What does API 653 require for storage tank inspections?

API 653 establishes the requirements for in-service inspection of welded above-ground storage tanks built to API 650 or equivalent standards. It requires external inspections at intervals not exceeding five years and internal inspections at intervals calculated from measured corrosion rates and remaining corrosion allowance (typically 10 to 20 years). The standard provides formulas for calculating minimum acceptable shell thickness based on the current product level and specific gravity, methods for evaluating floor condition, and criteria for determining whether repairs, alterations or reconstruction are required. All inspections must be performed by qualified inspectors and documented.

How often should a storage tank be inspected?

Monthly walk-around visual inspections should check the external shell, bunding, appurtenances and safety systems. Formal external inspections per API 653 should be performed at least every five years, including thickness measurements. Internal inspections require the tank to be taken out of service and cleaned, and are typically performed every 10 to 20 years based on the measured corrosion rate and remaining corrosion allowance. AS 1940 and state EPA licence conditions may impose additional requirements. After any event that may affect tank integrity, a targeted inspection should be performed immediately.

What is the relationship between API 653 and AS 1940?

API 653 is an international standard focused specifically on the in-service inspection, repair and alteration of welded above-ground storage tanks. AS 1940 is the Australian standard covering the broader topic of storage and handling of flammable and combustible liquids, including tank construction requirements, separation distances, bunding, venting, overfill prevention and maintenance obligations. In Australia, both standards are commonly applied together: API 653 provides the detailed technical framework for tank integrity inspection, while AS 1940 establishes the overall regulatory requirements for safe storage. State and territory dangerous goods legislation typically references AS 1940 as the compliance standard.

Why is bund inspection important for storage tanks?

Bunds (secondary containment walls) are the last line of defence against environmental contamination if a storage tank leaks or fails. AS 1940 requires bunds to contain at least 110 per cent of the volume of the largest tank within the bunded area. Cracks in bund walls, tree root penetration, rodent holes, deteriorated liners and open drain valves all compromise this containment capacity. If a bund is defective when a tank leak occurs, the product escapes to the environment, causing soil contamination, groundwater pollution and potentially waterway contamination. Bund inspections during tank inspections verify that the secondary containment will function when needed.

What thickness measurements are taken during a tank inspection?

Ultrasonic thickness measurements are taken on shell plates (typically at multiple locations on each shell course, with additional readings at areas of visible corrosion), the shell-to-bottom junction, floor plates (from inside during internal inspections or using magnetic floor scanners), and roof plates. These measurements are compared against previous surveys to calculate the corrosion rate in millimetres per year. The corrosion rate is then used with the API 653 formulas to determine the minimum acceptable thickness, maximum fill height, and the next inspection interval. Accurate thickness data is the foundation of the API 653 fitness-for-service assessment.

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Free storage tank inspection checklist (PDF-ready). Covers API 653 / AS 1940 shell condition, floor thickness, roof integrity, foundations and fittings.

Jarrod Milford

Commercial Director

Updated 3 May 2026

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What is a storage tank inspection checklist?

A storage tank inspection checklist is a structured document used to assess the condition and integrity of above-ground storage tanks (ASTs) used for petroleum products, chemicals, water and other bulk liquids. The checklist covers external shell condition including corrosion, dents, bulging and weld integrity, tank floor condition including underside corrosion and settlement, roof condition (fixed cone, floating roof or geodesic dome), foundation and ring wall assessment, appurtenances such as nozzles, manways, valves and vents, secondary containment (bund walls and liners), cathodic protection system checks where installed, tank gauging and overfill prevention systems, coating and paint condition, and documentation against API 653 (Tank Inspection, Repair, Alteration, and Reconstruction) and AS 1940 (The Storage and Handling of Flammable and Combustible Liquids) requirements.

Above-ground storage tanks are subject to corrosion from both the stored product (internal corrosion) and the external environment (atmospheric corrosion, soil-side corrosion on tank floors). Left unchecked, corrosion reduces shell and floor thickness to the point where the tank can no longer safely contain the stored product at its design level, risking leaks, structural failure and catastrophic product release. API 653 provides the internationally recognised framework for in-service inspection of welded storage tanks, including methods for calculating minimum acceptable shell thickness, maximum fill height, and inspection intervals based on measured corrosion rates. AS 1940 establishes the Australian requirements for storage and handling of flammable and combustible liquids, including tank construction, separation distances, bunding and maintenance obligations. Regular documented inspections using a standardised checklist are essential for maintaining compliance with both standards, protecting the environment from spills, ensuring worker safety and avoiding costly unplanned shutdowns for emergency repairs.

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Benefits of using this storage tank inspection checklist

Structural integrity: systematic inspection of shell, floor and roof components identifies corrosion, cracking and mechanical damage before they progress to leaks or catastrophic tank failure.
API 653 compliance: documented inspection records with shell thickness measurements and corrosion rate calculations demonstrate compliance with API 653 in-service inspection requirements.
AS 1940 compliance: verifying bunding, venting, overfill prevention and separation distances satisfies Australian regulatory requirements for flammable and combustible liquid storage.
Environmental protection: detecting corrosion, seal leaks and bund defects before product escapes the primary containment prevents soil contamination, groundwater pollution and costly remediation.
Optimised inspection intervals: API 653 allows inspection intervals to be extended based on documented corrosion rates, meaning thorough inspections with accurate thickness measurements can reduce the frequency and cost of future inspections.
Insurance and regulatory readiness: complete tank inspection records are required for insurance renewals, environmental licence conditions and regulatory audits conducted by state environment protection authorities.

Benefits of digitising forms in MapTrack

When you digitise storage tank checklists in MapTrack, you get:

Field users can easily scan a QR code to complete a form on mobile. Unlimited users.
Automatically get alerts when faults are identified.
Link every form digitally as a PDF to the relevant asset, location or person.
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Build conditional logic (show or hide questions based on answers).
Take pictures or attach photos. Not possible with a paper-based form.
Electronic signatures.
Edit forms later without reprinting.
Restrict permissions (who can view, complete or approve).
Build forms with AI (describe what you need and MapTrack suggests the form).
Trigger work orders automatically when a fault is logged during an inspection.
Track service intervals by hours, kilometres or calendar date in one place.
Attach supplier invoices and parts receipts to each maintenance record.

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What to include in a storage tank inspection checklist

This storage tank inspection checklist covers 9 key areas:

Tank identification: tank number, product stored, capacity, design code, construction date, last internal inspection date, shell material and design thickness.
External shell: visual inspection for corrosion, pitting, dents, bulging, weld defects, staining (indicating seepage), coating and paint condition, shell-to-bottom weld condition.
Tank floor: floor plate condition from external observation (settlement patterns, staining at shell-to-bottom junction), underside corrosion assessment from internal inspection or floor scan if tank is out of service.
Roof: fixed roof condition (corrosion, vent screens, pressure-vacuum valve operation), floating roof condition (seal condition, drainage, pontoon or deck plate integrity, guide pole and anti-rotation device).
Foundation: ring wall or slab condition, evidence of settlement (differential or uniform), erosion under the tank edge, drainage adequacy around the foundation.
Appurtenances: inspect all nozzles, manways, clean-out doors, drain valves, sampling points and instrumentation connections for leaks, corrosion and gasket condition.
Secondary containment: bund wall condition (cracks, vegetation penetration, drain valve closed and locked), bund capacity verification, liner condition if applicable.
Safety systems: tank gauging system operation, overfill prevention system test, pressure-vacuum relief valve condition, fire protection system condition (foam chambers, cooling ring if fitted).
Cathodic protection: check cathodic protection system readings if installed (impressed current or sacrificial anode), verify protection potential meets the criteria.

How to use this storage tank inspection checklist

Review the tank records including the design data sheet, previous inspection reports, thickness survey data and corrosion rate history. Identify any areas of concern from prior inspections.: Obtain the tank data sheet showing design code, shell and floor plate thicknesses, material specification, capacity and product service. Review the previous internal and external inspection reports and any thickness surveys. Calculate the elapsed time since the last internal inspection and compare against the API 653 interval. Identify areas flagged for monitoring in prior reports. Prepare the inspection checklist with the tank-specific data pre-populated.
Conduct an external visual inspection of the entire tank: walk around the full circumference inspecting the shell, shell-to-bottom junction, roof, foundation, appurtenances and coating condition.: Walk around the tank at ground level, inspecting the lower shell courses for corrosion, pitting, dents, bulging, staining (rust streaks or product staining indicating seepage) and coating deterioration. Inspect the shell-to-bottom weld area closely, as this is a common location for corrosion breakthrough. Check the foundation ring wall or slab for cracking, settlement or erosion. Inspect the roof from ground level (and from the roof if safe access is available) for corrosion, damaged vents, leaking seals and drainage condition. Inspect every nozzle, manway, valve and instrumentation connection for leaks and corrosion.
Inspect the secondary containment: check bund walls for cracks, deterioration and vegetation penetration. Verify the bund drain valve is closed and locked. Confirm bund capacity meets the requirement.: Walk the full perimeter of the bund (containment wall). Inspect for cracks, spalling, tree root penetration, rodent holes and any damage that could compromise containment capacity. Verify the bund drain valve is closed and padlocked to prevent accidental drainage of contained product to the environment. Confirm the bund capacity meets the AS 1940 requirement (typically 110 per cent of the largest tank within the bund). Check the bund floor for product staining or ponded water that may indicate a slow leak. Inspect bund liners where installed for tears, UV degradation or chemical damage.
Test safety systems: verify tank gauging, overfill prevention, pressure-vacuum relief valves and fire protection equipment are functional.: Check the tank level gauging system (float gauge, radar, or servo) for correct operation by comparing the indicated level to a manual tape gauge reading. Test the overfill prevention system by verifying the high-level alarm activates at the correct set point and triggers the correct response (alarm, pump shutdown). Inspect pressure-vacuum relief valves for corrosion, debris in screens and correct operation. Check fire protection equipment (foam chambers, cooling water ring, fixed monitors) for physical condition, valve operability and foam concentrate expiry date.
Perform ultrasonic thickness measurements on representative shell and floor locations if the inspection scope includes thickness surveying. Calculate corrosion rates and remaining life.: If the inspection scope includes thickness measurements, use a calibrated ultrasonic thickness gauge to measure shell plate thickness at representative locations on each shell course, focusing on areas of visible corrosion, the shell-to-bottom junction and windward faces exposed to weather. Measure floor plate thickness at accessible locations. Compare measurements against previous surveys to calculate the corrosion rate (mm per year). Use the API 653 formulas to determine the minimum acceptable thickness and the estimated remaining life of each component. These calculations determine the next inspection interval.
Document all findings with photographs, record thickness measurements, calculate corrosion rates and create corrective action items. Determine the next inspection due date per API 653.: Record all visual findings with descriptions, locations and severity ratings. Photograph all defects and areas of concern. Record thickness measurements in a tabular format with location identifiers. Calculate corrosion rates and remaining life for each measured area. Determine the next internal and external inspection due dates per API 653 interval calculations. Create corrective action items for all defects with assigned responsibility and due dates. Attach the completed checklist and all supporting documentation to the tank inspection file.

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How often should you complete this checklist?

API 653 establishes inspection intervals based on the measured corrosion rate and the remaining corrosion allowance of the tank. External inspections should be performed at least every five years. Internal inspections (which require the tank to be taken out of service, cleaned and confined space entry) are typically performed every 10 to 20 years, with the interval calculated based on the corrosion rate. However, AS 1940 and state or territory regulations may impose additional requirements.

Monthly walk-around visual inspections of the external shell, bunding, appurtenances and safety systems should be performed as part of the facility maintenance programme. After any event that may affect tank integrity (earthquake, significant storm, product overfill, fire, vehicle impact), a targeted inspection should be performed immediately. Floating roof tanks require more frequent seal inspections, particularly after heavy rainfall. In MapTrack, configure calendar-based maintenance triggers for monthly walk-around inspections and the API 653 calculated interval for comprehensive inspections.

Frequently asked questions

What does API 653 require for storage tank inspections?: API 653 establishes the requirements for in-service inspection of welded above-ground storage tanks built to API 650 or equivalent standards. It requires external inspections at intervals not exceeding five years and internal inspections at intervals calculated from measured corrosion rates and remaining corrosion allowance (typically 10 to 20 years). The standard provides formulas for calculating minimum acceptable shell thickness based on the current product level and specific gravity, methods for evaluating floor condition, and criteria for determining whether repairs, alterations or reconstruction are required. All inspections must be performed by qualified inspectors and documented.
How often should a storage tank be inspected?: Monthly walk-around visual inspections should check the external shell, bunding, appurtenances and safety systems. Formal external inspections per API 653 should be performed at least every five years, including thickness measurements. Internal inspections require the tank to be taken out of service and cleaned, and are typically performed every 10 to 20 years based on the measured corrosion rate and remaining corrosion allowance. AS 1940 and state EPA licence conditions may impose additional requirements. After any event that may affect tank integrity, a targeted inspection should be performed immediately.
What is the relationship between API 653 and AS 1940?: API 653 is an international standard focused specifically on the in-service inspection, repair and alteration of welded above-ground storage tanks. AS 1940 is the Australian standard covering the broader topic of storage and handling of flammable and combustible liquids, including tank construction requirements, separation distances, bunding, venting, overfill prevention and maintenance obligations. In Australia, both standards are commonly applied together: API 653 provides the detailed technical framework for tank integrity inspection, while AS 1940 establishes the overall regulatory requirements for safe storage. State and territory dangerous goods legislation typically references AS 1940 as the compliance standard.
Why is bund inspection important for storage tanks?: Bunds (secondary containment walls) are the last line of defence against environmental contamination if a storage tank leaks or fails. AS 1940 requires bunds to contain at least 110 per cent of the volume of the largest tank within the bunded area. Cracks in bund walls, tree root penetration, rodent holes, deteriorated liners and open drain valves all compromise this containment capacity. If a bund is defective when a tank leak occurs, the product escapes to the environment, causing soil contamination, groundwater pollution and potentially waterway contamination. Bund inspections during tank inspections verify that the secondary containment will function when needed.
What thickness measurements are taken during a tank inspection?: Ultrasonic thickness measurements are taken on shell plates (typically at multiple locations on each shell course, with additional readings at areas of visible corrosion), the shell-to-bottom junction, floor plates (from inside during internal inspections or using magnetic floor scanners), and roof plates. These measurements are compared against previous surveys to calculate the corrosion rate in millimetres per year. The corrosion rate is then used with the API 653 formulas to determine the minimum acceptable thickness, maximum fill height, and the next inspection interval. Accurate thickness data is the foundation of the API 653 fitness-for-service assessment.

Applicable regulatory standards

This template aligns with the following regulations and standards:

API 653 (Tank Inspection, Repair, Alteration, and Reconstruction)
AS 1940 (The Storage and Handling of Flammable and Combustible Liquids)
API 650 (Welded Tanks for Oil Storage - design standard)
State EPA licence conditions for bulk liquid storage

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