Research On Vibration Collision And Wear Of Heat Exchange Tube With Loose Supports

The heat exchange tubes in the shell-and-tube heat exchanger are the main component of the heat exchange between the cold and hot fluids,which are the pressure-bearing boundary as well.The structural integrity directly affects the safe and stable operation in industrial production process.As a typical shell-and-tube heat exchanger in the nuclear power field,the elbow section of the steam generator is subjected to an obvious cross flow,which is loosely supported by the anti-vibration bars(AVBs),resulting in significant flow-induced vibration(FIV)and fretting wear.Therefore,this paper focuses on the vibration and wear behavior of the heat exchange tube with the largest span in the elbow area of the steam generator.The numerical simulation of flow field and FIV analysis were carried out based on a precise tube array model.The results show that fluid instability is difficult to occur in the elbow section when the AVBs are effective,whose instability rate is less than 50%.Note that,the collision and wear caused by turbulent buffeting should be paid to more attention.The failures of single support and symmetrical supports on the opposite side contribute little to the FIV,however,that of the same side supports has a significant influence on FIV.Through numerical simulation of the vibration and collision of the heat exchange tube,the input conditions of the wear experiment were determined.The maximum contact force and normal work rate between the heat exchange tube and the AVBs were both at the first set of supports near the straight tube,which are 28N and5.4m W respectively.In addition,the normal work rate shows strong sensitivity to the clearance and damping.Fretting wear experiments were carried out in the room-temperature atmosphere and high-temperature steam/water.In the room temperature environment,the results indicated that the amount of wear increases steadily with the increase of cycles,which is extremely obvious for 8×10~4 to 10~5 cycles with twice the wear volume.The wear mechanisms are abrasive and delamination.As the normal force increases,the friction coefficient decreases,and the abrasive wear weakens while the delamination increases.The hardness of the sub-surface layer of the wear scar is positively correlated with the cycles and the normal forces.Work hardening not only increased the wear resistance but also aggravated the delamination.Temperature and operating environment have a significant influence on the amount of wear and wear mechanism in high temperature conditions.In steam,the maximum wear depth is 15.77μm at 100℃,and the wear mechanism is abrasive and adhesive;the damage at 200°C is the least,and the wear mechanism is delamination and oxidative wear.The coupling of wear and oxidation corrosion at 285°C caused severe damage.At this time,the wear volume was the largest,which is 1.4×10~7μm~3.In pure water,the wear volume and wear depth are the largest at100℃,which are 6.9×10~6μm~3 and 13.18μm,respectively.The wear mechanism is abrasive and adhesive;due to the protective effect of the dense oxide layer,the wear scars were slightly damaged,and the wear mechanism is abrasive at 200℃and 285℃.The research results of this paper could provide basis and reference for the vibration damping and life evaluation of heat exchange tubes with loose supports.