Structural integrity assessment of thermal power plant superheater collector

Thermal power plants (TPPs) belong to the important objects, the failure of which can cause accidents with severe consequences. A large portion of Ukrainian TPP has exceeded its design life, which is determined by the main elements of steam power systems. Therefore, the main task is to assess correctly the superheaters collectors limit state using modern approaches and taking into account the service degradation of material. TPP superheater collectors operate in the steamy environment under the pressure of 15.5 MPa at temperature 545 degrees C. As a result of combined action of prolonged thermo-mechanical stresses, corrosive and hydrogen environment and slow deformation, fatigue cracks emerge in these components on the inner collector surface. The limit state of boiler steam superheater collector model was assessed using failure assessment diagram (FAD). The FADs were built for K-mat = K-Ic, and K-mat = K-fc taking into account safety factors for plastic collapse and for brittle fracture mechanisms for the collector model with part circumferential internal surface crack for various ratio of crack length / to depth a. The critical sizes of the inner surface defect, that is perpendicular to the axis of the cylinder, considering fracture toughness of 12Cr1MoV steel for static and cyclic loading, were assessed. It was found out, that the increase of I/a ratio decreases the minimum crack depth that is critical for structural element. (C) 2014 Published by Elsevier Ltd.