The steam drum internals is necessary to reduce the moisture content of the saturated steam leaving the drum by mechanical means. By moisture reduction, the solids in the boiler water are reduced in the steam.

Normally the drum is divided into two sections. The rear section has the most active boiler riser tubes, the unheated downcomer tubes, and one-half of the furnace riser tubes. The front section contains the heated downcomer boiler tubes, the least active boiler riser tubes & one-half of the furnace riser.

Tubes with the upward flow are called ‘risers’ and the tubes with the downward flow are called ‘downcomers’.

Wet Steam entering the rear half of the drum from the riser tubes is collected in a sealed off compartment formed by horizontal and vertical baffles. From this compartment, the steam is led through openings in the horizontal steam collecting box/ chamber and pass through a row of cylindrical ducts or baffles.

Steam flows upward from the front & rear steam ducts to the final stage of separation & enter the drier box where remaining entrained water gets separated. Since the velocity is relatively low, this water cannot be picked up again and, therefore, drops inside.

If the internals is not secured or fitted properly there is a possibility of carryover which affects the super heater performance and also premature failure can happen further the drum level cannot be maintained due to the process of carryover.