The acidic ammonothermal method is a key technological route for the large-scale production of large-size, high-quality gallium nitride single crystals. The extreme service conditions impose exceptionally stringent demands on the design and manufacturing of the high-temperature and ultra-high pressure reactors used for growing gallium nitride crystals. In this paper, the design requirements for the high-temperature and ultra-high pressure reactors are introduced firstly, and the potential failure modes are identified. Then, the key design and manufacturing technologies are elaborated, including strength design of high-temperature and ultra-high pressure reactors, high-temperature and ultra-high pressure sealing, development of special-shaped cylinder forging made of high-strength and high-toughness nickel based superalloys, diffusion bonding by hot isostatic pressing, as well as the inspection and the in-service performance of the reactors. Finally, relevant research recommendations are proposed for the development of larger diameter reactors.

The accelerated development of deep and ultra-deep gas reservoirs characterized by high temperature, high pressure, high sulfur content, and sand production has exposed gas production wellhead valves to extreme service conditions, including large pressure-drop throttling, severe erosion, and multi-medium coupled corrosion. Under such environments, valve operational reliability has become a critical factor constraining safe, stable, and efficient gas field production. Focusing on typical operating conditions of ultra-high-pressure gas wells, this paper systematically summarizes the dominant failure modes and damage evolution characteristics of wellhead valves, with particular emphasis on the mechanisms of flow-path erosion, cavitation erosion, corrosion fatigue, and their coupled interactions. On this basis, recent research progress in structural optimization design, erosion- and corrosion-resistant materials and surface enhancement technologies, as well as online condition monitoring and inspection methods for ultra-high-pressure wellhead valves is comprehensively reviewed. In light of the increasing demand for equipment reliability in deep gas reservoir development, future technological trends are identified as follows: (i) long-life-oriented design targeting extreme service conditions, with breakthroughs in high-performance materials and surface strengthening technologies; (ii) a transition from performance improvement of individual valves to coordinated, modular, and integrated design of valve-manifold systems; and (iii) the development of intelligent operation and maintenance frameworks based on big data and digital twin technologies to enable state perception, damage evolution analysis, and life prediction, thereby shifting maintenance strategies from reactive to predictive and intelligent modes. The findings provide technical support for the localization and high-end development of wellhead equipment, as well as for ensuring intrinsic safety and high-efficiency exploitation of deep gas fields.

Hydrogenation reactors are the core equipment for the integrated refining and petrochemical operations and are crucial to safeguarding national energy security. With the petrochemical industry evolving towards large-scale of “10-million-ton” refining capacities, hydrogenation reactors are exhibiting a significant trend towards ultra-large diameters and ultra-large wall thicknesses. As a consequence, ensuring the intrinsic safety of the equipment while achieving lightweighting design becomes a key challenge for the industry. This paper comprehensively reviews the development of China’s hydrogenation reactor from the import dependence, through independent innovation, to achieving global leadership. Then, the integrated construction system satisfying the extreme-dimensional manufacturing demand is introduced, which is guided by advanced structural design, centered on efficient and high-quality manufacturing and precise residual stress control, and safeguarded by full-coverage non-destructive testing. Based on this system, China successfully developed the world’s first 2 000-ton class coal liquefaction reactor and the 3 000-ton class slurry bed reactor. As a result, the conversion rate of residual oil has increased from 30% to 95% and the batch production of extra-large hydrogenation reactors has been achieved and reliably deployed in multiple million-ton-class facilities. These accomplishments firmly marked China’s construction technology for ultra-large hydrogenation reactors has reached an internationally leading level.

The evolution of pressure vessel technology reflects the progress of industrial civilization. In major engineering applications in China, equipment is characterized by increasingly severe operating parameters, large structural dimensions, and complex service environments. These features impose new challenges and requirements on safety technologies of pressure vessels throughout the entire life cycle, covering strength design, manufacturing quality, and operation and maintenance. Meanwhile, the rapid development of artificial intelligence offers an unprecedented opportunity for upgrading intelligent safety technologies of pressure vessels. This paper reviews the traditional approaches for ensuring operation safety by analyzing the service conditions, damage mechanisms, and conventional assessment methods of pressure vessels, highlighting strength and safety as their fundamental supports. Recent advances in condition monitoring technologies for operational safety are summarized, including novel sensing methods, applicability evaluation, global and local state monitoring, and multi-source sensing fusion. With the integration of data science, intelligent technologies for life-cycle management of pressure vessels are further discussed from the perspectives of strength-life prediction, intelligent evaluation, and autonomous digital twin evolution, elucidating their promoting role in the progress of intelligent safety technologies. The concept of an intelligent pressure vessel is then proposed, and the challenges and countermeasures in its implementation are outlined. The importance of mechanical strength informatics in advancing intelligent pressure vessels is finally emphasized.

Special equipment includes boilers, pressure vessels, pressure pipelines, elevators, lifting machinery, large amusement devices, passenger ropeways, and on site (factory) specialized motor vehicles, and their operational safety is crucial to ensuring the operation of the national economy and the daily lives of the people. During the construction of special equipment, non-destructive testing (NDT) technology is applied to the inspection and control of raw material production, processing and forming, and welding quality. During the usage, NDT technology is used to promptly detect various damages and defects such as corrosion, cracking, and material degradation that occur during equipment operation. Based on the testing results, the safety status of the equipment can be evaluated, and its remaining life can be assessed. Firstly, discuss the importance and role of NDT and evaluation of special equipment. Secondly, provide the currently mature NDT technologies and various NDT standards for special equipment that have been formulated and published. Thirdly, the focus is on introducing NDT techniques such as microwave, terahertz, laser speckle, magneto acoustic emission, magnetic Barkhausen, and magnetic multi parameter fusion testing technologies, which are suitable for non-metallic material detection or early damage detection such as metal material fatigue and creep. The principles, characteristics, scope of application, instruments, and application of these techniques are summarized. Finally, an analysis and outlook are provided on the demand for NDT technology in future for special equipment, highlighting the main research areas and key tasks that need to be further developed in order to better ensure the high-quality development and safe operation of special equipment.

This paper reviews the process of organizing and implementing the projects under the National Key R&D Program during the periods of the 11th Five-Year Plan through the 14th Five-Year Plan. Guided by the development strategy for special equipment safety technology research, which was led by the former General Administration of Quality Supervision, Inspection and Quarantine (later restructured into the State Administration for Market Regulation) and spearheaded by the China Special Equipment Inspection and Research Institute, the authors present the overall technical framework and the integrated analysis-synthesis research methodology proposed by the research team for utility boiler safety technology research. The paper demonstrates the scientific achievements yielded through collaborative research, and illustrates how these outcomes have been translated into safety supervision systems, technical standards, as well as safety assessment and prediction-warning methodologies. These implementations have guided the safe production of utility boilers, boosted economic and social development, and established a practical safeguard for the long-cycle safe operation of utility boilers. Practice has proven that the successful pathways for addressing major demands through collaborative scientific and technological research include: systematic organizational leadership and management, sound research philosophies and methodologies, the formulation of research topics that realistically reflect the needs of the times, collaborative innovation across industry, academia and research sectors, and comprehensive responses to practical problems in the safe production of utility boilers.

Under the background of "double carbon" goal and energy transformation, coal-fired thermal power units are transformed from "base load power supply" to "regulatory power supply" and deep peak regulation and frequent start and stop have become the new normal operation mode. As a result, the pressure-bearing parts of the power plant boiler deviate from the design condition for a long time, under the thermo-mechanical fatigue condition of the alternating coupling of mechanical load and temperature load. The interaction between fatigue and creep significantly accelerates the damage and failure of materials commonly used in high temperature heating surfaces, headers and steam pipes, such as 15CrMoG (P12), 12Cr1MoVG, 12Cr2MoG (P22), 10Cr9Mo1VNbN (P91), 10Cr9MoW2VNbBN (P92), 07Cr18Ni9NbCu3BN (Super304H), 07Cr25Ni21NbN (HR3C). However, there is a lack of systematic comparative study on the failure mechanism of the above-mentioned material system under the specific condition of deep peak shaving. In this paper, low alloy steel heat-resistant steel, martensitic heat-resistant steel and austenitic heat-resistant steel are classified, the damage characteristics and failure mechanism of different generations of materials under flexible operation conditions are analyzed. The results show that under the interaction of fatigue and creep, the above materials have obvious differences in microstructure and precipitation phase evolution, cyclic deformation behavior and oxidation-assisted crack propagation. On this basis, combined with China's current GB/T 30580—2022 The technical guide for the life assessment of main pressure parts of power plant boiler, the applicability and limitations of the life assessment method based on the linear cumulative damage theory under deep peak-shaving conditions are discussed, and the necessity of transforming to the nonlinear model of physical mechanism is highlighted.

Cylinders are fundamental components in the field of pressure vessels, and axial compression buckling is a critical failure mode that must be addressed during the design process. The calculation method for the allowable axial compressive stress of cylinders in China’s fundamental design standard for pressure vessels, GB/T 150, has long been based on the American ASME method. This method, established decades ago, relies on linear buckling theory and exhibits limited accuracy. After more than a decade of dedicated research, the authors’ team proposed a new calculation method for the allowable axial compressive stress of cylinders based on elasto-plastic theory and the energy barrier theory. This method has been incorporated into GB/T 150.1—2024 Pressure Vessels—Part 1: General Requirements, marking an end to the long-standing reliance on the American ASME method for the buckling design of axially compressed cylinders in China. This paper elaborates on the scope of application, implementation process, and theoretical foundation of the new method. Through comprehensive comparative analyses with experimental data of buckling stresses for axially compressed cylinders reported in domestic and international literature, actual load-bearing capacities of large-scale industrial cylindrical components, and existing European and American standard methods, the advanced nature and safety of the new method are demonstrated. It is anticipated that this method will provide theoretical and technical support for the lightweight development of large cylindrical structures in China’s pressure vessel industry in the future.

Glass Fiber Reinforced Polymer (GFRP) is prone to damage during long-term service. Among its defects, flat-bottom hole defects are particularly challenging for achieving high-contrast imaging and precise localization. This study focuses on defect detection and imaging using a microwave reflection method. Firstly, the electromagnetic wave propagation characteristics in GFRP and the impact of internal dielectric discontinuities on reflection coefficients were analyzed. A defect localization and imaging method based on enhanced reflection features was developed. By combining reflection anomaly spectrum analysis, incrementally constrained peak identification, and fine two-dimensional spatial localization, stable detection and precise positioning of 8 mm flat-bottom hole defects with non-uniform distribution on the back side was achieved. The results indicate that this method can effectively suppress background interference, significantly improve the imaging contrast between defects and the matrix, and produce imaging results that closely match the actual defect distribution. The findings demonstrate that the proposed method is suitable for nondestructive testing and visual characterization of typical internal defects in GFRP, providing a technical reference for high-quality nondestructive imaging detection of composite material structural damage.

2219 aluminum alloy exhibits high specific strength and excellent mechanical properties at both high and low temperatures, but its insufficient surface hardness and corrosion resistance limit its application in special equipment fields. This study fabricated an AlCoCrFeNi high-entropy alloy (HEA) electron beam cladding layer on the surface of 2219 aluminum alloy. The effects of welding beam current, scanning speed, and scanning frequency on the microstructure of the cladding layer were systematically investigated. Combined with microstructure characterization and electrochemical corrosion tests, an in-depth analysis was conducted on the mechanism underlying the influence of microstructural evolution on the mechanical properties and corrosion resistance of the cladding layer. The results demonstrate that the optimal cladding parameters are a cladding beam current of 15 mA, a scanning speed of 150 mm/min, and a scanning frequency of 800 Hz. Under these parameters, the diffusion of Al elements from the substrate to the cladding layer is enhanced, while the dilution effect alleviates the constraint stress at the interface, thereby effectively suppressing the formation of cracks in the single-pass cladding layer. Ultimately, the microhardness of the resulting cladding layer stabilizes at approximately 400 HV, and its corrosion resistance is significantly superior to that of the 2219 aluminum alloy base metal (BM) and cladding layers prepared under other parameter combinations.