Assessment of Axial Cracking of a Steam ...

Steam generator (SG) tubes are extensively used in the form of thin-walled tubular structural members as heat exchangers for generation of steam in order to convert thermal energy to electricity in nuclear power plants. These tubes are exposed to aggressive environments such as high temperature, internal pressure and flow-induced vibration etc. Since at present no standard test procedure can guarantee accurate quantification of axial crack resistance of such tubes because of their unusual geometry, the present work attempts structural integrity assessment of an SG tube using a new method called pin loading tension test (PLT) as has been done by the authors for fuel cladding tubes fabricated with zirconium alloys in recent past. The current work involves experimental and analytical derivation of various geometric functions required for calculation of stress intensity factor (SIF) and J integral. Using the derived functions, J-R curve for an axially cracked SG tube made of Ni-Cr-Fe based alloy used in power plants of Indian pressurized Heavy Water Reactors (PHWR) is calculated. Also, the characterization of fracture surface by SEM fractography is done to predict suitable cracking mechanism.