Atmospheric storage tanks (Fuel, chemical and process fluids) can lose their integrity over time due to corrosion, settlement and welding fatigue. Regular inspection prevents the risks of leaks, environmental pollution, fire and structural collapse. AES Innovation provides atmospheric tank inspections. with our qualified engineers and certified NDT personnel It operates according to the relevant standards.
Short answer: Tank inspection includes both external (in-service) visual inspection and internal (out-of-service) inspection of the base, shell, and roof. Shell wall thickness (UT), welds (NDT), base plate, and safety equipment are evaluated. The aim is to detect leakage and structural integrity risks early.
What is Atmospheric Tank Inspection?
Periodic integrity inspection of atmospheric (non-pressurized) storage tanks involves evaluating the base plate, shell, roof, fittings, and safety equipment for corrosion, deformation, and leakage. This is performed in fuel terminals, chemical and food plants, and water/process storage applications.
Why is it critical?
- Leakage and the environment: Soil corrosion leads to soil and groundwater contamination.
- Fire risk: Leaks in flammable product tanks pose a serious fire hazard.
- Structural integrity: Trunk thinning and sitting increase the risk of collapse.
- Legal and insurance: Periodic inspections are required in legal and insurance processes.
Scope of Inspection
- External (in-service) inspection: Hull, roof, stairs, connections and foundation
- Base plate: Corrosion and leak assessment
- Carcass thickness: Ultrasonic (UT) thickness measurement
- Welding inspection: Non-destructive testing (NDT) with stitch check
- Roof and ventilation: Breathing valves and safety equipment
- Grounding and lightning protection: Electrical safety check
Technical Criteria and Inspection Intervals (API 653)
| Inspection / criteria | Maximum range or limit | API 653 |
|---|---|---|
| External visual inspection (by an authorized inspector) | 5 years (or RCA/4N — lesser) | Article 6.3.2 |
| Body ultrasonic (UT) thickness measurement | 5 years if corrosion rate is unknown; 15 years if known (or RCA/2N) | Article 6.3.3 |
| Initial internal examination | A maximum of 10 years | Article 6.4.2.1 |
| Subsequent internal examination | Maximum 20 years (risk/corrosion based, RBI) | Article 6.4.2 |
| Base plate minimum thickness (to be determined upon subsequent inspection) | 2.5 mm (no leak detection) / 1.3 mm (detection or liner present) | Table 4.4 |
Values are summarized based on API 653; final inspection intervals and acceptance criteria are determined based on tank service, corrosion rate, and risk assessment (RBI).
AES Innovation Inspection Process
- Planning: The tank's history, product, and inspection type (external/internal) are determined.
- Visual examination: The fuselage, roof, base perimeter, and attachments are inspected.
- Thickness and NDT: UT thickness measurement and weld NDT are performed.
- Evaluation: Corrosion rate and remaining lifespan are estimated.
- Reporting: Nonconformity, repair recommendation, and subsequent inspection period.
Commonly Encountered Nonconformities
- Base plate and body bottom row corrosion
- Roof and breather valve malfunctions
- Basically, sitting and body deformation.
- Secondary storage (bund) insufficiency
- Interruption in grounding continuity.
- Cracks and discontinuities in weld seams.
Relevant Standards
Atmospheric tank inspections; API 653 (tank inspection, repair and reassessment), API 650 / EN 14015 (tank design and manufacturing) and risk-based inspection EN 16991 It is carried out based on this principle. (Tank inspections are outside the scope of AES's TÜRKAK accreditation and are carried out by authorized engineers and certified NDT personnel.)
Frequently Asked Questions
What is the difference between external and internal examination?
External (in-service) inspection is performed while the tank is running; internal (out-of-service) inspection covers the base and interior surfaces after the tank has been emptied and cleaned.
How often should the tank be inspected?
The interval is determined based on the product, corrosion rate, and previous inspection results. External inspections are scheduled more frequently, while internal inspections are scheduled at longer intervals.
Which NDT methods are used in tank inspections?
Ultrasonic (UT) thickness measurement is used for the fuselage, magnetic leakage flux (MFL) for the base, and UT/MT/PT methods for welds.
Frequently Asked Questions
What are the inspection intervals for atmospheric storage tanks?
According to API 653, external visual inspection should be performed at least every 5 years; ultrasonic thickness measurement should generally be done every 5-15 years depending on equipment availability; the first internal inspection should be done at least every 10 years, and subsequent internal inspections should be carried out at least every 20 years using risk-based assessment (RBI).
What are the acceptance criteria for tank bottom plates?
API 653 defines acceptance criteria for the minimum thickness remaining in the base and shell plate; repair or replacement is required if the measured thickness is below the acceptance limit. The criteria vary depending on the tank's dimensions and service conditions.
How is the tank inspection interval determined?
Ranges are determined within the upper limits of API 653, based on the tank's corrosion rate and risk-based inspection (RBI) assessment.
Who conducts tank inspections?
The inspection is carried out independently by our qualified engineers.
Free: Atmospheric Tank Inspection Checklist
Download the API 653-based inspection intervals + 6-item practical checklist as a PDF.