Novel high temperature steam transfer pipes

Lead Research Organisation: University of Bristol
Department Name: Mechanical Engineering


This feasibility study concerns improving the efficiency of steam cycles used in nuclear and fossil fuel energy generation. Currently steam is transported using steel pipes which limit the temperature of the steam to no more than 640 degress C. To improve efficiency, power plants are proposed that will operate with steam temperatures possibly up to 760 degrees C. Using conventional steam cycle design, such temperatures will require the use of nickel-based alloys. These alloys are more costly than steels and are in scarce supply, considering the quantity required for new power plants worldwide.

An alternative plant design is proposed in this feasibility study that will allow steam pipes made of steel to be operated at much higher temperatures than at present. The proposed design is of a pipe with a ceramic thermal insulation coating (TIC) on its internal surface and cooling on its outer surface provided by exhaust steam from the high pressure turbine.

Three institutions will collaborate in this study: the University of Bristol, Cranfield University and the University of Nottingham. Each institution will investigate a central technical challenge that must be overcome before the alternative plant design can be considered viable.

Bristol will develop thermodynamic models of the proposed steam cycle. The model will calculate the rate of transfer of heat from the superheated steam through the TIC into the steel pipe, and then the rate of heat transfer to the reheat steam returning to the boiler being used to cool the steam pipe. The model will predict the maximum temperatures within the steam pipe and the efficiency of the plant, compared to that of a conventional design.

Cranfield will carry out corrosion testing of candidate TIC materials in steam at ultra-supercritical temperatures. The results of this corrosion testing will be used to provide estimates of the lifetime of the TIC in a power generation environment.

Nottingham will investigate the structural integrity of the coating and the steel pipe. Stresses will be generated in the TIC and steel during start-ups, shut downs and steady state operation. These stresses will be very different in character from those in conventional steam transport. Nottingham will use existing computational models of the properties of TIC and steel to predict their lifetime under realistic operation conditions.

The outcome of this feasibility study will be an assessment of the opportunity for the development of an alternative to the use of nickel-based alloys for pipework in advanced power plant.

Planned Impact

This multi-disciplinary research consortium will work closely with the conventional power generation industry to develop a novel dual pipe system that incorporates an internal coating and external cooling system. The success of this project is likely to lead to new steam pipe designs that increase operating efficiency without relying heavily on the use of nickel, an expensive alternative in limited supply.

This project will be of direct benefit to the conventional power research community, power generation and supply industries, energy policy makers/regulators, environmental organisations and government departments, for example DECC. The major impact envisaged will be delivered through the vision to provide industry with a viable dual pipe design that will address some of the current key challenges faced by conventional power generation companies to satisfy the future requirements of the policy-led transition to low carbon energy generation which will play a key role in balancing electricity network supply and demand.

The UK population and economy will benefit from this research programme in that it will enable the UK combustion power generation sector to maintain a cost-competitive, reliable, environmentally-acceptable generation option and export potential for UK developed products and services. The research will contribute to meeting agreed targets for CO2 emissions.
Description The aims of the project were to: see whether the novel pipe concept would cause an unacceptable loss in efficiency; investigate the long-term structural integrity of the system; and examine the rate of corrosion of the thermal insulation coating.

The results of the project showed that the novel pipe concept gave a loss in efficiency of 1%, but this is much smaller than the improvement in efficiency resulting in the increase in working temperature that the system allows. The stresses in the pipe system were generally high, higher than would be considered acceptable for a 50 year life, although modifications to the design of the system could be made to reduce the levels of stress. The project only carried out tests on one type of ceramic coating, Yttria stabilised Zirconia, the type of coating used to coat turbine blades in gas turbines. These tests showed high levels of corrosion in supercritical steam; an alternative coating would have to be used.
Exploitation Route The outcomes of the project are relevant to future designs of high temperature power plant and provide an alternative solution to the use of expensive, high temperature resistant materials. Additional work is required: to design the system so that the level of thermal stress is such that an adequate life would be achieved; and to develop insulating materials such as ceramic coatings that will tolerate exposure to supercritical steam.
Sectors Chemicals,Energy

Description The principal non-academic impact, as identified by the delegates from industry at the end-of-project workshop, is the finding that there is a significant gap in the knowledge of material behaviour for power plants intended to operate at high temperatures, such that designing a high temperature plant with current materials and current knowledge of their behaviour is unthinkable.
First Year Of Impact 2020
Sector Energy
Description Industry workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact A one-day workshop was held at the University of Bristol on novel materials and engineering solutions to the problem of the design of high temperature power plant. The workshop was organised by FESI (UK Forum for Engineering STructural Integrity), one of the project partners.

The workshop explored the current state of materials and engineering research to assess the likelihood of successful design and construction of high temperature plant and the requirement for further research and development. The workshop addressed the two linked approaches of improvements to properties of materials and new engineering design techniques.

There were 29 attendees from industry (Atkins, NNL, ONP, TWI, Rolls-Royce, UKAEA and Wood) and academia (Universities of Bristol, Cranfield, Leicester, Manchester and Oxford).

The URL provided below lists the outcomes of the workshop.
Year(s) Of Engagement Activity 2020