Boiler Tubes Research Articles

Seam tracking control for weld cladding of boiler tubes in thermal power plants

Seam tracking control for weld cladding of boiler tubes in thermal power plants

Effect of peripheral nonuniform distribution of furnace heat flux on thermo-hydraulic characteristics and design of riser downcomer circuit of natural circulation boiler

The usual practice of design of riser tubes of natural circulation boilers is with an assumption of uniform furnace heat flux. Using the uniform diameter of riser tubes inside the furnace zone is also very common. The effect of peripheral nonuniform distribution of furnace heat flux on thermo-hydraulic characteristics and design of the riser downcomer circuit of a natural circulation boiler is presented here for the first time. As the riser tubes are exposed under substantially high heat flux, the tubes containing water-steam mixture are vulnerable and susceptible to overheating, particularly at high flux zone. From systematic analysis, it is proposed that using different diameters and the number of riser tubes at various sections can overcome the early occurrence of tube dry-out. An appropriate two-phase flow model is developed with flow regime mapping, tube wall temperature calculation, and identification of possible dry-out. The peripheral nonuniform distribution of furnace heat flux is implemented analytically in the model by introducing a distribution parameter estimated from the actual furnace data. Results reveal that with an average heat flux of 150 kW/m2, the dry-out occurs near a riser tube height of 44 m for a typical 210 MW capacity boiler. However, considering the nonuniform heat flux variation, the dry-out appears near a height of 32 m and 73 m for higher and lower heat flux zone, respectively. The present analysis shows that the implementation of larger size and lower size diameter of riser tubes, respectively, in higher and lower heat flux regions has a 9.45 % cost-benefit compared to the usual design practice with a consideration of uniform diameter tube and heat flux. The present work concludes that instead of using uniform tube diameter with average heat flux assumption, the use of different diameter of tubes in different heat flux zone not only avoid the early onset of possible dry-out but also has a cost-benefit.

Prediction of the Time to Failure of Boiler Tubes Flawed With Localized Erosion

AbstractA failure mechanism prevalent with boiler tubes operating in harsh environmental conditions is localized erosion. The consequence of the erosion mechanism is a substantial reduction of the tube thickness, ultimately leading to plastic collapse and consequently rupturing of the tubes. Locating and repairing all the affected tubes within the boiler are time consuming and expensive. It will be worthwhile to rank all the identified flaws so that critical flaws that cannot survive till the next scheduled shutdown are prioritized for repair. Consequently, nonlinear structural analysis was conducted on various boiler tubes that failed by localized erosion. The tubes had a wide range of localized erosion flaws that required a detailed assessment technique. The failure was evaluated numerically using various stress and strain-based failure criteria as well as performing the American Petroleum Institute and the American Society of Mechanical Engineers (API-ASME) fitness-for-service (FFS) assessment on the tubes. A projected time to failure (Pt) for each tube based on the various criteria used in this study was determined. This enabled the ranking of the flawed tubes based on the priority of their repair. The outcome of this study demonstrates the potential for a tool which will enable industry users to prioritize the replacement or repair of critically flawed tubes and avert replacing tubes that are still safe for future operation.

High-temperature failure of steel boiler tube secondary superheater in a power plant

This work investigated the failure analysis of the boiler tube secondary superheats in a power plant utility. The tube was composed of low carbon steel with 2.25Cr-1Mo addition, which was ruptured after a 26 h working test. The investigation of the tube’s failure was performed through several analysis, such as microstructure, elemental analysis, and mechanical test. It was found the abrupt increase in the operating temperature as the primary factor of the material degradation of the tube. The microstructure analysis shows the existence of elongated grain with the formation of microcracks on the grain boundaries, indicating the exceeded stress applied in the material. The hoop stress in the ruptured tube was 42.47 MPa, which is higher than the allowable stress of 23.5 MPa at 605 °C. Furthermore, the equiaxed grain was observed in the unruptured tube, implying the microstructural change after exposure at high temperatures.

Increased hydraulic resistance in tubes of once-through boiler due to fouling: A case study of 650 MWe ligite fired unit

The analysis of pressure changes in water and steam flow along the entire once-through steam boiler tube system at the 650 MWe lignite fired Unit was carried out after the long operational period of almost 30 years without a chemical cleaning of the pipe system. A significant increase of the hydraulic resistance was recorded in comparison to the design values in the evaporator tubes, both in the water heating zone and in the evaporation zone with the two-phase mixture flow. The cause of this adverse effect is the formation of a wavy surface of the magnetite layer deposited on the inner wall of tubes. The significantly increased absolute roughness on the inner wall of tubes was determined on the basis of measured pressure drops at sections of the tube system and numerical calculation performed with a thermal-hydraulic model of single-phase and two-phase water and steam tube flows. The model is based on the steam-water two-fluid model with mass, momentum and energy balance equations and mechanistic correlations for the steam-water interface transfer processes. The model is suitable for the single and two-phase flow parameters prediction in the span from subcritical to supercritical and near critical pressure conditions. Conducted calculations provide detailed insight in the fluid pressure, velocity and temperature change in the boiler tube system. After the long operational period the pressure drop in evaporating tubes almost doubles in comparison to the design values. The presented results are a support to boiler's design, operational procedures and maintenance.

Failure Analysis of a Deep Pit on the Inner Wall of Water Wall Tube in a Power Plant

A deep pit on the inner wall of a water wall tube of a 600MW boiler was found at the extension end of the front of the furnace during an overhaul after 200 thousand hours of operation. To investigate the causes of the failure, various techniques including macroscopic inspection, chemical composition analysis, microstructural analysis, mechanical performance testing, scanning electron microscope (SEM) observation and energy dispersive spectroscopy (EDS) analysis were carried out. The results of investigations showed that the chemical composition of the as-received tube conformed with SA-178 Grade C and the mechanical properties were qualified. EDS analysis revealed that the main elements of the deposit on the surface of the pit were iron and oxygen, along with phosphorus, potassium and aluminium, which were identified with the constitutes of the under deposit corrosion products. Based on the results, the cause of the failure is under deposit corrosion. Possible measures to combat the corrosion were proposed.

A calculation and analysis of a cylindrical part of a steam boiler of a steam locomotive miniature model

The aim of this study is to calculate and analyze a cylindrical part of a steam boiler of a steam locomotive model. The cylindrical part of a steam boiler is the fundamental part of the steam boiler because it is designed to heat water and create steam using a large number (up to several hundred pieces) of boiler tubes passing through it, inside of which hot flue gases flow. Stress and reliability previous of the cylindrical part of the boiler were carried out using the methods of a theoretical analysis and the finite element method analysis.

Comparative corrosion study of HVOF coated Wc-10Co-4Cr, NiCrBSi and NiCr industrial waste coatings on AiSi304 stainless steel

The increasing demand for the high-velocity oxy-fuel (HVOF) thermal sprayed coated steel for boiler tube applications is the driving force behind this research work. Following the needs of the industry, the present study is aimed at understanding and comparing the corrosion resistance behavior of the WC-10Co-4Cr, NiCrBSi, and NiCrIW coating on AISI 304 stainless steel. A detailed microstructural characterization of the coatings before and after the corrosion experiment by FESEM, phase identification by XRD, and porosity determination by image analysis was performed. Corrosion behaviors of the coatings are examined by the electrochemical measurement technique after their immersion in a solution of 4 % NaCl for 1 hr, 12 hr, 36 hr, 102 hr, 200 hr, and 250 hr. Electrochemical impendence spectroscopy and Potentiodynamic polarization test results show that the porosity of the coatings and interface between unmelted particle and matrix (Formation of micro-galvanic cell) are potential sites for corrosion initiation. Electrochemical impedance spectroscopy (EIS) data indicates that the corrosion resistance of all types of coating initially decreases with increasing immersion time, but after some time corrosion resistance of the coatings again increases with increasing immersion time. This is because of the local accumulation of corrosion products in the defects hindering penetration of the electrolyte easily. Both the corrosion studies revealed that corrosion resistance of the coatings is in the following order: NiCrBSi > WC-10Co-4Cr > NiCrIW.

A generalised approach to the dynamic modelling of a water tube boiler

A generalised approach to the dynamic modelling of a water tube boiler

Improving the Disseminations of Boiler Tube Material T-SA213-T-11 at High Temperature Behavior of CNT Reinforced NiCrAlY with HVOF

It is pertinent to mention here that the high temperature behaviour of CNT-reinforced NiCrAlY with CNT 3%, 5% and 7% with HVOF on T-SA213-T-11 steel at 600°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 high elevated temperatures are underwent low porosity, opaque coatings, they are more viscid in nature and are due to its low porosity, high dense coatings, more adhesive in nature and strong bond. Kinematics hot corrosion, oxidation and erosion are to be analyzed by the attainment of mass gain after each and every progression under thermogravimetric studies (1hour heating and 20 minutes cooling). Results will be achieved by using visual examination, and advanced microscopy like XRD and SEM/EDS analysis. Keywords: High temperature, hot corrosion, Thermal spray coatings HVOF, XRD and SEM/EDS analysis.

Analisis Efisiensi Water Tube Boiler Berbahan Bakar Fiber dan Cangkang Sawit di PT Dhamasraya Palma Sejahtera

Palm oil mill processing companies in their operations use Water Tube Boilers which are fueled by shells and fiber. Boiler or Steam Kettle is a container that contains water or other fluids to be heated. Boiler with a capacity of 30 tons. In general, every machine produced by the factory is always equipped with a handbook/instruction book on how to install, maintain and operate it. Likewise with the boilers in the Company there are manuals regarding specifications for operation, maintenance, installation, and others. of various kinds of boiler fuel mixtures for combustion can produce different thermic efficiencies depending on the percentage of the mixture, in this study the results of laboratory tests obtained the calorific value of the fuel mixture of 70% fiber and 30% shells had the highest calorific value, namely 4604.7 Cal /g. The highest boiler efficiency value produced was 53.9% using 100% shell fuel, the efficiency using 100% fiber fuel was 51% and the lowest boiler efficiency value produced was 49.5% using a mixed fuel of 70% fiber and 30 % shell.

Failure analysis of the water-wall tube in once through Benson boiler

Failure analysis of a water wall tube of a once-through Benson boiler after 100,000 h of use of service is presented. A 15Mo3 material was used in the manufacture of the tube. In order to identify the root cause of the rupture, visual inspection, optical emission spectroscopy, microscopic examinations, mechanical strength measurements, and tube wall thickness measurements at various locations were performed on the failed tubes. Visual inspection revealed a fish mouth puncture opening with thin lips. As a result of optical spectroscopy, mechanical testing, and hardness measurements, the material was found to meet the requirements. Based on microstructure analysis, it appears that the pearlite spheroidized near the rupture site as a result of localized high temperatures. The failure mechanism of the tube was identified as a localized short-term overheating caused by high heat flux based on the results of all the tests and analyses conducted in this study.

Opt-TCAE: Optimal temporal convolutional auto-encoder for boiler tube leakage detection in a thermal power plant using multi-sensor data

Accurate and timely detection of boiler tube leakage in a thermal power plant is essential to maintain a stable power supply and prevent catastrophic failures. This paper proposes a novel, unsupervised learning-based leakage detection method, namely optimal temporal convolutional auto-encoder, which uses both acoustic emission signals and operating (i.e., temperature and pressure) signals. The proposed optimal temporal convolutional auto-encoder learns the characteristics of normal operating conditions by reconstructing input data and detects tube leakage by calculating its reconstruction error. Unlike conventional methods that mainly focus on modeling only inter-sensor relationships, the proposed method offers a deep learning structure that can effectively capture temporal as well as inter-sensor relationships. This paper also proposes a method to optimize the latent dimension of the auto-encoder structure by minimizing the entropy of the trained normal reconstruction errors. In a preprocessing step, the moving average filtering is used to reduce the effect of external noises in acoustic emission signals, thereby decreasing the number of false alarms. Kernel density estimation is adopted to automatically set the threshold. The effectiveness of the proposed method is verified through datasets acquired from real operating power plant. The results show that the proposed method can detect leakage more accurately than conventional methods.

Microstructure and high temperature oxidation behavior of laser cladding C22 coating

C22 coating was successfully prepared on TP347H tube by laser cladding. The main goal was to assess the possibility of using laser cladding C22 coating for high temperature oxidation protection of boiler tubes in ultra-supercritical power plant. The microstructure, phase composition, microhardness and high temperature oxidation behavior of C22 coating were investigated. The microstructure evolution, phase constitution and high temperature oxidation behavior of C22 coating and TP347H samples were investigated. The oxidation experiment were carried out at 600 °C, 700 °C, 800 °C for 168 h. The results revealed that C22 coating mainly contain Ni-Cr-Co-Mo solid solution. The average microhardness of coating surface is 1.5 time that of substrate. Coating exhibited superior oxidation resistance at 600-800 °C. A dense and continuous Cr 2 O 3 film was observed in inner layer of coatings. C22 coating can be used as an excellent oxidation resistant coating with wide application prospect. Coating exhibited superior oxidation resistance due to the formation of a dense and continuous Cr 2 O 3 film in inner layer at 600-800 °C.

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.

Analysis of boiler tubes using gas tungsten arc welding in Grade 91 alloy steel

Failure analysis of Boiler components is an important step in the Inspection process of Boiler. If this is not taken sternly, it may lead to leakage or even bursting. So research works should be conducted to upgrade the quality of the material and ensure the effectiveness of the components like boiler tubes. In this paper an experiment is conducted by welding Grade 91 Alloy steel with proper process parameters. The joints are then subjected to Non– Destructive Testing and the final conclusion is discussed at the end. Grade 91 alloy seems to be suitable for boiler tube material. If applied proper welding techniques, an effective boiler tubes can be obtained.

Performance enhancement of an industrial fire tube boiler

An Industrial boiler is considered as highly energy intensive equipment. The primary objective of this study is to identify and quantify the potential losses of different energy sections of the fire tube boiler and its overall performance. Several energy saving measures such as combustion optimization, excess air control, control of flue gases temperature and effect of excessive or uncontrolled steam blow down optimization, on the overall performance of boiler are also applied. Energy as a result of energy saving measure has been determined as well. In present study, some main causes of energy wastages are summed up, by using a Energy Auditing. From the results of energy audit, the boiler’s thermal energy efficiency and combustion efficiency are found to be 70.09% and 75.7% respectively. It was also observed that these losses can be reduced by controlling stack temperature, excess air and optimized blow down. There covered energy can be utilized to preheat the combustion air and feed water. Economic evaluation of energy saving measure resulted in annual fuel saving of 6.3 Million PKRs without any investment but only improving working methodologies. As a result of these efforts, the savings in terms of cost has also been determined.

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.

A Diagnostic Method Based on Active Thermography for the Degradation Assessment of Power Plant Boiler Tubes.

Proper maintenance management of power infrastructure requires inspections, in order to gather knowledge about the facility's current condition. For this purpose, periodic diagnostic tests are carried out, not only to determine the current state, but to also predict future conditions, and subsequently plan for the scope of necessary repair work. Currently, in the case of heat screens of power boilers, the diagnostic process takes many days, is very expensive, and usually does not cover the entire screen area. Therefore, it is necessary to develop new, noninvasive diagnostic methods. This study presents the concept and research for an alternative method of locating places with excessive energy boiler screen degradation that require replacement. It was assumed that the new method should be fast, require no scaffolding assembly, and permit checking of the entire screen surface; this is unlike the methods used currently, which require manual checking of selected screen tubes. The proposed method is based on active thermography, in which heat flux is forced by the liquid flowing inside the screen. Tests were carried out based on a model of an axial-symmetric system in the form of a tube, with controlled reductions in the wall thickness. An experiment was carried out many times by recording the pipe surface temperature in many characteristic places (different thicknesses of the tube walls) with a thermal imaging camera. A temperature change was forced by a controlled flow of hot or cold water. The methods of analysis were proposed and verified, allowing firstly, detection of places with a reduced wall thickness, and secondly, estimations of the wall thickness (i.e., excessive degradation). For the best-proposed model (one of the four analyzed), all of the thickness changes were detected, and the limit error of thickness obtained was 0.3 mm.