The deaerator

The steam and water circuits
The condensate and feedwater system
The presence of residual oxygen in the feedwater supply of a boiler or HRSG is highly undesirable because it will cause corrosion of the boiler pipe-work (particularly at welds, cold-worked sections and surface discontinuities), greatly reducing the serviceable life span of the plant.
The deaerator removes dissolved gases by vigorously boiling the water and agitating it, a process referred to as ‘stripping’.