Carbon Steel Trays
One of the most frequent causes of flooding is the use of carbon steel trays. Especially when the valve caps are also carbon steel, the valves have a tendency to stick in a partially closed position. This raises the pressure drop of the vapor flowing through the valves, which, in turn, pushes up the liquid level in the downcomer draining the tray. The liquid can then back up onto the tray deck and promote jet flood due to entrainment.
Of course, any factor (dirt, polymers, gums, salts) that causes a reduction in the open area of the tray deck will also promote jet flooding. Indeed, most trays flood below their calculated flood point, because of these sorts of problems. Trays, like people, rarely perform quite up to expectations.
The use of movable valve caps in any service where deposits can accumulate on the tray decks will cause the caps to stick to the tray deck. It’s best to avoid this potential problem. Use of grid trays with fixed cap assemblies is preferred for most services.