Metallurgical analysis of a corrosion failure

A Nicrofer 6025 HT alloy 602 tube in a furnace, used for the recovery of steel pickling liquors, failed during operation at 1100°C. Metallographic investigations—microstructural and energy dispersive X-ray spectrometry (EDS)—of the failed tube showed evidence of corrosion and the presence of chlorine and sulfur in the corrosion products. The failure of the furnace tube was due to the presence of sulfur dioxide in combination with chlorine.     

Basis of engineering specifications for a gas-turbine engine rotor

The main elements of a methodology are described that make it possible by mathematical modelling of the condition of a flexible rotor in the design stage to evaluate the effect of the main manufacturing and assembly parameters, and to prescribe their main limits in order to provide prescribed vibrational activity.     

Fracture analysis of compressor blade of a helicopter engine

This paper presents the failure analysis of the blade of a helicopter engine. From the visual examination of the fractured surface, it was possible to observe beach marks, typical of fatigue failure. The crack was initiated from the corrosion pit located on the attack edge of the blade. A non-linear finite element method was utilized to determine the stress state of the blade under rotation (operational conditions). In this analysis an undamaged blade was considered. Computations for the blade, working in the vibration conditions additionally were performed for analysis of phenomena occurring during the blade resonance. In this analysis first three mode of vibration were considered. Attention of this study is devoted to the mechanisms of damage of the compressor blade which works in the condition favorable for the pitting corrosion.     

Metallurgical investigation into the failure of a chopper blade used for cutting of hot-rolled steel coils

In the present work, failure investigation of a chopper blade received from an integrated steel plant has been presented. Chopper blades are used in chopping machines for cutting trimmed edges of hot-rolled coils into pieces to convert them into scrap. These blades are manufactured from hot forged or rolled billets or flats of high carbon high chromium cold work tool steel. The investigation consists of visual examination, chemical analysis, microstructural analysis through optical and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and hardness measurement. The chemical analysis confirmed the steel as equivalent to D2 grade in AISI notation. Carbide volume fraction of the broken blade was in the normal range of 10–15% as commonly observed in D2 tool steel. Microstructural examination under light and scanning electron microscopy showed non-uniform distribution of large eutectic primary carbides of irregular morphology forming strings or bands in tempered martensite matrix preferentially aligned in a specific direction. The uneven carbide arrangement in the matrix made the structure highly anisotropic and susceptible to localized stress concentration. The carbides were identified mainly as M₂₃C₆ type. Cracks were observed to initiate at the edges of the blade and propagate to the interior through clustered zones of carbides. SEM study suggests that the crack initiation was associated with decohesion of carbide particles in the cluster which culminated into final fracture by the mechanism of void coalescence and subsequent crack growth.     

Failure analysis of a second stage blade in a gas turbine engine

The failure of a second stage blade in a gas turbine was investigated by metallurgical and mechanical examinations of the failed blade. The blade was made of a nickel-base alloy Inconel 738LC. The turbine engine has been in service for about 73,500 h before the blade failure at 5:50 PM on 14 August 2004. Due to the blade failure, the turbine engine was damaged severely. The investigation was started with a thorough visual inspection of the turbine and the blades surfaces, followed by the fractography of the fracture surfaces, microstructural investigations, chemical analysis and hardness measurement.

The observation showed that a serious pitting was occurred on the blade surfaces and there were evidences of fatigue marks in the fracture surface. The microstructural changes were not critical. It was found that the crack initiated by the hot corrosion from the leading edge and propagated by fatigue and finally, as a result of the reduction in cross-section area, fracture was completed.

An analytical calculation parallel to the finite element method was utilized to determine the static stresses due to huge centrifugal force. The dynamic characteristics of the turbine blade were evaluated by the finite element modal and harmonic analyses. Finally according to the log sheet records and by using a Campbell diagram there was a good agreement between the failure signs and FEM results which showed the broken blade has been resonated by the third vibrational mode occasionally before the failure occurred.     

Metallurgical failure analysis of a BWR recirculation pump shaft

This paper presents the metallurgical analysis of a Recirculation Pump from a Nuclear Power Plant. The damaged component was the austenitic stainless steel shaft. As a result of a preliminary visual examination, some axial cracks were found in the threaded area of the shaft in the thermal barrier area. The analyses performed include liquid penetrant testing, metallography and deposits analysis. Based on the obtained results, it was concluded that the origin of the axial cracks was thermal fatigue caused by mixing of cold seal injection water and hot reactor coolant in the thermal barrier area.     

Investigation of a failed circular sawmill blade structures

The engineering materials fracture is an undesirable event due to human lives that could be in jeopardy, economic loss, and the negative interference with the availability of products and services. Sawmill blade performance depends on many factors ranging from the structure of the materials of the blade, applied load, operating conditions and the target body to cut. A sawmill blade cutting tooth must be of high carbide material for longer life span in service. A portion of a failed sawmill blade for cutting wood was examined for chemical composition. The X-ray characterization was carried out using diffractometer (XRD) and scanning electron microscopy (SEM) for the proper understanding of the blade phase composition and structure. The results obtained were compared with the standard steel blade properties to predict reasons for the failure apart from the torsion effects on the materials. The carbon content of the blade is 0.66% medium carbon steel class. The carbon content of the failed blade was less compared to that of the standard (0.8% C and above). Carburization treatment was recommended for improvement of the sawmill blade performance based on the material composition. The failure of small-sized component needs prevention to avoid catastrophic destruction and consequently injury or death that may cause expensive lawsuits.     

Stress concentration in sloping cooling circuits of a disk of a gas-turbine engine

The stressed state and stress concentration in sloping cooling circuits of the rim part of a disk of a gas-turbine engine are studied by using a three-dimensional finite-element model. It is shown that the numerical values of the stress concentration factors do not exceed their designed values. Translated from Problemy Prochnosti, No. 3, pp. 78–82, May–June, 1998.     

Selecting a thermodynamic cycle for the closed gas-turbine power plant of spacecraft in order to minimize surface of the cooler-radiator

The influence of the thermodynamic cycle scheme selected for a closed gas-turbine power plant of spacecraft on the specific surface of its cooler-radiator are evaluated. The dependence of the cooler-radiator characteristics on the regeneration, intermediate cooling, and heating of the working medium are analyzed.