This study investigates Fluidelastic Instability (FEI) of the tube bundles subjected to single phase cross flow. Experimental programs were conducted using straight and curved (helically coiled) tube bundles in various configurations, including slightly inclined square (SQ95, SQ99) and slightly rotated triangular (RT124, RT128) arrays. The test facilities and instrumentation were designed based on CFD and FE analyses to accurately capture the structural response in single-phase crossflow. Key observations indicate that straight tube arrays exhibit strongly-coupled behaviors and frequency synchronization near the onset of instability. In contrast, curved and mixed tube arrays demonstrate a sequential loss of stability, starting from the outermost layer and progressing according to the natural frequency order, generally speaking. Notably, the critical flow velocity was found to be higher than that of straight arrays, partly due to the frequency differences introduced between individual tubes. While out-of-plan vibrations showed abrupt amplitude increments, in-plan vibrations in curved tubes followed a saddle function behavior, what so- called, with two distinct humps as flow velocity increased. Based on the experimental data, constant K and a in FEI correlation formula, which is Conners equations, are proposed for curved tubing, which are 6 and 1/2, respectively. The results compared with ASME design guidelines and confirmed that the guidelines are applicable even to curved tube arrays