Publication InformationFarragher, TP, Scully, S, O Dowd, NP, Leen, SB (2013) 'Development of life assessment procedures for power plant headers operated under flexible loading scenarios'. International Journal Of Fatigue, 49 :50-61. PublisherElsevier ScienceDirect 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Abstract A finite element methodology for thermomechanical fatigue analysis of a subcritical power plant outlet header under realistic loading conditions is presented. The methodology consists of (i) a transient heat transfer model, (ii) a sequential anisothermal cyclic viscoplastic model and (iii) a multiaxial, criticalplane implementation of the Ostergren fatigue indicator parameter. The methodology permits identification of the local thermomechanical stress-strain response at critical locations and prediction of fatigue life and cracking orientation for complex transient, anisothermal, cyclic elastic-plastic-creep material behaviour. Measured plant data, in the form of steam and pipe temperature transients and steam pressure data, are employed to identify heat transfer constants and validate the predicted thermal response, with particular attention given to plant start-up and attemperation effects. The predictions indicate out-of-phase temperature-strain response at the header inside surface and in-phase response on the outside surface. Cooling transients are predicted to control damage and crack initiation at the inner bore, whereas heating transients are predicted to have a more damaging effect at weld locations. A representative test cycle is presented, which is shown to capture the salient thermo-mechanical cyclic damage of the realistic cycle. The predicted results correlate well with industrial experience in terms of crack (initiation) orientation, location and life. IntroductionThere is a need to understand the performance of candidate power plant materials for higher temperatures and pressures. 9-12% Cr steels are an example of such candidate materials, owing to their excellent mechanical properties, and steels such as P91 and P92 are already being utilised in power generation plant [1]. There is an increasing trend towards shifting of energy supply from conventional fossil fuel power plant to sustainable energies, e.g. wind power. To allow for the variable nature of renewable energy supply, there is a requirement to operate existing plant, designed for 'base-load' operation, with relatively infrequent shutdown and start-up, in 'load-following' mode, characterised by increased frequency of shutdown and start-up. This issue has increased the importance of design and assessment of materials and components for high temperature, pressurised plant with respect to thermomechanical fatigue (TMF) and creep-fatigue failure.Current header design does not consider cyclic thermal stresses and load cycling that can lead to creep-f...

The Q & U Bolometric Interferometer for Cosmology (QUBIC) is a novel kind of polarimeter optimized for the measurement of the B-mode polarization of the Cosmic Microwave Background (CMB), which is one of the major challenges of observational cosmology. The signal is expected to be of the order of a few tens of nK, prone to instrumental systematic effects and polluted by various astrophysical foregrounds which can only be controlled through multichroic observations. QUBIC is designed to address these observational issues with a novel approach that combines the advantages of interferometry in terms of control of instrumental systematic effects with those of bolometric detectors in terms of wide-band, background-limited sensitivity. The QUBIC synthesized beam has a frequency-dependent shape that results in the ability to produce maps of the CMB polarization in multiple sub-bands within the two physical bands of the instrument (150 and 220 GHz). These features make QUBIC complementary to other instruments and makes it particularly well suited to characterize and remove Galactic foreground contamination. In this article, first of a series of eight, we give an overview of the QUBIC instrument design, the main results of the calibration campaign, and present the scientific program of QUBIC including not only the measurement of primordial B-modes, but also the measurement of Galactic foregrounds. We give forecasts for typical observations and measurements: with three years of integration on the sky and assuming perfect foreground removal as well as stable atmospheric conditions from our site in Argentina, our simulations show that we can achieve a statistical sensitivity to the effective tensor-to-scalar ratio (including primordial and foreground B-modes) σ(r)=0.015.

Bolometric interferometry is a novel technique that has the ability to perform spectral imaging. A bolometric interferometer observes the sky in a wide frequency band and can reconstruct sky maps in several sub-bands within the physical band in post-processing of the data. This provides a powerful spectral method to discriminate between the cosmic microwave background (CMB) and astrophysical foregrounds. In this paper, the methodology is illustrated with examples based on the Q & U Bolometric Interferometer for Cosmology (QUBIC) which is a ground-based instrument designed to measure the B-mode polarization of the sky at millimeter wavelengths. We consider the specific cases of point source reconstruction and Galactic dust mapping and we characterize the point spread function as a function of frequency. We study the noise properties of spectral imaging, especially the correlations between sub-bands, using end-to-end simulations together with a fast noise simulator. We conclude showing that spectral imaging performance are nearly optimal up to five sub-bands in the case of QUBIC.

This paper is concerned with the cyclic plasticity modelling of welded, exservice P91 material. A multi-material model is developed for high temperature cyclic plasticity, including the effects of the three different material zones in the vicinity of the weld: parent metal, weld metal and heat-affected zone. The cyclic plasticity behaviour of the three zones is identified from previously-published high temperature, low cycle fatigue experimental tests on uniaxial parent metal, weld metal and cross-weld specimens on exservice P91 material. The heat-affected zone is shown to be significantly softer than the parent and weld metals and to act as a focus for concentration of plastic strain, leading to significantly inhomogeneous distributions of stress and strain in the weldment. The multimaterial cyclic plasticity model is applied, via a three-dimensional finite element model, to a welded T-piece header-branch connection, to predict the effects of cyclic internal pressure and small amplitude thermal fluctuations.