Investigation of a novel design for steam transfer pipes in high temperature power plant

Proposals for future nuclear and fossil fuel power plants envisage steam cycles of higher temperatures and pressures than existing plant. Such proposed operational conditions will require the use of nickel-based alloys for critical steam transfer piping to replace the steel alloys used in conventional plant. Nickel-based alloys are more costly than steel alloys and are in relatively scarce supply. The work described in this paper concerns an alternative approach, where a thermal insulation ceramic coating is applied to the bore of a steel pipe and combined with counter-cooling to the outside of the pipe to limit temperature of steel pipes. In our prosed design the coolant is exhaust steam from the turbines returning to the boiler for reheating.
The described in this paper was funded by the UK Engineering and Physical Science Research Council (EPSRC) and addressed aspects of the proposed design carried out by the Universities of Bristol, Cranfield and Nottingham. The work at the University of Bristol concerned thermodynamic modelling of the efficiency of the proposed design: the counter-cooled pipes will result in a loss of heat from the superheated steam and inevitably a loss of efficiency. This will partly offset the advanced efficiency achieved from higher operating temperatures. Cranfield University’s work focused on the integrity of the ceramic coating, and in particular the rate of corrosion of the coating resulting from exposure to supercritical steam. The University of Nottingham’s contribution to the work addressed the thermally induced stress in the pipe due to the temperature gradient through the pipe wall and its impact on the structural integrity of the pipework through the lifetime of the plant.