EFFECT OF ADJACENT TUBE EXPANSION ON THE RESIDUAL CONTACT PRESSURE OF TUBE-TO-TUBESHEET JOINTS

摘要

The tubular heat exchangers of nuclear, oil and gas industries often experience shutdowns due to failures of the tube-to-tubesheet joints. They are the very weak link between the heat transfer process thermos-fluids and separation boundary. The complex elasto-plastic behavior of the expanded joint and the lack of a proper design procedure of the expansion process are the two main factors contributing to the low quality and low performance of this kind of assembly. The inadequacy of a proper evaluation of the residual contact pressure achieved by the expansion process make the joint vulnerable and prone to leakage failure. Among the multiple parameters that effect the residual contact pressure is the adjacent tube-to-tubesheet expansion. It is proposed to study the elasto-plastic behavior of tube-tube to tubesheet joints during the expansion process using numerical FEM. The numerical FE model will be validated analytically prior to study the influence of adjacent expansion. Particular emphasis will be put on the effect of adjacent tube expansion and the expansion order sequence on the residual contact pressure. The effect of ligament size and the adjacent tube expansion sequence are also investigated. Such a study would provide general guidelines on how to control the expansion process and help the design engineer to predict accurately the residual stresses that are the major source of stress corrosion cracking and leakage failure.