ANS:C - both (a) & (b)

Corrosiveness of steam condensate can be due to the presence of dissolved gases such as CO2 (carbon dioxide) and O2 (oxygen). Both CO2 and dissolved O2 can lead to corrosion in steam condensate systems. CO2 can form carbonic acid when dissolved in water, leading to acidic conditions that can corrode metal surfaces. Similarly, dissolved O2 can react with water to form oxygen ions, which can accelerate the corrosion process, especially in the presence of moisture and other corrosive agents.

1. Corrosiveness due to CO2 (Carbon Dioxide):
   • When CO2 dissolves in water, it forms carbonic acid (H2CO3) through the following reaction: CO2+H2O⇌H2CO3CO2+H2O⇌H2CO3
   • Carbonic acid is a weak acid, but it can still lower the pH of the condensate, making it acidic.
   • The presence of acidic condensate can corrode metal surfaces in the steam condensate system, particularly carbon steel and iron components.
   • Corrosion caused by carbonic acid is often referred to as carbonic acid corrosion or acid attack.
2. Corrosiveness due to dissolved O2 (Oxygen):
   • Dissolved O2 in water can react with metal surfaces, particularly iron, through oxidation reactions.
   • The presence of oxygen ions (�2−O2−​) in the condensate can accelerate the corrosion process by promoting the formation of iron oxide (rust) on metal surfaces.
   • The formation of rust weakens the metal structure, leading to corrosion and potential structural damage over time.
   • Oxygen corrosion is a significant concern in steam condensate systems, especially in areas where oxygen ingress is not adequately controlled, such as during system startup or shutdown, or in poorly maintained systems.

In summary, both CO2 and dissolved O2 contribute to the corrosiveness of steam condensate by creating acidic conditions and promoting oxidation reactions on metal surfaces, respectively. These corrosive agents can lead to degradation of metal components in the condensate system, potentially causing leaks, equipment failure, and safety hazards. Therefore, it's crucial to monitor and control the levels of CO2 and dissolved O2 in steam condensate systems to mitigate corrosion and ensure the longevity and reliability of the system. So, the correct answer is: both (a) & (b).