High temperature corrosion of gradient tubes for high temperature application

Sanni Yli-Olli, Elisa Isotahdon, Satu Tuurna, Peter Brziak, Jouni Mahanen

    Research output: Contribution to conferenceConference articleScientific


    For competitive low carbon or carbon neutral combustion, future boilers will need to utilize an increasing amount of biomass. The resulting combustion environment poses a challenge by contain large amounts of severely corrosive constituents that attack existing materials and might drastically limit their durability and lifetime. New structural materials can be attractive in principle, but it has been challenging to simultaneously achieve good mechanical strength, high temperature corrosion/oxidation resistance and cost-effective composition in the candidate alloys. To avoid undue loss of thermal efficiency or facing an increasing number of unscheduled outages new solutions in protecting the existing material (by coatings and overlay welds) need to be developed. Newly developed creep resistant gradient tubes with increased fireside corrosion resistance, have shown good performance for the elevated conditions. Gradient tubes, made of 11CrMo9-10 low alloy body and 347H austenitic shell, are oriented for boilers burning aggressive flue gases/ashes producing feedstock, e.g. biomass/chip/straw boilers. The paper describes the high temperature corrosion resistance of the gradient tubes in accelerated laboratory scale tests and long term on-site tests in real boiler conditions. The results show that the thickness and microstructural state of the austenite layer as well as possible surface defects of the gradient tube have a great influence on the high temperature corrosion rate of the gradient material. Overall, the new material shows comparable performance to the conventional 347H material. The work was done within the GRAMAT project supported by EU Research Fund for Coal and steel. The main aim of project is to acquire knowledge necessary to develop new cost-effective manufacturing technology of boiler tubes made from semi products with through thickness gradient chemical composition, tailored to carry both creep loading (low alloyed body) and fireside corrosion resistance (high alloyed shell).
    Original languageEnglish
    Publication statusPublished - 1 Jan 2017
    MoE publication typeNot Eligible
    Event20th International Corrosion Congress & Process Safety Congress 2017, Eurocorr 2017 - Prague, Czech Republic
    Duration: 3 Sept 20177 Sept 2017


    Conference20th International Corrosion Congress & Process Safety Congress 2017, Eurocorr 2017
    Abbreviated titleEurocorr 2017
    Country/TerritoryCzech Republic
    Internet address


    • gradient tubes
    • high temperature corrosion
    • on-site testing
    • biomass
    • Gradient tubes
    • Biomass
    • On-site testing
    • High temperature corrosion


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