Tube Sheet Research Articles

The SG‐Climbot: An Adaptable, Efficient, Inspection and Repair Robot for Steam Generator Heat Transfer Tube Sheet

ABSTRACTThe steam generator plays a crucial role as a safety component and protective barrier in nuclear power plants. Regular inspection and repair of heat transfer tubes, which operate in high‐temperature, high‐pressure, corrosive, and abrasive environments for extended periods, are essential. Inspection and repair robots move inside the steam generator to conduct comprehensive inspections and evaluations of the heat transfer tubes. However, existing robots have relatively simple execution devices and fixed movement methods, resulting in poor adaptability to different specifications of tube sheets and limited flexibility in handling maintenance tasks. In response to these limitations, the SG‐Climbot, a quadruped crawling tube sheet inspection and repair robot, has been proposed. This robot is designed to adapt to full‐specification tube sheets and operate efficiently by conducting inspections while moving. By comparing different motion modes, a robot configuration with a quadruped parallel structure was suggested. Kinematic and static analyses were conducted, resulting in the development of both forward and inverse kinematic models, along with the identification of conditions leading to tipping. Using parametric modeling and optimization design, optimized design parameters were obtained. Finite element simulation analysis was performed on the overall structure and main components, leading to an optimized structural model. Finally, based on the design model and computational analysis, a prototype was developed and tested. The experimental results indicate that the robot has achieved the expected functionality and performance targets. Its efficient maintenance operation mode of conducting inspections while moving provides a basis for the autonomous and intelligent development of steam generators.

Study on the coupling mechanism and reinforcement effect of a shield tunnel reinforced by channel steel under side pit excavation

To investigate the internal force and deformation response law and reinforcement effect of a shield tunnel reinforced by channel steel in a pit excavation, a self-developed “hydraulic loading system” is used to conduct a full-size test and numerical simulation analysis on a three-ring staggered-seam assembled tube sheet. The results show that the internal force response of the tube sheet on the excavation side of the pit is complex and sensitive, the internal force is transformed in the direction under different load levels, and the bearing capacity can be effectively increased by 62.5 % through the channel steel reinforcement; the channel steel fails due to weld cracking, and the nonstructural bonding surface is damaged by sliding; and the maximum reinforcing efficiency of the combination of the channel steel and steel plate reaches 45.8 %, making it an economical and reliable reinforcing program.

Causes and Hazards of Perimeter Rock Cavities behind Shield Tunnels

The purpose of this paper is to discuss the reasons for the generation of voids in the surrounding rock behind water transmission shield tunnels and the potential hazards they bring. Firstly, it analyzes in detail the possible causes of cavities from the aspects of geological conditions, construction technology, material properties, etc. On the basis of literature research, the causes and distribution patterns of the perimeter rock cavities behind the water transfer shield tunnels were explored with respect to the locations and sizes of the cavities behind the tube sheets. Secondly, it systematically elaborates the hazards of cavities on tunnels from the aspects of structural stability, use function, operation safety, etc. Finally, it proposes corresponding preventive measures and countermeasures for the problem of cavities. This paper aims to provide valuable reference for the design, construction and operation management of shield tunnels, which is of great theoretical significance and practical value for the safe construction and long-term operation of shield tunnels.

PREPARATION OF COMPONENTS FOR ORBITAL WELDING OF TITANIUM TUBES WITH TITANIUM CLAD STEEL SIEVE BOTTOM

The article presents the method of preparing the tube sheet of a heat exchanger made of B265 Grade 1 titanium-clad steel with B338 grade 2 titanium tubes allowing for the qualification of the TIG (Tungsten Inert Gas) orbital welding technology. A test plate was made of A516M Grade 485 unalloyed steel clad with B265 Grade 1 titanium using the explosive method. The 300 x 300 mm plate consisted of a layer of 60 mm thick non alloy steel and 5 mm titanium clad. It had 20 holes drilled in a triangular arrangement, into tubes with a diameter of 34.93 mm made of B338 Grade 2 titanium with a thickness of 0.7 mm were welded. In order to obtain mechanical restraint inside the holes in the test plates, the titanium tubes were rolled out. For rolling, a five-roller was used, equipped with a retaining collar which allows the tube to move freely during rolling. The tests carried out showed that the proposed technology for preparing tube – sieve bottom elements allow for the preparation of a test plate for the qualification of welding technology. The test plate made in accordance with the technological assumptions met all the requirements necessary to qualify the technology for welding tubes with tube plates. Both in the case of non-destructive testing and macrographic testing, there were no problems with compliance with the PN-EN ISO 15614-8:2005 standard.

Lightweight Reseach of Tube Sheet for Spiral Wound Heat Exchanger Based on ANSYS

Abstract Tube sheet is the key pressure-bearing part in the spiral wound heat exchanger, and the high-strength and light-weight tube sheet structure is of great engineering significance for the development of a large-scale heat exchanger. In order to further realize the lightweight of the spiral-wound heat exchanger, this paper analyzes the influence of the thickness of the heat exchanger tube sheet on its strength based on the Ansys software and proposes the optimization design method of the tube sheet based on the strength safety factor F, which solves the problem that the software cannot take the stress linearization result as the state variable in the optimization calculation. The optimization results show that the thickness of the tube sheet is reduced by 40%. At this time, the stress strength at the connection between the tube sheet and the head and the center of the tube sheet first exceeds the design bearing capacity, indicating that the strength conditions of the two places are the controlling factors of the thickness. The results are important for the lightweight design of heat exchanger tube plate and material saving.

EFFECT OF SEGMENT DISLOCATION ON THE MECHANICAL PROPERTIES OF LINED TUNNELS IN A COMPLEX ENVIRONMENT

In complex environments, tunnels with a lined structure are more affected by the dislocation of a segment. This study uses finite element simulations to further investigate the relationship between environmental changes and segments in lined tunnels. Tunnels with and without a lining are simulated under varying strata resistance, buried depth, and water level conditions. The horizontal and vertical displacements and stress changes in the two tunnels are compared when segment dislocation occurs. The results show that the lateral displacement of the tunnel is relatively stable and less influenced by external loads. However, the longitudinal displacement change is the opposite, and it increases significantly when the displacement exceeds 10 mm. When the lined tunnel is subjected to a large external load and misalignment occurs, the performance of the tube sheet joint bolts deteriorates, resulting in a stress decrease. Furthermore, the lined tunnel exhibits an increased ability to resist deformation and does not exactly follow the law of small displacements from small misalignments. When a large misalignment occurs, the lined tunnel may be damaged by elliptical deformation along the 45° direction, and its internal forces would be much larger than those of the unlined tunnel.

Automated extraction of tunnel leakage location and area from 3D laser scanning point clouds

Water leakage is one of the common tunnel disease problems. Fast and accurate detection is crucial for timely management of leakage disease. This paper introduces a method for automatically extracting the location and area of tunnel leakage from 3D laser scanning point clouds. The method involves three key steps: segmenting the point cloud data along the tunnel axis based on the width of the tube sheet, correcting the intensity of the point cloud using a linear intensity correction model, and binarizing the point cloud data to extract the leakage area and calculate its area. To evaluate the performance of the proposed methodology, water leakage detection software is prepared based on the method, and tests are carried out in the urban subway tunnels in the leakage disease-producing sections. The results show a detection accuracy of 92 % and an improvement in detection efficiency of 7–8 times. The method proposed can be used to quickly and accurately extract the location and area of water leakage from point cloud data.

Research on Uplift Mechanism of Shield Tunnel Based on Multi-factor Construction Conditions

In order to investigate the influence degree of each factor on tube sheet uplift and tube sheet uplift law of shield tunneling, this thesis takes the background of Zhengzhou Railway Transit Line 6 Phase I Project Weizhuang Station ~ Cargo Station Street Station Interval Project, and establishes ABAQUS finite element numerical model based on the influence factors such as shield thrust, slurry density, grouting pressure, etc., and analyzes the interaction relationship between the influence factors of tube sheet uplift caused by the shield tunneling construction period. The paper investigates the uplift law of tube sheet and the mechanism of influencing factors during the construction period of shield tunnel, and obtains the relationship between grouting pressure and tube sheet uplift, jack thrust and slurry density and tube sheet uplift under the influence of a single factor; the thesis also discovers the location of the maximum uplift and the basic law, as well as the basic range of the uplift and the reduction of the uplift value in the late stage through the comprehensive analysis and calculation of the uplift and the influencing factors under different working conditions. The paper also finds out the location and basic law of the maximum uplift of the tube sheet under different working conditions, and the basic range of the downsizing value of the uplift in the later stage.

Crack Width Recognition of Tunnel Tube Sheet Based on YOLOv8 Algorithm and 3D Imaging

Based on the tunnel crack width identification, there are operating time constraints, limited operating space, high equipment testing costs, and other issues. In this paper, a large subway tunnel is a research object, and the tunnel rail inspection car is an operating platform equipped with industrial cameras in order to meet the requirements of the tunnel tube sheet crack width recognition of more than 0.2 mm, with the measuring instrument to verify that the tunnel rail inspection car in the state of uniform motion camera imaging quality has the reliability through the addition of laser rangefinders, the accurate measurement of the object distance and the calculation of the imaging plane and the angle of the plane to be measured, to amend the three-dimensional cracks. The pixel resolution of the image is corrected, the images imaged by the industrial camera are preprocessed, the YOLOv8 algorithm is used for the intelligent extraction of crack morphology, and finally, the actual width is calculated from the spacing between two points of the crack. The crack detection width obtained by image processing using the YOLOv8 algorithm is basically the same as the value of crack width obtained by manual detection, and the error rate of crack width detection ranges from 0% to 11%, with the average error rate remaining below 4%. Compared with the crack detection error rate of the Support Vector Machine (SVM), the crack extraction model is reduced by 1%, so using the tunnel inspection vehicle as a platform equipped with an industrial camera, YOLOv8 is used to realize the recognition of the shape and width of the cracks on the surface of the tunnel tube sheet to meet the requirements of a higher degree of accuracy. The number of pixels and the detection error rate are inversely proportional to each other. The angle between the imaging plane and the plane under test is directly proportional to the detection error rate. The angle between the vertical axis where the lens midpoint is located and the line connecting the shooting target and the lens center point is αi and the angle θi between the measured plane and the imaging plane is reciprocal, i.e., αi + θi = 90°. Therefore, using the inspection vehicle as a mobile platform equipped with an industrial camera and based on the YOLOv8 algorithm, the crack recognition of the tunnel tube sheet has the feasibility and the prospect of wide application, which provides a reference method for the detection of cracks in the tunnel tube sheet.

An analytical and numerical modeling method for predicting drilling force and hole expansion of a BTA drill processing Inconel 625 and FeCr alloy laminated materials

This paper aims to predict the drilling force and hole expansion of Boring and Trepanning Association (BTA) drill processing Inconel 625 and FeCr alloy laminated tube sheets, essential in petrochemical and nuclear industries. The paper proposes a combined analytical and numerical modeling approach that integrates discrete forces on multiple cutting edges and guide pads of the BTA drill, experimentally determines the mathematical relationship between the discrete forces, and predicts the drilling force using a calibrated finite element simulation of the cutting edge. Then, a comprehensive evaluation of the drilling forces revealed the torque and feed force distribution for cutting, guide pad burnishing, and friction. Furthermore, a precise finite element simulation model for guide pad burnishing hole wall is developed and combined with the burnishing force identified by the analytical model, enabling hole expansion prediction. The proposed model is validated by drilling experiments on Inconel 625 and FeCr alloy-laminated materials with average prediction errors of 8.4 %, 4.7 %, and 20.5 % for torque, feed force, and hole expansion, respectively, demonstrating the accuracy and industrial applicability of the modeling method.

Study of Non-uniform Seismic Response of Intercity Tunnels with Defective Shields

Based on the structural viscoelastic boundary theory, considering the geological changes of the soil layer and depth of tunnel crossing, the dynamic time course analysis is carried out for the defective lined tube sheet structure under non-uniform seismic excitation, to obtain the force and deformation law of the whole tunnel structure as well as the defective section. Analyze the dynamic response of shield tunnel structure under non-consistent seismic excitation under the influence of tube sheet misalignment factors, summarize the intrinsic mechanism of the dynamic response of defective tunnel tube lining structure, identify the phenomena affecting lining junction damage, and refine the seismic safety evaluation method of defective lining structure.

Behavior of grouted splice sleeve connection using FRP sheet

Most existing studies on grouted splice connections have focused on the bond behavior between connected steel rebars and conventional steel or iron sleeves. These research findings cannot properly predict the bond behavior and performance of the grouted splice connections, particularly when a new splice device, such as fiber reinforced polymer (FRP) materials, are adopted. The main purpose of this study is to investigate the feasibility of the proposed grouted splice sleeve connection (GSSC) using sheet materials of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP). A total of 45 GSSC specimens with various rebar embedded lengths and different polymer sleeve materials were tested to failure under incremental axial pull-out load to evaluate the bond performance of the connected steel rebars in confined grout provided by the FRP sleeves. To evaluate the confinement effect of FRP sleeves on the tensile strength of the grouted connection, an analytical model was developed. The pull-out test results showed that the rebar embedded length was the major parameter affecting the average tensile strength of the GSSC. Also, the effects of mechanical properties of FRP sheets, such as the number of FRP layers and type of FRP sheets, contributed to the tensile strength of the GSSC sleeves that allow the transmission of tensile load between rebars through the medium of grout, aluminum tube, and FRP sheets. The analytical model that incorporates the confinement effects predicted well the experimental ultimate tensile strength of GSSC connections.

Structural Performance of Strengthening of High-Performance Geopolymer Concrete Columns Utilizing Different Confinement Materials: Experimental and Numerical Study

The objective of this study was to investigate the effectiveness of different confinement materials in strengthening geopolymer concrete (GP) columns subjected to axial compression loading. This research encompassed both experimental and numerical analyses. The experimental phase involved testing seven circular GP columns, while the numerical phase involved developing 3D finite element (FE) models using ABAQUS software. The primary focus of this study was to assess the impact of using outer and inner steel tubes, as well as an outer polyvinyl chloride (PVC) tube and a carbon-fiber-reinforced polymer (CFRP) sheet. To validate the FE models, the experimental results were utilized for comparison. The findings of this study revealed that the outer steel tube provided superior confinement effects on the GP column’s concrete core compared to the PVC tube and CFRP sheet. The axial capacities of the columns confined with steel, PVC, and CFRP materials were observed to increase by 254.7%, 43.2%, and 186%, respectively, in comparison to the control specimens. Furthermore, the utilization of all confinement materials significantly enhanced the absorbed energy and ductility of the columns. The FE models demonstrated a reasonably close match to the experimental results in terms of load–displacement curves and deformation patterns. This correspondence between the numerical predictions and experimental data confirmed the reliability of the FE models and their suitability for generating further predictions. In summary, this study contributes to the field by exploring the efficacy of various confinement materials in strengthening GP columns. The results highlight the superior performance of the outer steel tube and demonstrate the positive influence of PVC and CFRP materials on enhancing the structural behavior of the columns. The validation of the FE models further supports their reliability and their potential for future predictions in similar scenarios.

Failure Analysis of Duplex Stainless Steel for Heat Exchanger Tubes with Seawater Cooling Medium

The present paper describes a study case of the failure investigation of duplex stainless steel (UNS S31803) on the tube and tube sheet sections of BEM TEMA-type shell and tube heat exchanger with seawater as the cooling medium. The heat exchanger’s shell design pressure was 22.6 MPa at 422 K, and the tube design pressure was 1 MPa at 339 K. Although UNS S31803 offers high strength, high resistance to chloride-induced SCC, and high resistance to pitting attack in chloride environments, the heat exchanger in this study experienced some material degradation after 28 months of use; 102 out of 270 tubes failed, 26 tubes leaked and were plugged on both sides, and scale plugged 76 tubes. The examination in this study case revealed the formation of white-colored biofilm inside the tubes; XRD examination revealed that the film contained CaCO3. Using microstructural examination on the inner surface of the tube, the austenite grains were shown to have been preferentially attacked; this phenomenon is typical in duplex stainless steel which fails due to crevice corrosion. According to the examination result, the failure in this case was caused by crevice corrosion between the substrate and surface deposits that was enhanced by microbiological-induced corrosion (MIC). Recommendations to avoid similar failures are also suggested in this paper.

High-efficiency inspecting method for mobile robots based on task planning for heat transfer tubes in a steam generator

Many heat transfer tubes are distributed on the tube plates of a steam generator that requires periodic inspection by robots. Existing inspection robots are usually involved in issues: Robots with manipulators need complicated installation due to their fixed base; tube mobile robots suffer from low running efficiency because of their structural restricts. Since there are thousands of tubes to be checked, task planning is essential to guarantee the precise, orderly, and efficient inspection process. Most in-service robots check the task tubes using row-by-row and column-by-column planning. This leads to unnecessary inspections, resulting in a long shutdown and affecting the regular operation of a nuclear power plant. Therefore, this paper introduces the structure and control system of a dexterous robot and proposes a task planning method. This method proceeds into three steps: task allocation, base position search, and sequence planning. To allocate the task regions, this method calculates the tool work matrix and proposes a criterion to evaluate a sub-region. And then all tasks contained in the sub-region are considered globally to search the base positions. Lastly, we apply an improved ant colony algorithm for base sequence planning and determine the inspection orders according to the planned path. We validated the optimized algorithm by conducting task planning experiments using our robot on a tube sheet. The results show that the proposed method can accomplish full task coverage with few repetitive or redundant inspections and it increases the efficiency by 33.31% compared to the traditional planning algorithms.

Effect of drilling parameters on the hole surface integrity of low alloy steel for nuclear power during BTA deep hole drilling

Boring trepanning association (BTA) deep hole drilling is widely used in machining tube sheet of steam generator. In order to get a better service integrity, the surface quality after machining is required to be higher. In this paper, the effect mechanism of BTA deep hole drilling on the integrity and quality of the machined surface layer of low alloy steel SA508Gr.3Cl.2 for nuclear power is investigated. The results show that the gradient microstructure can be obtained by BTA drilling on the surface of the inner hole, including the recrystallized layer with grain refinement and the plastic deformation layer with high-density sub-crystal structure and grain distortion. With the increase of drilling speed and feed rate, the thickness of deformation layer increases. During the BTA deep hole drilling, the proportion of low-angle grain boundaries (LAGBs) increases with the increasing depth from the machined surface. The increase of drilling speed leads to the increase of recrystallization degree and the proportion of LAGBs in the machined surface. The effect of feed rate on the proportion of LAGBs is opposite. The machined surface is characterized by regular peak and valley, and there are typical surface defects mainly involving feed marks, surface tearing, and plowing grooves. With the increase of drilling speed, the surface roughness will decrease. The effect of feed rate on surface roughness is obviously lower than that of drilling speed. With the increase of drilling speed, and feed rate, the depth of hardened layer increases gradually, which is caused by dislocation strengthening and fine grain–strengthening effect during BTA drilling process. Higher drilling speed is recommended in forming a better machined surface with a strengthening layer of a certain thickness.

Longitudinal Seismic Analysis of Tunnels with Nonuniform Strata Considering the Effect of Karst

The longitudinal direction of shield tunnels is prone to seismic damage due to excessive deformation under seismic action, especially in nonuniform stratum. In this paper, the longitudinal dynamic response of the tunnel under different seismic effects is calculated based on the longitudinal equivalent stiffness model using the stratigraphic load model, and the seismic indexes such as longitudinal corner, tube sheet and joint bolt stresses are verified. The calculation results show that the longitudinal seismic weakness of the shield tunnel is in the interface between soft and hard strata and karst development. The longitudinal axial force of the structure is larger during the longitudinal excitation of seismic waves, and the maximum bending moment is mainly in the vertical plane, i.e., the vertical bending moment. The axial force of the tunnel is smaller during the transverse excitation of seismic waves. The maximum bending moment is mainly the bending moment in the horizontal plane, i.e., the transverse moment. The South Lake section of the Two Lakes Tunnel has good seismic performance in the event of a rare earthquake with a 50-year exceedance probability of 2%. The investigation can guide the seismic design of the South Lake section of the Two Lakes Tunnel.

Mechanical and 1st Chemical Cleaning of NEK Steam Generators

Sludge removal is performed on two steam generators (SG’s) at the Krško Nuclear Power Plant (NEK) during every outage. SG’s are a meeting point of five major plant systems: Reactor Coolant System (RC) on the primary side and four systems on the secondary side – Auxiliary Feedwater System (AF), Blowdown System (BD), Main Feedwater System (FW), and Main Steam System (MS). Sludge removal activities take place on the secondary side of the SG’s on the top of the tube sheet. It always consists of classical Sludge Lancing (SL) which is done by spraying water at different angles (30°, 90°, 150°) between the tube gaps in the steam generator tube bundle with a pressure of around 220 bars. Another method is Inner Bundle Lancing (IBL) which means spraying water directly inside the tube bundle with a traveling lance tape with a spraying nozzle at the end. Water is sprayed at an angle or directly on the top of the tube sheet with a robot-guided manipulator which is placed inside a steam generator. The manipulator and therefore the spraying action is controlled by an operator and at times it is fully autonomous to provide the highest protection measures possible. Another method of sludge removal which was for the first time utilized in 2019 at the Krško site was Chemical Cleaning (CC) of both SG’s. During this process, a chemical was injected into the SG’s through the BD system and periodically pumped between the two SG’s to create a dynamic flow and maximize the cleaning effect. To achieve the best results, a constant temperature of the chemicals had to be maintained at all times. Upon completion of chemical cleaning, a rinsing phase was followed to remove any post-treatment chemicals. After all sludge removal activities, a televisual inspection (TVI) of the top of the tube sheet was performed to access the hard sludge area and to search for potential foreign objects in the SG’s. If for instance an object of importance during TV inspection is found, an attempt to retrieve it would usually take place. Other methods of sludge removal such as upper bundle flushing or ultrasonic cleaning have not been implemented in NEK thus far.
 Since the power plant uprate in May 2000, NEK conducted SL on both SG’s every outage also starting with IBL in 2013 and 2015, and the same method was used in the 2018 outage. During the outage in 2019, all three methods (SL, IBL, and CC) have been utilized with the main purpose to extend the full load operation of the plant, preventing and/or stopping denting processes in the SG’s from occurring, reducing and stopping the build-up of hard sludge area to increase/sustain efficiency and remove foreign objects found in the SG’s. SG’s U-tubes are a barrier between the primary side coolant and the secondary side of NEK and the environment. Therefore, it is crucial to keep the highest level of integrity of the U-tubes because any leak could potentially mean a release of radioactive material into the atmosphere. This paper describes the purpose and workflow of sludge removal activities in the outage of 2019 in NEK.

Analysis of the ductility dip cracking in the nickel-base alloy welding overlay on heat exchanger tube sheet

In this paper, the cracking failure of the weld overlay of the heat exchanger tube sheet was analyzed. The weld overlay, welded by ErNiCrMo-3, cracked several times within a short period after the heat exchanger was put into operation, resulting in internal leakage from the heat exchanger. The failure causes are investigated by means of macroscopic observation, metallographic analysis, scanning electron microscope (SEM) coupled with energy dispersive spectroscopy (EDS) analysis, and hardness test. The synthetical analysis shows that a sudden drop in ductility of the weld overlay material occurs at the time of microcracking, and a phenomenon similar to grain boundary sliding is observed in the fracture morphology image at high magnification. Therefore, the microcrack on the weld overlay is a kind of ductility dip crack at elevated temperatures. Improper welding strategy and inappropriate choice of welding material is the root cause of ductility-dip microcrack during the welding process. The microcracks on the weld overlay propagate during the operation of the heat exchanger, causing it to leak several times in a short period.

The influence of altitude on combustion characteristics within gas‐fired boiler by numerical simulation

AbstractThe reduced atmospheric pressure and oxygen mass concentration at high altitudes have brought tremendous problems to the operation of gas‐fired boiler, mainly due to their influence on gas combustion and flow within furnace. Boilers designed for plateau region generally experience insufficient output, incomplete combustion, and reduced thermal efficiency when operating at high altitudes. However, the impacts from increasing altitude to the combustion characteristics within furnace are still ambiguous, which greatly hampers the boiler design for high‐altitude area. In this paper, the influences of altitude on the gas combustion characteristics within furnace were explored by using the computational fluid dynamics (CFD) method. The simulation shows that when altitude rises from 0 to 4000 m, the flame length and width increase as well as the temperature within furnace, but the burnout rate decreases due to the reduced residence time. The furnace length and diameter of the boiler designed for high altitudes should be appropriately increased to avoid the high temperature flame from scouring the back tube sheet and the furnace liner. While the CO emissions are generally very low, an increasing trend with altitude was observed. In addition, for each 1000 m of altitude rise, the NOx emissions increase by about 14 mg·m−3 at 100% loads and α = 1.05. The present work reveals the influence of altitude on combustion characteristics within gas‐fired boiler, which can guide the design and operation of the gas‐fired boiler at high altitudes.