What is the best way to protect the interior surface of sealed structural steel tubing against corrosion?

Using linseed oil to protect the interior surface of sealed structural steel tubing against corrosion is effective due to its properties as a natural drying oil. When applied, linseed oil forms a protective barrier that not only helps to seal the metal from moisture and oxygen — two primary contributors to corrosion — but also allows the steel to maintain a degree of flexibility. This flexibility can be crucial in preventing cracks in the protective layer, which might occur due to stress or temperature changes.

The drying process of linseed oil also leaves a hard finish, further enhancing its protective capabilities. The oil penetrates the steel surface, providing an additional layer of defense. This method is commonly used in various applications where long-term corrosion protection is needed without the use of more complex chemical coatings.

In contrast, boric acid is typically used as a pest repellent and for its antifungal properties, while aliphatic and aromatic naphtha are solvents primarily used for cleaning or thinning paints and coatings, lacking the protective qualities needed for corrosion resistance in steel structures.