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Standardizzazione – una via per promuovere l’accettabilità del metodo di prova a creep Small Punch

pubblicazioni - Articolo

Standardizzazione – una via per promuovere l’accettabilità del metodo di prova a creep Small Punch

The Small Punch (SP) test technique is capable of generating tensile, toughness and creep strength data from very small specimens. The ability to sample test material from large components, almost non-destructively, is accelerating the industrial interest in SP testing, particularly in the energy sector. Harmonisation of the test procedure for this new emerging method is essential for gaining acceptability, in particular for remanent life estimation of industrial plant components operating at elevated temperature. In order to kick off interest and bring about the eventual goal of a standardised SP Test method, a Round Robin SP creep testing programme was organised within the EPERC network. In this paper, the results of those SP creep tests performed on a 1CrMoV rotor steel at several temperatures and at one load level are analysed in order to assess their inter-comparability. The SP loading geometry features appeared to be a key parameter in the evaluation of the SP results, in particular for correlation with uniaxial creep behaviour. Such features form essential elements in the preparation of a standard when combined with other information emanating from similar test programmes worldwide. In establishing an appropriate test procedure, not only loading geometry, but also temperature, environment, strain measurement and most importantly the fundamental creep behaviour of the material itself must be rigorously investigated. The work approved in CEN WS21 covers both standardisation of the test procedure and also the analytical procedures required to interpret the results in engineering terms. The paper describes a Code of Practice for SP creep testing which, when linked to the results of a similar exercise for the low temperature determination of tensile and toughness properties, is intended to form the foundation for a European standard for a widely applicable SP test methodology. Finally, the translation from a Code of Practice to a Standard will require verification and the paper closes with a proposal for the framework of a substantial validation testing programme to be carried out on a European, or better still, a global scale.

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