Simulating High-Temperature Fretting Wear Degradation in Representative Environments

Abstract

In nuclear plant environments, vibration-induced fretting-wear damage can cause the failure of critical components such as heat exchanger tubes and fuel cladding. Fretting wear is a degradation mechanism characterized by high-frequency oscillations between two components. Of particular interest is impact fretting wear, whereby a combination of sliding and impact occurs between the components in contact, because the wear behaviour cannot be predicted based solely on material properties such as hardness. The assessment and prediction of fretting-wear damage requires knowledge of in-service vibration conditions in conjunction with the wear characteristics of the components in contact. The wear properties are known to not only depend on factors like component material combinations and geometry, but also on environmental conditions such as temperature, process fluid, and process chemistry. Fretting wear testing conducted at low temperature and in non-representative process conditions can result in wear coefficients that vary by orders of magnitude from those obtained at operating conditions. Furthermore, wear rates assessed in air at high-temperature have been found to differ from those assessed in water due to differences in corrosion properties that may affect the wear mechanisms, such as the formation of protective passivation layers.

High-temperature fretting-wear tests conducted at CNL’s Chalk River Laboratories in representative environments have provided valuable insights into the wear characteristics of nuclear power plant components since the 1970s. This test capability successfully enabled investigators to predict the life of CANDU®¹ and light water reactor components subjected to in-service vibrations, for example in the case of fuel fretting and steam generator tube/support fretting. CNL has recently upgraded its test facilities to provide enhanced test chemistry monitoring and control capabilities in a static autoclave environment. CNL is also developing the capability to perform fretting wear testing in a refreshed autoclave environment. The current presentation will provide an overview of recent fretting-wear test results conducted in a volatile chemistry at 280°C for a steam generator tube and tube support pair. An overview will also be provided for CNL’s refreshed autoclave fretting-wear facility which is currently under development.