Metallurgical Failure Analysis

Vertical cylindrical vessel-chambers as a part of coal — drying plants, whose purpose is to collect wastewater, are supported at 3 points in upper dish head area and are made of fine-grained Mn steel plates, joined by welding. Significant thinning and leaking in upper dish head area of the vessel occurred due to original design provoking an intensive abrasion, cracking and rupture. After reconstruction, in the upper zone of cylindrical shell, two new joints were made in sity by manual arc welding, with subsequent, local post-weld heat treatment. However, cracks appeared firstly in new welded zones in radial and axial joints, and then in zones of openings. Later, the similar failure features began to appear in the area of original welded joints. All of these cracks were repaired by properly specified technology. Unfortunately, after some period of exploitation the initiation of new cracks was observed, at first by the visual inspection. This problem was detected in the repaired areas...

The topic of the manufacturing process of chemical storage tank and its cause of failure is totally based on the working of individual process of every step and the study of the material use in the whole process. This topic is base on the working process of chemical storage tank and what failure takes place during the load acting on the tank, where as it gives manufacturing process step by step in the formation of tank. Now days several industries face the problem of leakage of chemical from the tank, these things also face by Bhavi Plast Pvt. ltd. Where there are no criteria for the consumption of raw material and no specific method to use the raw material in the formation of chemical storage tank. Aim of this investigation to minimize the leakage of the tank and proper method for the use of raw material. Make a job card for chemical storage tank and give every individual step to its own consumption of the raw material. Some leakage of the tank is also based on the mechanical property of the material, its stress-strain curve and calculation of the failure stress. Thus, the study of this thesis is required deeper knowledge of the subject along with the practical knowledge as well. Due to the failure of the tank annually plethora amount of money waste into the various industries. Useful knowledge and deeper understanding improve the productivity of the product and error-less  chemical storage tank manufacturer into the industry.

Reliability centered maintenance (RCM) has a key role in the quality system of thermal power plants. Electricity production is definitely not only production of a product, but also becomes a customer service. Reliability is the top quality tier of this service. Incorporation in the Integrated energy system means fast transformations of organization on all levels. The reliability of modern generation components basically influences the efficiency and capacity of a power plant as a whole. This paper presents the results of RCM practice on Unit Two of The Thermal Power Plant ″Nikola Tesla -B″, 2x600 MW, Yugoslavia. RCM implementation on current problems during exploitation emphasized problems with the boiler tubing system. The methodological approach included outages analyses, marking of the most significant ones, determination of main causes of damage (determination of the material exhaustion state based on expert analyses), application of adequate remaining life assessment methodology and finally the recommendations. Based on these analyses, certain technical solutions were performed and as a result, the mean time between failures of the plant increased, as well as its reliability. According to cost efficiency, RCM methodology presented the most effective cost-benefit method for reliability upgrade.

Este artículo describe el análisis de falla realizado en dos muestras de cables de acero que sufrieron falla súbita bajo condiciones de carga de trabajo normales. La falla fue causada por una carga menor a la capacidad nominal. Luego de inspección óptica se evidenció que la falla fue ocasionada por fatiga del material de uno de los cables.

MSC: 81.70.Bt

Many efforts have been made to understand the effects of hydrogen on steels, resulting in an abundance of theoretical models and papers. However, a fully developed and practically applicable predictive physical model still does not exist industrially for predicting and preventing hydrogen damage. In practice, it is observed that different types of damages to industrial boiler components have been associated with the presence and localization of hydrogen in metals. In this paper, a damaged boiler tube made of grade 20 – St.20 (or 20G, equivalent to AISI 1020) was investigated. The experimental research was conducted in two distinctive phases: failure analysis of the boiler evaporator tube sample and subsequent postmortem analysis of the viable hydrogen embrittlement mechanisms (HE) in St.20 steel. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature hydrogen attack (HTHA) during service, as a result of the development of hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, tube wall thickness measurement, tensile testing, hardness measurement, impact strength testing (on in-strumented Charpy machine), analysis of the chemical composition of corrosion products – deposit and the microstructural characterization by optical and scanning electron microscopy – SEM/EDX. The HTHA damage mechanism is a primary cause of boiler tube fracture. Based on the multi-scale special model, applied in subsequent postmortem investigations, the results indicate a simultaneous action of the hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of hydrogen in investigated steel. The model is based on the correlation of mechanical properties to the SEM fractography analysis of fracture surfaces.

Many efforts have been made to understand the effects of hydrogen on steels, resulting in an abundance of theoretical models and papers. However, a fully developed and practically applicable predictive physical model still does not exist industrially for predicting and preventing hydrogen damage. In practice, it is observed that different types of damages to industrial boiler components have been associated with the presence and localization of hydrogen in metals. In this paper, a damaged boiler tube made of grade 20 – St.20 (or 20G, equivalent to AISI 1020) was investigated. The experimental research was conducted in two distinctive phases: failure analysis of the boiler evaporator tube sample and subsequent postmortem analysis of the viable hydrogen embrittlement mechanisms (HE) in St.20 steel. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature hydrogen attack (HTHA) during service, as a result of the development of hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, tube wall thickness measurement, tensile testing, hardness measurement, impact strength testing (on in-strumented Charpy machine), analysis of the chemical composition of corrosion products – deposit and the microstructural characterization by optical and scanning electron microscopy – SEM/EDX. The HTHA damage mechanism is a primary cause of boiler tube fracture. Based on the multi-scale special model, applied in subsequent postmortem investigations, the results indicate a simultaneous action of the hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of hydrogen in investigated steel. The model is based on the correlation of mechanical properties to the SEM fractography analysis of fracture surfaces.

This paper looks at the fateful 1988 fuselage failure of Aloha Airlines Flight 243 to suggest and illustrate a new perspective on the sociology of technological accidents. Drawing on core insights from the sociology of scientific knowledge, it highlights, and then challenges, a fundamental principle underlying our understanding of technological risk: a realist epistemology that tacitly assumes that technological knowledge is objectively knowable and that ‘failures’ always connote ‘errors’ which are, in principle, foreseeable. From here, it suggests a new conceptual tool by proposing a novel category of man-made calamity: the ‘Epistemic Accident’, grounded in a constructivist understanding of knowledge. It concludes by exploring the implications of Epistemic Accidents and a constructivist approach to failure; sketching their relationship to broader issues concerning technology and society, and reexamining conventional ideas about technology, accountability and governance.

A study was conducted on BGA lead-free C5 solder joint system to compare SnAgNiCo versus conventional Sn3.8Ag0.7Cu solder alloy. This study showed that SnAgNiCo C5 solder system performed better than Sn3.8Ag0.7Cu in terms of joint strength and brittle mode failure. Shear and pull strength was measured by Dage which is representative of the intermetallic (IMC) strength between the C5 solder sphere and Cu/Ni/Au pad finishing. Tray drop test and packing drop test were done to gauge solder joint performance against handling and impact force. A comprehensive study was done to study the effect of microstructure and interface intermetallics of both solder system after assembly, after test, after high temperature storage (HTS) at 150°C for 168 hours and 504 hours and after 6x reflow towards the joint integrity. Microstructure studies on SnAgNiCo solder reveals that formation of rod shape Ag 3Sn IMC distributed across the solder surface helps to act as dispersion hardening that increases the mechanical strength for the SnAgNiCo solder after thermal aging. EDX analysis confirmed that in SnAgCu solder/Ni interface, Cu-rich IMC formed on top of the Ni-rich IMC. For SnAgNiCo system, only Ni-rich IMC is found. Therefore, it is highly suspected that the presence of Cu-rich IMC posed a detrimental effect on the joint strength and tends to cause brittle joint failure. Both of the effect is then showed in ball pull result that after 6x reflow, SnAgCu solder has 100% brittle mode failure, where SnAgNiCo solder has only 5%. This result correlates with missing ball responses after packing drop tests. Thus, SnAgNiCo lead-free solder is a potential candidate for lead-free solder joint improvement for overall lead-free package robustness.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5507840&tag=1

Hydrogen induced damages in metallic components of fossil fuel power plants are usually followed by unpredicted events and very intensive. In the course of clarifying a very large complex of problems associated with hydrogen damage, it is necessary to apply a multidisciplinary approach. Much of this work is based on the theory and, particularly, on experimental tests performed on boiler water wall tube samples, taken from a domestic 210 MW power plant, that had experience hydrogen damages during service. Possible mechanisms for metal–hydrogen interaction are considered from material point of view; fluid hydrodynamics in furnace wall tubes; and from the complexity of structural – exploitation plant characteristics. The aim of this paper is to present a contribution to the methodology of hydrogen damaging of boiler water wall tube based on formulation of the model of damage – influenced by the "micro-departure from nucleate boiling" (micro-DNB) of working fluid.

Hydrogen embrittlement could be one of the several causes of rupture on carbon steel boiler tube. Cracking occurs primarily because of the precipitation of molecular hydrogen along the grain boundary. The result of this process is formation of methane due to reaction of dissolved hydrogen with carbon in the steel. The hydrogen cracks morphology is specific, i.e.significantly different from the cracks affected by the long time or short time overheating. During hydrogen embrittlement decreasing of steel plasticity is taking place. Also the intensive hydrogen decarburization of the waterside surface of the tube is the process which is simultaneously occurs. Deposits, which could be formed on the waterside of the tube, especially in localized area, may have a great influence on a probability of hydrogen precipitation on grain boundaries and cracks appearing. Disturbance of boiling regime as well as departure from nucleate boiling that is taking place in particular area of waterwall tubing has a great influence o heat transfer process as well as on intensity and localization of hydrogen attack process. Some experimental investigation results of failure of boiler water wall tubes made of 0,2 C 0,5 Mn 0,25 Cr steel are presented.

Problem of boiler component erosion is a very complex and present in practically all fossil fuel power plants burning low heating value coals irrespective of their particular design and operating characteristics. Major fly coal erosion accelerating factors are large amounts of abrasive components in the air-coal mixture and its high velocity. In general terms, there is a trend of implementation of appropriate erosion protection in critical place of pulverized boiler coal preparation equipment. In this paper are presented results of erosion tests provided on samples with different erosion protection materials. Erosion damage profiles of different protection materials were investigated and analyzed on tested samples.

Corrosive wear failure in gas pipelines can potentially cause substantial human and economic losses. This work presents the failure analysis of an API 5L X52 steel grade section of a pipeline used in an underground transportation, which is located next to a natural gas extraction plant. A T-shape section of this line, failed by perforation under unknown circumstances. Chemical and mechanical characterization of the steel pipe section was performed. Optical microscopy, electron microscopy and energy disperse spectroscopy were performed near the failure origin site in order to identify the composition of the corrosion products. Based on the microscopic and visual analyses, a corrosive wear sequence was identified as follows: the scales adhered to the inner wall of the pipe were easily loosened and detached in certain sites due to the turbulent gas stream. This resulted in the exposure of the fresh steel surface to the highly corrosive environment that prevails inside the pipeline. The unprotected areas acted as preferential sites for pitting corrosion of the steel until the final failure of the pipe was produced.

Thick walled components such as high pressure (HP) steam turbine casings operating under high parameter conditions are subjected to a complex stress state. As a result of that stress state, some parts of HP turbine casing undergo to the creep fatigue caused by the combination of thermal fatigue resulted from repeated start/stop operation and the creep which occurs during long-term operation at high temperature and high-pressure. It is well known that domestic thermal power plants have been in use over 100000 h which means that significant cost is required not only for maintenance, but often for renewal of equipment. Based on comprehensive investigation, the results of residual life assessment of one high pressure steam turbine casing, which belongs to the older turbine generation, taking into account simultaneous action of thermal fatigue and creep, are presented in this paper. Also, the critical flaw crack size of HP turbine casing is determined because this parameter has a strong influence on casing integrity and residual life. The results of residual life assessment provide not only a basis for further maintenance, but also estimated time for reparation or renewal.

Reliability centered maintenance (RCM) has a key role in the quality system of thermal power plants. Electricity production is definitely not only production of a product, but also becomes a customer service. Reliability is the top quality tier of this service. Incorporation in the Integrated energy system means fast transformations of organization on all levels. The reliability of modern generation components basically influences the efficiency and capacity of a power plant as a whole. This paper presents the results of RCM practice on Unit Two of The Thermal Power Plant ″Nikola Tesla -B″, 2x600 MW, Yugoslavia. RCM implementation on current problems during exploitation emphasized problems with the boiler tubing system. The methodological approach included outages analyses, marking of the most significant ones, determination of main causes of damage (determination of the material exhaustion state based on expert analyses), application of adequate remaining life assessment methodolog...

This paper deals with determination of the failures causes of supporting tubes in a 350 MW fossil fuel power plant. Due to frequent fractures of supporting pipes occurring always at the same location and the ensuing reduction of the plant availability as well as substation financial losses, there was an urgent need to resolve the problem [K. Takahashi, M. Yokouchi, S.K. Lee, K. Ando, J. Am. Ceram. Soc., 86-12, 2003]-[3]. This work describes the test results and the conclusions drawn from the results.

Convective boiling beyond critical-heat-flux is encountered in a number of applications, one of which is water wall tubing of steam generators. Sometimes, the heat transfer process in particular zones of heated surfaces of boiling tubes system is combined with fluctuation of wall temperature. This phenomena is connected with heat transfer crises during departure from nucleate boiling (DNB) as well as dry out and causes the interruption of water layer along a tube wall provoked the formation of drying areas. This process has a great influence on intensity and localization of hydrogen attack and deposits formation on the waterside of the tube. Standard investigation procedure were applied on specimens taken from furnace walls tubing, made of 0.2C0.5Mn0.25Cr, steel in the purpose of failure analysis..

Transfer line tubes of an ethane pyrolysis furnace, operating at 850 ±20°C and 1.0 atm pressure, developed longitudinal cracks after less than one third of their expected service life. The tubes were constructed of Fe-based USN N08810 alloy with a wall thickness of 10 mm. Metallurgical evaluation revealed that the mode of failure was high-temperature carburization attack leading to intergranular cracking. The cause of failure was overheating, likely to have occurred during decoking operations. Better control of furnace temperature was recommended to avoid overheating. Alternatively, a wrought alloy capable of developing highly protective aluminum oxide (Al 2 O 3)-base scale such as Ni-based UNS N07214 could be used as a replacement.

The service lift of thick-walled power plant components exposed to creep, as is the case with pipelines of fresh- and reheated steam, depend on the exhaustion rate of the material Plant operation at elevated temperatures and at temperatures below designed temperatures all relates to the material exhaustion rate, thus complicating remaining life assessment, whereas the operating temperature variation is a most common cause in the mismatching of real service and design life. Apart from temperature, the tube wall stress is a significant variable for remaining life assessment, whose calculation depends on the selected procedure, due to the complex pipeline configuration. In this paper, a remaining life assessment is performed according to the Larson-Miller parametric relation for a phi 324 x 36 pipe bend element of afresh steam-pipeline, made of steel class ICr0.3Mo0.25V, after 160.000 hours of operation. The temperature history of the pipeline, altogether with the pipe bend, is determined based on continuous temperature monitoring records. Compared results of remaining life assessment are displayed for monitored temperature records and for designed operating temperature in the same time period. The stress calculation in the pipe bend wall is performed by three methods that are usually applied so to emphasize the differences in the obtained results of remaining life assessment.

Filler material choice for repair welding of stop valve spindle of thermal power plant by-pass pipeline was presented in this paper. Repair welding of the stop valve spindle was necessary because of plant operating problems due to very frequent localized damage appearance in the form of erosive wear on it. For this purpose it was necessary to choice appropriate filler material with high wear resistance characteristic. Experimental investigation and testing (hardness measurement, chemical composition analysis and microstructural investigation) of prepared specimens after welding simulation with different kind of filler material was performed. On the basis of obtained results it was recommended procedure for application of the filler material with generally preferable characteristic.

A failure analysis of superheater tube supports of the primary reformer in a local fertilizer factor is presented. A number of tube supports failed at approximately half of their designed service life. Following the failure, the factory was visited, and relevant information and samples were collected. The samples were investigated in the laboratory by chemical analysis, macro- and microhardness measurements, macro-and micrometallographic examinations, and X-ray diffractometry. The analysis showed the supports were fabricated from HH-type heat-resisting alloy and that the failure mode was high-temperature creep. The microstructure of the alloy showed the presence of massive intergranular as well as intragranular σ-phase and intragranular needle-shaped M 23C 6 carbides. It was also concluded from the formation of massive σ-phase in the tube that the failure was hastened because the supports were operating at approximately 800 °C. The alloy composition led to the formation of σ-phase under the operating conditions of the reformer, and the use of an alloy with a higher concentration of austenite-stabilizing element(s) could have avoided the failure.

http://link.springer.com/article/10.1361/15477020523473