Fifty Years of Welding in Chinese Power Plants

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1 Overview of Power Plant Welding: With the development of China’s power industry, power plant welding has a history of fifty years. Looking back on these past fifty years, we cannot help but feel proud and satisfied at the outstanding achievements made by the field of welding. Today, our country’s electricity industry has evolved from 1,850 MW at the beginning of the nation’s establishment, ranking 21st in the world, to becoming a major global power in electricity production. By the end of 2001, China’s installed electricity capacity had reached 338 million kilowatts, with annual power generation amounting to 1.478 trillion kilowatt-hours; both its installed capacity and annual power generation ranked second in the world ； Currently, there are 92 power plants in the country with an installed capacity of 1,000 MW or more; among them, 16 are hydroelectric plants and 1 is a nuclear power plant ； There are currently 848 thermal power generators in the country with a capacity of 100MW or more, of which 290 have a capacity of 300MW or more ； 354 units of 40MW and above, of which 52 are 300MW and above ； 5 nuclear power units of 300MW and above, with 6 under installation. Large-scale units have become the main power generation units in China. At present, China has begun to form an overall structure of power generation equipment characterized by thermal power generating units, supplemented by rapidly developing hydroelectric and nuclear power units. The power generation capacity basically meets the needs of the national economic development. All these advancements and developments are closely related to the hard work of welders in the power industry. Due to the increase in unit capacity and parameters, the types and specifications of steel and welding materials used have become increasingly complex. The volume of work has increased, the number of welds has risen, there are more welds between different types of steel, the wall thicknesses of pipes have increased, and the requirements regarding safety have also become stricter. As a result, the standards for welding process quality and inspection have become more rigorous. These technological changes require welders in power plants to improve quality, enhance efficiency, and increase the durability and safety of welds, in order to meet the demands of modern advanced power plant welding technologies. 2 Development and Current Status of Welding Technology in Power Plants. As the most economical and effective method of joining, welding has evolved alongside the development of steel materials. Over the past century, with the advancement of industrialization, the variety of steel grades has increased rapidly, and welding technology has seen swift development, making great progress in various aspects such as welding methods, welding materials, welding processes, and welding quality control. China’s power plant welding technology has also evolved in line with this trend. The development trends and characteristics of welding work in power plants vary depending on the type of unit, with the main difference lying in the different development trends of the steels used in various types of power plants (the materials that are welded). Given the current situation, thermal-strength steel is regarded as the main focus for welding research and development in thermal power plants ； For hydropower stations, high-strength steel is the main direction for research and development in welding. 2.1 Thermal Power Plants 2.1.1 Steels Used for Key Equipment in Power Plants and Their Welding From 1879, when China’s electric power industry began, until the early 1950s, low-pressure units as well as a small number of medium-temperature and medium-pressure units were in use. The steel primarily employed was 20 steel (high-quality carbon steel), with a large amount of cast steel components also being used; welding was used less frequently. It was not until the installation of medium-temperature and medium-pressure units as well as high-temperature and high-pressure units in the early 1950s that welding could truly be considered a practical technique. On this basis, over the past 50 years, the steels used for the main equipment in power plants in our country, as well as the welding techniques associated with them, have gone through the following development stages: (1) Ordinary carbon steel and high-quality carbon steel, supplied in hot-rolled or quenched and tempered condition, with operating temperatures below 450°C. Welding in this context did not have any specific industry-specific characteristics; the focus of welding control was on improving the quality of welds by enhancing the skills of welders. Such steels were used in power station boilers and pressure pipes before the 1950s; today they are mostly used in auxiliary equipment and pipes operating at temperatures below 450°C. During this period, 12Mo steel was developed, which could slightly increase the heat resistance temperature (below 480°C). Welding of this steel did not present any new characteristics, and it is now rarely used due to the graphitization tendency of Mo steel. (2) Cr-Mo and Cr-Mo-V low-alloy heat-resistant steels generally have a Cr content of less than 3%. Almost all of them are supplied in a quenched and tempered condition, allowing their service temperature to be raised to below 545°C. These types of steel have been in use since the 1950s to the present; represented by 12CrMo, 12Cr2Mo (10CrMo910), and 12Cr1MoV, they can be considered the first generation of heat-resistant steels. Since it is supplied in a quenched and tempered state, its welding characteristics differ significantly from those of the steel mentioned in category (1) above. The addition of heat-resistant alloy elements increases the likelihood of weld cracks, and the complexity of the welding process also rises; in most cases, preheating before welding and post-weld heat treatment are required, although there is still a considerable margin for variation in the process parameters. In the 1960s, several low-alloy heat-resistant steels reinforced with multiple compounds were developed in our country; Steel 102 (12Cr2MoWVTiB, suitable for use at temperatures below 580°C) is a representative example, and its welding characteristics are similar to those of other steels in this category. (3) The early 9Cr-1Mo and 12Cr-1Mo steels were all supplied in the quenched and tempered condition, and their operating temperatures were also increased to below 600°C; these steels can be regarded as the second generation of heat-resistant steels. 9Cr-1Mo steel appeared in imported units installed in China during the 1960s, such as Sweden’s HT7 ； 12Cr-1Mo steel appeared in imported units installed in China in the early 1970s, such as the German F12 and F11 models and the Swedish HT9 model. Due to their high carbon and alloy element content, these types of steel have very poor weldability, and strict adherence to welding procedures becomes a key requirement during the welding process. Its typical processing sequence includes preheating, welding (with strict control of the heat input during welding), cooling to a temperature below the martensite transformation temperature for a certain period of time, and then immediately raising the temperature to carry out post-weld heat treatment. It took welding workers in the power industry many years to understand this characteristic of welding; despite investing a great deal of effort and time in research, their focus remained on overcoming welding cold cracks. (4) Modified 9Cr-1Mo steels, namely T91/P91 steels, were developed in the United States from the 1970s to the 1980s based on earlier 9Cr-1Mo steels. They appeared in imported units installed in China in the mid-1990s, and are now widely used in large power plant boilers in our country. This type of steel can be regarded as the third generation of heat-resistant steels. Its main feature is a reduced carbon content; it also relies on multi-element composite strengthening, but the amounts of each alloying element are strictly controlled, which improves the steel’s plasticity and weldability as well as its high-temperature stability. Its endurance strength at 600°C is nearly 70% higher than that of F11 and F12. In the process of welding such steels in the power industry, access to advanced foreign technical literature and decades of experience in welding steels of categories (3) and (4) have brought about a significant shift in welders’ mindset. They have gradually moved away from the previous approach—which paid little attention to the amount of heat input during welding of steels of categories (1) and (2)—to today’s understanding: that welding procedures and operating techniques are not the same thing; in the welding of such steels, the importance of the welder’s operating technique has become secondary ； The welding process used must be evaluated. The basis for this evaluation is no longer a series of room-temperature mechanical properties; instead, emphasis is placed on verifying whether the welded joint can achieve the desired plasticity, toughness, and metallographic structure ； Welding of such steels should be strictly controlled throughout the entire welding process. Compared to earlier 9Cr-1Mo steels, this type of steel requires greater rigor in welding procedures. The allowable heat input during welding must be strictly controlled; furthermore, the temperature and holding time of post-weld heat treatment have a significant impact on the toughness of the welded joints, and thus must be given due attention. (5) T92/P92 (NF616) and T122/P122 (HCM12A) steels: In the early 1990s, first in Japan and then in Europe, based on the accumulation of extensive long-term operating data for T91/P91 steel, research and development efforts were carried out to further improve and standardize T91/P91 steel as well as 12Cr-1Mo steel. These efforts resulted in a new generation of heat-resistant steels aimed at ensuring stable performance under prolonged high-temperature conditions. They can be regarded as the fourth-generation products among heat-resistant steels. Its main features include the addition of tungsten, a reduction in elements such as molybdenum that impair the steel’s high-temperature stability, and the improvement of the rolling process through controlled rolling technology. As a result, its high-temperature stability has been significantly enhanced; its creep strength at 620°C is nearly 40% higher than that of T91/P91. T92 steel was already used in imported units at the end of the 1990s. The characteristic of welding this steel is that it has been thoroughly studied and manufactured; even with stringent requirements for the welding process, it is not possible to achieve the performance levels of the steel itself, which further underscores the importance of the welding process. Some large domestic boiler manufacturers have completed the welding procedure qualification for T92/P92 steel; its widespread application is imminent. T122/P122 steel was also developed following this approach, based on F12 steel, and has since been put into use. It has not yet been introduced in China, so it is necessary to gather more technical information and build up technical capabilities. 2.1.2 Changes in pipe specifications In addition to advancements in steel materials, another characteristic of welding in thermal power plants is that the diameter and wall thickness of steel pipes tend to increase along with the growing capacity and parameters of the units. For example, the main steam pipes for 500 MW supercritical units are made of 15Cr1Mo1V steel, with specifications of φ426×80 mm ； The main steam pipeline of the 600MW supercritical unit is made of P22 steel, with specifications of φ654×136.5mm ； The main steam pipeline of the 660MW unit is made of P91 steel, with specifications of φ450×40mm ； The workload for welders increases, and high standards are required of their skills. 2.1.3 Increase in welded joints of dissimilar steels. In particular, for imported units, different steels are selected according to various temperature ranges. Consequently, while ensuring that the inner diameter remains the same, welds involving dissimilar steel joints with different outer diameters and wall thicknesses have come into existence. 2.2 Hydropower Stations The welding of hydropower stations in China can be traced back to the mid-1950s; until the mid-1980s, welded hot-rolled steel was used, typically materials such as Q235, 16Mn, 18MnMoNb, or steel with strength levels equivalent to these. The welding process for hot-rolled steel is relatively simple; however, since the 1970s, with the use of steel grades such as 16Mn and 18MnMoNb with higher strength, post-weld heat treatment became an additional step in the welding process as the wall thickness of the pipes increased. In the mid-1980s, represented by the Shisanling Pumped Storage Power Station, welding in hydroelectric power stations entered a new era. Although to this day no new types of steel have been developed for the structural components of hydroelectric plants, the use of imported high-strength steels in pressure pipes, along with the welding techniques associated with them, has brought welding in this sector into a new phase. Research on high-strength steel around the world constitutes a distinct field, and great progress has been made in increasing the yield strength of such steel. High-strength steels with yield strengths of 60 kg/mm2, 70 kg/mm2, and even above 100 kg/mm2 are already in use in practical applications. The lower horizontal section of the pressure pipes at the Shilin Pumped Storage Power Station uses HY-70, which is produced in Japan and has a yield strength of 70 kg/mm2. There is a trend in China’s hydropower stations toward using steel with even higher strength levels. To achieve high strength, modern high-strength steels exhibit the following development trends: they adopt a multi-element micro-alloying approach; in order to increase strength while minimizing losses in ductility and toughness, the carbon content is reduced alongside the addition of alloying elements to ensure good weldability ； During the steel production process, it is supplied in a quenched and tempered heat-treated state to improve its overall properties ； Controlled rolling technology is used in the production of higher-grade steel, and the extremely fine grains ensure that the steel possesses superior properties. Due to the performance characteristics of high-strength steels, as well as their smelting and rolling conditions, the following welding process characteristics have emerged, with the main purpose of preventing cold cracks: As the strength level of the steel increases, its hardenability also rises; consequently, preheating prior to welding and maintaining the interpass temperature become even more important. For fine-grain high-strength steel, the requirements regarding welding heat input are extremely stringent; even a slightly higher heat input leads to grain growth, resulting in unacceptable impact toughness. Therefore, for welders in hydropower stations who mainly work with welded hot-rolled steel, in addition to the need to improve their welding skills, it is even more important to change their mindset and enhance their awareness and understanding of welding processes. Great progress has been made in this area over the past decade or so. To prevent the occurrence of delayed cracking, post-weld heat treatment is also a necessary measure. In summary, the complexity of welding processes in hydropower stations has also seen significant improvement due to the use of high-strength steel. The steel pipes used in hydropower stations are mainly large-diameter thin-walled pipes; in recent years, the pressure pipes used in such stations have also tended to be thicker-walled. For example, the lower horizontal section of the pressure steel pipe in the Shisanling Pumped Storage Power Station has a wall thickness of 40 mm and a diameter of 600 mm, which is similar to that of the high-temperature resistant steel pipes used in thermal power plants. In contrast, the largest steel pipe in the Three Gorges Project has a diameter of 12.4 meters and a wall thickness of 60 mm. The welding method primarily used for installing the pressure pipes in hydropower stations is shielded metal arc welding, while submerged arc automatic welding is mainly used for the manufacturing of these pipes. Additionally, with the implementation of large-scale water conservancy projects in China, the hydraulic metal structures used in hydropower stations are also trending towards larger sizes. For instance, the total weight of the metal structures and hoists used in the Three Gorges Project amounts to 147,100 tons. There are 282 gates in total, including various service gates and maintenance gates. For these steel gates manufactured through welding, the welding deformation must not exceed 5–10 mm over a length range of 40–60 meters. This places very high demands on the ability to control welding deformation during the manufacturing process. 2.3 Development of welding application technologies in power plants 2.3.1 Mastery of welding processes for medium and high-alloy heat-resistant steels. Taking the welding of F11 and F12 steels (12Cr-1Mo steels) in the early 1970s as an example, this difficult welding problem was successfully resolved through a series of processes: the design and preparation of welding procedure documents, welding procedure qualification, the preparation and technical briefing of welding work instructions, control of the welding process (preheating, welding, heat treatment), as well as intermediate and post-weld inspections. During this development process, it became evident that the concept of \"welding technology\" was gradually being accepted, which provided the necessary technical foundation for the subsequent welding of 9Cr-1Mo steel, T/P91 steel, and T/P92 steel. 2.3.2 Promotion of TIG welding process In the 1970s, with the installation of imported generating units, the welding practices in the power industry began to adopt TIG welding for the root pass and shielded metal arc welding for the finish pass; subsequently, the all-TIG welding process for thin-walled pipes was also introduced. Within just a few years, TIG welding achieved significant development in the power industry. The use of TIG welding increases the qualification rate of welds while **reducing** the leakage rate at the weld seams. 2.3.3 Promoting efficient and advanced welding methods Throughout 50 years of welding in power plants, efforts have been made to promote and adopt efficient and advanced welding methods. As early as the 1970s, the power industry developed technologies such as TIG all-position automatic welding with small-diameter pipe control, CO2 all-position automatic welding with short-circuit transition for medium and large-diameter thin-walled pipes, narrow-gap MIG all-position automatic welding with spray transition for large-diameter thick-walled pipes, and magnetic crawling flame cutters. Among them, the magnetic crawl-type flame cutting machine technology was introduced to Beijing Welding and Cutting Tools Factory in the early 1980s, and it is still being produced and sold to this day ； The program-controlled TIG all-position automatic welding using small-diameter pipes has been successfully applied to welding in difficult-to-access locations during power installation, demonstrating remarkable effectiveness in ensuring welding quality. Over the past 50 years of development in power plant welding, the power industry has evolved from using shielded metal arc welding and gas welding methods to today’s practices. Presently, apart from the predominant method of TIG welding for root runs combined with shielded metal arc welding for filler passes in the welding of medium- and high-alloy steel pipes, the overall field of power plant welding also encompasses various other methods such as submerged arc automatic welding, CO2 welding, solid-wire MIG welding, flux-cored wire MIG welding, and semi-automatic welding using mixed gases. At the national welder competition organized by the China Engineering Construction Welding Association, in the CO2 welding event that was introduced for the first time, electric welders won first place. In China’s oil industry, the downward welding method using shielded metal arc welding for long-distance pipelines has been practiced for nearly 20 years; however, it has never been applied in the power industry. During the construction of the Shaanxi-Beijing natural gas pipeline in 1997, which involved units responsible for electrical work, the electric welders obtained their certificates after 7 days of training, and passed the on-site supervision exam on the 15th day; they were highly praised by the project owner. In short, new processes and methods have brought benefits to power plant welding as well as an improvement in welding quality. 2.3.4 Use of new electronic rectifier-inverter welding power sources: In the early 1980s, the AX series of rotary arc welding generators were explicitly phased out, and their production was banned in the 1990s. In the early 1990s, the power industry first introduced foreign-made rectifier-inverter arc welding power sources; by the mid-1990s, domestic rectifier-inverter arc welding power sources were widely promoted. Currently, there are around 15,000 rectifier-inverter arc welding power sources of various models in use in the power industry. The efficiency of these power sources ranges from 85% to 93%, and their output characteristics, process performance, and stability meet the requirements for welding in power plants more effectively. 2.3.5 Widespread adoption of far-infrared radiation automatic temperature control heating technology In the early 1980s, the power industry began to widely adopt far-infrared radiation heating technology. This new technology was quickly accepted by the welding sector in power plants due to the absence of the \"skin effect\" and its ease of automated control, and it soon evolved into a heating method that incorporates computer-based automatic temperature control. Automatic temperature control and automatic recording by computers play a significant role in effectively improving the quality control of heat treatment processes, as well as reducing the impact of human factors on these processes. 2.3.6 Use of advanced welding inspection equipment and methods: To improve the quality of flaw detection in pipeline welds, the power industry has developed gamma-ray sources such as cesium-137, iridium-192, and selenium-75, along with their safety devices, thereby further enhancing the level of inspection for pipeline welding in power plants. In the 1960s, the power industry began to use ultrasound for the non-destructive testing of welds. Over nearly four decades, significant progress has been made in terms of the types and methods of probes, the application methods and conditions for various waves, as well as the testing standards. The development of ultrasonic probes for thin-walled tube welds, the creation of inspection methods, and the establishment of standards are all at the leading level in China. Since the 1950s, on-site spectral qualitative analysis has been an important inspection task in thermal power plants. In this regard, great progress has been made over the past 50 years. The emergence of semi-quantitative techniques has improved the accuracy of detection, and their application has expanded from laboratories to the field. In recent years, many laboratories in the power industry have imported advanced foreign spectral equipment (which can be referred to as optical emission spectrometers). Although these devices are expensive, they are primarily used for quantitative analysis, and this new technology has raised the level of metal chemistry analysis in power plants. Since the 1980s, pen-type hardness testers have been widely used in the field within the power industry. The ease of use, accuracy, and the built-in small printer of these devices quickly rendered impact-type hardness testers obsolete. In summary, the power industry has always placed emphasis on the adoption of new technologies and equipment, resulting in rapid development of technical capabilities, which has laid a solid foundation for the advancement of technical management. 2.4 Development and production of welding materials specifically for power plants
In the early days of the People’s Republic of China, the country relied heavily on imports for welding electrodes used with heat-resistant steels in power plants. Starting in 1958, the power industry established its own welding materials manufacturing plant—the Shanghai Electric Power Repair and Manufacturing General Factory. After years of efforts, a full range of carbon steel and alloy heat-resistant steel welding materials required for power plant applications has now been developed. In particular, over the past two years, special welding wires (PP.TIG R717) and electrodes (PP.R717) designed for T91/P91 steel have been successfully developed; these can replace imported T91/P91 welding materials. At present, it is capable of producing over 80 types of welding electrodes across seven categories, with an annual production capacity of 15,000 tons. This capacity is sufficient to meet the needs related to the installation and maintenance of high-temperature, high-pressure pipelines in power plants. It can also supply various types of welding electrodes required for welding in power plants, including heat-resistant steel electrodes, surfacing welding electrodes, low-alloy high-strength steel electrodes, stainless steel electrodes, and TIG welding wires. 3 Team and organizational development for power plant welding 3.1 Development and growth of the welding team The prerequisite for implementing a quality management system is having a team composed of qualified personnel. The welding teams in the power industry have grown and developed alongside the progress of the industry itself. As early as the early 1950s, to meet the welding requirements of the high-temperature and high-pressure units supplied by the former Soviet Union, the Ministry of Electric Power organized the first training course in Ufa, thereby training a group of welders and welding technicians for China’s electric power industry. These individuals became the core of the welding workforce involved in electric power infrastructure construction, and Ufa came to be known as the cradle of China’s electric power welding technicians and high-pressure welders. Subsequently, the second and third national high-pressure welding training courses were held in 1956 (Jilin) and 1957 (Lanzhou), training over 100 high-pressure welders across the country. A welding workforce for the power industry began to take shape, and placing emphasis on the development of such a workforce became a tradition in the power industry. “The saying \"Speed is for lifting, quality is for welding,\" which was popular in the 1960s, reflects this tradition of the power industry from a certain perspective. 3.1.1 Training of welding technicians In the late 1950s and mid-1970s, nearly 200 welding technicians were trained through joint programs with research institutions and colleges. Since 1978, the metal welding and non-destructive testing programs established in the Department of Mechanical Engineering at Wuhan University of Water Resources and Electric Power have trained nearly a thousand welding technicians for the power industry. Together with students from other colleges and vocational schools who specialize in welding, the power industry now has a strong team of skilled welding technicians and managers. Since the 1970s to the present, national training courses for welding technicians have been held on an ongoing basis to ensure that welding professionals in the power industry keep up with the advancements in welding technology used in modern power plants around the world. 3.1.2 Welder Training and Assessment The history of welder training in the power industry can be traced back 50 years, starting with the first training course in Furkalaki. Great progress has been made in various aspects, including the establishment of training systems as well as the approaches and methods used for training management; this progress continued without interruption throughout a period during which China’s industry faced significant challenges and setbacks. Paying attention to welder training, as well as adhering to training standards and examination regulations, is a tradition of which the power industry has always been proud. Through years of practical experience, the industry has developed a comprehensive set of documented practices for welder training that reflect its own characteristics. Currently, there are around 20,000 high-temperature and high-pressure welders in the country’s power system, and an advanced set of welding techniques has been developed. Therefore, in various national welder competitions, electric welders have consistently ranked at the top and have managed to win the top positions. 3.1.3 Training and Assessment of Welding Instructors In the late 1980s, the power industry initiated training programs for welding instructors. Between 1999 and May 2000, drawing on years of experience in such training programs as well as referring to international standards for the assessment of welding instructors, the power industry developed the \"Rules for Assessing the Qualifications of Practical Welding Instructors in the Power Industry,\" thereby bringing the training, assessment, and qualification verification of welding instructors under standardized procedures. Currently, there are over 900 trained and certified welder instructors registered in the power industry. 3.1.4 Training and Assessment of Welding Quality Inspectors In the mid-1980s, the power industry began offering training programs to qualify welding quality inspection personnel, thereby laying the foundation for carrying out welding quality inspections in a standardized and regulated manner. Through years of hard work to date, the power industry now has a well-structured team of welding quality inspectors, comprising over 900 senior and intermediate quality inspectors. 3.1.5 Training and assessment of personnel related to welding; training and assessment of non-destructive testing personnel. Starting from the early 1980s, training and assessments were conducted for personnel involved in non-destructive testing, and certification was required before they could work. This approach was quickly integrated with the safety supervision efforts related to boilers and pressure vessels. As a result, the power industry developed a high-quality team of over 2,000 skilled professionals at intermediate and senior levels, all of whom held certificates issued both by the power industry and the **Technical Supervision Bureau. Training and assessment for heat treatment workers. In the late 1980s, power industry organizations initiated training programs to certify workers in heat treatment. To date, 16 such training sessions have been held, and over 1,100 individuals have obtained certification as qualified heat treatment workers. The regional and provincial bureaus have also trained some certified heat treatment workers. Training and assessment for physical and chemical inspection personnel. Since the 1980s, the power industry has been carrying out training and certification programs for physical and chemical testing personnel. In the late 1990s, standards were established to initiate formal training for personnel involved in physical and chemical testing, and to date more than 400 such professionals across the country hold certified qualifications. 3.2 Establishment of welding institutions 3.2.1 Setting up welding research institutions to carry out welding research in power plants. Since the 1950s, welding research institutions for the power industry have been established across the country. In addition to the \"Power Construction Research Institute,\" \"Xi’an Thermal Engineering Institute,\" and \"Suzhou Thermal Engineering Institute\" affiliated with power companies, which have established welding and materials research institutes (sections), the power science academies (institutes) in various provinces (cities, regions) have all set up metal materials research institutes (sections). These research institutions have conducted studies on the problems that arise in power plant welding, thereby contributing to the development of welding technologies for power plants. Over the past 50 years, significant research achievements have been made in power plant welding: development of copper-aluminum welded joints, welded high-pressure tees, repair welding of cylinders and steam drums, full-position automatic welding of pipelines, repair welding of turbine shafts, repair welding of turbine blade keyways and turbine blades, development of T91/P91 welding wires, electrodes, and flux-cored wires, research on the welding repair of wear-resistant components in power plants, and studies on the weldability of heat-resistant steels. 3.2.2 Establishment of the Special Committee on Power Plant Welding of the Chinese Society for Electrical Engineering and the Welding Group for the Power Industry: To promote the exchange and development of power plant welding technologies, the Welding Group for the Power Industry was established in 1979. Administratively, it was under the leadership of the Science and Technology Committee of the Ministry of Electric Power, while operationally it was guided by the Welding Subcommittee of the Chinese Society of Mechanical Engineering. In the early 1980s, it was admitted as the Special Committee on Power Plant Welding of the Chinese Society for Electrical Engineering. Over the past 20 years, eight national academic conferences on power plant welding have been held, and delegations have participated in the 52nd and 53rd IIW international conferences; it has become the main channel for exchanging knowledge in power plant welding technology and a hub for professionals in this field. 3.2.3 A number of first-class welding training centers have been established, featuring scientific management, systematic training, and advanced equipment. In accordance with the former Ministry of Electric Power’s \"Regulations on the Approval of Welding Training Institutions,\" and after rigorous evaluation by expert panels, 72 welding technology training centers have been set up across the national electric power system; some of these centers have an investment of over 5 million yuan. In addition, grassroots power plants and electric power construction companies have established a number of welder training centers, which ensure hierarchical training for welders of categories I, II, and III, thereby guaranteeing the quality of welder training. 3.2.4 Establishing a Welding Training Collaboration Network To improve the quality of welder training and exchange experiences in this area, the Power Plant Welding Committee also set up a “Welding Training Collaboration Network,” holding regular meetings for the exchange of insights. 3.2.5 Establishment of the Power Plant Welding Standardization Committee The creation of the Power Plant Welding Standardization Committee has led to a more professional, standardized, and regulated approach to welding management in power plants, enabling comprehensive development and continuous improvement in the quality control of welding work there. 3.2.6 Establishment of qualification assessment committees for power plant welding and related professionals: In order to improve the professional standards in power plant welding and related fields and implement a system requiring certification for working in these areas, State Power Corporation established the “Qualification Assessment Committee for Non-Destructive Testing Personnel in the Power Industry,” the “Qualification Assessment Committee for Welding Training Instructors in the Power Industry,” and the “Qualification Assessment Committee for Physicochemical Personnel in the Power Industry.” These committees are responsible for providing standardized training, assessment, and certification processes for non-destructive testing personnel, welding training instructors, and physicochemical specialists. 4 Welding Quality Management in Power Plants: Quality is the lifeblood of a company, and welding is crucial for the quality of power equipment. Since power equipment operates under high temperature and pressure conditions, the importance of welding quality becomes even greater. To a certain extent, the stable operation of the unit depends largely on the quality of welding, and the quality of welding is ensured through proper management. Over the fifty years of development in electric welding, alongside the progress in welding techniques and processes, welding quality management has also seen significant advancement. In the mid-1990s, the power industry introduced a rule requiring that quality system certification certificates account for a certain percentage in bidding processes, which first pushed construction companies onto the path toward ISO9000 certification. To this day, the vast majority of basic construction units in the power industry have obtained ISO9000 certification. In recent years, the process of obtaining ISO9000 certification for power plants or the maintenance companies that work on these plants has been progressing at a rapid pace. This situation provides momentum for advancing welding quality management. 4.1 Basic work for welding quality management in power plants To carry out welding quality management in power plants, it is first necessary to have a foundation for quality management. In the case of welding work in power plants, this means establishing a quality management system while also standardizing the effective and successful basic management practices that have been developed over the years and integrating them into this quality management system. 4.1.1 Organizational structure for quality management At present, the power industry already has a quality management team specialized in welding and related fields. Based on years of experience and tradition, most construction units have an associate chief engineer specifically responsible for quality management in welding tasks. The relevant functional departments have engineers dedicated to welding and metal-related work, and there are organized structures for managing welders (such as welding sites or welding teams). Power plants also assign engineers specialized in welding and metal work within their functional departments, thereby creating a well-structured framework for welding quality management that ensures the proper conduct of quality control activities. 4.1.2 Development of a standardization system for welding in power plants: The electric power industry began to develop rapidly in the mid-to-late 1950s; the number of power plants increased, and an increasing number of domestically produced high-temperature and high-pressure units came into use. Based on the electrical construction experiences of countries such as the former Soviet Union, the power industry formulated China’s first set of welding regulations for thermal power plants in 1962, namely the “Interim Technical Regulations for Arc Welding of Carbon Steel and Low-Alloy Steel Tubes” and the “Interim Technical Regulations for Gas Welding of Carbon Steel and Low-Alloy Steel Tubes”. These regulations provided a basis for quality management of welding techniques in the power industry.