Pressure vessels are widely used in industrial production, especially in some dangerous industries, such as chemical industry, industrial manufacturing, high-temperature boilers, etc. Based on the particularity of the welding process of pressure vessels and the particularity of their use, the welding quality is directly related to the use of pressure vessels. Effect. If the welding quality is not up to standard, it will have a great impact on the safety of the pressure vessel. Therefore, quality control is the top priority in the management of pressure vessel welding production. This paper makes an in-depth analysis of the defects in the welding process of pressure vessels and briefly expounds on the effective measures to strengthen the welding quality of pressure vessels.
1 Problem and causes in the welding process of pressure vessels
1.1 Poor welding slag inclusion
Slag inclusion is a common problem in the welding process of pressure vessels. It is mainly manifested as impurities remaining in the weld, which not only affects the appearance but also affects the quality. There are many reasons for welding slag inclusion. First, during the welding process, the adjustment of the current parameters is small, and the molten metal pool is heated slowly and the temperature is low, and the molten pool cannot effectively float before the liquid metal solidifies. , the reason is that the viscosity of liquid metal is relatively large, the welding process is fast, and the solidification speed is insufficient, and it will be mixed in the metal molten pool to form welding slag; There are usually acid electrodes and alkaline electrodes. Different electrode types have different requirements for current. If the current regulation is not standardized and reasonable, it will cause slag inclusion in the pressure vessel. Third, the structure of the pressure vessel is special. Many pressure vessels adopt multiple or double-layer structures. If the welding surface is promptly and thoroughly cleaned during multi-layer welding, flux or residues will remain at the weld to form slag inclusions.
1.2 Poor welding pores
The porosity problem is also one of the typical problems of the welding quality of pressure vessels. Poor porosity of pressure vessels can exist on the surface or inside the pressure vessel. The internal porosity is often difficult to find, and therefore the best repair opportunity is lost. affect the quality of the pressure vessel. The main reason for the porosity is that the liquid metal molten pool itself is very easy to generate gas during the welding operation. In addition, the external gas will also be continuously mixed. If the gas cannot be effectively discharged before the metal molten pool solidifies before welding, it will form pores. Second, the wind and wind direction during welding can also cause gas to be mixed into the molten metal pool to form poor pores; third, due to raw material problems, the welding raw materials themselves have impurities remaining, and these residues will also lead to pore defects; Fourth, gas discharge The speed of the molten metal cannot keep up with the solidification speed of the liquid metal molten pool, resulting in the inability of gas residues to be discharged in time and the formation of pores.
1.3 Poor welding undercut
Undercutting is also a common quality defect in pressure vessel welding, and there are many reasons for the poor undercut.
(1) The adjustment of the current by the welding personnel is not standardized, the welding method is not scientific enough, and the welding angle is not properly grasped;
(2) When melting welding is used, the liquid metal molten pool is affected by the surface tension and its own gravity. Welding and standing welding often cause undercuts. At the same time, undercut defects are prone to occur due to the influence of gravity and tension when welding the corners and gaps of pressure vessels ;
(3) When applying electric current for pressure vessel welding, if there is a displacement deviation in the position of the welding circuit of the vessel, it will lead to arcing. Deviating from the original track to form undercut defects ;
(4) The welding speed is not well controlled, and the liquid metal molten pool cannot be filled enough when it is too fast, which will lead to the formation of a corresponding depth at the weld and cause undercut defects.
2 Problems exist in welding quality management of pressure vessels
2.1 There are loopholes in the quality management system, and the implementation of quality management is insufficient
Welding quality management is an important factor affecting the function of pressure vessels, and it is also a key link in the production of pressure vessels. With the development of the industry, the welding process and welding materials are constantly updated and improved. However, there is still a lot of room for optimization in the details of the welding quality control of pressure vessels. There are still some problems in the quality management of pressure vessels, mainly in several aspects. (1) The quality control system is not comprehensive enough. At present, a lot of new materials, new processes, and new technologies have been produced in the welding production of pressure vessels. The details and focus of the corresponding quality control have also changed, but the quality, however, the management system has not been improved in a targeted manner, which leads to the poor guidance and operability of the quality control system. (2) The factors of quality control personnel, the welding progress, and welding cost are often the top priority of enterprises, but the awareness of the importance of quality control is not enough, and the corresponding reward and punishment system in quality management is also ambiguous, resulting in quality control personnel. The sense of responsibility is not strong and the enthusiasm is not high, which leads to the inability to effectively implement the quality management system and the poor quality management effect.
2.2 The professional and technical level of the welding team is uneven
Pressure vessels are special tools, and welding processes are also special jobs. Based on the particularity of this industry, welding operators need to have good theoretical knowledge and rich practical experience. The operation requirements and quality points of different pressure vessels must be Understood and be able to implement the relevant regulations of welding quality management in place. (1) The uneven professional and technical level of the welding team is still serious. The pressure vessel welding positions are relatively hard, and the work content is boring. The mobility of the welding team is relatively large, and the frequent replacement of operators in the welding positions is not conducive to the quality management system. Due to the limitation of their own consciousness and cultural level, some welding personnel has limited willingness to improve their professional skills and accept new welding processes, resulting in low welding level. (2) The company lacks corresponding training for welding operators. Different welding requirements for different vessels have different welding processes, and the focus of quality control will also be quite different. However, the professional skills training of employees is insufficient, and some new personnel does not grasp the main points and key points of container welding, and the quality awareness is weak. If they do not operate according to the requirements of the welding process, the current adjustment and control are not in place, the welding process is random, and the quality requirements in the welding process are not clear and blind. Welding leads to hidden quality problems, these are typical problems affecting the quality of containers, and they are also obstacles in welding quality management.
2.3 The welding operation process management is not strict, and the detection level is backward
The welding process of pressure vessels requires a high level of professional skills and a high degree of quality awareness. Based on the particularity of the product form of pressure vessels, the omission of any detail in the welding process will cause quality problems to varying degrees, which will lead to subsequent problems. Use to bury a safety hazard. At present, in the specific welding process of pressure vessels, the process management and supervision of welding operations are not strict, and there is no effective supervision of the welding process in combination with the quality requirements of pressure vessels. In addition, the quality inspection level and inspection methods of pressure vessels are still relatively backward, and the lack of application of advanced inspection technology concepts and means has resulted in some hidden quality problems not being discovered, so they cannot be carried out during the welding process. Effective prevention, resulting in hidden quality problems in pressure vessels.
3 Optimization measures for welding quality of pressure vessels
3.1 Improve the content and process of pressure vessel welding quality inspection
The welding quality inspection of pressure vessels is divided into several parts, and the inspection content and process should be improved according to these steps and links, so as to ensure the welding quality. (1) Inspection before welding. The pre-welding inspection mainly includes: whether the welding technical documents are complete, whether the raw materials involved in the welding are qualified, whether the performance and condition of the equipment involved in the welding are good, and whether the auxiliary materials such as welding rods and fluxes to be used in the welding meet the quality requirements and process requirements. , whether the welding operators have received relevant training and are certified to work. The main contents of the welding process inspection: ①Whether the operation of the welding equipment is in good condition and there is no potential safety hazard. ②Whether the operation methods of welding operators meet the quality standards, the inspection of the welding process is the core link. Strengthening the inspection of this link can effectively prevent the formation of welding defects, and at the same time, it can also play a good role in preventing defects. (2) Inspection of finished products. The inspection of the finished product is the final stage of welding quality assurance. The inspectors must conduct meticulous inspections in strict accordance with the quality standards and related inspection steps, and deal with specific problems.
3.2 Apply advanced welding quality inspection technology
The welding process of pressure vessels is relatively complicated, especially for some vessels that require multi-layer welding, it is impossible to accurately detect welding defects only by simple visual inspection. Therefore, advanced welding inspection techniques such as non-destructive testing should be actively applied. Non-destructive testing refers to a method of quality inspection of the internal structure, nature, and state of the weldment with the help of advanced equipment and technical means on the basis of not damaging the weldment. One of the most reliable methods found to show exactly the shape, location, and size of the defect inside the weld. Non-destructive testing technology for welding quality can be divided into radiographic testing technology, magnetic particle testing technology, ultrasonic testing technology, penetrant testing technology, thermal imaging infrared testing technology, pulsed eddy current testing technology, etc. Different testing technologies have their own characteristics and advantages. Therefore, the detection of welding quality should also be combined with materials, requirements, and technology to achieve a good detection effect.
3.3 Reform the welding process and improve the professional skills of welding personnel
To fundamentally improve the welding quality of pressure vessels, it is necessary to strengthen the welding process and improve the professional skills of welding personnel. (1) The welding process should be optimized, especially in terms of equipment parameters such as current adjustment, welding techniques, angles, etc., to summarize the experience, and to form standardized texts, which will be fully and systematically implemented. (2) It is necessary to strengthen the professional skills training of welding operators. Welding is a comprehensive professional technology. Factors such as material, equipment, and the process will affect the final welding quality. Systematic and targeted training will help the operation. Personnel can master the differences in welding processes applied to different containers and materials, and effectively improve their professional level.