above-ground storage tanks

Inspection Services

Internal vs. External Inspections of Above-Ground Storage Tanks: Making the Right Choice

Above Ground Storage Tanks (ASTs) are vital for industries like oil, gas, and petrochemicals. These tanks store large quantities of hazardous materials, making their integrity and safety critical. Regular API inspection services are essential to identify potential issues before they become serious problems. Inspections can be classified into two main categories: internal and external. 

In this article, we’ll the differences between these inspection methods and provide insights to help you make the right choice for your above ground storage tanks.

Why Inspections Are Essential

Before delving into the specifics of internal and external inspections, it’s crucial to understand why these inspections are essential. Proper inspection practices offer several benefits:

  • Safety: Ensuring the structural integrity of ASTs prevents leaks, spills, and catastrophic failures that can lead to environmental disasters and pose significant safety hazards.
  • Compliance: Regulatory bodies often mandate regular inspections to ensure environmental and safety regulations compliance.
  • Asset Protection: Early identification of corrosion, leaks, or other issues helps protect your valuable assets.
  • Cost Savings: Preventative maintenance, guided by inspections, is often more cost-effective than reactive repairs or replacements.
  • Environmental Stewardship: Properly maintained tanks reduce the risk of soil and water contamination, making inspections an environmentally responsible practice.

External Inspections

External inspections are typically the first line of defense in maintaining the integrity of your ASTs. These inspections involve visual assessments, which may be supplemented with various non-destructive testing methods, such as ultrasonic thickness measurements. Key aspects of external inspections include:

  • Visual Examination: Inspectors visually assess the external surfaces of the tank for signs of corrosion, cracks, or other damage.
  • Ultrasonic Testing: Ultrasonic equipment can measure the thickness of the tank’s steel walls to identify potential thinning due to corrosion.
  • Soil and Foundation Inspection: Soil settlement or uneven tank foundations can impact tank stability and safety. External inspections often include surrounding soil and foundations checks.
  • Cathodic Protection Assessment: External inspections can evaluate the performance of cathodic protection systems, which prevent corrosion.

Internal Inspections

Internal inspections are more invasive and require the tank to be taken out of service. These inspections are typically performed less frequently than external inspections but are crucial to assess the tank’s condition from the inside. Internal inspections include:

  • Confined Space Entry: Internal inspections involve entering the tank, which requires adherence to strict safety protocols due to the confined space nature.
  • Assessment of Corrosion: Internal inspections allow for a detailed assessment of corrosion and pitting on the tank’s interior surfaces.
  • Weld and Seam Inspections: All welds and seams are thoroughly checked for integrity.
  • Floor Inspection: The tank floor is a critical area for inspection, as it’s susceptible to settlement and corrosion. Internal inspections provide a detailed view of the floor condition.
  • Tank Roof and Shell Examination: The roof and shell’s interior surfaces are inspected for damage, corrosion, and structural integrity.

Selecting the Right Inspection

The choice between internal and external inspections depends on various factors:

Regulatory Requirements: Regulatory bodies may stipulate the type and frequency of inspections. Ensure you comply with API 653 tank inspection services requirements.

Tank Size and Use: Smaller tanks may be adequately assessed with external inspections, while larger tanks or those holding hazardous materials may require internal assessments.

Previous Inspection Results: The findings of previous inspections can guide your choice. Internal inspections may be necessary for a more detailed evaluation if external inspections have identified potential issues.

Budget and Downtime: Internal inspections are more time-consuming and costly, often requiring the tank to be taken out of service. Consider your budget and scheduling constraints.


In the world of above-ground storage tanks, inspections are your best defense against potential disasters. Whether you choose internal or external inspections, performing them regularly and diligently is key. The choice between internal and external inspections should be made based on factors like regulatory requirements, tank size and use, previous inspection findings, and your budget. By investing in proper inspections, you’re safeguarding your assets and the environment and ensuring the safety of your workforce and the communities in which you operate.…