Flow accelerated corrosion management in Indian NPPs: current practices

Carbon steel piping in primary heat transport system and secondary steam circuit in a nuclear power plant is susceptible to wall thinning due to flow accelerated corrosion. Reduction of wall thickness reduces the load carrying capacity of the piping leading to leakage or rupture. In India, flow accelerated corrosion failure was observed in Kakrapar Atomic Power Station-2 (KAPS2) where a failure in secondary piping was observed. Flow accelerated corrosion has also been a major concern in feeders of PHWR plants. Internationally also catastrophic failure related to wall thinning have been observed. It becomes important to understand what techniques and tools are adopted in India for tackling the issue of flow accelerated corrosion. This paper aims to give an overview of the steps taken during design, construction and operation of NPP to tackle flow accelerated corrosion. It aims to bring out metallurgical and chemical considerations which are taken to reduce the FAC susceptibility, the inspection and surveillance programs adopted, the flow accelerated corrosion prediction models adopted for Indian NPPs. Another important element of flow accelerated corrosion management is to make a decision about dealing with the thinned component (its continuous service or replacement). All these elements of flow accelerated corrosion are presented in this paper, taking KAPS 2 secondary piping failure as a case study. (author)