What type of tank requires inspection annually, regardless of corrosion protection?

The correct choice identifies steel tanks without any corrosion protection as requiring annual inspection. This is due to the inherent susceptibility of unprotected steel to corrosion, especially in environments that may expose the tank to moisture and various chemicals. Over time, this deterioration can compromise the structural integrity of the tank, creating potential leaks or failures that could pose safety hazards or lead to environmental contamination.

Annual inspections help to identify any corrosion issues early, allowing for preventative maintenance or repairs to be made before more serious problems develop. Keeping steel tanks without protection under regular scrutiny is essential for ensuring their continued safety and functionality.

Other types of tanks like plastic, copper, and fiberglass typically have characteristics that either provide inherent protection from corrosion or do not pose the same level of risk associated with unprotected steel, allowing for less frequent inspections depending on specific regulations and guidelines.