MANDZIEJ Stan Advanced Materials Analysis

An effective way to economy of energy generation is the extension of operation life of fossil fueled thermal power plants. It can be achieved by progressive repairs involving replacing the exploited components by new ones aiming to higher regimes of operation. The repairs involve welding and the heat-affected zones of the repair welds on the side of the exploited material become the critical regions of the whole upgraded structure. As after the repair the plant must be brought as soon as possible into operation, therefore one must very soon estimate its allowable operation parameters and life. For this the conventional creep tests are useless as being very long lasting. A recent physically simulated accelerated creep test (ACT) on Gleeble allows solving of this problem and from the collected materials data determining the long-term behaviour of such repair welds. In this test, executed on bulk 10mm diameter cross-weld samples, the creep cracks nucleate in the most vulnerable portion of the welded joint, which location cannot be predicted in the true weld by any method until the failure occurs. The simulative ACT on Gleeble “identifies” the location of potential crack appearance without violating the micro-mechanism of the ductile fracture characteristic of creep. It also tells if the partly exploited components of power-gen structure can be repaired and allows estimating how long the repaired structure will last in the allowable operation conditions. An example of the repair weld is presented in this paper and the microstructures after ACT are discussed.

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