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API 653 External Tank Inspections: What You Need to Know

The EPA requires that field-erected ASTs have formal external inspections. Here's what you can expect.


Regular formal external inspections are important for ensuring the safety and reliability of large above-ground storage tanks (ASTs). These in-service examinations are required in addition to routine monthly inspections (which can be conducted by the tank owner or operator) and formal internal inspections.

In this article, we’ll discuss the basics of formal external inspections, when they need to be conducted, and why you must have them performed on your ASTs.

What is an API 653 Formal External Inspection?

A formal external inspection is an assessment process that is carried out by a certified tank inspector in accordance with the API 653 standard. It focuses on the external condition of the tank and associated equipment (foundations, supports, secondary containment, etc.). The inspector will examine the tank for issues such as corrosion, structural damage, leaks, and other potential hazards.

What Type of Tank Requires an API 653 External Inspection?

The API 653 standard applies to above-ground storage tanks that are field-erected or field-built, made of a metal alloy, and have a diameter of 30 feet or more or a height of 50 feet or more. The capacity is typically greater than 75,000 gallons. These tanks are often used to store petroleum, chemicals, and other hazardous materials in industrial facilities such as refineries, chemical plants, and terminals.

How Often is a Formal External Inspection Required?

According to the API 653 standard, formal external inspections should be conducted at least once every five years for ASTs. However, more frequent inspections may be necessary based on factors such as the age of the tank, operating conditions, and the findings from previous inspections. Tank owners should consult with a qualified inspector to determine the appropriate frequency based on their specific circumstances.

Why are Formal External Inspections Important?

These assessments are critical for identifying potential issues that could compromise the safety and reliability of ASTs. By identifying issues early on, tank owners can address them promptly, preventing tank failures, spills, or other hazardous incidents.

The API 653 standard meets the EPA's Spill Prevention, Control, and Countermeasure (SPCC) rule, which mandates measures to prevent and respond to oil spills and other releases. By conducting these inspections, tank owners can ensure compliance with the SPCC rule.

What happens during the API 653 external inspection?

An external inspection does not require entry into the tank’s interior, so the tank can remain in service. A certified inspector will examine the external condition of the tank and its associated equipment. Here's what typically happens during the inspection:

  • Visual inspection: The inspector conducts a visual examination of the tank's exterior for any visible signs of damage or deterioration. The inspector will look at the roof, shell, nozzles and other appurtenances. If necessary, he may remove insulation to assess the condition of the base material and ensure that there are no hidden defects or damage that could compromise the integrity of the tank.

  • Non-destructive testing (NDT): Non-destructive testing methods are typically used and allow for the examination of the tank shell and roof without damaging or altering the tank's structural integrity. Common NDT methods used may include ultrasonic thickness testing (UTT) and magnetic particle testing (MPT). Each method is chosen based on the specific requirements of the inspection and the characteristics of the tank being inspected.
  • Documentation review: The inspector will review the tank's maintenance and inspection records to ensure that the tank is being properly maintained and inspected in accordance with industry standards.

  • Final report: Based on the findings of the examination, the inspector will prepare a final report that summarizes the inspection results and identifies any issues found. It will also include recommendations for repairs or maintenance, as well as a timeline for any necessary follow-up inspections. Tank owners must promptly address any issues identified to ensure the safety and reliability of their tanks.

In summary, formal external inspections are a crucial aspect of tank maintenance and safety. They help to identify potential issues before they lead to tank failures, spills, or other hazardous incidents. By having these examinations conducted, you can ensure the longevity and safety of your tanks, while protecting the environment and meeting the necessary regulatory requirements.


-- Genesis Environmental Solutions provides API 653 and STI SP001 storage tank inspections throughout Illinois, Iowa, Kansas, Missouri, Nebraska and Oklahoma. We provide AST services for all types of tanks, including fuel oil tanks. All work is carefully documented and compliant with federal, state and local regulations. Contact us today for more information.

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