Steel structure anti-corrosion and quality inspection

Steel structures have advantages such as high strength, good plasticity and toughness, and light weight, and are widely used in construction projects. Most steel structural components can be manufactured in the factory in advance and then transported to the site for assembly, greatly shortening the construction period. However, the corrosion resistance and rust resistance of steel are poor, causing certain economic losses every year due to corrosion. In addition, when corrosion problems occur, the stability and quality of the steel structure will also be affected, posing huge hidden dangers. Therefore, it is of great significance to analyze the corrosion causes and anti-corrosion measures of steel structural engineering.

1、 Damage caused by corrosion of steel structures

1. The main causes of corrosion in steel structures

The steel structure factory building is exposed for a long time and undergoes corrosion due to moisture and other corrosive media in the air. The corrosion of steel at room temperature is mainly electrochemical corrosion. In a normal atmospheric environment, steel materials are affected by factors such as oxygen, moisture in the air, and external dirt, rust layer, and welding slag on the structure, presenting rust and corrosion conditions. When the air humidity is below 60%, the steel structure is subject to slight corrosion; When the air humidity exceeds the maximum limit of steel (critical humidity of 60%~70%), the corrosion condition is relatively severe. When steel structure factories are located in areas with severe air pollution or coastal areas for a long time, the salt content in the air is high, and the critical humidity is lower compared to normal atmospheric environment, which will form a water film on the surface of the steel. The incomplete treatment of welding slag, rust layer, oxide scale, etc. on the surface of the steel structure is the cathode, while the steel structure components are the anode. Electrochemical corrosion reactions occur in the water film, which is the main cause of steel structure corrosion.

2. Damage caused by corrosion of steel structures

The corrosion problem of steel structures that has not been resolved in a timely manner will cause damage to the strength, stability, and other aspects of the steel structure as the service time prolongs, making its load-bearing capacity unable to meet the requirements of safe use. With the passage of time, the fatigue level of steel will further worsen due to the influence of natural environment, which will lay huge safety and quality hazards.

2、 Corrosion types of steel structures

The common types of corrosion in factory steel structures can be divided into three categories: atmospheric corrosion, partial corrosion, and stress corrosion.

1. Atmospheric corrosion

Atmospheric corrosion is one of the most common types of corrosion in factory steel structures, which can have a significant impact on the overall stability and bearing capacity of the steel structure. The main reason for atmospheric corrosion is due to long-term exposure of steel structures to outdoor environments, where metal elements in the steel structure react with water, air, and other elements in the atmosphere, leading to the formation of corrosion phenomena. Atmospheric corrosion in the steel structure of the factory building is a long-term and continuous process that gradually invades the interior of the factory building structure, damaging the quality and safety of the factory building structure.

2. Stress corrosion

Stress corrosion is a relatively special corrosion phenomenon that belongs to sudden corrosion. It generally occurs when the steel structure of a factory building is under certain stress. There is a significant connection between stress corrosion and the stability of the steel structure. Due to the sudden fission of the internal structure of the factory building steel structure, the corrosion phenomenon of the factory building steel structure is caused.

3. Partial corrosion

Partial corrosion is also a common corrosion phenomenon in factory steel structures, which can be divided into crevice corrosion and galvanic corrosion. In detail. Gap corrosion refers to the corrosion problem of steel structures caused by cracks on the surface of the steel structure during the construction process of the factory building. Media such as water and air enter the steel structure through the cracks, gradually causing corrosion over time; And galvanic corrosion is a corrosion phenomenon caused by the positive and negative potentials of different metal elements in steel structures. Generally speaking, negative potentials are simpler than positive potentials to cause corrosion, and the corrosion phenomenon that occurs is more severe.

3、 How to prevent corrosion of steel structures?

1. Self preservation

Weathering steel, which has better corrosion performance than general structural steel, is selected. This steel generally contains phosphorus, copper, nickel, chromium, titanium and other metals to form a protective layer on the metal surface to improve corrosion resistance. Its low-temperature impact toughness is also better than ordinary structures.

2. Coating anti-corrosion

This method is currently the most common and commonly used method in steel structures. The anti-corrosion coating for steel structures is basically composed of particles, i.e. pigments, dispersed in the liquid. When the coating is modified on steel, the liquid coating gradually dries and binds the pigment particles together to form a tightly bonded curing film, preventing corrosive media such as air and water from invading the interior of the steel structure, preventing the steel from being corroded by harmful media, and then protecting the integrity and service life of the steel structure.

In addition to selecting appropriate anti-corrosion materials, the performance testing of anti-corrosion coatings for steel structures is also of utmost importance. The performance testing of anti-corrosion coatings for steel structures mainly includes:

(1) Measurement of coating film thickness is an important indicator of coating protection performance. By measuring the coating film thickness, it can be determined whether the coating has achieved a regular anti-corrosion effect.

(2) Adhesion testing: The adhesion between coatings and steel structures is the key to ensuring long-lasting anti-corrosion of coatings on the surface of steel structures. The commonly used adhesion testing methods include peel test, tensile test, etc.

(3) Corrosion resistance testing is one of the main properties of coatings. Detect the corrosion resistance of coatings by simulating the corrosion of the surface of steel structures in environments such as acid, alkali, and salt mist.

(4) Water resistance testing of steel structures is often carried out in humid environments, and the importance of the water resistance performance of coatings for their protective effect is self-evident. Test the water resistance of coatings by simulating water corrosion.

(5) UV resistance test: In outdoor environments, coatings are easily exposed to UV radiation and exhibit phenomena such as aging and detachment. Testing the UV resistance of coatings can determine their durability.

(6) In addition to protecting steel structures, impermeability testing coatings also need to have certain impermeability properties to prevent corrosion of steel structures by corrosive media such as water and solution under the coating film.

(7) Wear resistance testing: Steel structures are often used in high-strength environments, and coatings need to have strong wear resistance to ensure that the coatings do not wear for a long time.

On the other hand, in the anti-corrosion process of steel structures, the construction process of anti-corrosion coatings is also crucial, and scientific and reasonable construction techniques need to be developed. During the construction process, the following points need to be noted:

(1) Surface treatment of steel structures

Before anti-corrosion, all steel structures need to be sandblasted or polished to remove various dirt attached to the surface of the steel, including oxide skin, rust, old coatings, dust, and grease. The surface treatment should comply with the requirements of the rust removal grade in the standard GB/T 8923 "Rust Grades and Rust Removal Grades of Steel Surfaces before Painting". The surface roughness of the treated steel is between 40 and 70 μ m. Moreover, anti-corrosion paint spraying must be carried out within 24 hours after surface treatment to prevent rust on the surface of the steel after sand spraying.

(2) Appearance treatment inspection

After the surface treatment of all steel structures is completed, construction personnel need to conduct self inspection according to the surface treatment requirements of the steel structure. If the surface roughness level of the steel structure does not meet the requirements, it is necessary to conduct another surface treatment until it meets the requirements. Records must be kept together before subsequent anti-corrosion operations can be carried out.

(3) Construction process of anti-corrosion paint

After the surface treatment level of the steel structure is inspected and qualified, the first anti-corrosion paint spraying operation must be carried out within 4-8 hours. If there is floating rust on the surface of the steel structure, it must be removed thoroughly before the anti-corrosion paint spraying operation can be carried out. Construction personnel need to measure the wind speed, temperature, humidity, and dew point values of the surrounding environment for steel structure construction every day and keep records.

During the spraying process of anti-corrosion paint, it is necessary to strictly follow the requirements of the anti-corrosion paint construction process and register the mixing time, spraying time, and interval time of each anti-corrosion paint. Special attention should be paid to the fact that only construction personnel who have been trained and qualified can carry out anti-corrosion paint spraying operations.

Choosing appropriate and quality tested anti-corrosion coatings and the correct construction process are the key to ensuring the success of steel structure anti-corrosion, and both are indispensable.

4、 Conclusion

In short, with the continuous acceleration of urbanization in China, significant progress has been made in the field of construction. As one of the most common structural forms, steel structure has been widely used in construction projects. However, if corrosion problems occur in construction projects, the bearing capacity of steel structure will decline, and the fatigue degree of steel will gradually increase, which will affect the overall stability and reliability of steel structural engineering, laying potential safety hazards for future use, and also damaging the service life of buildings. Therefore, doing a good job in anti-corrosion work can help improve the reliability and safety of steel structures, and avoid the occurrence of serious accidents.

Anticorrosion work is the key content to be paid attention to in the construction of steel structural engineering, and also the key to improve structural stability and reliability. Whether in design, construction, or use, it is necessary to comprehensively consider various factors such as the environmental conditions, structural characteristics, costs, etc. in the construction of steel structures. The most effective and reasonable anti-corrosion measures should be adopted according to engineering requirements to avoid damage to the safety of the construction structure caused by corrosion. It is of positive significance to promote the development of steel structural engineering to maximize the corrosion resistance of steel structures.