How is the inside of structural steel tubing protected from corrosion?

• A. The tube is filled with hot linseed oil and then drained.
• B. The tube is coated with a waxy sealant and left to dry.
• C. The tube is filled with water and vented to dry.
• D. The tube is filled with rust inhibitor powder and sealed.

Answer: (A)

Protecting the hollow interior surfaces of steel tubing is achieved by coating them with a protective oil film. Filling the tube with hot linseed oil allows the oil to reach every inner surface because heat lowers the oil’s viscosity. After draining, the oil leaves a thin, durable film on the interior walls that blocks moisture and oxygen, keys to rust formation, and helps prevent corrosion during storage and service. This method is preferred because it provides an even internal barrier without leaving solid residues that could interfere with subsequent assembly. Other options either wouldn’t form a continuous protective coating inside the tube or would introduce substances that could trap moisture or cause contamination.