Experimental investigation of long-term fretting wear of multi-span steam generator tubes with u-bend sections

摘要

Accurate prediction of the growth rate of fretting wear damage of steam generator (SG) and heat exchanger (HX) tube is needed for safe, reliable and economical operation of the nuclear power plant. The methodology currently used to predict thelong-term fretting wear behaviour of the tube is based on combining the short-term wear data base with non-linear finite element impact simulation of the tube/support dynamic interaction. The main objectives of this investigation are: (a) to generatelong-term experimental data that will be used to verify this methodology, (b) to investigate whether the fretting wear of a multi-span SG tube with a V-bend section is self-limiting, and (c) to examine the dynamic interactions between adjacent tubesupports. An experimental set-up has been developed to simulate the fretting wear behaviour of a full scale multi-span SG tube with U-bend section. Straight and U-bend tube supports were instrumented for in situ measurement of the tube orbital motion andimpact forces. On-line calculation of the energy dissipated at the tube/support interface in the axial and out-of-plane directions was performed. Analysis of the results indicated that the increase in the tube/support clearance results in a non-monotonicchange in the rate of energy dissipated in the wear process (work rate). This behaviour, which suggests that the fretting wear behaviour of a multi-span tube could be self-limiting when the forcing function is invariant, is in agreement withcomputer-simulation predictions. The results indicated also the strong dynamic interaction between adjacent supports. It has also been concluded that the specific wear rate coefficient is not constant, and depends on the magnitude of he work rate. For the work rate range investigated, the wear rate coefficient at the U-bend section decreases and approaches an asymptotic value, as the work rate increases. Analysis of the results also showed that the ratio between the maximum and average wear depths.