Hundreds of European units of power plant will need renewal or refurbishment within the next 10 years for continuing economic viability. The required enhancement in perforrnance, efficiency and subsequently reduced O&M costs can be achieved by using the new generation ferritic steels, including the new European steel E911. This is largely due to the 20 to 30% superiority in creep strength of these materials. Steels for long term high temperature service are in practice qualified mainly through uniaxial creep testing, and any potential differences between such results (typically >30 000 h) and real long term behaviour in actual welded structures under complex loading (ie. after 150 000 to 200 000 h duty) are traditionally assessed later from service experience.
Since such experience is not available for the new steels, an industrial need exists for alternative means to evaluate welded structures made of these materials. For this purpose, a special accelerated damage enhancement (ADE) Methodology will be used to quantify the expected long term service behaviour for weldments of steels E911, P92 and P91, as well as for the typical refurbishment weld joint to 2 1/4Cr IMo (P22) steel.
Instead of conventional uniaxial tests, multiaxial tests employing fracture mechanics CT specimens or tubes (with and without notches) will be used. These tests are known to produce a high degree of multiaxiality in loading, which will enhance the damage evolution in time so that relevant cavitation damage can be reached within reasonable durations. The results from these tests will identify the most efficient type of testing for ADE. In addition to reducing the test durations necessary to generate long time service related damage in the new creep ductile steels, the multiaxial specimen approach provides similarity with the loading conditions experienced in real components. This will guarantee that the test results are
representative for characterising the damage behaviour of the steels and for establishing the correlation between remanent life and the observed degree of cavitation damage.
To fully realise the related economic opportunity in well quantified terms for both design and service performance, the objectives of the proposed project encompass
the development of a generic LICON Methodology for the
condition and lifetime assessment of anv new materials, which will (i) be applicable to all future steel developments for employment in power plant components, and (ii) be used directly by the plant manufacturer and end user partners in conjunction with a draft Code of Practice defining the new procedures;
the development of Guidelines for the employment of new
generation alloys ( E911, P92, P91), including their welded joints, in refurbishment and new plant; and
an evaluation of the economic benefit of utilising the new
generation steels, demonstrated through worked examples using the LICON ADE Methodology.
Achievement of the declared goals lies in the hands of an aptly constituted consortium comprising end users (EDP, ENEL, LE, and NE), a European manufacturer of the new generation steels (MFI), two plant equipment manufacturers (GECA for turbines and BEL for boiler plant), experts in welding and component testing (BIL) and plant inspection and training (ISQ), two ADE experts (JRC for special multiaxial testing and VTT for inspection experience), and a university (IC) renowned for modelling and validation test design.
Funding SchemeCSC - Cost-sharing contracts
1755 ZG Petten
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GL4 7RS Gloucester