Out-of-service tank inspections, also known as internal inspections, are complete official inspections of all accessible internal and external parts of tank surfaces, piping, and appurtenances undertaken by authorized inspectors. This sort of inspection necessitates the removal of tanks from service to undertake a complete inside evaluation. Tanks are inspected for structural integrity and serviceability. Tanks are checked for leaks, corrosion, and any other possible or probable fluid or product leakage that could harm the environment.

An authorized inspector conducts an in-service inspection, also known as an external inspection, which includes a visual inspection of the tank's outer surface. This inspection is typically carried out while the tank is in use or when the interior of the tank is not accessible or accessible for inspection. APEX inspects the tank systems for evidence of leaks, shell distortion, signs of settlement, corrosion, and the condition of coatings, insulation, and appurtenances during the in-service inspection.