Boiler Tube Failures Research Articles

Improved Early Detection of Tube Leaks Faults in Pulverised Coal-fired Boiler Using Deep Feed Forward Neural Network

Boiler tube leaks significantly reduce the operational availability of power units, yet their early detection and prediction have not been fully realised in the industry. This paper introduces a novel approach employing deep feedforward neural networks for early detection of boiler tube leaks in pulverised coal-fired boilers. Early detection enhances repair planning, minimising downtime and production losses. It also improves monitoring and control of boiler tube failures, thereby optimising power plant operations and revenue. Diverse deep neural network models were developed and rigorously tested by leveraging 9 years of operational data (2012–2020). Exhaustive hyper-parameter optimisation, involving seven parameters, substantially improved predictive accuracy. By achieving training and testing accuracies of 82.8% to 99.3%, the study assessed their ability to detect boiler tube leaks over the same 9-year span, providing insights into leak detection capabilities. The models notably predicted all 12 identified tube leak events, averaging a 14-day lead time before boiler shutdown. In addition to leak prediction, a leak detection matrix was devised to analyse residual behaviour and reduce the likelihood of false alarms. However, the models’ predictive performance was observed to be limited to the following year, with satisfactory results for 2021 only. Incorporating the 2021 data into retraining significantly improved the predictions for 2022. The study concludes that while the models demonstrate robust short-term prediction capabilities, they require continuous retraining to maintain accuracy and relevance. This ongoing refinement is essential for keeping the models up-to-date and reliable in predicting future boiler tube leaks.

Corrosion of Waste Heat Boiler Tubes in Methanol Plant

A thorough failure investigation was conducted into a failure of waste heat boiler tubes in a methanol plant to determine the failure mechanism, and contributing factors. The investigation was performed utilizing different characterization techniques, including optical light microscopy, scanning electron microscopy, mechanical testing and chemical analysis techniques. The investigation findings showed that the tubes failure is attributed to corrosion under deposit. Details of the failure’s contributing factors, and recommendations to avoid similar failures, are discussed in this article.

Four-Stage Multi-Physics Simulations to Assist Temperature Sensor Design for Industrial-Scale Coal-Fired Boiler.

The growth of renewable energy sources presents a pressing challenge to the operation and maintenance of existing fossil fuel power plants, given that fossil fuel remains the predominant fuel source, responsible for over 60% of electricity generation in the United States. One of the main concerns within these fossil fuel power plants is the unpredictable failure of boiler tubes, resulting in emergency maintenance with significant economic and societal consequences. A reliable high-temperature sensor is necessary for in situ monitoring of boiler tubes and the safety of fossil fuel power plants. In this study, a comprehensive four-stage multi-physics computational framework is developed to assist the design, optimization installation, and operation of the high-temperature stainless-steel and quartz coaxial cable sensor (SSQ-CCS) for coal-fired boiler applications. With the consideration of various operation conditions, we predict the distributions of flue gas temperatures within coal-fired boilers, the temperature correlation between the boiler tube and SSQ-CCS, and the safety of SSQ-CCS. With the simulation-guided sensor installation plan, the newly designed SSQ-CCSs have been employed for field testing for more than 430 days. The computational framework developed in this work can guide the future operation of coal-fired plants and other power plants for the safety prediction of boiler operations.

Effect of flue gas constituents on boiler tube failure of a captive power plant

Water leakage was reported from one of the superheater tubes of boiler during operation. The power plant is a part of copper ore smelting and refining industry. It was observed, that the leakage took place through cracked region of the tube, which was severely damaged due to chemical attack. Damage occurred due to reaction between flue gas and outer wall of super heater tube. Inefficient treatment of flue gas resulted in retention of metal particles, SO2 gas and particulate within the same in substantial concentration. When the same flue gas was used in boiler, SO2 reacted with tube surface at elevated temperature. The incident lead to wall thinning and deep pit formation over tube surface. Metal particles was fused, adhered to tube surface and triggered secondary cracking during operation. Gradual wall thinning, increment in pit size and crack propagation through thickness resulted in ultimate failure of tube material.

Failure in power plant system related to mitigations and economic analysis; A study case from steam power plant in Suralaya, Indonesia

The failure mitigation and economic analysis related to the damage of the boiler tube in the power plant system were evaluated in the present study. The research was conducted at Indonesia's Suralaya power plant (PP). The boiler was built in 2011 and experienced a boiler tube failure after operating for less than 5 years. This condition is not common since boilers generally can be used with a lifetime of approximately 30 years. In the present study, different analyses were used i.e., macro-fractography, metallography inspection, hardness test, SEM/XRD analysis, and hydro test. These tests investigated the failure modes, evaluated the tube's mechanical properties, and assessed the boiler water feed's quality. The results showed that the damage is caused by the below-standard quality materials and is triggered by the poor quality of boiler feed water and exhibit corrosion. It is proven that the high value of sodium, conductivity, and silica content causes corrosion of the inner tube, which came out from methane gas. It is also shown that the damage drastically decreased the quality of the water wall tube strength, indicated by the HRV value from 179 HRV to 112 HRV. The analysis was a brief study that can be used for manufacturers and industries that use the boiler to check the material quality and the detailed specification. Moreover, the below-standard materials have proven to cause economic loss and burden many sectors' maintenance and operation costs.

Computational Analysis of Tube Wall Temperature of Superheater in 1000 MW Ultra-Supercritical Boiler Based on the Inlet Thermal Deviation

Local over-temperature is one of the main reasons for boiler tube failures (BTF). By accurately monitoring and controlling tube wall temperature, local over-temperature can be avoided. Based on the measured flue gas parameters and numerical simulation, a method of thermal deviation calculation is proposed in this study for the on-line calculation of the tube wall temperature of boiler superheaters. The full-size three-dimensional numerical simulation was presented on the combustion in a pulverized coal-fired boiler of 1000 MW ultra-supercritical (USC) unit. A difference in the thermal deviation of the vertical direction was innovatively introduced into a segmented discrete model, and the thermal deviation condition conforming to reality was introduced into the calculation. An on-line calculation system developed based on the current calculation method was applied in a 1000 MW USC unit. The calculated local high-temperature zone was consistent with the actual over-temperature position and conformed to the law of the allowable metal temperature of the final superheater (FSH) serpentines segment. The comparison results showed that the calculated data by this method were more reflective of tube wall temperature change with boiler loads than the measured data. According to the calculated local over-temperature zone, the immediate warning response can effectively reduce the possibility of over-temperature BTF.

Condition Assessment of Boiler Water Wall Tubes using Robotics

Boiler tube failures continues to be the primary cause for forced outages in boilers. To get the boiler back on line and reduce (eliminate) future forced outages due to tube failure, it is extremely important to determine and correct the failure root cause. Detecting and sizing flaws before they cause failures is of critical importance in boiler maintenance. Localized and general wall thinning due to corrosion & erosion in boiler water-wall tubing is a significant inspection concern for boiler operators. There are at least four (4) other methods used for the inspection of Boiler Water walls. These methods are Spot Check UT, A-Scan UT, EMAT, and Scanning Thermograpy. Spot Check UT only gives thickness readings and gets very minimal coverage of the total surface area of the furnace water walls; the chances of finding I.D. flaw mechanisms using Spot Check UT are minimal at best. If Boiler Water walls have been sandblasted, A-Scan UT may be used to inspected larger areas of the furnace walls; in these cases, a steady flow of water is most often used as the couplant. The EMAT technique requires that any Boiler Water wall surfaces be sandblasted. This paper will present a discussion on the deployment of robotic wall crawler using electromagnetic technique to inspect boiler water walls from outside of the tube together with the theoretical background of the technique which explains the quantitative nature of the inspection. Further, case studies will be presented for the technique that allows the extraction of tube wall thickness information from the inspection data.

Failure Analysis of Bank-Wall Side Boiler Tube in a Petrochemical Plant

Failure analysis of the petrochemical plant’s bank-wall side boiler tube has been conducted to determine the root cause of tube failure. The tube material is low carbon steel ASTM A178 grade A. Visual examinations of the cracked surface revealed that the fractured surface is flat, without plastic deformation, and several longitudinal and transverse fissures are present. The SEM and optical microscope examinations show that the cracks were intergranular and transgranular. A hydrogen attack caused the intergranular crack, and thermal fatigue produced the transgranular crack. Boiler tube failure was caused by a steam blanket on the sloping tube’s top inner diameter that induced iron oxide deposition and accumulation. Hydrogen was produced after a chemical reaction at the deposit-metal interface between the iron oxide deposit and ingress steam. Local temperature variation on the top part of the sloped tube occurred during the splashing and evaporation of water, promoting thermal fatigue.

A coupled combustion and hydrodynamic model for the prediction of waterwall tube overheating of supercritical boiler

Tube overheating is the leading cause of boiler tube failures that had led to tremendous replacement and maintenance costs. Boiler tube temperature is simultaneously affected by the heating effect of hot combustion gas in the furnace and the cooling effect of steam flow in boiler tubes. Thus, prediction of tube temperature needs to include the simulations of both the gas and steam flows of the boiler in the model. To compromise the significant scale difference between the boiler furnace and tubes, a coupled model that integrates a three-dimensional (3D) CFD model describing the gas flow and combustion processes in the furnace with a one-dimensional (1D) hydrodynamic model describing the steam flow in the boiler waterwall tubes was developed in this paper. The 3D CFD and 1D hydrodynamic models are coupled by iterative data exchange of boiler heat flux and steam temperature between the two models. In this way, this coupled model can incorporate all the key parameters that strongly affect the waterwall tube temperature, including the distributions of boiler heat flux, steam temperature and the convective heat transfer coefficient of steam flow in boiler tubes. In particular, the critical effects of steam maldistribution caused by both the structure of tube network system and uneven heat absorption of parallel tubes on tube temperature can be resolved by this model. This coupled model provides the capability to predict the detailed distribution of waterwall tube temperature and locate the areas of tube overheating under different boiler operating parameters. This coupled model was employed to predict the tube temperature distribution of the spiral waterwall of a 350 MW supercritical boiler. The predicted results show that the areas having higher risk of tube overheating are located near the outlet of spiral waterwall tubes where the steam temperature is the highest and on the wall areas where the local wall heat flux is the highest. The results strengthen the necessity of incorporating both the gas and steam sides of boiler into the model for accurate prediction of waterwall tube temperature.

Evaluation of Cyclic Tensile Stress Effect in Boiler Tube Failure

Boiler is one of the critical parts and plays an important role in Steam Generation Power Plant. It transforms the chemical energy of fuel into heat or thermal energy. During plant operations, some problems occurred in the boiler and Superheater leakage is the heaviest problem that interfered the whole operations, and the units needed to stopped for maintenaces outages. Failure analysis is necessary to determine the cause of failure. Root Caused Failure Analysis methods was through mechanical tests in the laboratory, which is Visual Observation included Macrofractography Structure examination, Metallographic or Microstructure Examination, Hardness Test. The metallographic examination result shows that the microstructure of the base metal is ferrite pearlite, and there is no indication of microstructure changes in tube as effect from high operation temperature. Likewise, microstructure in the weld region is in normal conditions, no weld failure phenomenon. Hardness value for base metal, weld and HAZ area are still in a good condition. Macrofractrography structure examination shows that the fracture is in mechanical fatigue condition. Based on those results the source of the tube leak is not caused by operating errors, inside or outside deposit nor weld failure. Superheater tube failures caused by mechanical factors, namely due to cyclic tensile stress as result in vibration by gas flow coupled with an increase in the local area due to the welding heat, therefore, increases the rate of crack propagation. To verified the data from mechanical test, CFD simulation will be used. CFD can detect the direction of the gas flow around the Superheater tube. The simulation result shows the possibility of turbulence flow around the tube, which creates the vibrations on the tube due to gas flow velocity. Thus, the superheater tube leakage mostly because vibration that create cyclic tensile stress.

Analysis of corrosive degradation and failure of water wall tubes

In a modern power station, the malfunction of the boilers causes the whole unit to shut down resulting in disturbance of productivity. The failure of water wall tubes (WWT) is typically the reason for the shutdown, which is mainly caused by corrosion and degradation. The current study has gone over the various sources of the corrosive effects on the WWT in great detail. Identifying the right failure mechanism is usually beneficial in assuring the equipments reliability. Hence, this research work focuses on the analysis of the cause for boiler tube failure in Thermal Power Stations. By introspecting the mechanisms of a tube failure, methods of failure detection and remedial measures are suggested.

Metallurgical investigation of boiler tube failure in a power plant

The boiler tube used in the power plant industry had failed prematurely after 11 years of service, which was used to supply steam at working temperature – 420 °C (approx) and working pressure of about ∼ 146 kg/cm2. The failed tube cut off the steam supply to the power plant industry and caused the plant to shut down for several days. So in this paper, the root cause failure of the boiler tube has been investigated. The tube was made from SA 210 Gr. C steel supplied in hardened and tempered conditions. However, certain defects in the manufacturing process and corrosion/erosion in the tube have initiated to thin the tube and resulted in failure of the tube. Due to these defects, the wall thickness was reduced by more than 20% of the nominal thickness. The microstructure analysis around the failure zone and away from the failure zone confirms the normal microstructure of ferrite and pearlite. Finally, it is recommended to use a defect-free tube and in case of severe erosion, ultrasonic wall thickness measurement may be carried out to check the reduction in thickness, so that the premature failure of the tube can be avoided in the near future.

A review paper on factors that causes the bulging failure of the metal tube

This paper is a systematic review of the Literature on the general parameters of bulging tube failure. Generally, boiler tubes show bulging tube failure in hot temperature zone in thermal power plants. Unpredictable tube failure affects the utility boiler's effectiveness in power plants due to uncertainty in utility boilers. In this report, the actual circumstances of battling the elevated temperature long-term overheating and short-term overheating and talking over corrosion to the boiler surface. The literature survey and the real-time data obtained from two thermal power stations; highlight that boiler tube failure occurs due to different causes. Overheating and creep deformation are the most prominent causes of bulging tube failure. This article may help understand the leading causes of the bulging tube failure placed in the hot temperature zone and its factors.

Hot corrosion behaviour of CNT-reinforced ZrO2-Y2O3 composite coatings on boiler tube steel at 900°C

PurposeIn Indian thermal power plants, the main cause of boiler tube failure is the presence of molten sulphates and vanadates, which deteriorate the tube material at high temperatures. To combat the hot corrosion failure of metals, thermal spray technology is adopted. This study aims to investigate and study the effect of hot corrosion behaviour of carbon nanotube (CNT)-reinforced ZrO2-Y2O3 composite coatings on T-91 boiler tube steel in a molten salt environment at 900 °C for 50 cycles.Design/methodology/approachA plasma spray technique was used for development of the coatings. The samples were exposed to hot corrosion in a silicon tube furnace at 900 °C for 50 cycles. After testing, the test coupons were analysed by X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and cross-sectional analysis techniques to aid understanding the kinetics of the corrosion reaction.FindingsCNT-based reinforced coatings showed lower weight gain along with the formation of protective oxide scales during the experimentation. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix.Originality/valueIt is pertinent to mention here that the high temperature behaviour of CNT-reinforced ZrO2-Y2O3 composite on T-91 steel at 900°C temperature in molten salt environment has never been studied. Thus, the present research was conducted to provide useful results for the application of CNT-reinforced composite coatings at elevated temperature.

Remnant creep life estimation approach for Alloy 617 tubes of ultra-supercritical thermal power plants

The efficiency of the coal-fired boilers can be enhanced through increasing the operating steam pressure and temperature. Though, higher steam pressure and temperature may potentially lead to increased boiler tube failure. In this work, a simple and practical procedure is proposed to estimate the remnant creep life of Alloy 617 for superheater and reheater tubing of ultra-supercritical (USC) boilers operating at a 700 °C or higher/35 MPa steam condition. Based on the estimations demonstrated here, operating 750 °C or higher with 35 MPa steam conditions for Alloy 617 required further viability studies and careful consideration, especially with regard to the increased rates of creep strength degradation. The use of Alloy 617 with considerably suitable tube geometries at 700 °C/up to 35 MPa steam conditions seemed to be allowable in service. A combination of the tube geometry and steam condition for the use in USC thermal power plants shall be carefully considered for reliable and continued services.

A Failure Mechanism Study of Boiler Water-Wall Tube using Numerical and Experimental Analysis

The aim of this study is to investigate the boiler tube failure mechanism using finite element analysis and experimental Analysis. The numerical software used is ANSYS steady-state thermal and static structural analysis. The independent variable for the analysis is temperature from flue gas and wall thickness of boiler tube. The scope of the study is to determine the temperature distribution, von mises stress, deformation and safety factor by implemented design of experiment. The material of boiler tube sketch in two dimensional for simulation is SA210 Grade C. this is standard requirements for the boiler made of seamless medium-carbon steel with superheater tubes according to ASTM. From the result and discussion, the potential of failure mechanism will determine upon independent variables. In addition, hoop stress or circumference stress will help to support the statement of failure of boiler tube.

Experimental Analysis of Hot Corrosion Behaviour of some Composite Coatings on Boiler Steel at Elevated Temperature

Hot corrosion is the main reason of failure of boiler tubes used at high temperature in thermal power plants. This paper is an attempt to investigate the effect of different composite coatings on boiler tube steel in corrosive environment of Na2SO4 – 60%V2O5 at 900°C for 50 cycles. The coatings have been deposited with high velocity oxy fuel process. The samples were exposed to hot corrosion in a Silicon tube furnace at 900°C for 50 cycles. The kinetics of corrosion behaviour were analysed by the weight gain measurements after each cycle. Corrosion products were analysed with weight change statistics, X-ray diffraction, and scanning electron microscopy. It is found that 100Cr3C2 composite coatings provided the higher resistance to corrosion as compared to other types of coatings. Cr carbide layer was formed on the surface and these layers provided the protection from hot corrosion.

Failure investigation into the boiler tubes of power plant

Failure of tubes is a very critical problem in boilers. The current study describes the detailed investigation for failure of boiler tubes in the power plants. Different characterization techniques like; metallography/microscopy, hardness, chemical analysis, SEM/EDS were utilized to find out the actual cause of failure. The tubes were failed within one year of its service. It was concluded that the brittle fracture (rupture) of tubes was occurred due to over-heating caused the formation of thermally insulating thick iron oxide scale on the inner surface of the boiler tube. Evidence of hydrogen embrittlement of the boiler tube in the rupture region was also found. Insights of this investigation might be helpful for the prevention of this type of failures in future.

A study of T11 boiler steel protection by cold sprayed Inconel 738 coating against high temperature erosion

The failure of boiler tubes, superheater tubes and turbine blades, due to high-temperature erosion, is a serious issue in the power generation industry. The investigation focuses on the applicability of cold sprayed Ni-based coatings for boiler tubes and turbine blades, by improving the erosion resistance of the base material. The present work includes high-temperature solid particle erosion behaviour of Inconel 738 (IN 738) coatings deposited on ASTM SA213 T11 steel substrate, by means of cold spray deposition. A comparison of the temperature effects on the erosion performance of coated and uncoated samples have been examined by an air jet erosion tester. After the erosion tests, both uncoated and coated specimens were characterised using a scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. Erosion resistance of the coating is approximately three and two times higher than T11 steel at 700°C for 30°and 90° impact angles, respectively. Consequently, cold spray IN 738 coating offers higher resistance to high-temperature erosion than that of the base steel, which is essential in a power plant environment.

Coal-fired thermal power plant performance optimization using Markov and CFD analysis

In the present stimulated business environment, power sector is playing a major role in the economic growth of India. During the last 20 years, the country had been facing a poor supply of energy and this supply–demand gap is increasing continuously. Therefore, it is important for power plants to improve its power generation capacity drastically by reducing the failure rate. In the present paper, to analyze the causes of poor availability, thermal power plant has divided into six different systems and a system comprising waste gases heating system has been considered. With the help of transition diagram, mathematical equations have been used to find out the availability. After analyzing, it was found that the value of availability is very low and boiler tube failure is one of the most critical factors for this low availability of system. The power plants have low availability causing serious concern and need to identify the responsible factors for this low availability. Boiler tube failure is identified as a responsible factor for low availability, and economizer is the zone where maximum failure occurred. From the maintenance history sheet, it was identified that economizer is a critical zone where maximum tube failures occur and the main cause of economizer failure is due to high-velocity flue gas particle, i.e., erosion. To increase the availability and minimize the failures, erosion process must be reduced in economizer tubes which is mainly responsible for economizer failure and then CFD analysis has been done for this purpose. This results in a decrease in the shutdown period of the plant and an increase in the system availability as well as the power of the system.