Final answer:
The inside of structural steel tubing is protected from corrosion through galvanization with a zinc layer for cathodic and prophylactic protection. Chromium or tin might also be used for their oxide coatings that hinder oxidization. If exposed or damaged, sacrificial zinc blocks or electrodes ensure the steel remains corrosion-free.
Step-by-step explanation:
The inside of structural steel tubing is protected from corrosion typically through a process known as galvanization. Galvanization involves the coating of the steel with a layer of zinc, which acts as a sacrificial layer. Since zinc is more readily oxidized than iron, it will corrode first, providing a form of cathodic protection. Hot-dip galvanizing leaves a crystalline surface on the steel that serves both as prophylactic protection by isolating the steel from oxygen and as cathodic protection, where the zinc corrodes before the underlying steel if exposed.
In instances where the protective zinc layer is damaged, the steel is still protected via cathodic protection. This method may involve attaching sacrificial electrodes or blocks, commonly zinc, which preferentially corrode, keeping the steel intact. To maintain the cathodic protection, these blocks will need to be periodically replaced.
Furthermore, prophylactic protection is also employed by using protective coatings of metals like chromium or tin, which form protective oxide coatings that inhibit the access of oxidizing agents such as oxygen and water to the underlying steel.