Abstract
The simulative accelerated creep test (ACT) was developed as a response to an overall need of gaining in a short time useful physical data for determining long-term behaviour of materials exposed to operation under stress at elevated temperatures in power generation and chemical processing industries. Additionally, the recently frequent power plant shut-downs due to adding solar/wind power to the net call for creep-fatigue data which standard creep tests cannot provide. In response to these needs, a thermal-mechanical fatigue procedure ACT was designed, taking into account physical phenomena causing microstructure transformation during creep, in particular generation of dislocation substructures, their role in nucleation of voids and cracks, intensification of carbide precipitation and decay of mechanical properties during long-time exposure to elevated temperatures. The actual ACT procedure generates adequate data for calculating true lifetime of the tested creep resisting material for a nominal stress.
Highlights
Conventional “constant-load” creep tests of new steels and welds for thermal power generation and chemical processing are very long lasting, delaying the application of newly developed steels for years
The important factor is the initial hardness. It shows that the drop of hardness after just a few thousand seconds in the accelerated creep test (ACT) follows the tendency of multiyear real creep
Low-cycle thermal-mechanical fatigue of martensitic-ferritic creep resisting steels, applying direct electric resistance heating, accelerates transformation of microstructure and intensifies precipitation of secondary phases, causing depletion of matrix in alloying elements similar to that occurring during the real creep
Summary
Conventional “constant-load” creep tests of new steels and welds for thermal power generation and chemical processing are very long lasting, delaying the application of newly developed steels for years. While most of the design of components and estimation of power plants lifetime is based on long-term creep data, which are generally available for the plate and pipe creep resisting steels, in case of the welded joints on these components, such data are not always found, for example, the repair welds are very often not available, especially when repairs were performed outside. To address all these issues, a simulative test was developed allowing to obtain creep life data in less than 24 h. The accelerated creep test is a low-cycle thermal-mechanical fatigue procedure designed to transform the creep resisting steels and welds in the same manner like true creep, only occurring in much shorter time
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