To investigate the microstructural and mechanical properties of 1 000 MPa grade ultra-high strength steel submerged arc welding welded joints for hydroelectric engineering, the microstructure of different regions of the welded joint was characterized using scanning electron microscopy (SEM). Mechanical properties of the welded joint were determined through tensile testing, impact testing, and bending testing. The results reveals that, the weld metal of the root pass and fill passes is composed of columnar, dendritic, and equiaxed grains, with a microstructure dominated by acicular ferrite and a small amount of granular bainite. The heat-affected zone (HAZ) exhibits multiple typical regions, including a critical coarse grain zone and a coarse grain zone near the fusion line along the thickness direction. Away from the weld, fine grain zones and critical zones are observed, with a microstructure primarily consisting of granular bainite, M-A constituents, and lath martensite. The weld metal of the cap pass exhibits typical columnar grains with a microstructure primarily composed of acicular ferrite. The HAZ of the cap pass includes coarse grain, fine grain, critical, and subcritical zones. Due to the absence of subsequent welding passes, no critical coarse grain zone is formed, and the microstructure is primarily composed of lath martensite, granular bainite, and M-A constituents. The average tensile strength of the welded joint reaches 980 MPa grade, the low-temperature impact absorption energy of the weld zone and the HAZ at –40 ℃ is 118.7 J and 149.3 J (at T/4), 67.0 J and 154.0 J (at T/2), respectively. No cracks appear in the lateral bending.

In cooling systems of thermal and nuclear power generating unit, the bearing fault signal of the motor is weak and nonlinear, which is easily masked by running signals and invalid signals, and the use of a single vibration monitoring may not be sufficient to collect complete defect information. To address this problem, vibration and sound signals are combined to monitor bearing fault signals, and the collected sound and vibration signal features are fused. To process the sound and vibration signals of motor bearings, a WR-VMD algorithm that integrates wavelet ridge (WR) and varational mode decomposition (VMD) is proposed. The WR is used to analyze the components of the original signal, and then the acquired information is used to determine the parameters of the VMD, which makes up for the shortcomings of the original VMD method that requires the parameters to be set empirically in advance. The simulated signal results show that, compared with the same type of methods, the features extracted by the WR-VMD method are the most obvious and have the least interference information. Finally, the acoustic and vibration signal fusion technique and the WR-VMD algorithm are applied to the measured motor bearing fault data, and the results show that, compared with other feature extraction algorithms of the same type, the WR-VMD extracts the most obvious features and has the highest accuracy in fault diagnosis. The acoustic and vibration signal fusion has at least a 7% increase in accuracy compared with a single vibration or acoustic signal in fault diagnosis.

Compared with magnetic particle detection and ray detection, magnetic memory detection is more sensitive. The magnetic memory technology is employed to carry out nondestructive testing and evaluation for weld defects of 20 steel plate. The results show that, the magnetic memory detection method can effectively characterize the weld defects of steel plates. Compared with the magnetic field intensity parameter, the magnetic field gradient value is more sensitive to the weld defects of the four tested steel plates, which manifested as its normal component increases significantly and presents a convex peak, and the abnormal magnetic memory signals also appear in some places of the weld with local stress concentration. In practical application, the rapid characteristics of the magnetic memory detection technology can be used to extract the abnormal signals of the weld seam of the tested components at first, and then compare it with other non-destructive testing methods, to effectively improve the accuracy and reliability of defect detection.

Against the dynamic operation characteristics of three-pressure reheat waste heat recovery steam generator (HRSG) of gas turbine combined cycle (GTCC) unit, the Modelica open-source programming language is used to build the simulation model for the HRSG, and the simulation results are compared with the actual operation data during peak load regulation process of the power plant. Under actual operating conditions, the established model can accurately predict the dynamic response laws of main parameters of the HRSG in the dynamic process of steady-state operation after the load drops from full load to low load, then increases from low load to full load, as well as unit shutdown and boundary parameter disturbance. When the unit load decreases from 320 MW to 280 MW, the power of the steam turbine decreases from 124.0 MW to 111.5 MW. The high pressure main steam flow rate decreases from 70.12 kg/s to 63.62 kg/s, and the high pressure main steam pressure decreases from 8 250 kPa to 7 612 kPa. The flue gas parameters at inlet of the HRSG change in about 300 s with the decrease of the unit load, while the steam parameters of the HRSG need about 600 s to complete dynamic response and reach steady state at low load, indicating there is a certain lag in steam parameters of the HRSG compared to the change of gas turbine exhaust gas parameters over time. In the dynamic process the unit shut down, the power of the steam turbine decreases from 130.4 MW to 5.4 MW, the high pressure main steam temperature of the HRSG decreases from 600.1 ℃ to 224.5 ℃, and the high pressure main steam flow rate reduces from 76.1 kg/s to 15.3 kg/s.

A method of identifying data by considering the excitation characteristics is proposed to solve the problem that it is difficult to select suitable samples from the historical operation data to identify the turbine work model. Firstly, Fisher’s information matrix condition number is applied to extract the excitation characteristics of the historical operating data, which together with the trend characteristics and the correlation between parameters constitute the set of feature variables. Secondly, by using the feature variables as inputs and the identification results generated based on the standard turbine work model as outputs, the Random Forest classification algorithm is used to generate a classification rule model for the identification data to realize the online selection of identification data. Finally, the accuracy of the model classification results and the identification effect of the selected data are verified. The result proves that the accuracy of the classification rule model is 97.561%, which can accurately select the sample segments containing sufficient incentives in the historical operation data, and the identification results of the turbine work model are in high consistency with that of the the standard model.

The two basic structures and working principles of open type heat source towers, as well as the technology of gas-liquid heat and mass exchange inside the tower are introduced. It systematically summarizes the structural components, antifreeze fluids, heat and mass transfer characteristics, and the current research status, with a focus on the research hotspots and major advancements in the development of antifreeze fluids and the heat and mass transfer processes of the open type heat source tower. Although the open type heat source tower technology still has disadvantages such as insufficient safety and environmental protection of antifreeze, corrosiveness and toxicity, unstable regeneration technology, and high energy consumption, it has a large heat exchange intensity, high heat recovery efficiency, simple structure, and low maintenance cost. It has broad application prospects in the field of building heating. In the future, open type heat source tower technology will develop towards a more efficient, stable, safe, environmentally friendly, energy-saving and low-carbon direction, and build a better green and low-carbon heating system.

In order to study the unstable characteristics of vapor-liquid two-phase flow in water-cooled wall pipe of an opposed combustion natural circulation boiler during deep peak shaving, a frequency domain mathematical model suitable for different working conditions is established. By performing small perturbation linearization on the mass, energy, and momentum equations, eliminating high-order infinitesimal perturbations and steady-state quantities, and conducting Laplace transformation, the transfer function used to describe stability of the vapor-liquid fluid flow in the pipeline is obtained through the Nyquist diagram. The graphical method is used to judge the stability of the working fluid flow in the pipe. The calculation results show that, the critical heat flux densities of typical circuits operating at 25% BMCR and 50% BMCR are 182.20 kW/m² and 240.13 kW/m². Moreover, this model is used to calculate the unstable boundary of the water wall pipe section of a 350 MW natural circulation boiler and study the influence of parameters such as inlet subcooling, mass flow rate, pipe length, inclination angle and inlet throttling coefficient on the flow instability characteristics. The calculation results show that, the influence of inlet subcooling on critical heat flux density is non-unique, and the unstable boundary diagram shows a “double-C” shape. Increasing the mass flow rate reduces the density difference between the inlet and outlet of the fluid, which is beneficial to the flow stability. Increasing the heat flow density increases the density difference between the inlet and outlet of the fluid, which is not conducive to the stability of the flow. Enhancing the inlet throttling coefficient can suppress the pulsation of the flow at the inlet, which is conducive to the stability of the flow. Increasing the inclination angle of the pipe will increase the weight pressure drop and increase the disturbance caused by it, which is not conducive to the stability of the flow.

The requirements of over limit evaluation and measuring points layout of vibration/swing in hydropower units in industry standards and national standards are compared. The layout of vibration/swing measurement points on the project site is also described. It is found that the standards related to evaluation and the ones related to measuring points arrangement are inconsistent or unclear with the engineering site, such as vibration evaluation boundary conditions, evaluation criteria, evaluation working conditions and measuring points arrangement. Analysis shows that all the differences between the standards appear in vibration evaluation and measuring points arrangement for fixed parts, and the provisions on radial vibration (swing) of the unit shafting are relatively unified. Inconsistencies in all standards are not conducive to broad-spectrum application, and are prone to ambiguity and disagreement. The phenomenon that the evaluation standard is inconsistent with the measuring points standard, is not conducive to on-site comprehensive vibration evaluation of large or giant units. All the standard evaluation criteria lack the consideration of weight coefficient of amplitude exceeding the limit and cumulative duration, which is not conducive to the development of vibration fault and condition based maintenance, and data accumulation in the new role of hydropower units. The conclusion is expected to provide analytical help and reference for the practitioners of vibration standard compilation, installation and acceptance, operation management and scientific research and test of hydropower units.

To solve the problems of slow milling response and poor control precision occurred in direct-blow pulverizing systems, a novel pulverizing system adding small pulverized coal silos is designed, and the corresponding air-powder control strategy is proposed. Moreover, based on the dynamic simulation model of an ultra-supercritical unit, the operation and control strategy of the novel pulverizing system is simulated and validated. The results demonstrate that, the proposed control strategy enables precise and rapid response of air-powder parameters. In the load response simulation tests conducted within the load variation range of 75%~85% of rated load, after the small pulverized coal silos were put into operation, the load response rate of the unit’s model can reach 5%/min and recover stability faster. Therefore, the novel pulverizing system and its operational control strategy significantly enhance the unit flexibility. The research provides a viable technical approach and guidance for improving the flexibility of coal-fired boilers.

The effect of chloride ion mass concentration (0, 1, 20 mg/L) on stress corrosion cracking of Inconel 740H, a candidate nickel based alloy for high parameter ultra-supercritical units at 630~700 ℃, were investigated by slow strain rate tensile testing and stress corrosion crack propagation testing. Moreover, the relevant mechanism of high mass concentration chloride ions promoting the initiation and propagation of stress corrosion cracks was explored. The results showed that, high mass concentration of chloride ions promoted the stress corrosion cracking of 740H alloy, and the stress corrosion sensitivity index I_scc(δ) of the alloy increased with the chloride ion mass concentration. When the mass concentration of chloride ions increased to 20 mg/L, both the middle and edge of the fracture exhibited intergranular brittle fracture characteristics, with a large number of secondary intergranular cracks near the fracture. At this point, the alloy experienced stress corrosion cracking. The average crack propagation rate in a 20 mg/L chloride ion water environment reached 1.15×10^–6 mm/s, which is 111.7 times the average crack propagation rate in high-purity water.