American Petroleum Institute (API) Standard 653 is the Industry Standard most commonly used for tank inspection repair, alteration, and reconstruction. Out-of-service tank inspections, sometimes described as internal inspections, are formal complete inspections that are conducted by authorized inspectors on all accessible internal and external areas of tank surfaces, piping, and appurtenances. This type of inspection requires tanks to be out of service so that a thorough internal evaluation can be conducted. Tanks are evaluated for integrity and suitability for service. Tanks are inspected for leaks, corrosion, and any other possible or potential leakage of fluids or product that might cause environmental damage.
Areas inspected include tank shells, roofs, containments, piping, and appurtenances using various methods of NDE. Using ultrasonic thickness evaluations, the rate of uniform general corrosion is determined. Tank bottom plates are inspected over their entire surface to assess the presence of any type of significant underside corrosion. Most common method used by InterSpec for evaluating tank bottoms is Magnetic Flux Leakage (MFL). The MFL device allows our inspectors to quickly and accurately detect any problem areas. Another method used by InterSpec inspectors is Low Frequency Electromagnetic Technique (LFET) scanner, which is a nondestructive evaluation instrument that is designed to quickly and accurately inspect tank floors in ferrous above ground storage tanks. Welds may be inspected using vacuum box testing, magnetic partical testing, and penetrant testing. Penetrant testing may also be used to find holes and cracking in metal plates. This inspection includes all facets of the in-service tank inspection.
The reason for tank inspection in accordance with API 653 is generally to determine the mechanical integrity of the tank and its rate of corrosion. After reviewing the inspection results, steps are taken to reduce the potential for failure and release of stored product. Maintaining a safe operating condition, along with determining any deterioration, is another reason for tank inspection.