The API 653 Standard calls for both in-service and out-of-service inspections based on the characteristics of corrosion rates for tanks storing oil products. The Fertilizer Institute recommends the same types of inspections as required by API 653. However because fertilizer products are more corrosive than oil products, The Fertilizer Institute recommends slightly different inspection intervals for fertilizer ASTs compared to the API 653 intervals. The Fertilizer Institute outlines the following fertilizer tank inspections and corresponding frequencies:
- Routine Monthly External In-Service “Walk Around” Inspection
- Formal External In-Service Inspection (every 5 years)
- Formal Internal Out-of-Service Inspection
- Tanks with Bladder System (every 5 years)
- Tanks with Internal Coating (every 5 years)
- All Other Tanks (interval determined by corrosion rates but not to exceed 10 years)
Routine External Inspections are usually conducted by the owner’s personnel. API 653 requires and The Fertilizer Institute recommends these inspections occur monthly. Such inspections involve carefully looking over the external condition of the tank shell, foundation, and appurtenances to detect any “[e]vidence of leaks; shell distortions; signs of settlement; corrosion; and condition of the foundation, paint coatings, insulation systems, and appurtenances.” (API 653 18.104.22.168) Although Routine External Inspections are informal, it is important to keep inspection records, especially notations of any changes observed on the tank. These records can help detect a pattern over time that would indicate the start of a problem. Performing these inspections will save you money. They detect issues in their infancy when repairs are smaller, easier, and less expensive to remedy. Furthermore, the earlier the problem is caught, the less time the tank needs to be out of service to perform the repair. Diligence and organization are critical in maintaining a routine inspection schedule, but the effort is rewarded with lower repair and operation costs.
For formal inspections performed by a certified API 653 inspector, The Fertilizer Institute recommends that most tanks be inspected by the lesser of 5 years or a timeline based on the corrosion rates of the tank materials. Several states have fertilizer containment rules and regulations that also set requirements for frequency of tank inspection. These inspections are normally tied to obtaining renewal of tank operation licenses or permits. To minimize tanks being unnecessarily out of service, you should be aware of the state required frequency for internal inspections. Coordinating these inspections with when your operation schedule calls for the tank to be empty will prevent needless tank downtime. Formal Out-of-Service Inspections require a complete cleaning of the tank’s interior, which could range from a power wash of 2500 psi up to 4000 psi to sand blasting, depending on the amount of product or sludge on the tank floor and internal shell. Because the floor plates and lower tank shell courses have the highest rates of corrosion, the API certified inspector must be able to visually inspect these areas of the tank.
For a Formal Out-Of-Service Inspection, the basic components to the inspection should include:
- Internal and External Visual Inspection of All Welds, Plates, Appurtenances, and Coatings
- Ultrasonic Thickness (U.T.) Testing of Shell Courses, Floor, and Roof
- Vacuum Testing of All Floor Weld Seams, Unless Epoxy Coated
- Bottom-Side Corrosion Testing on Floor By Floor Scan or Destructive Coupon Testing
- Settlement Survey to Check for Planar Tilt and Floor Bulges/Depressions
- Inspection of Repairs to Verify Compliance with API Specifications
- Calculations for Safe and Maximum Fill Height
At the conclusion of such inspections, the inspector should provide you with an inspection report that includes:
- Executive Summary Describing the Activities Performed with Summary Conclusions
- Tank Data Page, Including Maximum and Recommended Fill Heights
- Detailed Discussion of Observations and Recommendations for Foundations, Shell, Roof, Floor, Appurtenances, and Ancillary Equipment
- Overall Recommendations on Repairs
- Engineering Calculations for Remaining Shell Life, Settlement Survey, and Remaining Thickness for Floor and Roof
- Log and Mapping of All U.T. Readings
- Pictures of Tank and Areas in Need of Repair or Monitoring
- Non-Destructive Examination and API-653 Certifications
By maintaining a regular tank inspection schedule for both routine and formal inspections, you will not only meet the state AST maintenance requirements, but you will also decrease your long term operating costs. Feel free to call Heartland Tank Services, Inc. to further discuss the benefits of regular tank inspection and whether you are meeting the applicable state inspection requirements.
Schedule your tank inspection today.