H. Roy

High Temperature Corrosion Failure of a Secondary Superheater Tube in a Thermal Power Plant Boiler

Failures of boiler tubes are a foremost cause of the unscheduled outages of the thermal power plant boiler. The failure of the boiler tubes occurs due to various reasons like creep, fatigue , corrosion and erosion. This paper highlights a case study of typical premature failure of a platen superheater tube of thermal power plant boiler. Visual examination, dimensional measurement, chemical analysis, oxide scale thickness measurement, microstructural examination, Energy Dispersive spectroscopy (EDS) were carried to ascertain the probable cause/causes of failure of inner leg of platen super heater tube. From the investigation, it was finally concluded that the presence of potassium (K) and sulphur (S) in the deposited ash may be responsible for formation of low melting compound alkaliiron trisulfate. The combination of localized high tube metal temperature and wall thinning due to high temperature fireside corrosion led to the premature tube failure.

Study of Microstructure Evolution during Semi-Solid Processing of an In-Situ Al Alloy Composite

In the present work, effect of pouring temperature (650°C, 655°C, and 660°C) on semi-solid microstructure evolution of in-situ magnesium silicide (Mg2Si) reinforced aluminum (Al) alloy composite has been studied. The shear force exerted by the cooling slope during gravity driven flow of the melt facilitates the formation of near spherical primary Mg2Si and primary Al grains. Shear driven melt flow along the cooling slope and grain fragmentation have been identified as the responsible mechanisms for refinement of primary Mg2Si and Al grains with improved sphericity. Results show that, while flowing down the cooling slope, morphology of primary Mg2Si and primary Al transformed gradually from coarse dendritic to mixture of near spherical particles, rosettes, and degenerated dendrites. In terms of minimum grain size and maximum sphericity, 650°C has been identified as the ideal pouring temperature for the cooling slope semi-solid processing of present Al alloy composite. Formation of spheroidal grains with homogeneous distribution of reinforcing phase (Mg2Si) improves the isotropic property of the said composite, which is desirable in most of the engineering applications.

Failure Investigation of Condensate Pump Shaft

The premature failure of condensate pump shaft was investigated in this paper. The shaft was attached with feed water condensate pump system in thermal power plant boiler. The shaft was fabricated from martensitic stainless steel. A detailed study was carried out to determine the root cause of the shaft failures. Visual examination, macroanalysis, chemical analysis, microstructural characterization, and fractography examinations were also carried out to ascertain the probable cause of shaft failure. Finally, it was concluded that the failure of the shaft was due to the torsional fatigue initiated by the cracks at the thread roots.

Failure Investigation of High Temperature Stud

The premature failure in a high-temperature stud is investigated in this article. The visual examination, dimensional measurement, and wet fluorescent magnetic particle, and chemical compositions are carried out as part of preliminary investigation. Apart from these tests, microstructural examination, tensile, impact and fractographic analyses are also conducted as part of the investigation. Finally, it has been concluded that the failure of the stud is caused because of the presence of severe localized, elongated, and oriented inclusions along the thread profile, particularly near the thread-root region. The inclusions may act as stress inducers under service load and facilitate initiation of cracks. The cracks are further propagated, finally leading to premature failure of the stud.

Failure Investigation of Radiant Platen Superheater Tube of Thermal Power Plant Boiler

Abstract This paper highlights a case study of typical premature failure of a radiant platen superheater tube of 210 MW thermal power plant boiler. Visual examination, dimensional measurement and chemical analysis, are conducted as part of the investigations. Apart from these, metallographic analysis and fractography are also conducted to ascertain the probable cause of failure. Finally it has been concluded that the premature failure of the super heater tube can be attributed to localized creep at high temperature. The corrective actions has also been suggested to avoid this type of failure in near future.

Investigation into Cause of High Temperature Failure of Boiler Superheater Tube

Abstract The failure of the boiler tubes occur due to various reasons like creep, fatigue, corrosion and erosion. This paper highlights a case study of typical premature failure of a final superheater tube of 210 MW thermal power plant boiler. Visual examination, dimensional measurement, chemical analysis, oxide scale thickness measurement, microstructural examination are conducted as part of the investigations. Apart from these investigations, sulfur print, Energy Dispersive spectroscopy (EDS) and X ray diffraction analysis (XRD) are also conducted to ascertain the probable cause of failure of final super heater tube. Finally it has been concluded that the premature failure of the super heater tube can be attributed to the combination of localized high tube metal temperature and loss of metal from the outer surface due to high temperature corrosion. The corrective actions have also been suggested to avoid this type of failure in near future.

Rheological behavior of semi-solid TiB2 reinforced Al composite

Abstract The rheological behavior of the semi-solid TiB 2 reinforced Al–Mg alloy composite slurry was investigated, which is required for the mould filling simulations during the semi-solid processing. TiB 2 reinforced in-situ Al–Mg alloy composite samples were remelted and subsequently brought to the semi-solid temperature regime within the heating chamber of a Searle type rheometer. In order to understand the rheological behavior of composites, three different types of experiment were carried out, namely, steady state test, continuous cooling test and isothermal test. Apart from that, the thixotropic nature of the slurry was confirmed from the obtained hysteresis loops during the experimentation. The results indicate that when isothermally held, the composite slurry exhibits pseudo-plasticity and shows shear-thinning behavior up to the shear rate of 1300 s −1 , and at higher shear rates (>1300 s −1 ), it shows a shear thickening tendency, which is probably due to the agglomeration of non-deformable nano-TiB 2 particles. The pseudo-plastic behavior of the slurry was also estimated employing intermittent step changes of shear rate (shear jump test).

A comparative assessment of crystallite size and lattice strain in differently cast A356 aluminium alloy

In this investigation, A356 aluminium alloy has been prepared by different routes viz. gravity casting, rheo pressure die casting (RPDC) and RPDC with T6 heat treatment. X-ray diffraction studies of these samples have been done in the scanning range of 20 – 90°. X-ray peak broadening analysis has been used to estimate the crystallite size and lattice stain, in all the samples. The sample prepared by RPDC with T6 treatment has comparatively smaller crystallite size and lesser lattice strain than gravity cast and RPDC samples.

High-Temperature Graphitization Failure of Primary Superheater Tube

Abstract Failure of boiler tubes is the main cause of unit outages of the plant, which further affects the reliability, availability and safety of the unit. So failure analysis of boiler tubes is absolutely essential to predict the root cause of the failure and the steps are taken for future remedial action to prevent the failure in near future. This paper investigates the probable cause/causes of failure of the primary superheater tube in a thermal power plant boiler. Visual inspection, dimensional measurement, chemical analysis, metallographic examination and hardness measurement are conducted as the part of the investigative studies. Apart from these tests, mechanical testing and fractographic analysis are also conducted as supplements. Finally, it is concluded that the superheater tube is failed due to graphitization for prolonged exposure of the tube at higher temperature.

Corrosion Failure of an In-service Economizer Tube

This investigation was primarily aimed to examine the in-service failure of an economizer tube. Apart from preliminary visual examination, the analysis for the probable cause of failure was supplemented with radiographic examination, metallographic examination, energy dispersive spectroscopy, and scanning electron microscopy. Finally, it was concluded that there was seepage of water from an unusual blowhole-like through-thickness hole in the weld region of the economizer tube. This water vaporized and reacted with the flue gases and caused localized corrosion and led to the ultimate failure of the tube.