefore, the degree of damage to the static corrosion of the 304 stainless steel is increased. However, in the case of increasing chloride ion concentration, the 304/AL2O3 wear rate and wear coefficient will be significantly reduced, and the worn surface will be smoother, indicating that the wear is affected by corrosion under the action of chloride lubrication. The degree is gradually weakened. Therefore, the increase of corrosion concentration can greatly reduce the corrosion and pure mechanical wear in wear corrosion. This study points out the new research direction of corrosion resistance of metal materials.
2.2 Electrochemical influence One of the more widely used methods in protective corrosion technology is the sacrificial anode cathodic protection method, which first applies the cathode current to the metal material to be protected, and applies the anode current to the auxiliary anode. To form a corrosion current, the method is a method of forcing a current. Therefore, the applied potential has the effect of wear and corrosion of the protective material, and the key factor of this method is the applied potential. It is proved by experiments that when the potential of the pitting corrosion of the purified film is higher than the applied potential, the wear and corrosion interact with each other, which obviously increases the total loss of the material; when the pitting potential is lower than the applied potential, the corrosion of the material is inhibited, so the material loss is mainly passive. Mechanical wear.
2.3 Influence of materials The intrinsic properties of materials such as wear resistance, corrosion resistance and hardness are important factors affecting the wear and corrosion properties of materials. Therefore, the comparison of the wear and corrosion properties of different metal materials has become an important technical basis for the selection of seawater valves. . By testing the wear and corrosion results of various metal materials, it is known that austenitic stainless steel is more suitable for corrosive seawater environment than stainless steel compared to martensitic stainless steel. For example, 304 and 316L stainless steel, 316L The corrosion damage performance is significantly reduced, and the wear damage is significantly reduced when the corrosion accelerates. In addition, the austenitic and ferritic 2205 duplex steels have significantly improved valve corrosion resistance compared to a single austenitic stainless steel, and the service life of the valve in the corrosive medium is significantly prolonged. For example, the wear damage of the 2205 duplex steel slag accounts for 11.6% of the total damage of the material, while the 304 stainless steel accounts for about 20% of the total damage of the material. Therefore, the corrosion resistance can be significantly reduced due to corrosion and accelerated damage. For titanium alloys and stainless steels, titanium alloys have superior wear resistance.
3 Anti-corrosion and wear-resistant technology integration research 3.1 PVD anti-corrosion and wear-resistant technology is difficult to carry out system replenishment maintenance in the offshore or deep sea operation, so the stability and reliability of the valve have high requirements, and it is necessary to carry out anti-corrosion and wear-resistance. Enhanced protection technology. For PVD coatings such as TiN GLC CrN, through the study of the mechanism of interaction between corrosion and wear, the structure is dense, the interface is multi-layered, and the corrosion-resistant channel coating material is impeded. The series is resistant to wear and low friction. Anti-corrosion and anti-wear materials with anti-corrosion properties, which promote the corrosion resistance of metal materials.
Compared with metal materials, the PVD coating hardness is significantly improved, such as CrN coating with a hardness of about 2000 HV, TiN coating of 2800 HV, diamond-like 2500 HV, 2205 dual-phase steel lower than 300 HV, and 316L. Therefore, based on the proportional relationship between wear resistance and hardness, it is speculated that the resistance to mechanical wear of coated metal materials with high hardness performance PVD anti-corrosion and wear resistance is significantly improved. Experiments show that the mechanical wear of CrN coating is The loss of 41.2% of total wear and corrosion is much higher than that of metal materials. Therefore, the improvement of the hardness of the material is an important means for further improving the mechanical wear of the metal material.
Further analysis and comparison of PVD anti-corrosion and wear-resistant coatings with different systems have been carried out, and the properties related to TiN, GLC and CrN coated metal materials have been effectively improved. For example, 316 stainless steel wear and anti-corrosion performance. In the CrN coating in seawater, the effect of the structural coating of Cr2N/CrN on lubrication reduction is more prominent. In addition, the wear rate and friction coefficient of CrN coatings with Si, C and other elements were reduced, especially the mass fraction of Si was 1.44%. When the C element was 5.72%, the wear and friction of CrN coatings were significantly improved. Therefore, the CrN coatings of the quaternary and ternary systems play an important role in the full play of the wear and corrosion resistance of metal materials.
3.2 Thermal spray anti-corrosion and wear-resistant technology In nickel-based coatings, metal nickel is the main material, so its corrosion resistance is better, but it has shortcomings such as poor wear resistance and low hardness. Therefore, in daily work, the WC ceramics of the equipment are usually sprayed with plasma to promote the nickel-based composite coating, and the coating abrasion resistance in seawater conditions is studied. The WC-reinforced ceramic nickel-based composite coating component mainly includes a ribbon phase and a continuous phase, respectively tungsten carbide and solid solution y-Ni. From the abrasion test in seawater conditions, the wear rate and friction coefficient of the coating are lower than the two-numbered grade compared with the 316L stainless steel. It proves that the coating has good abrasion resistance and can protect the surface of 316L stainless steel.
3.3 Electroplating technology In the electroplating coating, the application rate of nickel plating is typical, which is a coating method widely used in contemporary industrial applications. The same problem of metal abrasion resistance needs to be solved. Tests have shown that when the size of the crystal grains is gradually reduced from 50 nm to 5 nm, the corrosion resistance of the plating layer is continuously enhanced, and the amorphous nickel plating layer achieves the best corrosion resistance; the corrosion resistance of the amorphous nanocrystalline coating layer is located at 20 nm. Between -50nm, compared with large-sized nanocrystals, its corrosion resistance is superior. In addition, the difference in grain size, the hardness of the nickel plating layer is 50 nm>20 nm>amorphous>amorphous/nanocrystal>5 nm. Therefore, the amorphization and grain refinement can improve the corrosion resistance and hardness of the plating layer.
4, the practical application of integrated technology in the shipbuilding industry, the erosion caused by erosion is widespread, erosion wear can accelerate the failure of equipment, resulting in frequent valve replacement, maintenance, increase economic losses, so, special coating resistant to erosion and corrosion The development and use of the layer can greatly extend the service life of the valve and reduce the production cost. A research institute of engineering and materials technology is responsible for the corrosive erosion problems encountered in the production of seawater valves in enterprises. Through the design of mechanical properties, and the resin materials resistant to chemical and high temperature corrosion-modified polymers, screening and grading resistance The abrasive and high-hardness ceramic particles combine with the anti-corrosion and mechanics of filler materials such as graphene, polyetheretherketone fiber and carbon fiber, and have synergistic anti-corrosion and anti-shock function. The development of the anti-corrosion and anti-corrosion coating has been applied in the production of the enterprise, and the economic and social benefits obtained are good.
references:
[1] Ding Zhangxiong, Gao Rongyi, Wang Qun. Study on properties of Ni-based alloy spray-melting layer of ship seawater valve[J]. Thermal Spray Technology, 2010, 02(3): 35-39.
[2]CHEN Jun,LI Quan-an,ZHANG Qing, et al.Effect of seawater corrosion on wear resistance of several metal materials[J].Transactions of Materials and Heat Treatment,2014,35(12):166-171.
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