Heat Treatment of Creep Resistant Steels

Before discussing the heat treatment of creep resistant steels, a few words about creep will be in order. When a metal is subjected to a stress for long time at an elev-ated temperatures, it undergoes plastic deformation; this time dependent accumulation of strain is known as creep. Creep limits the life time of components

Some Case Histories of Failure of Reheater Tubes

Failure of reheater tubes in some coal-fired boilers are encountered very frequently. This is in spite of the fact that the operating pressure in reheater is far less than that of superheater. In reheater the pressure is about 30 kg/cm2 whereas in superheater it is 150 kg/cm2. A dominant factor causing premature failure is the overheating and consequently creep or hot corrosion failure. The reheaters begin to receive steam only when the turbine is started up i.e., they are not cooled at all for appreciably long time during boiler start up. The same is true in an emergency shut-down of the boiler. In order to avoid overheating, reheaters are usually of convective type & less frequently of platen type. They are arranged in the zone of moderate heating where the flue gas temperature is around 750°C. In some places reheaters are cooled at a start up and shut down by fresh steam supplied through an attEmperature

High temperature boiler tube failures: case studies

Numerous investigation on high temperature failures of boiler tubes received from different thermal power plants had been carried out This paper presents three case studies of such failures. These include failures of (i) reheater tube of 1.25Cr-0.5Mo steel, (ii) carbon steel tube and (iii) final superheater tubes of 2.25Cr-IMo steel. The reheater tube had extensive damage in the form of pitting on outersurface. X-ray microanalysis using SEM revealed the presence of corrosive elements viz. K, Ca etc. on the pitted surface. Sticking of fly ash particles containing such elements causing reduction in effective tube wall thickness is responsible for the failure of reheater tube. The carbon steel tube showed a brittle window fracture. Decarburized metal containing intergranular cracks at the inner surface is indicative of hydrogen embrittlement responsible for this failure. In contrast, an extensive study on final super heater tube conclusively proves that the failure took place due to short term overheating. The extent of overheating had been estimated from the kinetic data on oxide scale growth and was found to be about 830'C. Surprisingly the tube had experienced a circumferential expansion as high as 19%. The wall thinning due to fireside corrosion, embrittlement and oxidation are primarily responsible for the failure of these tubes. It had been estab¬lished considering the influence of wall thinning that irrespective of operating temperature, pressure and damage development, modified 9Cr 1 Mo steel exhibits longest life among the various grades of Cr-Mo steel

Short-term performance variations of different photovoltaic system technologies under the humid subtropical climate of Kanpur in India

The study discusses the short-term performance variations of grid-connected photovoltaic (PV) systems installed in Kanpur, India. The analysis presents a holistic view of the performance variations of three PV array technologies [multi-crystalline (multi-Si), copper indium gallium diselenide and amorphous silicon] and two inverter types (high-frequency transformer and low-frequency transformer). The analysis considers the DC–AC conversion efficiency of the inverter, system performance through performance ratio (PR) calculations, energy variations between fixed and tracking systems and the comparison between calculated and simulated data for the examined period. The energy output difference between the tracking and fixed systems of the same PV technology show that these are dependent on differences in temperature coefficient, shading and other system related issues. The PR analysis shows the effect of temperature on the multi-Si system. The difference between the simulated and measured values of the systems was mostly attributed to the irradiance differences. Regarding the inverter evaluation, the results showed that both inverter types underperformed in terms of the conversion efficiency compared with nameplate values

Characteristics of Urban Centres and Urbanization in Uttarakhand <Article>

The pace of urbanization in Uttarakhand, particularly after the 1980s, has been alarming, and thousands of people from rural areas are settling in nearby urban centres every year. Even after the creation of the state, the growth of the towns in the plain areas is many times higher than the growth of hilly towns, due to migration from rural hilly region to flat areas of Uttarakhand. About 80% of the urban population of the state is concentrated in the plain parts of Uttarakhand. It is interesting to see that the urban population of Uttarakhand had increased by 1,859.0% between 1901 and 2011, which is more than the national growth of urban population in India (1,358.5%). This paper attempts to analyse the growth and distribution levels and trends of urbanization, and towns by size class, from 1901 to 2011, in Uttarakhand. It also deals with the distribution, literacy, sex ratio, and occupational structure of the urban population. It is based on the data released by the Census of India in 2001 and 2011

A Geographical Study of the Himalayan Towns of India <Article>

An attempt has been made in this paper to analyze the population growth, population density, and sex ratio of a total of 540 urban centers/towns belonging to twelve states/ regions of the Indian Himalaya. We analyze the population distribution, town distribution, growth of towns, density patterns of towns, sex composition, and status wise population based on the size class of towns as per the 2011 Census in particular. In the 2011 Census, the Indian Himalayan Region (IHR) consisted a total of 46,790,642 persons living in 61,592 inhabited villages and 540 urban centers, accounting for 3.87% of the total population of the country. The Indian Himalaya hold an urban population of 12,079,291, persons, which accounts for 3.2% of the nation’s total urban population as of 2011. The urban population constitutes 25.8% of the total population of the IHR. Of the total 109 districts in the IHR, two districts (1.83%) of Himachal Pradesh, namely Lahul and Spiti and Kinnaur districts, have no urban population. It is interesting to note that the urban population of the IHR had increased by 567.3% in the period 1901–2011, which is more than two folds (1,358.5%) of the national growth of urban population in India. Of the total 540 urban centers studied, 92 (17%) places were recognized as urban centers for the first time in the 2011 Census. One of the striking issues affecting the Himalayan demography is that one-tenth (56) or 10.4% of urban centers have registered negative growth ranging from 0.2% to 81.8% on the one hand, and 32 (5.9%) towns have registered a range of 100% to 3,909.9% decadal growth from 2001 to 2011 on the other hand. However, the growth of urban population in the IHR has been fluctuating from decade to decade. The density used for calculating the pressure of population on the land of the Indian Himalayan towns varies from 49 persons per km2 to 85,654 persons per km2; however, it has not been computed for 59 (10.9%) towns because of the unavailability of the land area in the towns of Arunachal Pradesh (27), Nagaland (26), and Manipur (6). The sex ratio of the Himalayan towns varied from 4 females per 1,000 males to 1,209 per 1,000 males in the 2011 Census. Only 93 (17.3%) towns recorded more than 1,000 females per 1,000 males, with 82.7% of the towns recording low sex ratio

Mechanical and Durability Characteristics of High Performance Concrete Using Copper Slag as Fine Aggregate

This paper reports the results of an experimental study on the high performance concrete made with copper slag as fine aggregate. The percentage of Copper Slag(CS) added by weight in a range viz. 0, 25, 50, 75 and 100% as a replacement of sand used in concrete and cement was replaced with 15% Metakaolin. The properties studied include compressive strength, splitting tensile strength, Sorptivity, Rapid Chloride Permeability Test (RCPT), Accelerated Carbonation test and Microstructural properties. The test results showed that the compressive strength increases up to 50% copper slag as replacement of sand, beyond which decrease in strength was observed. The results of RCPT and sorptivity with different proportions of copper slag at 28, 90, 120 days of curing period showed the lowest value for the mix containing 25%  and 50 % copper slag at each curing age. Carbonation results show that concrete mixes with 85% cement and MK 15% with increasing percentage of copper slag, the carbonation depth increases slowly especially for 75% and 100%. The microscopic view from Scanning electron microscopy (SEM) demonstrated more voids, capillary channels, and micro cracks with the increment of copper slag as substitution of sand as compared to the control mix, profoundly visible at 100% replacement of sand which is due to the presence of free water

Mechanical and Durability Characteristics of High Performance Concrete Using Copper Slag as Fine Aggregate

This paper reports the results of an experimental study on the high performance concrete made with copper slag as fine aggregate. The percentage of Copper Slag(CS) added by weight in a range viz. 0, 25, 50, 75 and 100% as a replacement of sand used in concrete and cement was replaced with 15% Metakaolin. The properties studied include compressive strength, splitting tensile strength, Sorptivity, Rapid Chloride Permeability Test (RCPT), Accelerated Carbonation test and Microstructural properties. The test results showed that the compressive strength increases up to 50% copper slag as replacement of sand, beyond which decrease in strength was observed. The results of RCPT and sorptivity with different proportions of copper slag at 28, 90, 120 days of curing period showed the lowest value for the mix containing 25%  and 50 % copper slag at each curing age. Carbonation results show that concrete mixes with 85% cement and MK 15% with increasing percentage of copper slag, the carbonation depth increases slowly especially for 75% and 100%. The microscopic view from Scanning electron microscopy (SEM) demonstrated more voids, capillary channels, and micro cracks with the increment of copper slag as substitution of sand as compared to the control mix, profoundly visible at 100% replacement of sand which is due to the presence of free water

Early Detection of Temporal Constraint Violations

Software systems rely on events for logging, system coordination, handling unexpected situations, and more. Monitoring events at runtime can ensure that a business service system complies with policies, regulations, and business rules. Notably, detecting violations of rules as early as possible is much desired as it allows the system to reclaim resources from erring service enactments. We formalize a model for events and a logic-based rule language to specify temporal and data constraints. The primary goal of this paper is to develop techniques for detecting each rule violation as soon as it becomes inevitable. We further develop optimization techniques to reduce monitoring overhead. Finally, we implement a monitoring algorithm and experimentally evaluate it to demonstrate our approach to early violation detection is beneficial and effective for processing service enactments