When should sodium nitrite be added for maximum effectiveness in a lay-up?

Sodium nitrite is commonly used as a corrosion inhibitor in boiler systems, particularly during lay-ups. For maximum effectiveness, it should be added before filling the boiler. This ensures that the sodium nitrite can dissolve completely and distribute evenly throughout the water, allowing it to effectively protect the metal surfaces from corrosion.

Adding sodium nitrite before filling the boiler allows it to achieve the desired concentration in the water, which is critical for its corrosion-inhibiting properties to function optimally. If it were added after the boiler is filled, there may not be adequate mixing or time for the inhibitor to work effectively, potentially leaving parts of the boiler unprotected.

In contrast, adding sodium nitrite during operation or at the end of a lay-up would not render the same level of protection as pre-filling, as it would either be too late to prevent corrosion during non-operational periods or not tailored to support the initial treatment of surfaces while they are exposed to water.