Flow-induced vibration tube failure

Flow-induced vibration problems are mostly found in tube bundles used in shell-and-tube, duct-mounted tubular and other tubular exchangers in nuclear, process, and power industries. Less than 1 percent of such exchangers may have potential flow-induced vibration problems. However, if it results in a failure of the exchanger, it may have a significant impact on the operating cost and safety of the plant. 

Any action in mitigating flow maldistribution must be preceded by an identification of possible reasons that may cause the performance deterioration and/or may affect mechanical characteristics of the heat exchanger. The possible reasons that affect the performance are [131,147] (1) deterioration in the heat exchanger effectiveness and pressure drop characteristics, (2) fluid freezing, as in viscous flow coolers, (3) fluid deterioration, (4) enhanced fouling, and (5) mechanical and tube vibration problems (flow-induced vibrations as a consequence of flow instabilities, wear, fretting, erosion, corrosion, and mechanical failure). 

Evidence of fretting on a further 13 tubes adjacent to the baffle was found, all close to the seams between the six plates forming the baffle. It was concluded that sodium leakage through the seams, shown in Figure 2.3, caused flow-induced vibration of the tubes resulting in contact with the duct and giving rise to wear and the eventual failure of tube 6. 

In a number of cases, heat exchanger tube failures attributed to flow-induced vibration have resulted In consequential damage to other equipment within a plant. Failures of this nature have proven to be the most destructive, most costly, and have required the longest plant shutdowns for rectification. 

Baffles Baffles aie installed perpendicular at tube bundle to 1) control the shell side fluid velocity (also the shell side heat transfer coefficient and pressure drop), 2) prevent tube failure due to the flow induced tube vibration, and 3) support the tubes to avoid sagging. There are two types of baffles plate type and rod type, We will discuss plate ty baffle only in this chapter. 

Premature failure of exchanger tubes can occur through vibrations induced by the shell-side fluid flow. Care must be taken in the mechanical design of large exchangers where... 

---