Assessment of creep and rupture behavior of 2.25Cr-1Mo steel – A strain-based approach and its limitation

Increasing demand of 2.25Cr-1Mo steel, among different grades of low alloy Cr-Mo steels, in power plants and petrochemical industries is mainly because of its high creep resistance. Application of a strain based approach for a reliable assessment of creep and rupture behavior is thus of great importance. Creep data were generated under different microstructural conditions in the laboratory and collected from literature as well. The influence of thermal ageing and pre-strain on the shape of creep curves has been studied. Analysis of data revealed that irrespective of initial microstructures, thermal ageing increases the tendency to soften but not the pre-strain. Softening due to carbide coarsening thus appears to be the dominant mechanism of creep. Based on this, a strain based approach for creep life assessment was developed. A fairly accurate prediction of creep life up to 5% creep is achieved using eight materials constants extracted from the creep curves of steel having similar initial microstructure. The limitation and reliability of the approach used to assess creep behavior of service-exposed steels have been discussed

Ab initio determination of the lifetime of the 62P3/26^2P_{3/2} state f or 207Pb+^{207}Pb^+ by relativistic many-body theory

Relativistic coupled-cluster(RCC) theory has been employed to calculate the life time of the $6 ^2P_{3/2}$ state of single ionized lead($^{207}Pb$) to an accurac y of 3% and compared with the corresponding value obtained using second order r elativistic many-body perturbation theory(RMBPT). This is one of the very few ap plications of this theory to excited state properties of heavy atomic systems. C ontributions from the different electron correlation effects are given explicitl y

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

Use of expert system software for life monitoring of power plant components

Life management of primarily high temperature components in power/process plants is a very involved task. Various components in a running power plant are subjected to different loading cycles, temperature, pressure and environmental conditions. The dependence of running power plant on various components as well as interdependence of various components on each other adds to the enormity of the task and requires different maintenance/ repair/ replacement schedules. A systematic and smooth functioning of the plant necessitates a step-by-step analysisfor each components based on its operating parameters, material. In present days, various commercial softwares are used for life monitoring, deciding different schedules in these plants. In the present paper an effort has been made to show the use ofALIAS (Advanced Life Assessment System) and its effectiveness in handling problems related to plant life monitoring, risk analysis, preparing maintenance/repair/replacement schedules

Probing liquid surface waves, liquid properties and liquid films with light diffraction

Surface waves on liquids act as a dynamical phase grating for incident light. In this article, we revisit the classical method of probing such waves (wavelengths of the order of mm) as well as inherent properties of liquids and liquid films on liquids, using optical diffraction. A combination of simulation and experiment is proposed to trace out the surface wave profiles in various situations (\emph{eg.} for one or more vertical, slightly immersed, electrically driven exciters). Subsequently, the surface tension and the spatial damping coefficient (related to viscosity) of a variety of liquids are measured carefully in order to gauge the efficiency of measuring liquid properties using this optical probe. The final set of results deal with liquid films where dispersion relations, surface and interface modes, interfacial tension and related issues are investigated in some detail, both theoretically and experimentally. On the whole, our observations and analyses seem to support the claim that this simple, low--cost apparatus is capable of providing a wealth of information on liquids and liquid surface waves in a non--destructive way.Comment: 25 pages, 12 figures, to appear in Measurement Science and Technology (IOP

TITAN's Digital RFQ Ion Beam Cooler and Buncher, Operation and Performance

We present a description of the Radio Frequency Quadrupole (RFQ) ion trap built as part of the TITAN facility. It consists of a gas-filled, segmented, linear Paul trap and is the first stage of the TITAN setup with the purpose of cooling and bunching radioactive ion beams delivered from ISAC-TRIUMF. This is the first such device to be driven digitally, i.e., using a high voltage ($V_{pp} = \rm{400 \, V}$), wide bandwidth ($0.2 < f < 1.2 \, \rm{MHz}$) square-wave as compared to the typical sinusoidal wave form. Results from the commissioning of the device as well as systematic studies with stable and radioactive ions are presented including efficiency measurements with stable $^{133}$Cs and radioactive $^{124, 126}$Cs. A novel and unique mode of operation of this device is also demonstrated where the cooled ion bunches are extracted in reverse mode, i.e., in the same direction as previously injected.Comment: 34 pages, 17 figure

Dynamic modeling of mean-reverting spreads for statistical arbitrage

Statistical arbitrage strategies, such as pairs trading and its generalizations, rely on the construction of mean-reverting spreads enjoying a certain degree of predictability. Gaussian linear state-space processes have recently been proposed as a model for such spreads under the assumption that the observed process is a noisy realization of some hidden states. Real-time estimation of the unobserved spread process can reveal temporary market inefficiencies which can then be exploited to generate excess returns. Building on previous work, we embrace the state-space framework for modeling spread processes and extend this methodology along three different directions. First, we introduce time-dependency in the model parameters, which allows for quick adaptation to changes in the data generating process. Second, we provide an on-line estimation algorithm that can be constantly run in real-time. Being computationally fast, the algorithm is particularly suitable for building aggressive trading strategies based on high-frequency data and may be used as a monitoring device for mean-reversion. Finally, our framework naturally provides informative uncertainty measures of all the estimated parameters. Experimental results based on Monte Carlo simulations and historical equity data are discussed, including a co-integration relationship involving two exchange-traded funds.Comment: 34 pages, 6 figures. Submitte