With the continuous growth of the social economy. All walks of life have also entered a stage of rapid development. Because stainless steel has good corrosion resistance and processing performance. It is very suitable for making pipelines for transporting chemicals. So, storage tanks and pipelines made of stainless steel are used to transport more and more chemicals. With the gradual increase in the quality of stainless steel rectangle tube. It is an inevitable trend to strengthen stainless steel rectangle tube processing technology.
1. Corrosion resistance and common corrosion phenomena of stainless steel rectangle tubes. Because of the existence of oxide film, stainless steel has good corrosion resistance. This is because when the metal is damaged to a certain extent. The oxide film exists as a protective cathode to prevent the metal from being corroded. The chemical composition of the stainless steel base material is also very important.
The most common corrosion of stainless steel rectangle tube is as follows:
(1) Pitting corrosion. As the name implies, Pitting corrosion is local corrosion. Caused by local damage to the oxide film. Due to the presence of dust on the surface of the steel. The stainless steel rectangle tube has some holes invisible to the naked eye during the production process. And the pitting corrosion of the stainless steel rectangle tube under the action of the external environment.
(2) Crevice corrosion. Crevice corrosion is making stainless steel rectangle tubes. There are some unavoidable cracks at the joints of the pipes, or the lower ends of gaskets and screws. These cracks will cause local corrosion of the stainless steel rectangle tubes.
(3) Stress corrosion. The phenomenon of stress corrosion of stainless steel rectangle tubes is not very common. The pipes are often subjected to larger tensile forces. Causing cracks on the stainless steel surface, causing stress corrosion.
(4) Intergranular corrosion. The intergranular corrosion of stainless steel rectangle tubes is caused by chromium carbide deposits. When stainless steel is heated, which reduces the chromium in the adjacent area. So that the stainless steel rectangle tube usually has severe intergranular corrosion.
(5) Electric corrosion. Stainless steel is brought into contact with another alloy in an electrolytic solution. Resulting in a potential difference. The above-mentioned corrosion phenomena are usually caused by improper maintenance or improper use. For example, there is a high chloride content in the pipeline. Becomes the most corrosive stagnant solution. If the weld of the pipe is not cleaned completely. It will be High-temperature oxides are produced on both sides of the root.
2.6.9 Material selection and pipe joint connection.
When selecting the material of stainless steel rectangle tube. The chemical composition and the content of the required elements should be considered. Also, attention should be paid to the connection form of the stainless steel rectangle tube. In this way, stainless steel rectangle tubes’ corrosion resistance can be ensured. But this puts higher requirements on the processing technology of stainless steel rectangle tubes.
(1) Treatment of butt welding of pipes. To achieve corrosion resistance of stainless steel rectangle tubes, the welding requirements are high. And it is required that each joint of the pipe should be tested for flaws. To cut pipe corrosion during welding. It is necessary to fill the pipe with argon for protection during the welding process. If the oxide film is processed at the construction site of the pipe. It is easier for the surface passivation of the pipe. But more difficult to passivate the inside. Which involves a large amount of waste liquid and flushing water. , Not only requires a lot of costs, but the effect is not very satisfactory.
(2) Features of flange connection. Facing a series of problems caused by traditional butt welding. stainless steel rectangle tubes are connected by flanges, which can avoid problems. Although the flange connection method increases the production cost to some extent. compared with the traditional passivation process. The flange connection method is not only easy to operate. But also the quality of the stainless steel rectangle tube is more assured. The passivation treatment of the flange connection is to coat the inner. The pipe finish with specific passivation pastes to achieve the purpose of passivation. The technology of flange connection is very simple. And no special treatment is required in the later stage of pipe production.
3. Analysis of the key points of the processing technology of stainless steel rectangle tube
(1) The blanking of stainless steel rectangle tubes. Blanking stainless steel rectangle tubes, according to the actual processing conditions. Use special stainless steel cutting machinery as much as possible. And try to avoid using plasma machine flames to cut stainless steel. Also, for the cut stainless steel blanking, carbon steel must not be used as the blanking shelf.
(2) The school tube of stainless steel tube. Stainless steel tube calibration. Strict requirements must be made on the environment of the calibration tube. The tube calibration must be performed on a specific platform for the stainless steel tube. In the production process of stainless steel rectangle tubes. No contact with carbon steel materials is allowed. Because once the iron powder in carbon steel comes into contact with stainless steel. It will cause stainless steel pollution and cause different degrees of corrosion.
(3) Connection of pipes and valves and other equipment. In stainless steel rectangle tube systems, butterfly valves are generally used to connect pipes to each other. Although the butterfly valve is compact in structure. And beautiful in appearance when connected, its strength is not very high. When performing stainless steel rectangle tube calibration. Special attention should be paid to the distance between pipe flanges. So on cause excessive stress on the stainless steel rectangle tube in use. Causing the butterfly valve to rupture or stress corrosion. When performing partial repairs on stainless steel rectangle tubes. If and assembly is difficult due to the rigidity of the pipes. The range of stainless steel rectangle tubes should be expanded to avoid local force and assembly. Resulting in insufficient connection of stainless steel rectangle tubes. In the welding process in the field, flanges should be used for connection as far as possible. The use of flanges for connection can avoid the problem. That stainless steel rectangle tubes cannot be passivated after butt welding.
It is worth noting that ordinary wrenches can be used to fasten stainless steel rectangle tubes. But it is necessary to avoid direct collision between the wrench and the pipes. To avoid scratches and corrosion. (Next to page 277) 277 Management and other Management and others will also be improved.
After testing, it is about 0.64mL/100g~0.66mL/100g. This value will continue to increase with the increase in temperature. Omit aluminum alloy welding, the temperature of the molten pool is high. Different welding methods have certain differences in the temperature of the molten pool. The solubility of hydrogen dissolution.
Cooling and solidification of aluminum alloy will also continue. Once the solubility exceeds a certain value. The state of hydrogen is unstable and even repelled. If hydrogen cannot pass through the interface between solid and liquid. Pores will be formed at the joint. It can be seen that during the welding process of aluminum alloy.
The formation of pores and hydrogen pores is also related to the temperature and the molten pool. The effective intervention of the condensation time of the molten pool can be achieved by increasing the cooling rate. Promoting the operation and discharge of bubbles. thereby reducing the number of hydrogen holes or reducing the size of hydrogen holes.
(2) Suppression measures for hydrogen pores. The hydrogen contained in the aluminum alloy comes from the moisture adsorbed. On the surface of the welded material. The organic matter of the filler material in the aluminum alloy. During the process of welding the aluminum alloy. The oxide film on the surface of the welded material can absorb moisture. The main source of hydrogen in the welding process is the main factor causing hydrogen pores.
Before welding, through reasonable chemical treatment measures. And milling treatment measures to cut the oxide film on the surface of the welded material. The purpose of reducing the hydrogen content. Reducing the hydrogen pores can be achieved. The use of physical measures, such as sandblasting, polishing, laser treatment, etc. Removing oxides on the surface of the welded material. It can also reduce the hydrogen generated during the welding process.
After testing, compared with polishing, sandblasting, etc., the laser treatment effect is best, but after the surface treatment, welding should be carried out in time, otherwise, the surface of the welded material will form an oxide layer again.
Welding strength and efficiency can also interfere with the cooling rate of the molten pool. To inhibit the formation of hydrogen pores. Under the same surface condition. The improvement of the cooling rate of the molten pool. It can be achieved by increasing the welding speed.
The increase in welding speed inhibits the precipitation and condensation of hydrogen. The increase in cooling speed can get supersaturated joints. Thereby reducing the number of hydrogen holes. Also, high-strength welding, such as high-density laser welding. It can improve the stability of the keyhole during the welding process. Extend the solidification time, allow the hydrogen to be mobilized. Promote its overflow, and reduce the number of hydrogen holes.
During the welding process, the outside air temperature, humidity. And the atmosphere will also affect the formation of hydrogen holes. The test results show that in the case of low outside temperature conditions. The number of hydrogen holes for welding aluminum alloys is small. If the temperature is higher and the humidity is higher.
The number of hydrogen holes will increase. Under high-temperature conditions, the gas turbulence is strong. And the surrounding air will enter the molten pool during the welding process. Thereby producing more hydrogen. The ambient temperature during welding is not less than 5℃ and the humidity is not less than 65℃. There should be no draught during welding.
4.6.9 The pores that often appear in aluminum alloy welded joints. It can be roughly divided into two types: cavities and hydrogen pores. The formation mechanisms of the two pores are somewhat different. During the welding process. It is necessary to analyze the factors that lead to the increase of pores. And select targeted suppression methods based on the mechanism of cavitation. And hydrogen pore formation so on improves the welding quality. The suppression methods mentioned in the article may be shallow. These contents can provide a reference for the majority of practitioners. More in-depth issues are expected to be further explored by the practitioners.
(4) Surface treatment of stainless steel rectangle tubes. When the stainless steel rectangle tube is passivated. Also to the passivation of its surface and interior. It is also necessary to perform strict passivation on each weld of the pipe. There is no way to passivate the pipes in the infields that process stainless steel rectangle tubes. And they need to be sent to specialized manufacturers for passivation.
(5) Requirements for the processing area of stainless steel rectangle tubes. Whether processing or storage, stainless steel rectangle tubes have high environmental requirements. This is to avoid contamination and corrosion of stainless steel rectangle tubes. So, in the production process of stainless steel rectangle tubes.
Appropriate protective measures must be taken. Omit to transport stainless steel rectangle tubes, it is necessary to use lifting tools that can be covered. No matter an iron rope or a chuck. It should not contact the stainless steel to avoid iron contamination and corrosion.
Using stainless steel coffins, try to take them from the hanging basket as much as possible. And try not to place them on the ground. If the pipe must be placed on the ground. Then non-metallic insulation materials need to be laid on the ground. stainless steel rectangle tubes should be placed in a separate storage area as much as possible.
It is forbidden to mix them with other metal materials. Which may cause contamination of stainless steel rectangle tubes. During the storage process, contaminants on the surface of the pipe must be cleaned up in time. And the storage environment must be kept clean and dry.
4.6.9 Process of surface treatment of stainless steel rectangle tube. To ensure that the stainless steel rectangle tube has good corrosion resistance. The surface of the stainless steel rectangle tube should be cleaned and maintained to a certain extent.
(1) Surface pickling. The use of surface pickling is to remove the remaining high-temperature. Nitrides on the surface of the stainless steel rectangle tube. And at the same time, it can also restore the corrosion resistance of the stainless steel. Before pickling the stainless steel rectangle tube. It is necessary to clean the stains on the surface of the pipe with a suitable cleaning agent. And then pickling can have a better effect. After the pickling is completed. Rinse the cleaning residue on the pipe finish with clean water.
(2) Sandblasting. Some high-temperature oxides and pollutants on the surface of stainless steel rectangle tubes. It cannot be completely removed by pickling. Now, sandblasting is required for cleaning. Sandblasting is used to clean, and the requirements for sand are high. The sand must be clean and clean. And it must not contain iron that pollutes the stainless steel rectangle tube, and it must be new sand. Once the sand has been used, it cannot be used for secondary sandblasting.
According to the relevant staff, if the stainless steel rectangle tubes are cleaned by pickling. Corrosion will appear after a period of use. So, the pickling method is not suitable for cleaning stainless steel rectangle tubes. Because of the inside of the stainless steel rectangle tube. It can no longer be passivated after welding, which causes corrosion. In the manufacturing process of modern stainless steel rectangle tubes. High-foot flange connections are used. This eliminates the defect that the pipe cannot be passivated. So that pickling will not cause corrosion of stainless steel.
5.6.9 The strong corrosion resistance of stainless steel rectangle tubes has an influence on pipes.
The requirements for the manufacturing process of stainless steel rectangle tubes are getting higher and higher. From the joining process. And processing technology of stainless steel rectangle tubes to the surface treatment process of stainless steel. Strict requirements are required according to the characteristics of stainless steel rectangle tubes. To manufacture high-quality stainless steel rectangle tubes, we have strengthened the process technology.