Which component is typically tested for line tightness separately from the tank body?

• A. The tank interior coating.
• B. The external shell paint.
• C. The product piping and fill lines, including risers.
• D. The ventilation duct.

Answer: (C)

Line tightness testing focuses on the piping that connects the tank to the rest of the system. The component typically tested separately for line tightness is the product piping and fill lines, including risers, because these paths carry the product and have joints, valves, and fittings where leaks are most likely to occur. Checking them separately ensures any leak paths in the lines are identified without conflating them with the tank shell. The interior coating and the external shell paint relate to protection and appearance, not to leak paths in piping, and the ventilation duct is part of the ventilation system, not the product line being assessed for line tightness.