Failure analysis of O-ring gaskets of the electric hydraulic system in the nuclear power plant

In this paper, premature failure of the O-ring gaskets for the electric hydraulic system in a nuclear power plant in China was investigated. A series of macroscopic and microscopic analysis methods were conducted to identify the root causes of this unexpected failure, and the results showed that mismatch of the sizes between the O-ring gaskets and the groove of metal union was the primary reason, which gave rise to the permanent distortion and surface damage of the O-ring gaskets, and consequently leading to fracture under service conditions. Countermeasures were then proposed to prevent the recurrence of similar incidents, and were proved effective on site.