Improving the energy efficiency of power plants by increasing steam operating temperature up to 700 degrees C can be achieved using novel engineering design concepts such as coated steam pipe systems. This paper presents an optimised design for a novel coated dual pipe system to be used in advanced ultra-supercritical power plant. The approach developed in this study uses a combination of an optimisation algorithm and FE simulation, based on the reduction of the hoop stress at top coat/bond coat interface generated by the thermal and mechanical stresses. This allows determination of the optimum dimensions and material properties of the system. A unified viscoplastic model which combines a power flow rule with non-linear anisothermal evolution of isotropic and kinematic hardening has been used for the thermo-mechanical analysis of the coated dual pipe system under the cyclic loading. The results of the optimisation show that the value of the hoop stress at the top coat/bond coat interface is reduced significantly, compared with that in the baseline model. Finally, the potential technical challenges and future works for the proposed steam dual pipe system are discussed.

ABSTRACT The effect of stress changes on dislocation subgrain sizes developed in α-iron is examined. Uniaxial creep tests at 873K, over the stress range 13 to 22 MPa, were interrupted at a given steady state strain and then continued at a different stress. The resulting dislocation arrangements were examined using optical and electron microscopy and subgrain sizes established using X-ray back diffraction. Irrespective of the sequence of the stress change the subgrain size corresponded to the final stress.

A reheat treatment cycle for Durehete 1055 has been developed, the first stage of which removes grain boundary creep cavitation. Subsequent stages control microstructural parameters such as prior austenite grain size and allow in-service degradation of the vanadium carbide precipitate distribution to be reversed. Samples have been examined using a range of optical and electron optical techniques, and the compositions of extracted carbide precipitates have been determined using STEM-EDS X-ray microanalysis. It is shown that by reheat treatment the uniaxial creep life of creep-ruptured, ex-service material can be restored, and the creep ductility of previously coarse-grained material improved. The application of the results to life regeneration of service components is briefly discussed.

The measurement of stress on machined surfaces using the X-ray diffraction method is discussed. The influence of surface profile on the diffracted peak position is evaluated and considered with respect to its effect on the accuracy of stress measurement.

The distribution of electrode reactions occurring in a stress corrosion crack which is growing by enhanced anodic dissolution has been used to analytically establish the electrode potential distribution within the crack. This calculated potential distribution is discussed with reference to existing models for stress corrosion crack growth. The results of the analysis have been applied to the growth of stress corrosion cracks in a low alloy steel in 8 m sodium hydroxide solution at a temperature of 373 K.

Preparation procedures are examined by which the length of amosite fibres may be reduced so that preferred orientation is removed thereby providing samples suitable for quantitative X-ray diffraction analysis. Grinding in methyl alcohol produced samples from which X-ray diffraction gave major peak intensities reproducible to within ±2%. X-ray analysis has been carried out on samples of either calcium silicate powder or a lagging material which consists largely of a calcium silicate matrix reinforced with rockwool fibres which contain known additions (≤ 10 wt %) of amosite. The limits of detectability of amosite in both of these matrix materials, based on three diffraction peaks 110; 060:310; 240, have been established. It is concluded that for a mixture of amosite in calcium silicate powder, the limit of detectability is 0.4± 0.1 wt % and for amosite in lagging material, the limit of detectability is 0.2± 0.1 wt %. These are discussed in terms of differences in the physical distribution of the matrix materials.