from the conferences organized by TANGER Ltd. provisional website
A creep damaged area was found during the routine control of the steam pipeline bend of 200 MW fossil-fuelled power plant boiler close to the outer fibre and near the top of the bend. The damaged area with identified creep cracks was about 250 x 600 mm in size and the maximum depth of the cracks was 7 mm. Metallographic analysis carried out in this area confirmed the non-homogeneous cavitation damage. Density of cavities continuously decreased throughout the affected area from the outer to the inner surface of the pipe, around the pipe circumference and also in the axial direction along the length of the bend.The actual extent of degradation of material properties was then evaluated by testing the mechanical properties, notch and fracture toughness and the results were used to calculate the residual life of the bend. The results of these analyses showed that although the creep damage extent was probably one of the worst, which had been ever detected in the boiler of this type, cracks would propagate through the bend by stable growth until the mid-wall thickness and only then would the final rapid failure occur. This result confirms the possibility of extending the life of the steam pipeline bends far beyond the limits of the currently used criteria.Keywords: 0.5Cr-0.5Mo-0.3V steel, long-term creep exposure, cavitation, creep damage, residual life
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