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Understanding External STI SP001 Tank Inspections

Discover how certified inspectors help ensure that your aboveground tanks remain compliant and avoid problems.


For industrial safety and compliance, the importance of regular tank inspections cannot be overstated. Adhering to the Steel Tank Institute’s (STI) SP001 Standard for external tank inspections is not just a regulatory requirement, but a critical safety practice.

This article delves into what the STI SP001 Standard entails and why it's essential for your facility.

What is STI SP001?

The STI SP001 Standard was developed by the Steel Tank Institute for the inspection of above-ground storage tanks (ASTs). Instituted to address the need for a standardized safety protocol, this standard provides guidelines for regular inspections, ensuring tanks are maintained safely and in compliance with environmental regulations, including EPA mandates.

Who Needs STI SP001 Tank Inspections?

The STI SP001 Standard applies to aboveground storage tanks with dimensions up to 30 feet in diameter and 50 feet in height. Primarily, this standard is utilized for inspecting shop-fabricated tanks made of welded carbon or stainless steel with a maximum capacity of 75,000 gallons. However, it can also extend to field-erected tanks within these size limits, accommodating capacities up to 264,000 gallons. These ASTs can be either horizontal or vertical, and may feature single or double-walled designs. Typically, such tanks are employed in industrial settings for storing various liquids, including those that are flammable, combustible, or hazardous.

If your tank's manufacturer plate indicates compliance with the Underwriters Laboratory Standard (UL) or smaller tanks meeting American Petroleum Institute (API) standards, it's likely suitable for inspection under the STI SP001 standard. Look for a standard certification plate for further verification. Additionally, reviewing the owner's purchase records can assist in determining whether your tank is shop-fabricated or field-erected.

Why Are Formal Inspections Necessary?

Formal external inspections are an important component for meeting the EPA's Spill Prevention Control and Countermeasure (SPCC) regulation. These inspections help tank owners identify and address problems early on before they escalate into major repairs, failures, or accidents. This preventative approach saves money compared to emergency fixes later down the road. Trained inspectors using STI SP001 guidelines know what subtle signs of wear, corrosion, leaks, instability or other red flags to check thoroughly for during assessment.

It's important to note that formal internal STI SP001 inspections are an integral part of the external inspection process. This approach ensures a thorough and comprehensive evaluation of the tank's overall condition, as these inspections are designed to complement each other.

How Often Should Tanks Be Inspected as per STI SP001?

The frequency of inspections for tanks is determined by their size and category. For instance, Category 1 tanks equipped with spill control measures and a continuous release detection method (CRDM) do not require an internal inspection throughout their lifespan.

Conversely, Category 2 tanks that have spill control but lack a CRDM do need internal inspections. The intervals for these inspections vary based on the tank's size. Tanks in Category 2 with a capacity ranging from 5,001 to 30,000 gallons must undergo an internal inspection every 20 years. Tanks holding between 30,001 and 50,000 gallons require these inspections every 15 years.

Tanks classified under Category 3, which lack both spill control and CRDM, necessitate more frequent internal inspections. This increased frequency is due to heightened risk factors, such as the tank's bottom being in direct contact with the earth or the absence of secondary containment and leak detection systems.

Who is Qualified to Perform the Inspection?

Only certified professionals who meet the specific criteria set forth in the STI SP001 standard should conduct inspections. These individuals must possess the necessary certifications for confined space entry and be officially certified as inspectors by the Steel Tank Institute, having thorough knowledge and training in inspection procedures.

Components of an External STI SP001 Tank Inspection

A typical STI SP001 external tank inspection thoroughly examines numerous components to evaluate the overall integrity and safety compliance of the storage tank system. This includes assessing the thickness and condition of the tank. During an external inspection of a double walled tank, the primary tank cannot be assessed. Therefore, the external wall or secondary containment is assessed. The structural foundation and elements keeping the tank secured and stable require inspection to identify corrosion or weaknesses. Gauges and monitoring devices are checked to ensure proper operation and accuracy in tracking tank inventories. Overflow controls and valves must undergo testing to confirm adequate spill prevention performance.

From there, any insulation or cladding is inspected. Vents are examined to ensure adequate ventilation and pressure relief abilities remain intact. Likewise, piping connections and valves around the tank perimeter get inspected for problematic fittings or blockages, which could increase risk. Additional defensive elements like release prevention barriers and spill control systems also undergo review during the inspection process.

Again, the external inspection is typically done at the same time as the internal, so many inspection components will overlap.  

Preparing for an External Tank Inspection

Preparation is key to a successful inspection. Facilities should ensure access to all tank areas, maintain clear documentation of previous inspections, and rectify any known issues beforehand. This proactive approach can significantly streamline the inspection process.

Inspection Reports and Post Inspection

Post-inspection, you will receive a detailed report outlining the findings. This report includes information on the tank's condition, any areas of concern, and recommendations for maintenance or repairs. Be sure you understand these reports for taking appropriate follow-up actions. It’s imperative to address any recommendations promptly. Regular maintenance based on these findings can prevent potential hazards and extend the life of your tanks.

Choosing the Right Inspection Service

Selecting a qualified inspection service is vital. Look for services with certified inspectors who have a proven track record in your industry. Their expertise ensures your tanks are inspected thoroughly and in accordance with the latest standards.

The Bottom Line

Regular external STI SP001 tank inspections are a cornerstone of industrial safety and environmental compliance. By understanding and adhering to these standards, facilities can ensure the safe and efficient operation of their storage tanks.


-- 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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