Storage Tank Safety Starts with API 653

Aboveground storage tanks (ASTs) play a critical role in industries such as oil & gas, petrochemicals, power plants, terminals, refineries, and chemical processing. These tanks store millions of gallons of flammable, toxic, and valuable products. A single failure can cause catastrophic safety, environmental, and financial damage. To prevent such failures, the American Petroleum Institute (API) developed API 653, the globally recognized standard for the inspection, repair, alteration, and reconstruction of aboveground storage tanks. This standard ensures that tanks originally designed under API 650 and API 620 remain safe, reliable, and compliant throughout their operating life.

This article by Multisoft Systems provides a comprehensive explanation of API 653 tanks online training, including inspection requirements, testing methods, inspector qualifications, repair rules, and how the standard helps protect people, assets, and the environment.

What Is API 653?

API 653 is an internationally recognized standard developed by the American Petroleum Institute (API) for the inspection, repair, alteration, and reconstruction of aboveground storage tanks. It applies to tanks that were originally designed and built according to API 650 or API 620 and are used to store petroleum products, chemicals, water, and other industrial liquids. Over time, storage tanks are exposed to corrosion, environmental conditions, temperature changes, and operational stresses that can weaken their structure. API 653 provides a systematic approach to monitor these conditions and ensure that tanks remain safe, reliable, and fit for continued service throughout their operational life. The standard establishes clear requirements for routine, external, and internal inspections, defining how often they should be performed and what components must be evaluated, including the tank shell, bottom, roof, foundation, and appurtenances. It also sets engineering-based criteria for measuring corrosion, calculating remaining life, and determining when repairs or replacements are required.

In addition, API 653 specifies how repairs and alterations must be performed, including welding procedures, material selection, and post-repair testing such as hydrostatic testing when needed. Only certified API 653 inspectors are authorized to carry out official inspections and approve repairs, ensuring a high level of technical competence and consistency worldwide. By enforcing standardized inspection and maintenance practices, API 653 helps prevent leaks, structural failures, fires, and environmental contamination, while also extending the service life of tanks and reducing unplanned shutdowns. For tank owners and operators, compliance with API 653 is essential not only for regulatory and insurance requirements but also for protecting people, assets, and the environment.

Why API 653 Is So Important?

API 653 is important because aboveground storage tanks operate for decades while being exposed to corrosion, weather, foundation movement, and changing operating conditions. These factors slowly weaken the tank structure, often without visible warning, until leaks, ruptures, or even catastrophic failures occur. API 653 provides a structured, engineering-based system to detect damage early, evaluate risk, and correct problems before they become dangerous. By enforcing regular inspections, corrosion monitoring, and controlled repair practices, the standard ensures that tanks remain safe, environmentally secure, and fit for continued service. It also gives tank owners and regulators a common technical framework for determining whether a tank can continue operating or needs repair, modification, or retirement. In industries that store flammable or hazardous liquids, this is critical for preventing fires, explosions, and contamination that can result in loss of life, legal penalties, and massive financial losses. API 653 training therefore plays a central role in protecting people, assets, and the environment while extending the useful life of storage tanks.

Key reasons why API 653 matters:

• Prevents tank leaks and structural failures
• Reduces fire and explosion risks
• Protects soil and groundwater from contamination
• Ensures compliance with industry and regulatory requirements
• Extends the service life of storage tanks
• Reduces unplanned shutdowns and costly repairs
• Improves overall safety and reliability of tank operations

Who Must Follow API 653?

API 653 applies to:

• Oil refineries
• Bulk storage terminals
• Pipeline tank farms
• Power plants
• Chemical plants
• Biofuel storage facilities
• Ports and marine terminals

If you own, operate, or insure aboveground storage tanks, API 653 compliance is usually mandatory or contractually required.

What Is an API 653 Tank?

An API 653 tank is any aboveground storage tank that is maintained, inspected, repaired, or modified in accordance with the API 653 standard. These tanks were originally designed and constructed under API 650 or API 620 and are used to store petroleum products, chemicals, water, or other industrial liquids. Once a tank is placed into service, it is no longer governed only by its original design code; instead, its continued safety and integrity are managed through API 653. This means the tank is regularly inspected for corrosion, structural damage, settlement, and other forms of deterioration, and any required repairs or alterations are carried out using approved engineering methods and qualified personnel. An API 653 tank certification is therefore not a special type of tank by design, but a tank that is being properly managed throughout its operating life to ensure it remains safe, reliable, and compliant with industry standards.

Types of API 653 Inspections

API 653 defines three main inspection categories.

1. Routine In-Service Inspection

Routine in-service inspections are the most frequent type of API 653 inspection and are carried out while the tank remains in normal operation. These inspections are usually performed by trained operators or inspection personnel and focus on identifying visible signs of deterioration before they develop into serious problems. Inspectors look for product leaks, corrosion on the shell and roof, coating damage, foundation movement, abnormal vibrations, roof drain blockages, and signs of settlement or distortion. The objective is to detect early warning signs such as staining, wet spots, rust, or cracks that could indicate a loss of containment or weakening of the structure. Because these inspections are done regularly—often monthly or quarterly—they provide continuous monitoring of the tank’s condition and help ensure that small issues are corrected quickly. Routine in-service inspections are a critical first line of defense in preventing unexpected tank failures.

2. External Inspection

External inspections are more detailed evaluations conducted by an API 653–certified inspector while the tank is still in service. These inspections involve a thorough examination of the tank shell, roof, nozzles, welds, insulation (if present), and foundation. The inspector looks for corrosion, cracking, deformation, settlement, and any signs of mechanical or environmental damage. Measurements may be taken to assess shell thickness and identify corrosion rates, allowing the remaining life of the tank to be calculated. External inspections are typically required at least once every five years, although high-risk tanks may require more frequent evaluations. This type of inspection provides a deeper technical assessment of the tank’s overall condition and helps determine whether repairs or further testing are necessary to maintain safe operation.

3. Internal Inspection

Internal inspections are the most comprehensive type of API 653 inspection and require the tank to be taken out of service, emptied, cleaned, and made safe for entry. Once inside, certified inspectors closely examine the tank bottom, internal shell surfaces, welds, roof structure, and any internal components. Ultrasonic thickness measurements and visual inspections are used to detect corrosion, pitting, cracking, and other forms of deterioration that cannot be seen from the outside. Special attention is given to the tank bottom, as it is the most common location for corrosion-related failures. The data collected during an internal inspection is used to calculate corrosion rates, determine the remaining service life, and establish the next inspection interval. Although more costly and time-consuming, internal inspections are essential for ensuring the long-term integrity and safety of the tank.

API 653 Thickness Measurements

Corrosion is the main cause of tank failure. API 653 requires:

• Ultrasonic thickness testing (UT)
• Corrosion rate calculations
• Remaining life estimation

Inspectors measure:

• Shell plates
• Bottom plates
• Roof plates
• Nozzles

The data is used to calculate:

• Minimum required thickness
• Next inspection date
• Fitness-for-service

Tank Bottom Inspection

Tank bottom inspection is one of the most critical aspects of API 653 because the bottom plates are the area most vulnerable to corrosion and leaks. The tank bottom is in direct contact with water, soil, and corrosive contaminants, which can lead to thinning, pitting, and eventually through-wall failures if not properly monitored. API 653 requires regular evaluation of the tank bottom to determine its condition and remaining service life. This can be done through internal inspections when the tank is taken out of service, allowing inspectors to visually examine the plates and measure thickness using ultrasonic testing. In some cases, advanced non-destructive testing methods such as magnetic flux leakage or ultrasonic scanning are used to assess the bottom from outside the tank while it is still in operation. The results of tank bottom inspections are used to calculate corrosion rates and determine when repairs, replacements, or re-bottoming are required. Proper tank bottom inspection is essential for preventing leaks, protecting the environment, and ensuring the long-term integrity of the storage tank.

API 653 Repair and Alteration Rules

API 653 strictly controls how tanks can be repaired. It governs:

• Weld procedures
• Patch plates
• Nozzle replacements
• Shell plate replacement
• Bottom replacement

All welding must be performed by:

• Qualified welders
• Approved procedures
• Certified inspectors

Repairs must restore the tank to a condition equal to or better than the original design.

Reconstruction and Major Alterations

Reconstruction and major alterations under API 653 apply when a storage tank undergoes significant changes that affect its structural integrity or original design, such as increasing the tank height, changing the roof type, replacing large sections of shell or bottom plates, relocating the tank, or modifying its capacity. These activities go beyond routine repairs and must be treated with the same level of engineering control as the construction of a new tank. API 653 requires detailed engineering design, material traceability, qualified welding procedures, and strict inspection oversight for all reconstruction and major alteration work. In many cases, a hydrostatic test is also required after completion to verify the strength and leak-tightness of the tank. The goal is to ensure that, even after being altered or rebuilt, the tank meets safety and performance requirements equal to or better than its original condition. Properly managing reconstruction and major alterations helps extend tank life while maintaining safe and reliable operation.

API 653 vs API 650

Many people confuse the two.

API 650 builds the tank.
API 653 keeps it safe for decades.

Risk-Based Inspection (RBI)

Risk-Based Inspection (RBI) is an advanced approach allowed under API 653 that helps determine how often a storage tank should be inspected based on its actual risk of failure rather than using fixed time intervals alone. RBI evaluates both the likelihood of failure and the consequence of failure by analyzing factors such as corrosion rates, product type, operating temperature, historical inspection data, tank age, and environmental conditions. A tank storing highly flammable or toxic products in a sensitive location, for example, would be considered higher risk and therefore require more frequent inspections, while a low-risk tank in a controlled environment may qualify for extended inspection intervals. By focusing inspection resources on tanks with the greatest risk, RBI improves safety, reduces unnecessary downtime, and allows operators to manage assets more efficiently. When properly applied, RBI ensures that API 653 inspections remain technically justified, cost-effective, and aligned with real operating conditions while still maintaining a high level of safety and regulatory compliance.

Documentation and Recordkeeping

API 653 requires detailed records including:

• Thickness readings
• Corrosion rates
• Repair history
• Inspection reports
• Engineering calculations

These records must be kept for the entire life of the tank.

Benefits of API 653 Compliance

• Improves overall safety of aboveground storage tanks
• Reduces the risk of leaks, fires, and explosions
• Protects soil, groundwater, and the environment from contamination
• Extends the service life of storage tanks
• Ensures compliance with industry and regulatory requirements
• Lowers the likelihood of unplanned shutdowns
• Reduces costly emergency repairs and product losses
• Improves reliability and operational confidence
• Helps meet insurance and audit requirements
• Supports better maintenance planning and budgeting
• Enhances asset value and long-term performance
• Builds trust with regulators, customers, and stakeholders

Conclusion

API 653 is the backbone of storage tank integrity management. It ensures that aboveground storage tanks remain safe, reliable, and compliant from the day they are built until the day they are retired. By combining inspection, engineering, corrosion science, and strict repair rules, API 653 protects people, assets, and the environment while maximizing tank service life.

If you own or operate storage tanks, understanding and applying API 653 is not optional—it is essential. Enroll in Multisoft Systems now!