If condensable fluids are handled in either the shell or tubes, vacuum breaker vents can help prevent steam hammer damage resulting from condensate accumulation. Modulating control valves also are preferable to fluid flow-control valves, which open or close suddenly and cause water hammer.
To avoid the risks of steam or water hammer, cooling water flow always should be started before heat is applied to the exchanger. Then, the stagnant cooling water is heated beyond its boiling point to generate steam, and the resumption of the flow causes a sudden condensing of the steam, which produces a damaging pressure surge, or water hammer. In a water or steam heating application, damaging pressure surges can result in an interruption to the flow of cooling water. Pressure surges or shock waves - caused by the sudden, rapid acceleration or deceleration of a liquid - can cause steam or water hammer. The resulting pressure surges have been measured at levels up to 20,000 psi, which is high enough to rupture or collapse the tubing in a heat exchanger (figure 1).įIGURE 1. Pressure surges or shock waves caused by the sudden and rapid acceleration or deceleration of a liquid can cause steam or water hammer. Where density is in pound-mass per cubic foot (lbm/ft3) and velocity is the shell nozzle velocity in feet per second (ft/sec). Typical shell-side nozzle-velocity limits to prevent impingement erosion on the outside of tubes can be established with the following: Wet-gas impingement is controlled by oversizing inlet nozzles, or by placing impingement baffles in the inlet nozzle. The maximum recommended velocities in heat exchanger tubes and entrance nozzles are shown for materials such as steel, stainless steel and copper-nickel.Įrosion problems on the outside of the tubes can occur with impingement of wet, high velocity gases such as steam.