To control the effect of acid corrosion at high pressures, what is maintained in a congruent phosphate program?

In a congruent phosphate program used for the control of acid corrosion in high-pressure boilers, it is crucial to manage the ratio of sodium ions to phosphate ions. This is because phosphate acts as a buffering agent, helping to maintain the proper pH in the water while preventing the precipitation of insoluble compounds that could lead to scaling or other detrimental effects within the boiler.

When the appropriate ratio of sodium to phosphate is maintained, it promotes the formation of stable sodium phosphate complexes, which can effectively control pH and minimize corrosion rates. This balance is essential in maintaining the integrity of the boiler under high-pressure conditions, preventing acid attack on metal surfaces and allowing the boiler to operate efficiently.

The other options do not adequately address the specific requirements of a congruent phosphate program for controlling acid corrosion. The pH level option focuses on a specific threshold that might not always relate directly to the effectiveness of the phosphate program. Reducing the temperature of the boiler and adding excess phosphate regularly could lead to operational issues or chemical imbalances, rather than providing the precise control needed for effective corrosion management.