Above Ground Storage Tank Inspections: The API-653

Big storage tanks can be a big problem if they aren’t maintained through regular cleanings and inspections. One of the most important inspections is the API-653. Tanks that fall under this program are field built and typically larger than 30 feet in diameter. The code for the program is written and maintained by the American Petroleum Institute (API-653), and it details all required inspections, inspection intervals, the acceptance of inspection results, and tank repairs. All of the records regarding inspection reports and repairs must be kept on file for the life of the tank. Ready to learn more about one of the most common above ground storage tank inspections?

Above Ground Storage Tank Inspections

The API-653

OFF-STREAM INSPECTION

An off-stream inspection (tank taken out of service) is required every ten years. The tank floor plates and (at least) the first shell course must be completely clean inside to facilitate the inspections of the tank’s internal components. The floor plates cannot have any product, water, or rust on them, because this would interfere with the MFL and visual inspection of the floor plates. The following inspections are typically performed during an off-stream inspection:

• Internal & External Visual Inspection (VT) performed by a certified API-653 inspector. API-653 has a visual checklist that inspectors are recommended to follow when performing this inspection. It includes the following components:
  • Secondary containment (i.e. dikes)
  • Foundation
  • Shell (internal and external), including out-of-roundness and bulge inspection
  • Floor plating (internal)
  • Nozzles (internal and external)
  • Roof (internal and external)
  • Columns for roof
  • Sumps and internal piping
  • Ancillary equipment (i.e. gauge levels)
• Ultrasonic Thickness Testing (UTT) Inspection performed by an ASNT Level II Certified UT inspector. The following components are usually examined through UTT:
  • Internal floor
  • Shell (internal or external)
  • Nozzles
  • Roof
• Vacuum Box Testing of Floor Plate Lap Welds & Chime Weld (Floor Plate to Shell Weld), which must be performed by trained personnel.
• Magnetic Flux Leakage (MFL) Inspection of floor plates. This inspection is used to locate bottom-side corrosion on the floor plates that cannot be visually inspected. It is backed up by UTT to determine the remaining thickness of the floor plates and the size of the corrosion area. Most tank leakage is caused by corrosion on the underside of floor plates, where the plates are in contact with the foundation.
• Settlement survey performed by trained personnel to determine if the tank is settling more to one side than another. This inspection is performed using survey transits or (more recently) laser measuring equipment.

Additional inspections may be required depending on the results of the initial inspections (i.e. Magnetic Particle (MT) on the welds).

A final report must be completed showing all inspection results and recommendations. This report should show the short- and long-term corrosion rates as well as a remaining life calculation. Finally, the report must be reviewed by a client-approved engineer to determine if the tank is suitable for continued service.

ON-STREAM INSPECTION

An on-stream inspection (tank not taken out of service) should be performed every five years. The following normal inspections are typically performed during on-stream inspections:

• Visual inspection performed by an API-653 certified inspector of the following components:
  • Secondary containment (i.e. dike)
  • External shell
  • External roof
  • External nozzles
• UTT inspection of the following components:
  • External shell
  • External roof
  • External nozzle

Additional inspections may be required depending on the results of the initial inspections (i.e. Magnetic Particle (MT) on the welds).

A final report must be completed showing all of the inspection results and recommendations. This report should show short- and long-term corrosion rates and a remaining life calculation. Finally, the report should be reviewed by a client-approved engineer to determine if the tank is suitable for continued service.

– – – – –

Is your storage tank due for any above ground storage tank inspections? Lean on EWI.

With more than 30 years of experience managing major environmental projects, you can feel comfortable trusting us with your storage tank needs. We provide API-653 Inspections as well as cleaning and confined space entry. Request a quote or give us a call today!