Various equipment, pipelines, and other metal structures of anti-corrosion treatment can not only play the role of beautification and identification, at the same time, also relates to the long-term safe operation of these components; however, in the actual use of anticorrosion technology in the process of anti-corrosion treatment of finished products or will often appear rust phenomenon, especially in the seaside under the high corrosive environment of the situation is particularly prominent. Therefore, how to better deal with the corrosion of metal parts to ensure their safe operation is a technical difficulty. The article and the seaside high corrosion environment corrosion control problems are briefly analyzed.
Seaside corrosion control in a highly corrosive environment has been a technical difficulty. After the anti-corrosion treatment of pipelines and equipment metal components after a long operation, most of them will produce corrosion problems. Corrosion of equipment and pipeline corrosion, perforation, and leakage will cause huge economic losses and impact the environment. At present, China’s high corrosion environment in the anti-corrosion treatment has made certain achievements, but the problems still cannot be ignored. First of all, the research on anti-corrosion technology needs more attention; anti-corrosion theory and technology still need improvement. Secondly, the quality of personnel engaged in anti-corrosion work needs to be improved, which is also an important reason for the backwardness of anti-corrosion work. Finally, the pipeline anti-corrosion system needs to be sound; many enterprises in the anti-corrosion work as a sham. All of these are serious obstacles to our anti-corrosion work.
1. The current situation of seaside corrosion
1.1 Equipment corrosion status
First of all, the treatment of substrates. For the steel structure of the equipment frame, equipment manufacturers in the production process, most manufacturers of the substrate are not sandblasted, even if part of the sandblasted treatment, the general level of treatment is not enough, resulting in the adhesion of the outer coating does not meet the requirements. Secondly, the quality of the anti-corrosion coating is generally low. Some manufacturers need to fully by the design requirements for coating, individual manufacturers even in the case of not painted primer directly painted surface paint. In the coating thickness of most equipment manufacturers, the coating thickness does not meet the design requirements; according to years of on-site testing experience, the coating thickness of most of the 80 – 150 individuals is even lower to only 30, so the corrosion is very serious. For equipment manufacturers of outsourcing accessories, the general anti-corrosion standard is low. Still, manufacturers did not do special treatment, and some even directly painted alkyd paint, resulting in most of these parts failing to meet the requirements of using the marine high corrosive environment, resulting in a more serious corrosion phenomenon.
1.2 Corrosion of pipeline fittings
The corrosion of pipeline fittings is also relatively serious, mainly due to the carbon steel pipeline in the sandblasting anticorrosion and field paint construction process is not in strict accordance with the corresponding construction standards for construction, for example, the site environment of the temperature, humidity, and paint ratio is not by the requirements and not in strict accordance with the construction procedures for construction. In addition, sandblasting anti-corrosion components in the transportation and site lifting process destroyed the anti-corrosion layer. It did not paint in time to repair, causing corrosion.
1.3 Field material corrosion
Factory use of stainless steel piping and components, galvanized components, etc., also often occur more serious larger area corrosion; the reason is that these special materials cannot withstand the impact of the highly corrosive environment of the seaside, but also did not take special protection measures, in the use of a longer period caused by corrosion phenomenon occurs.
2. Seaside corrosion repair
2.1 Repair of steel structure and the main body of equipment
2.1.1 Material matching test before repairing
In the main body of the equipment, to determine whether to use the coating and the original coating is matched, the specific method is in the original coating on the new coating of a small area of the coating, 1d after the observation of the coating epoxy coating condition, if the new coating is not wrinkled, biting the bottom of the phenomenon occurs, it can be considered that you can use the new epoxy coating directly for repair.
2.1.2 Surface treatment
For the original coating, which has a good match with epoxy coating, it is only necessary to mechanically polish the coating surface and remove the rust, oxidized skin, and other pollutants which are not firmly attached without affecting the adhesion of the original coating. For epoxy coatings that cannot be a good match for the coating system and cannot be directly coated repair, the surface should be a comprehensive sandblasting treatment until the original coating is removed and all cleaned before repair coating. In addition, for the surface of the equipment is not easy to remove rust parts, can be used in the removal of floating rust with rust primer for primer coating.
2.1.3 Common programs for repair coating
- Option 1: Spray 2 coats of 725l-h06-1 thick-slurry epoxy zinc-rich primer, then spray 2 coats of 725l-h53-1 thick-slurry epoxy ferro-iron-preventive paint, and finally spray 2 coats of 725l-s43-2 aliphatic urethane topcoat, with the total thickness of the coating being 310µm.
- Option 2: Spray 3 coats of 725lh53-1 super thick slurry epoxy ferro-iron-preventive paint and 2 coats of 725l-s43-2 aliphatic polyurethane topcoat after mechanical sanding of the surface, the total thickness of the coating is 290µm.
- Option 3: After removing the loose floating rust on the surface of the equipment, spray 2 coats of 725l-hl-38 super-adhesive long-lasting antirust primer, then spray 2 coats of 725l-h53-1 thick-slurry epoxy ferro-iron-preventive paint, and finally spray 2 coats of 725l-s43-2 aliphatic urethane topcoat to make the total thickness of the coating reach to 320µm.
2.2 Repair of equipment fittings
The original coating of the equipment parts is mostly thermal spraying, considering that the general thickness of the shell of the equipment components is small; it is unrealistic to imitate the above method. Therefore, the general plan is: firstly, remove loose floating rust after simple mechanical grinding of the corroded parts, spray 2 courses of 725l-hl-38 super-adhesive long-lasting antirust primer, and then spray 2 courses of 725l-h53-1 thick-slurry epoxy ferric iron oxide antirust paint, and finally spray 2 courses of 725l-s43-2 aliphatic polyurethane top coat, so that the total coating thickness reaches 320µm. Then spray 2 coats of 725l-h53-1 thick slurry epoxy ferric oxide paint, and finally spray 2 coats of 725l-s43-2 aliphatic polyurethane top coat so that the total thickness of the coating reaches 320µm.
2.3 Repair of stainless steel
The refinishing program for stainless steel is to firstly polish the whole surface of stainless steel, then spray 3 coats of 725l-h53-1 super thick slurry epoxy ferro-iron-preventive paint, and then spray 2 coats of 725l-s43-2 aliphatic urethane topcoat so that the total thickness of the coating reaches: 290µm.
3. Anti-corrosion in the high corrosive environment at the seashore
3.1 Design to strengthen the application of anti-corrosion technology
As far as possible, use special materials suitable for coastal high corrosion environments, improve the corrosion resistance of steel itself, that is, the use of high corrosion resistance of weathering steel, enhance the corrosion resistance of the material itself. At the same time, the design as far as possible to use a long-lasting anti-corrosion process.
3.1.1 Hot-dip zinc corrosion prevention process
This treatment method is the first of the steel components’ rust treatment, and then immersed in the melted zinc liquid so that the surface of the steel components is attached to the zinc layer to achieve the purpose of corrosion prevention. The main advantage of this anti-corrosion treatment method is that the durability of anti-corrosion is good and, under normal circumstances, can reach about 10 years. At the same time, industrialized production quality is easy to ensure.
3.1.2 Heavy anti-corrosion coating technology
The basic idea of this anti-corrosion technology is to use the primer, intermediate paint, and top coat composed of a multi-layer coating system to improve the anti-corrosion effect and durability. The paint varieties used are epoxy zinc-rich primer, epoxy mica iron oxide intermediate paint, and epoxy or polyurethane or chlorinated rubber top coat. In addition, zinc powder in the primer can also provide cathodic protection for steel components. It can be seen from the process concept that this protection method is mainly based on isolation protection. Therefore, it has the disadvantage of aging and chalking of the coating to affect the protective effect.
3.1.3 Thermal spraying zinc or aluminum coating technology
This protection method has been developed from flame spraying to arc spraying, spraying materials from the original zinc spraying development to spraying aluminum and various alloys. Due to the use of arc spraying to improve efficiency and safety, the coating quality has also been greatly improved and, therefore, widely used. The durability of this anti-corrosion technology is ideal, general protection life of up to 30 ~ 50 years or more; therefore, thermal spraying long-lasting anti-corrosion technology has great potential for development.
3.1.4 Cathodic protection
Cathodic protection is a kind of electrochemical anti-corrosion method that has been widely used in the anti-corrosion of underground and underwater pipelines. Its principle is to use the conductivity of water or soil through the anode or continuously applied current to the pipeline to transport electrons to protect the pipeline. Cathodic protection can be divided into applied current and sacrificial anode in two ways; the choice should be based on the size of the project, the availability of a convenient power supply, the density of the protection current required by the protected body, the size of the soil or water resistivity and other factors for comprehensive consideration. The cathodic protection should be constructed simultaneously with the main project and operated within 6 months after the pipeline is put into the ground or water.
3.2 Application of anti-corrosion measures in construction
- (1) Construction method control in several key points. (1) Before construction, we should remove the dust and oil on the surface of the workpiece and then grind or sandblast. (2) After the surface treatment should be sprayed primer in time to prevent secondary pollution. (3) To strictly control the paint ratio to ensure the quality of the paint ratio. (4) After each process’s completion, protective measures should be taken to ensure that the surface is not contaminated. (5) Due to transportation and installation of the coating damage caused by timely repair. (6) Special material selection in line with the local climate conditions of the material type for procurement to avoid corrosion of special materials on site.
- (2) The use of total quality management methods in strict accordance with the construction program construction. The construction unit should be set up to monitor the quality of the specialized agencies and develop appropriate quality management rules and regulations. Clear responsibilities and authority, the responsibility and power to each responsible department, to enhance the effectiveness of management. For example, the person in charge of technology should be responsible for the quality of construction, and the relevant person in charge must be on the spot to solve various technical problems promptly to ensure that the construction by the design requirements. In addition, it is also necessary to strengthen staff training and learning, clear construction requirements for each subsection, construction methods, and quality standards, and thus organize construction, inspection, and acceptance.
Coastal corrosion in a highly corrosive environment is a technical problem. Corrosion not only affects the equipment and steel structure of the beautiful but also affects the service life of the equipment and the operation of the important safety factors. Therefore, it is necessary to take all the measures to control and solve the corrosion of equipment and pipeline to avoid safety hazards. This paper combines their work experience for the coastal areas of metal equipment, pipelines, and components of the corrosion resistance of the current situation, repair methods, and how to strengthen the coastal high corrosion environment corrosion problems were briefly analyzed and reached some useful conclusions.
Author: Fang Gang