Boiler Tubes Research Articles

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.

Failure investigation of the tube of a dual fired steam boiler in a western nigerian food and beverage manufacturing plant

This paper investigates the causes of failure in the tubes of a 12,000 kg/hr. dual fired steam boiler used in a Food and Beverage manufacturing plant located in southwestern Nigeria. The techniques adopted in analyzing the failure includes visual examination, chemical composition analysis, microstructural analysis, and water chemistry analysis. All the investigations were carried out in accordance with the British standard code BS 3059 PART 1 GR 320 ERW. Physical examination revealed some levels of rupture both on the flue gas side and the water sides. Decarburization and grain growth were observed on the outer diameter (OD) of the tubes while pitting and thermal oxidation were noticed on the internal diameter (ID). Uneven heat distribution in the boiler tube was attributed to corrosion emanating from the scaling in the OD. The failure mechanism in the boiler tubes was attributed to significant localized corrosion and uneven heat distribution in the tubes which caused thermal oxidation.

PERL: Probabilistic energy-ratio-based localization for boiler tube leaks using descriptors of acoustic emission signals

This paper proposes a novel method for boiler tube leak localization in a thermal power plant, using acoustic emission sensors. In industrial settings, due to computational and storage capacity, the measured acoustic emission signal is often processed through the use of descriptors, such as the root mean square (RMS), which is related to the signal energy. Computational and storage capacity issues make it difficult to use conventional methods, including time difference of arrival, which uses a high-sampling-rate signal. In addition, the measured RMS may have uncertainty that arises due to sensor disturbance or unpredictable process conditions. Thus, this study newly proposes an approach called probabilistic energy-ratio-based localization (PERL) to estimate the location of a boiler tube leak. In the proposed approach, acoustic dissipation theory is used to calculate the ratio of the signal energy from the specific band energy. To account for background noises and sensor disturbance, the uncertainty of the measured RMS is characterized in a probabilistic manner. Using this information, the probability that a boiler tube leak has occurred at a specific location is estimated hypothetically. Case studies confirm that the proposed method enables localization of a boiler tube leak position with high accuracy.

Evaluation of Internal Pressure Creep Rupture Life of Boiler Tube Using Miniature Tensile Creep Test

Abstract Many studies have been made for evaluating the creep rupture life of a boiler tube. The working stress of a tube under internal pressure is calculated mostly by the mean-diameter formula adopted in design for pressurized components. However, this stress is not always representative of a complex stress state under internal pressure. So, focusing on the representative stress, internal pressure and uniaxial creep tests were conducted using unused and 90,000-h used boiler tubes of Type 321 stainless steel in this study. A miniature specimen (1.5 mm in width, 1.5 mm in thickness, and 25 mm in length) for the uniaxial test was taken from the middle of the tube wall in the direction of the maximum principal stress. As a result, the mean-diameter formula did not present good agreement between internal pressure and uniaxial creep rupture lives. Hence, as an alternative stress, von Mises equivalent stress, which presents good correlation between uniaxial and multiaxial creep rupture properties, was chosen. The equivalent stress, σ*, at the middle of a tube wall was calculated using Rimrott’s solution to internal pressure creep of thick-walled tubes considering large deformation. Because σ* increases with creep strain under internal pressure, σ* at εθo = εθof / 2 (where, εθo and εθ0f are tangential and tangential rupture strains on the outer diameter, respectively) was employed as the representative stress. Consequently, this stress resulted in good agreement between both creep rupture lives for the unused tube. However, the internal pressure creep rupture life of the used tube was inconsistent with the uniaxial life, which was attributed to the existence of an outside layer due to exposure to combustion gas. Using a reduction rate of the rupture ductility of the layer, the internal pressure creep rupture life of the used tube was evaluated well with the unused tube.

Неметалеві включення в металі котельних безперервнолитих заготовок

The article presents results of studies of contamination of metal of undeformed continuously cast billets (CCB) for boiler tubes from carbon steel supplied by various manufacturers with non-metallic inclusions. Contamination was investigated by metallographic means using methods of observation under a microscope in light and dark fields of vision in polarized light. Application of these methods has made it possible to determine the inclusion types (silicates, oxides, sulfides) with high probability based on optical properties (color, transparency, etc.). Shape, size and type of inclusions and the nature of their location along the billet cross-section were determined for the data set of actual level of contamination of the CCB metal with non-metallic inclusions. In addition, the methods Sh and L according to DSTU 8966 were used. To determine the number, dimensions and types of inclusions, an automated control method using the VIDEOTEST-METAL 1.0 software was also used for the Axiovert 200MAT microscope. Composition of some non-metallic inclusions was studied by means of X-ray spectral microanalysis using the MS-46 microprobe of the Cameca Co. (France). It was established that irregular and rounded silicates of both homogeneous and heterogeneous composition (including individual large ones up to 150 μm in size) are main types of inclusions in metal of continuously cast billets. In most cases, these inclusions are located in axial and peripheral zones along the CCB section. Intermittent film precipitation of non-metallic inclusions of varying degrees of dispersion (mainly of small size) which can have a negative effect on service characteristics of tubes made from such CCB was also detected. The study results have important scientific and practical significance in conditions of wide use of such CCB in the production of tubes of responsible purpose. The obtained study results will make it possible to further develop an advanced methodology of assessing the contamination of non-deformed continuously cast billets (with scale) with non-metallic inclusions in their metal and introduce them in regulatory documents on the CCB. The results of studies of metal contamination with non-metallic inclusions will also be useful for improving the CCB production technology with the aim of producing boiler tubes of high operational reliability. Keywords: undeformed continuous cast tube billet, non-metallic inclusions, silicates, film precipitation of non-metallic inclusions.

Coupled CFD-FEA simulation of bulging tube failure in hot temperature zone

Bulging tube failure is common when tubes are exposed to high temperatures. The most prevalent reasons of bulging tube failure are more heating and creep deformation. This research article simulates the most typical causes of tube bulging failure. Coal-fired power station boiler tubes from diverse processing industries display identical bulging tube failures when loaded with pressured fluid and placed inside a higher temperature zone.The differential in temperature between the outside and inner tube walls and compressed fluid inside the tube demonstrates efficient thermal expansion on the metal tube wall in the form of creep ductile deformation. By merging traditional CFD (Computational Fluid Dynamics) and FEA (Finite Element Analysis) models, this research provides a technique based on fluid structures. The thermal-structural behavior of tube deformation can be predicted using a combined CFD-FEA simulation of tube bulging failure. The CFD modeling solves the increment in fluid pressure inside the metal tube and the increment in temperature inside and outside the metal tube. FEA modeling aims to solve the thermal and structural behavior due to radial deformation and thermal expansion caused by thermal loads. Coupled CFD-FEA Simulation swelling tube failure in a hotter zone shown a clear idea of the high pressure and enhanced temperature, creep ductile deformation of tube wall in which the possibilities of tube failure are greater.

Effects of hydrostatic preload on strain hardening and strain aging of boiler tubes

Tests were conducted to identify the effects of existing defects on strain hardening and strain aging of boiler tubes. Electron backscatter diffraction (EBSD) and finite element analysis (FEA) were used to quantify the local plastic strain near the pre-existing defects. Strain hardening and strain aging effects depend on the degree of plastic deformation. Any existing defects in the boiler tubes can act as stress raisers during the room temperature hydrostatic test. For the morphology and orientations of the defects, a preload of 95 MPa which is equivalent to the hydrostatic test pressure was enough to induce local plasticity. When heated to boiler service temperature and tested to fracture, the mechanical properties of boiler tubes were affected. The test results justify a recommendation that the hydrostatic pressure to be kept near 110% of maximum allowable operating pressure (MAWP) to avoid significant alteration of mechanical properties at stress concentration points in defect-containing boiler membranes.

Development of CNT reinforced Al2O3-TiO2 coatings for boiler tubes to improve hot corrosion resistance

This study examines the hot corrosion behaviour of plasma-coated T12 steel for 10 cycles of 100 h each in an industrial boiler. The coating contains CNT (carbon nanotubes) reinforced alumina-titania powders. The substrates were exposed to the boiler at 750 °C. A thermogravimetric examination was conducted to evaluate the kinetics of corrosion. Corroded samples were examined with scanning electron microscopy and x-ray diffraction analysis after the end of the corrosion cycle. This research study concludes that CNT-reinforced coatings provide better corrosion resistance than conventional alumina coatings in the boiler environment.

Effect of nano yttria-stabilized zirconia on properties of Ni-20Cr composite coatings

In the present work, 5 wt.% and 10 wt.% yttria-stabilized zirconia (YSZ) nanoparticles were reinforced in Ni-20Cr powder and deposited on boiler tube steel using a high-velocity oxy-fuel spraying process. The effect of YSZ reinforcement on microhardness, surface roughness and porosity was investigated. The hardness was the highest for nanocomposite coating reinforced with 10 wt.% YSZ and hardness was found to increase with a decrease in porosity. The coating microstructure and elements were characterized using field emission scanning electron microscopy (FE-SEM) with an energy dispersive spectroscope (EDS). The constituents of the coating were identified using X-ray diffractometer. It was found that the composite coating with 10 wt.% YSZ reinforced nanocomposite coating has the highest microhardness, in the range of 1008-1055 hv. During the coating process, nano YSZ particles were dispersed in the gaps between the micrometric Ni-20Cr particles, providing a better coating matrix than conventional Ni-20Cr. The Ni-20Cr with 10 wt.% of YSZ nanoparticles showed better results in terms of mechanical and microstructural properties during the investigation.

Case Study on Fireside Erosion of Platen Superheater Boiler Tubes of a Coal-Fired Power Plant

Case Study on Fireside Erosion of Platen Superheater Boiler Tubes of a Coal-Fired Power Plant

Control of Acoustic Energy Input for Cleaning of Industrial Boilers

A non-intrusive cleaning method for boiler tubes at Sasol Synfuels power station at Secunda, in the Mpumalanga province of South Africa, is preferred over conventional methods that require boiler shutdown. The elected non-intrusive cleaning method utilizes sound energy waves, produced by an acoustic horn. Due to the nature of sound propagation and the effectiveness required, there is a requisite to control and operate the sonic horn. If the acoustic horn’s sound frequency is too low, it will produce higher sound energy waves that will resonate with the plant’s harmonious frequency and cause structural damage. Conversely, if the sonic horn’s sound frequency is too high, excessive noise levels may be reached and annoy plant personnel. To prevent these undesirable outcomes posed by adopting acoustic cleaning, there needs to be a regulatory system incorporated into the configuration to mitigate vibrations and limit noise. The regulatory system comprises a control system that drives the acoustic horn’s sound frequency as intended through a set point. The designed control system meets the anticipated requirements, such that it has an ideal transient response of 0.562 s, a steady-state error achieved in 1.05 s, with 0.201% overshoot, and most importantly the closed-loop system is stable.

Microstructural and mechanical properties of CNT-reinforced ZrO2-Y2O3 coated boiler tube steel T-91

The main purpose of this study was to fabricate carbon nanotubes (CNTs) reinforced zircon­nium yttrium coatings on boiler tube steel and to investigate the microstructural and mechanical properties of these coatings. Plasma sprayed conventional ZrO2-Y2O3, ZrO2-Y2O3 and 1 wt.% CNT and ZrO2-Y2O3 and 4 wt.% CNT were prepared and deposited successfully on boiler tube steel material T-91 (ASTM SA-213) by plasma thermal spray technology. Microhardness, porosity, XRD (X-ray diffraction), SEM/EDAX (scanning elec­tron microscopy/energy dispersive X-ray spectroscopy), X-ray mapping and cross-sectional analyses were used to analyse the specimens. The hardness of CNT reinforced ZrO2-Y2O3 increased with the increase in the percentage of CNT, whereas the porosity of the composite coatings decreased with the increase in the CNT percentage. The observed increase in hardness may be attributed to the content of CNT in the composite coating. The present research gives important information related to the fabrication and physical characteristics of CNT-reinforced ZrO2-Y2O3 coatings deposited on T-91 boiler tube steel.

High Temperature Fracture Resistance of Model Kraft Recovery Boiler Deposits

In kraft paper mills, supersonic steam jets are used to remove deposits that build up on the heat exchanger tubes in the recovery boiler. In this study, the fracture toughness KC and work of fracture, WF, of simulated boiler deposits were measured at temperatures up to 500 °C to determine the optimal conditions for deposit removal. The model deposits experienced an important brittle to ductile transition at ~450 °C. Above this temperature, ductile deposits required lower peak force, but four times more energy to fracture when compared to those tested at lower temperatures. The transition was clear in scanning electron micrographs of the fracture surfaces. The findings have significant implications for mills wishing to optimize sootblower performance.

High-temperature corrosion investigations of deposit containing eutectic KCl-K2SO4 mixture on AISI 1015 and SS304 steels

This study investigated corrosion behaviours of biomass fly ash containing eutectic KCl-K2SO4 mixture on carbon steel AISI 1015 and stainless steel 304 (SS304) at 700 ℃ for 12 h in air. The observed corrosion behaviours were validated by comparing with corrosion on similar materials, including carbon steel STBA 12 boiler tube and SS304 erosion guard, exposed in actual boiler environments. Similar corrosion behaviours were found in both laboratory-scale and field tests. Active oxidation, caused by chlorine, dominated over internal sulfidation for carbon steels. For SS304, presence of chlorine depleted protective oxide layers of SS304, followed by internal sulfidation from sulphur species.

Investigation on joining P91 steel and Incoloy 800HT through gas tungsten arc welding for Advanced Ultra Super Critical (AUSC) power plants

The present study focuses on dissimilar metal weld (DMW) of P91 ferritic-martensitic steel and Incoloy 800HT. The DMW was made nickel-based filler ERNiCrCoMo-1 filler using Tungsten Inert Gas (TIG) welding. Exhaustive microstructure analysis was done for the DMW. A stable austenitic microstructure was observed in the DMW solidified weld fusion zone (WFZ). Based on the peak welding temperature exposure in the different regions, the corresponding microstructure was observed to investigate the grain size transformations, phase transformations, diffusion, and segregation of constituent solute elements. Advance microstructure analysis was performed using Electron Probe Micro Analyzer (EPMA). Further, the effect of the observed microstructure feature on the mechanical property of the DMW was studied. The developed residual stresses were relaxed by post-weld heat treatment (PWHT). The tensile strength of the DMW was recorded less than the tensile strength of base metals. Also, impact toughness in as-welded (AW) WFZ was 117 J and reduced to 102 J after PWHT. Microhardness analysis showed maximum value in P91 heat-affected zone (HAZ) due to the dissolution of precipitates. It was reduced through tempering. The DMW of P91 and Incoloy 800HT was successfully produced without any major defect and with sufficient mechanical strength to put it in consideration for use in advanced ultra-supercritical (AUSC-Generation IV) boiler pipes and tubes as per the ASTM standards.

Use of High-Frequency Ultrasound Waves for Boiler Water Demineralization/Desalination Treatment

Isolated ultrasonic vibrations were used to treat feed water from a 20 bar steam-producing water tube boiler. Physical treatments such as ultrasounds and reverse osmosis (RO) are recommended as the most eco-friendly for this purpose. A novel bench-scale prototype delivering 6 L/h of treated water was designed and built. The ultrasonic atomization of raw water with 1.7 MHz piezoelectric transducers and subsequent humidification and dehumidification of drag airflow was the innovating sequence of operations used as a treatment technique. To ensure greater humidification capacity to the drag air, the energy available from the thermal inertia of the liquid column (raw water) in the prototype vaporization chamber was used to heat this air flow. After a single pass of raw water through the bench-scale prototype, a 98.0% reduction in conductivity and a 99.0% decrease in the content of total dissolved solids were obtained at a drag air temperature of 70 °C. Compared to RO, two of the main advantages of the proposed ultrasonic wave method are the elimination of the use of chemical agents in the pre-treatment phase and a significant reduction in maintenance costs by membrane replacement.

Failure Mode and Effect Analysis of Fire Tube Boilers Under Specific Operative Conditions

Failure Mode and Effect Analysis of Fire Tube Boilers Under Specific Operative Conditions

Failure mechanism of superheater tubes of waste heat boiler for waste incineration in complex environment

In order to further understand the failure mechanism of superheater tubes of waste heat boiler in a complex environment, sample sections cut down from the failed and non-failed tubes had been investigated by using visual observation, micro-zone analysis and Stress calculation check. Results showed that S content of 15MoG slightly exceeded the standard, and the main composition of corrosion products were related to the oxygen, sulfur, chlorine, sodium, potassium, calcium. Ash samples on the failed tube and at the bottom of the furnace were analyzed by EDS and XRD. The on-site operation and shutdown of the boiler were also considered. The failure mechanism was corrosion thinning raised by high temperature oxidation corrosion, sulfide corrosion, chloride corrosion, and dew point corrosion. The prerequisite of corrosion was that corrosive medium, over-temperature operation, severe fouling deposits were present simultaneously. Measures to limit these factors which can alleviate corrosion thinning are suggested and put forward.

Study on The Improvement of Heat Recovery Steam Generator Efficiency – A Review

Boilers are widely used in industries to produce steam. In some sectors, the steam generated is utilized directly in the production line for heating. Certain industries use steam to produce electricity. Fire tube boilers are limited to generating steam for processing; meanwhile, water tube boilers are widely used in electricity generation besides steam generation for processing lines. Subcritical boilers, supercritical boilers, and Heat Recovery Steam Generator (HRSG) are types of boilers commonly used to produce high capacity steam. This review article focuses on the optimization of HRSG operational efficiency. Industry players are keen on the improvement of operational efficiency since these directly influence the operating cost. Steam pressure, steam output, heat transfer efficiency and temperature distributions are key areas comprehensively reviewed in this article. Generally, improvement studies on boilers are not feasible to conduct during operation. Therefore, the scaled-down model used in the experiment or the boilers CFD models are simulated to understand the characteristics of the boilers. This review article is expected to overview HRSG boiler efficiency improvements and factors influencing boiler operational parameters.

ANALISIS EFISIENSI ENERGI PADA BOILER INDUSTRI TIPE FIRE-TUBE KAPASITAS 2TON/JAM DENGAN BAHAN BAKAR COMPRESSED NATURAL GAS (CNG) DI PT.X

ABSTRACT
 Boiler is a high pressure vessel or tank that functions to produce hot steam. Problems that often occur in the field on boiler machines are not efficient well when the work system or operating process in the field, especially when the process is under operating conditions on a fire tube boiler engine always experiences heat loss in the steam or steam system and the fuel system which affects the efficiency of the engine. fire tube boilers are not optimal for steam output. Therefore, with these conditions, it is necessary to calculate the efficiency of a good fire tube type boiler engine in order to meet the appropriate efficiency value standards in the operating process in the field. The method used in this study is the calculation of efficiency carried out by two methods, namely the direct method and the indirect method. Based on the results of efficiency calculations using the direct method, the efficiency value is 81.04%, while the results of calculations using the indirect method are 85.65%. The results of the calculation of efficiency values ​​that have been carried out from two methods, namely the direct and indirect methods meet the standard efficiency value of the boiler engine ≥ 80 %.
 
 Keywords: Fire Tube Boiler, Efficiency, Heat Loss, Direct and Indirect Method