Shaft failures in coal handling plants

An analysis of premature failures in coal pulveriser mill shafts brings out the facts that the auxiliary units, in a power plant, like coal feeders, pulverizer mills etc., do not receive much attention during routine inspections and lack in property specification for the materials. It is brought out in this investigation that mere specification of material composition and hardness is not enough for load bearing components operating under cyclic loads

Shaft Failures in Coal Handling Plants

An analysis of premature failures in coal pulveriser mill shafts brings out the facts that the auxiliary units, in a power plant, like coal feeders, pulverizer mills elc., do not receive much attention during routine inspections and lack in property specification for the materials. It is brought out in this investigation that mere specification of material composition and hardness is not enough for load bearing components operating under cyclic loads

Advances in computer-aided crack length measurement during fatigue crack growth testing

The accurate measurement of crack length is one of the most important aspect of fatigue crack growth rate (FCGR) testing. Of the various methods available for crack length measurement, compliance technique is very popular due to the facilities it provides for easy automation. In the compliance technique, compliance crack length (CCL) rela-tions are used for correlating the compliance, computed from measurements of displacements & loads during fatigue cycling, to the crack length contained in the specimen. CCL relations are specific not only to the specimen geometry, but also to the location on the specimen body at which displacements are measured. This specificness is not very conducive to the experimentalist as it introduces errors in the measured crack length if the location of displacement measurement is not accurately maintained. With variations in specimen geometry and size, the accu-rate positioning of displacement measurement transducers is not an easy task. In order to provide greater flexi-bility in the use of the compliance technique, a new scheme has been proposed in this paper. Modelling the defo-rmation of a fracture mechanics specimen during fatigue cycling as rotation of two rigid hinge about a hringe point, the relationship between the location of the hinge-point with crack length has been established using finite element analysis for the single-edge notched three point bend specimen. Further -an iterative method has been developed which can be implemented in the background software for on-line crack length measurement. It has been shown that the iterative method converges rapidly to give the crack length with high accuracy

Compliance crack length relations for the four-point bend specimen

Compliance crack length relations for the four-point bend specimen geometry have not been reported in the literature in spite of this geometry being one of the popularly used specimens for fatigue crack growth studies. An effort has been made in the present work to fill this gap. Accordingly, the finite element technique was employed to simulate loading and calculate displacements at various locations in a four-point bend specimen. The load-displacement data thus obtained were processed to yield compliance crack length relations. These relations were employed to calculate the crack length during fatigue testing of four-point bend specimens in which the crack length was also measured by optical means. A good correlation was observed between the predicted crack length and that measured optically

Remote sensing applications: an overview

Remote Sensing (RS) refers to the science of identification of earth surface features and estimation of their geo-biophysical properties using electromagnetic radiation as a medium of interaction. Spectral, spatial, temporal and polarization signatures are major characteristics of the sensor/target, which facilitate target discrimination. Earth surface data as seen by the sensors in different wavelengths (reflected, scattered and/or emitted) is radiometrically and geometrically corrected before extraction of spectral information. RS data, with its ability for a synoptic view, repetitive coverage with calibrated sensors to detect changes, observations at different resolutions, provides a better alternative for natural resources management as compared to traditional methods. Indian Earth Observation (EO) programme has been applications-driven and national development has been its prime motivation. From Bhaskara to Cartosat, India's EO capability has increased manifold. Improvements are not only in spatial, spectral, temporal and radiometric resolutions, but also in their coverage and value-added products. Some of the major operational application themes, in which India has extensively used remote sensing data are agriculture, forestry, water resources, land use, urban sprawl, geology, environment, coastal zone, marine resources, snow and glacier, disaster monitoring and mitigation, infrastructure development, etc. The paper reviews RS techniques and applications carried out using both optical and microwave sensors. It also analyses the gap areas and discusses the future perspectives

Application of fracture-mechanics for weld integrity assessment

The structural integrity assessment of a weld joint by conventional techniques is inadequate, because of unavoidable defects in the weld composite. The stress situation in a component having a defect is quite different from that of a homogeneous material. The significance of fracture mechanics to deal with such integrity assessments is brought out. A brief review on the basic formulations in the application of fracture mechanics is followed by established guidelines for evaluating the integrity of engineering components containing crack-like defects

Microstructural damage evaluation in Ni-based superalloy gas turbine blades by fractal analysis

Ni-based superalloys are used as turbine disc and blade material in which creep, fatigue and creep-fatigue are the important damage mechanisms. Mechanical properties of these alloys depend upon the amounts of gamma-gamma-prime present in the microstructure as well as precipitation of carbides along the grain boundaries. The distribution of gamma-prime depends on the chemical composition, operating temperature and the length of service exposure. During service exposure, as damage accumulates progressively, the morphological characteristics of microstructure change which needs to be assessed using metallographic technique. Conventionally, the extent of damage resulting in deterioration of mechanical properties is quantified by hardness measurement. The variation in hardness is correlated with the morphological features in the metalographic images by identifying precipitation of carbides, presence of cuboidal gamma-prime and the structural changes that occur in the matrix. In this paper, we report fractal dimensions of the insitu metallographic images which can correlate the progressive damage accumulation at various locations of the blades

Remaining life assessment of service exposed reheater and superheater tubes in a boiler of a thermal power plant

This paper presents the high temperature tensile and the stress rupture properties of 150,000 hours service-exposed superheater and reheater tubes made of 2.25Cr-1 Mo steels in a 120 MW boiler of a thermal power plant. These were used to estimate the remaining life for safety. Experimentally determined yield strength and ultimate tensile strength as well as estimated 10,000 hours - 100000 hours rupture strength as obtained from experimental data in the temperature range of 793 to 853K exhibit a decreasing trend with increasing temperature. Microstructural study did not reveal any significant degradation in terms of creep cavities, cracks, graphitization etc. In general, analysis of tensile and stress rupture data reveal that the service exposed superheater and reheater tubes can remain in service for a length of more than ten years at the operating hoop stress level 40 MPa / 813K, provided no localised damage in the form of cracks or dents has been developed. It is recommended that a similar health check should be carried out after 50,000 hours of service exposure at 813K

Short-term changes on MRI predict long-term changes on radiography in rheumatoid arthritis: an analysis by an OMERACT Task Force of pooled data from four randomised controlled trials

Objective: In rheumatoid arthritis (RA), MRI provides earlier detection of structural damage than radiography (X-ray) and more sensitive detection of intra-articular inflammation than clinical examination. This analysis was designed to evaluate the ability of early MRI findings to predict subsequent structural damage by X-ray. Methods: Pooled data from four randomised controlled trials (RCTs) involving 1022 RA hands and wrists in early and established RA were analysed. X-rays were scored using van der Heijde-modified or Genant-modified Sharp methods. MRIs were scored using Outcome Measures in Rheumatology (OMERACT) RA MRI Score (RAMRIS). Data were analysed at the patient level using multivariable logistic regression and receiver operating characteristic curve analyses. Results: Progression of MRI erosion scores at Weeks 12 and 24 predicted progression of X-ray erosions at Weeks 24 and 52, with areas under the curve (AUCs) of 0.64 and 0.74, respectively. 12-week and 24-week changes in MRI osteitis scores were similarly predictive of 24-week and 52-week X-ray erosion progressions; pooled AUCs were 0.78 and 0.77, respectively. MRI changes in synovitis at Weeks 12 and 24 also predicted progression of X-ray joint damage (erosion and joint-space narrowing) at Weeks 24 and 52 (AUCs=0.72 and 0.65, respectively). Conclusions: Early changes in joint damage and inflammation detected with MRI predict changes in joint damage evident on subsequent X-rays. These findings support the use of MRI as a valid method for monitoring structural damage in short-duration RCTs

Using Relational Verification for Program Slicing

Program slicing is the process of removing statements from a program such that defined aspects of its behavior are retained. For producing precise slices, i.e., slices that are minimal in size, the program\u27s semantics must be considered. Existing approaches that go beyond a syntactical analysis and do take the semantics into account are not fully automatic and require auxiliary specifications from the user. In this paper, we adapt relational verification to check whether a slice candidate obtained by removing some instructions from a program is indeed a valid slice. Based on this, we propose a framework for precise and automatic program slicing. As part of this framework, we present three strategies for the generation of slice candidates, and we show how dynamic slicing approaches - that interweave generating and checking slice candidates - can be used for this purpose. The framework can easily be extended with other strategies for generating slice candidates. We discuss the strengths and weaknesses of slicing approaches that use our framework