Boiler-water corrosion control Which combination of treatments is appropriate to prevent corrosion in boiler systems handling feedwater?

Introduction / Context:Steel corrosion in boilers is accelerated by dissolved oxygen, low alkalinity, and poor chemical control. A robust water-treatment programme must address oxygen removal, pH/alkalinity, and residual oxygen scavenging to protect the system and maintain efficiency.

Given Data / Assumptions:

• Standard low- to medium-pressure boiler service is considered.
• Materials of construction are typical carbon steel.
• Conventional treatment chemicals are available.

Concept / Approach:Corrosion is mitigated by: (1) deaeration (thermal or vacuum) to remove most dissolved oxygen; (2) alkalinity/pH control to passivate steel and minimise acid corrosion; and (3) oxygen scavengers (e.g., sodium sulphite, hydrazine-based products) to mop up residual oxygen after deaeration. Together, these reduce the driving forces for corrosion and promote protective magnetite films on steel surfaces.

Step-by-Step Solution:

Verification / Alternative check:Industry standards and boiler vendors prescribe this three-part programme; failure in any part correlates with increased corrosion, pitting, and tube failures.

Why Other Options Are Wrong:

• Each single-measure option is incomplete; residual oxygen or improper pH would still permit corrosion.
• Using only phosphate without deaeration/pH control is inadequate and risky.

Common Pitfalls:Assuming oxygen scavenger alone replaces proper deaeration; scavengers are polishing steps, not primary oxygen removal methods.

Final Answer:All (a), (b) and (c)