Wall thinning measurement, physical & chemical test, FEM analysis was conducted on one of an ASG small bore tube. The results show that wall thinning area mainly distribute downstream of the orifice and typical FAC feature were observed. According to FAC mechanism, influence factors and the service conditions, wall thinning are due to FAC. The function of this tube is keep the auxiliary feed water pump always ready, but the tube material and service temperature are susceptible to FAC. This paper discusses the preventive maintenance strategy of this kind of tubes and recommends that the wall thickness measurement should be conducted after 4 years serving. The thickness inspection area is twice times tube diameter downstream of the orifice; furthermore, the suitability assessment rule for similar tubes was established.

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