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First, large-scale steel structure thermal spraying long-term anti-corrosion

Because the steel structure has good mechanical properties, strong bearing capacity, simple manufacturing, easy to adopt industrial production, short construction and installation period, good sealing performance, etc., it has been widely used in national economic construction, such as large-span structure (bridges, stadiums). Roof trusses, etc., light steel structures (large and medium-sized workshops), high-rise buildings (New York World Trade Center and Shanghai Jinmao Building, etc.), and shell-and-shell structures (pressure vessels and long-distance pipelines). However, during the service period, the steel structure is prone to chemical, electrochemical or physical interactions with the environmental medium in which it is located, causing deterioration of the material and failure of the steel structure. It is often referred to as corrosion of the steel structure.

It has been recognized that the steel structures used by humans are rarely caused by mechanical factors (such as tension, pressure, impact, fatigue, fracture and wear) or other physical factors (such as heat, light, etc.). The destruction of most metal structures is related to the corrosive factors of their surroundings. Therefore, the corrosion and corrosion protection of steel structures has become a major issue that cannot be ignored in the fields of materials science, chemical industry and engineering, and has received attention from various industries related to government and steel structure applications.

Second, the necessity of long-term anti-corrosion engineering application of steel structure

So far, the corrosion of steel structures is causing huge losses to the national economy of countries around the world. According to statistics from some industrialized countries, the annual economic losses caused by corrosion of steel structures account for about 2% to 4% of the gross national product. The economic losses caused by corrosion in the United States in 1975 were about 70 billion US dollars, accounting for 4.2% of the gross national product of the year, up to 126 billion US dollars in 1982; the corrosion loss in Britain in 1969 was 1.365 billion pounds, accounting for 3.5% of the gross national product. %; Japan's corrosion loss in 1976 was 9.2 billion US dollars, accounting for 1.8% of the gross national product; according to China's 1995 statistics, corrosion losses amounted to more than 150 billion yuan, accounting for about 4% of the gross national product. At present, the annual economic losses caused by corrosion of steel structures in the world have reached hundreds of billions of dollars.

Moreover, the accident caused by corrosion of the steel structure jeopardizes the safe operation of the structure. Catastrophic accidents caused by corrosion are common and the consequences are extremely serious. Especially for welded steel structures and steel structures subjected to large stress conditions, corrosion will be greatly accelerated due to stress, that is, so-called stress corrosion problems occur in steel. Structural damage is extremely common. For example, bridge structures or high-altitude truss structures must be reconstructed due to serious corrosion problems. Otherwise, serious consequences will result. Of course, the economic investment is quite large. Now, building a large steel bridge in China will cost at least Several hundred million yuan. In 1970, Japan’s large-scale underground railway line was broken due to corrosion, causing gas explosions and passengers died on the spot. In 1979, a liquefied petroleum gas storage tank in a certain city in China was ignited by corrosion and explosion, causing dozens of casualties and direct economic losses of 6.3 million yuan. Moreover, the indirect economic losses caused by accidents and suspension of production due to accidents may exceed several times of direct economic losses.

Because of this, the use of steel structure anti-corrosion technology, especially the use of long-lasting anti-corrosion technology, is particularly important. If the steel structure can be maintenance-free for 15 to 50 years, the user will save a lot of maintenance funds and greatly improve the safety and service life of the steel structure.

So far, from the aspects of steel structure engineering users, designers and construction parties, the importance of long-term corrosion protection of steel structures is still insufficient, and the traditional anti-corrosion technology remains in consciousness. May not keep up. Moreover, even if it is a traditional coating anti-corrosion, due to the anti-corrosion construction technology during the construction process, the steel structure is often corroded or damaged prematurely. For example, in March 1965, a gas pipeline in the United States was ruptured by stress corrosion, killing 17 people. Another example is that the construction engineering technology of a swimming pool in the early years of paint construction is not long-lasting anti-corrosion, causing premature corrosion of local parts of the steel structure, as shown in Figure 1, plus the early limitations of the roofing system design on anti-corrosion technology, making the user It must cost millions to replace or maintain it.

In addition, some engineering users also have a big problem, that is, there is no expert in anti-corrosion engineering before the implementation of the project to evaluate the overall anti-corrosion technology of the steel structure; when the project is handed over, there is no professional anti-corrosion construction engineer or Experts conduct strict inspection on the quality of the entire steel structure anti-corrosion; after the anti-corrosion construction, they will sit back and relax, and basically do not carry out regular inspection and maintenance in the later period; or reduce the cost of the anti-corrosion project regardless of the actual situation, and combine with the construction unit, thus An unqualified "tofu residue project" was produced.

When all aspects are brought together, the life of the entire steel structure is certainly doubtful. So far, many steel structure damage accidents have occurred, and the direct consequences are catastrophic, which directly proves the above. Analysis.

The reason why the steel structure long-term anti-corrosion project is called a system engineering is precisely because it involves a combination of steel structure engineering users, engineering design parties, engineering construction parties and construction supervision parties. The safety and service life of the steel structure can be reliably guaranteed only by reasonable combination of various aspects and multi-party attention.

Third, the comparison of steel structure long-term anti-corrosion technology

Large steel structures, such as bridges, hydraulic structures, towers, chemical tanks, pressure vessels and other anti-corrosion, especially long-term anti-corrosion treatment (15-20 years or more) can have a variety of options. Examples include hot dip galvanizing or aluminum technology, heavy anti-corrosion coating coating technology, thermal spray zinc or aluminum coating technology. Among them, the most suitable is thermal spray aluminum or zinc (with a seal layer) coating.

It is assumed that the steel structure used under severe conditions has a protection period of 20 years, and the thermal spray Zn or Al coating life is 20 years; the organic coating is applied in 3 years, and the construction needs to be applied nearly 7 times in 20 years, and it is not included in the construction. Other losses caused, such as business downtime. Therefore, it can be obtained that the total price of the thermal sprayed Al or Zn coating is: 4-6 yuan/year·m2, with an average of 5 yuan/year·m2; and the organic coating is 1.7-27 yuan/year·m2, with an average of 14.35. Yuan/year·m2 is about 3 times of the long-lasting anti-corrosion technology of thermal spraying.

The damage caused by re-construction during the protection period (20 years) due to coating failure is significant. For example, the steel structure of the large gantry crane used for the ship lock gate and the lifting gate of the Yangtze River Gezhouba Project, and the steel structure of the ship lift. The original paint anti-corrosion was overhauled in 2-3 years. During each overhaul, the navigation capacity of 20 ships was reduced every day, and the navigation capacity of nearly 1,200 ships was reduced, with an average of 400-600 ships per year, causing great losses to the Yangtze River shipping. . Therefore, the important hydraulic gates, the Huangbaihe Bridge and the Xiajuxi Bridge in the Three Gorges Project should be protected by thermal sprayed Al or Zn coatings.

In terms of comprehensive pricing of comprehensive engineering users, thermal spray long-lasting anti-corrosion technology has a high performance-price ratio compared to paint coating technology and hot dip technology.

Arc spraying technology has been applied in the field of steel structure manufacturing and maintenance in many countries in the 1950s. However, due to the technical level of arc spraying equipment at the time, arc spraying is considered to be a high efficiency, low quality thermal spraying. method. Until the 1960s and 1970s, some industrialized countries such as the United States and Germany made relatively large modifications to the arc spraying equipment, which greatly improved the quality of the coating and promoted the universal application of arc spraying technology in steel structure manufacturing. In the late 1990s, arc spray technology became one of the fastest growing thermal spray technologies in recent years.

For example, in Norway, Dalseide & Floysand has built a 2,300-tonne Norwegian offshore oil platform (see Figure 2). The entire arc-spraying anti-corrosion project uses 14 G35-LD/U3 spraying equipment and 100 spraying workers for 3 months. Spraying 35 tons of AlMg5 wire is one of the world's largest examples of long-lasting anti-corrosion engineering for thermal spraying. Thermal spray anti-corrosion technology is also used in the long-term anti-corrosion of petrochemical pipelines.

Of course, there is a certain amount of noise and dust when applying thermal spray technology. The environmental protection requirements for the production of steel structure factories are quite strict. At present, there is basically no high requirement for the installation of the field or the maintenance of the old steel structure, but the protection of the construction personnel must be strengthened.

Fourth, the quality inspection of steel structure long-term anti-corrosion engineering

Now, for the design and construction of steel structure engineering, quality lifelong system is adopted. In recent years, the government has set clear life requirements for the design and manufacture of steel structures such as bridges. Therefore, no matter what anti-corrosion technology is adopted for the steel structure for protection treatment, professional strict quality inspection and supervision must be carried out during the production or maintenance process. In the spirit of being responsible for steel structure engineering, engineering users, construction parties and professional supervisors should attach great importance to this important link. For each anti-corrosion construction process, clear quality technical specifications must be proposed. For example, the blasting grade or manual pretreatment grade of steel structure pretreatment, the environmental requirements of anti-corrosion construction, the construction procedure of paint, the combination of the correct choice of paint coating or thermal spray coating and the thickness sampling test, sampling Corrosion experiments in the simulated environment, coating appearance inspection, etc., all need to be responsible.

Regardless of the construction party or the engineering user, when the strict quality inspection of the anti-corrosion coating is carried out, more sophisticated testing means and equipment must be used. At present, many steel structure manufacturers or engineering users how to detect the construction. The performance of anti-corrosion coatings is basically not well valued, and some simply do not have testing equipment or conditions. This is one of the main causes of many disasters in which the service life of steel structures is greatly shortened and damage may occur.

Fifth, the long-term anti-corrosion conclusion of steel structure

Through the above analysis, the following conclusions can be drawn:

1. Today's society has begun to seriously treat the long-lasting anti-corrosion system project of steel structure, which is closely related to the safe operation of steel structure and the guarantee of life.

2. Strengthening the management and supervision of anti-corrosion construction in the process of steel structure fabrication and maintenance is of vital importance to the project users, construction parties and professional supervisors.

3. In the process of designing and manufacturing steel structures, professional anti-corrosion engineering technicians and experts must participate or guide.

4. In China, the long-lasting anti-corrosion technology of arc spraying is an emerging technology developed in recent years, and has received more and more attention. The organic combination with coating technology will have more market advantages.