FRETTING-WEAR PREDICTION IN HEAT EXCHANGER TUBES: THE EFFECT OF CHEMICAL CLEANING AND MODELLING ILL-DEFINED SUPPORT CONDITIONS

摘要

Chemical cleaning of heat exchangers increases the clearances between tubes and their supports, which may lead to increased fretting-wear damage. This paper presents the results of a fretting-wear damage analysis of a U-bend tube at nominal and post-cleaning conditions. In multi-span heat exchanger tubes, the boundary conditions at the supports are ill-defined due to tube-support clearances. The fretting-wear rate at a support is a function of the gap (the distance between the tube and the support if the tube is not contacting the support) and preload (the contact force between the tube and the support if the tube is contacting the support). The configurations of gap/preload for a typical multi-span tube are numerous and not all possibilities can be analysed. Instead, a randomly selected group of tube-to-support configurations that is representative of the whole set needs to be used. In this paper, results of simulations for 40 randomly chosen tube-to-support configurations are presented. These indicate that when random vibration is considered, on the average no significant increase in fretting-wear damage will occur after chemical cleaning.