炉管破裂原因分析

采用宏观检验、化学成分分析和金相检验等方法对锅炉管破裂原因进行了分析。结果表明：由于锅炉长期在高温下使用,形成的沿晶碳化物组织削弱了晶界原子间结合力,加速了炉管的内外壁的氧化腐蚀,从而引起其快速破裂。     

One-way Fluid Structure Interaction modelling methodology for boiler tube fatigue failure

A modelling methodology developed for dealing with fatigue failures on large boiler tube assemblies, as used by power generation industries, is described. Boiler tube fatigue failures are resultant to a coupled combination of fluid flow and heat transfer mechanisms, inducing thermal expansion leading to fatigue failure. A combination of modelling tools is effectively combined for one-way Fluid Structure Interaction, solving for and extracting stress results efficiently. A one dimensional fluid solver is used to approximate and model the thermal flow components. The study case considered implemented the developed methodology on a quarter boiler hopper section made up of 3022 tube and membrane structure with a collective length of 4787 m. Operating conditions are iteratively adjusted in the one dimensional pipe flow model until a correlation is formed with instrumented data. This validated model enables further use for various postulated plant conditions and operational sequences through transient start-up conditions. The boiler tube temperatures obtained from the one dimensional model are transferred and used as boundary conditions in a full three dimensional finite element analysis where deformations are solved for and stress results obtained due to thermal expansion within the boiler tube walls and the adjacent support structure. The model is used for redesign of sections of the boiler to reduce stress in those areas and subsequently reduce fatigue failures.     

Fatigue Failure of 321 Stainless Steel Superheater Tubes from a Thermal Incinerator

Several boiler superheater tubes showed circumferential cracking at weld seams after 2 years in noncontinuous service (several shutdowns). On-site inspection revealed that several tubes were cracked and leaked; while many others were cracked, however, the severity was less pronounced. Two types of superheater tubes samples were collected: one with butt-welded tubes and the other with fillet-welded sleeve. The latter was found to be out of the boiler fireplace, and the sleeve was used as tubing support to the boiler shell. Detailed investigation showed that the butt-welded tubes contained circumferential fatigue cracks that initiated from the internal surface. The cracks initiated in the heat-affected zone and propagated as a result of tube vibration. The variations in the tube internal diameter and tube wall thickness are expected to play a role in tube fatigue failure. On the other hand, tubes with fillet-weld sleeve showed circumferential cracking as a result of fatigue crack initiation from weld defects on the tube external surface. The high vibration during several unscheduled shutdowns in addition to several other factors such as variations in tube inside diameter, wall thickness, and weld defects resulted in the initiation and propagation of fatigue cracks and premature failure. White deposits, similar to those observed when boiler tubes failed by caustic exposure, were seen in the vicinity of the tube cracks. Therefore, it was difficult to confirm whether the boiler tubes failed because of the fatigue cracks or because of the caustic salts (pH control chemical).     

Corrosion of a copper U-shaped heating element: Some morphological and microstructural observations

In this work, observations of the corrosion on a failed copper U-shaped tube, of 1 mm nominal thickness, are presented. This tube was subjected to severe corrosion and subsequent cracking after a month of operation as the heating element of an electrical boiler. Morphological and microstructural observations of the failure area as well as cross sections of the corroded copper tube are presented. Moreover, the chemical composition of the material and the principal physicochemical characteristics of the tap water used for boiler operation were determined in the context of the failure investigation. The quality of the water used for boiler operation was a significant factor influencing the heating element efficiency and reliability. Hard water with high electrical conductivity accelerated salt precipitation and led to the corrosion and premature failure of the components.     

“He who ignores the mistakes of history is doomed to repeat them”: a case study of boiler tube failures in NSW 1987–2005

Abstract

Boiler tube failures are largely responsible for the largest annual availability losses in thermal power stations. By the late 1980s NSW boiler tube failures were causing availability losses of more than 5%. The disaggregation of the NSW power industry in 1996 resulted in the abandonment of the program implemented to reduce the number of failures. A smaller utilities panel was formed retaining many elements of the program including the keeping of records on the NSW boiler tube failures. In 2005, the boiler technical panel system was re-introduced. This paper presents results from the 2003–05 review of boiler tube failures in NSW.     

锅炉给水预热器管板的优化设计与分析

目的对锅炉给水预热器的管板进行结构优化设计及有限元分析。方法首先通过给定设计参数计算出管板的厚度及受力分析,进而明确管板的结构设计确定主要参数,利用SolidWorks软件建立管板的三维分析模型,并用Ansys软件进行管板应力应变分析及温度场的分析,按标准方法计算4种工况下管板应力、壳程筒体的轴向应力以及换热管的轴向应力,同时采用JB/T 4732的方法对管板与筒体的应力进行评定,采用GB/T 151的方法对换热管的轴向应力、拉脱应力进行评定。结果该预热器能够在给定工况下安全运行。结论采用的设计方法为锅炉给水预热器管板的结构性能优化提供了理论依据和判定标准。     

Investigations on the Failure of Economizer Tubes in a High-Pressure Boiler

This article describes the results of an investigation concerning the failure of economizer tubes of a high-pressure boiler in a dual-purpose power/water cogeneration plant. The failure was observed in the form of rupturing of one tube and a macrohole or pinhole in another tube. The boiler had an operating period of 116,123 h since its inception. For approximately the first 100,000 h, the fuel for the boiler was crude oil, which was replaced by Bunker C oil. The boiler tube is fabricated from carbon steel SA 210A1. The location of the failure was determined by on-site visual inspection of the boiler. Detailed macro- and microexaminations of inner and outer scales on the tube were begun to determine the cause of the rupture. The composition of the fire- and waterside scale and ash deposited on the outer surface of the tubes was analyzed by energy-dispersive x-ray (EDX) technique. The reduction percentage of wall thickness of the tube facing inside and outside the furnace was calculated. The cause of the failure of the economizer tube appears to be H₂SO₄ dew-point corrosion. The relatively low temperature of feedwater lowered the tube metal temperature and promoted the condensation of H₂SO₄. The external deposits on the tubes, as a result of bunker oil firing, further helped to lower the tube metal temperature, thus promoting H₂SO₄ condensation over the deposit and subsequent corrosion of the tube wall. Recommendations are given to prevent/minimize such failures.     

Effect of creep lifetime on geometric optimization of boiler tubes for thermal power plants

In this study, thermomechanical and creep analyses of boiler tubes are performed and a procedure for cost-based optimization of boiler tube geometries is presented. First, analytical thermal convection and conduction heat transfer under ultra-supercritical (USC) and advanced ultra-supercritical (A-USC) conditions as well as numerical evolution of creep stresses in the boiler tube are obtained. Subsequently, the results are used to calculate the thermal efficiency and creep lifetime of austenitic stainless steel Super 304H and Ni-based alloy Nimonic alloy 80A. The geometric parameters of the boiler tube are then optimized to minimize the total cost related to the boiler tubes including capital investment and operational costs. Comparing with the conventional approach which assumes a fixed creep lifetime for simplicity, the present results also showed that creep lifetime assessment is important and should be included in the optimization. This optimization procedure can also be applied to other boiler tube materials under various operating conditions of thermal power plants.     

Metal dusting (catastrophic carburization) of a waste heat boiler tube

A waste-heat boiler at a chemical plant suffered an unusual tube failure. The boiler is part of the partial oxidation (POx) syngas production for a 2-ethyl hexanol unit. The syngas primarily consists of H₂, CO and CO₂ with trace amounts of CH₄. Steam is also reportedly injected into the process. The syngas enters the boiler at approximately 1800°F (980°C) on the internal side of the tube and is cooled, while generating approximately 640 psi (4.41 MPa) steam at 490°F (255°C) on the outside of the tube. The internal surface of the tube contained a region of metal loss that was approximately 1 inches long by inch wide (44.5 mm by 19 mm). The metal loss was very localized with little evidence of attack elsewhere on the tube's surface. Molten salt attack, sulfidation and metal dusting were considered as possible mechanisms for the metal loss. It was determined that metal dusting, also called catastrophic carburization, was the cause of the metal loss. The cause of the metal dusting was localized overheating of the tube, which developed because of water/steam flow disruption due to contact of the tube baffle with the tube. Approximately one year after this tube failure, the boiler suffered two more tube failures, which were also attributed to metal dusting.     

Caustic Corrosion Failure of Back Wall Riser Tube in a High-Pressure Boiler

This article describes the results of an investigation concerning the failure of the back wall riser tube of a high pressure boiler in a SWCC dual purpose power/water cogeneration plant. The failure occurred in one tube (facing furnace) which contained eight ruptured openings covering a length of approximately 1.8 m. The tube material was carbon steel (SA 210A1). The cause of the failure was determined by on-site visual inspection of the boiler and detailed macro and micro examinations of inner and outer scales on the tube. The in situ non-destructive testing of selected boiler riser tubes was carried out using boroscope and ultrasonic test (UT). The composition of the tube material and fire and water-side scale deposits were analyzed by energy dispersive x-ray (EDX) and inductively coupled plasma (ICP) techniques. The cause of the failure of the riser boiler tube appears to be caustic attack. The inside brown scale that developed during service resulted in overheating, wall thinning due to caustic corrosion, and the associated ruptures of the tube in areas of high stress. The escaping steam eroded the outer surface of the tube resulting in heavy loss of metal around the rupture points (punch). Recommendations are given to prevent/minimize such failures.     

Erosion-corrosion behaviour of Ni-based superalloy Superni-75 in the real service environment of the boiler

The super-heater and re-heater tubes of the boilers used in thermal power plants are subjected to unacceptable levels of surface degradation by the combined effect of erosion-corrosion mechanism, resulting in the tube wall thinning and premature failure. The nickel-based superalloys can be used as boiler tube materials to increase the service life of the boilers, especially for the new generation ultra-supercritical boilers. The aim of the present investigation is to evaluate the erosion-corrosion behaviour of Ni-based superalloy Superni-75 in the real service environment of the coal-fired boiler of a thermal power plant. The cyclic experimental study was performed for 1000 h in the platen superheater zone of the coal-fired boiler where the temperature was around 900°C. The corrosion products have been characterized with respect to surface morphology, phase composition and element concentration using the combined techniques of X-ray diffractometry (XRD), scanning electron microscopy/energy-dispersive analysis (SEM/EDAX) and electron probe micro analyser (EPMA). The Superni-75 performed well in the coal-fired boiler environment, which has been attributed mainly to the formation of a thick band of chromium in scale due to selective oxidation of the chromium.     

电站锅炉水冷壁管失效分析

某钢铁公司电站锅炉仅服役15000h就发生水冷壁管破裂事故。采用化学成分分析、金相检验及水垢结构X射线衍射分析等方法对失效水冷壁管进行分析,并结合锅炉运行状况进行调查。结果表明：水冷壁管破裂是管壁内侧水垢阻碍热传导所致。水垢则是锅炉运行过程中注入未经软化水造成的。     

Experimental studies on fly-ash erosion behavior of Ni-Cr based nanostructured thermal spray coating in boiler tubes

Erosion study was performed on the uncoated and coated SA210Gr-C boiler tube substrates. This study was performed in a view to reducing the scaling on boiler water-wall and super-heater tubes. In the present work, the High Velocity Oxygen Fuel (HVOF) coating process was used to deposit nanostructured and conventional coatings on the boiler tube substrates. Fly-ash produced after the combustion of coal in an Indian thermal power station was used as erodent. The erosion loss of coated and uncoated substrates was recorded at a regular interval of 30?minutes. The study was conducted at 30°, 60°, and 90° impingement angles and at two different operating temperatures (300°C, 550°C). Surface morphology of eroded samples was analyzed using macro and micro imaging techniques, and surface roughness was also recorded for the eroded samples. The phases present in the eroded substrates were indexed using the X-Ray diffraction (XRD) analysis. HRTEM images of nanostructured coated samples at 550°C with varying impingement angles were analyzed. The result reveals that the nanostructure in the coating was retained even after high-temperature erosion test. Comparative study was made with nanostructured and conventional coatings against the uncoated materials.     

20t／h锅炉水冷壁管爆裂原因探讨

通过对锅炉结构及运行状态系统调查和综合检验分析,认为水冷壁管焊裂的根本原因是蒸汽量达不到额定值所致。另外,水冷壁管存在的组织缺陷,轧制不均匀以及弯曲处壁厚减薄也是造成水冷壁管爆裂不可忽略的因素。     

Boiler Stack Economizer Tube Failure

A metallurgical evaluation was performed to investigate the failure of a type 304 stainless steel tube from a boiler stack economizer. The tube had three distinct degradation mechanisms: pitting corrosion, chloride stress corrosion cracking, and fatigue fracture. The primary failure mechanism for the tube was fatigue fracture, but the other mechanisms may have eventually caused a tube failure in the absence of fatigue. This paper details the visual, SEM/EDS, and metallographic examinations used to determine that these failure mechanisms were each present in the same tube.     

管座角焊缝接头D-N疲劳曲线试验研究

锅炉大直径厚壁管与小径管的管座角焊缝焊接接头常常因受疲劳作用而发生失效,这种疲劳导致的失效多数是由于小载荷、长力臂产生的弯曲应力反复作用造成的。基于锅炉承压部件管接头的特征及其服役背景,设计了模拟焊接接头试样,采用悬臂弯曲加载方式,通过成组试验方法,研究了锅炉管座角焊缝焊接接头的位移-寿命曲线（即D-N曲线）。结果表明：锅炉管座角焊缝焊接接头的D-N曲线可以用来对其进行疲劳有限寿命设计,D-N数据分布可以用幂函数规律进行表达。     

Thermal fatigue and corrosion fatigue in heat recovery area wall side tubes

In this paper, findings of visual inspections, chemical analysis on deposits, metallurgical examinations and creep analysis on the failed SA210-A1 heat recovery area (HRA) wall side tubes of a boiler unit are presented. The investigations were carried out following two boiler tube failures at heat recovery areas involving the left hand side (LHS) and right hand side (RHS) side wall tubes. Findings from the microscopic examinations are used to support the investigation in determining the failure mechanisms. The first failure at LHS HRA side wall tube is identified due to thermal fatigue while the second failure is as a result of combination of the corrosion fatigue, thermal fatigue and creep damage. Recommendations are made to reduce unavailability of the boiler unit due to the HRA side wall tube failures.     

Feed Water Chemistry-Related Corrosion Failures in Subcritical 250 MW Coal-Fired Boiler

This paper emphasis on the study of typical premature failure of water wall tubes of two thermal power plant boiler of same capacity (250 MW) and same operational parameter but with different boiler water chemistry. The investigation concludes on the water-side corrosion in both of the cases. One boiler is running with coordinated phosphate treatment (CPT) and another with all volatile treatment (AVT). The causes of corrosion were discovered and proposed measures for their elimination were given. Visual examination, chemical analysis of deposits, oxide scale thickness measurement, and microstructural examination were carried to ascertain the probable cause/causes of failure. From the investigation, it was finally concluded that the combination of localized high tube metal temperature and wall thinning due to under deposit corrosion led to the premature tube failure in boiler running with CPT and localized pitting corrosion in boiler running with AVT. Based on the results and discussions, a possible way to combat the corrosion was proposed.     

热喷涂技术在锅炉管道防护中的应用进展

综述了锅炉管道防护的研究现状,详细阐述了用于锅炉管道防护的金属涂层、金属陶瓷复合涂层、Fe-Al基复合涂层、Al基涂层等及涂层制备方法的研究进展.     

某锅炉水冷壁腐蚀原因分析及其改进措施

针对某电厂锅炉水冷壁管的严重腐蚀问题,通过宏观形貌检查、化学成分分析、微观组织分析及能谱分析等方法进行了系统分析。结果表明:该锅炉燃用高硫煤时,炉膛火焰中心偏斜导致水冷壁局部出现还原性气氛,产生硫化物型高温腐蚀。最后针对具体原因,提出了控制燃煤质量、调整燃烧、增加贴壁风等改进措施,有效地解决了该锅炉水冷壁高温腐蚀问题。