Overview of STI SP001 vs. API 653 Tank Inspections
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This document provides an overview of the STI SP001 and API 653 tank inspection standards. STI SP001 applies to shop-built and smaller field-erected tanks, while API 653 applies to larger field-erected tanks. Both standards provide regulatory compliance for tank integrity inspections and reduce inspection frequency for tanks with release prevention barriers. STI SP001 inspections typically cost $700-$2,000 while API 653 inspections are more at $3,500-$5,500 due to applying to larger tanks. The document compares the two standards and provides details on their inspection components, categories, frequencies, and definitions.
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Overview of STI SP001 vs. API 653 Tank Inspections
- 1. 1 Overview of STI SP001 vs. API 653 Tank Inspections Gary Diewald P.E., STI Inspector #AST-1755 Antea Group September 10, 2019
- 2. 2 Overview of STI versus API Tank Inspections So you have Aboveground Storage Tanks (ASTs) at your facility. Which tank inspection protocol applies? • Steel Tank Institute STI SP001 OR • American Petroleum Institute API 653 ?
- 3. 3 Why Inspect ASTs? Regulatory Drivers EPA – SPCC (40 CFR 112. 8(c)(6)): • Test or inspect each aboveground container for integrity • Accordance with industry standards State and Local Regulations • Health and Environmental Protection Agencies • Building Codes • Fire Codes Best Practices • Reduce Risk/Costs (Spills, Clean up , Product loss)
- 4. 4 STI SP001 Standard (6th Edition, January 2018) Inspection and evaluation criteria required to determine suitability for continued service. Inspect to identify the condition of and changes to AST. • ASTs storing flammable and combustible liquids at atmospheric pressure • Can be applied to AST storing other liquids following proper evaluation Applicability • Shop-Built/Fabricated AST – Horizontal or Vertical, Single or Double Walled • Steel Diked AST – Open or Closed • Concrete Exterior AST • Field-Erected AST – Limited Size • Portable Containers – Drums, Totes (IBCs) – Plastic, Steel, Stainless
- 5. 5 STI SPOO1 Inspection Components Primary tank – thickness determination Secondary tank (if present) Tank foundation, supports and anchors Tank gauges and alarms Overfill valves and alarms Insulation covering Tank appurtenances Normal vents Emergency vents Release prevention barriers Spill control systems Tank valves and connections (piping) Example Periodic Inspection Checklist provided in Standard
- 6. 6 Shop-Fabricated AST Welded carbon or stainless steel AST fabricated in manufacturing facility • Capacity of 75,000 gallons or less • Constructed in accordance with UL 142, UL 2085, UL 2080, UL 2244, UL 2245, SwRI 93-01, SwRI 97-04, or STI (AST F911, AST F921) standards How to determine if you have a Shop- Fabricated AST? • Manufacturer Tank Plate • Standard Certification Plate • Capacity • Lifting Lugs • Tank Specifications • Owner Purchase Records
- 7. 7 Evidence of Shop Fabrication
- 8. 8 Steel Diked ASTs Integral steel secondary containment dike • Open or Closed
- 9. 9 Concrete Exterior ASTs UL 2085 • Steel Tank • Integral containment liner • Concrete Shell
- 10. 10 Smaller Field-Erected ASTs Limited in size: • Greater than 75,000 gallons • 50 feet maximum height • 30 feet maximum diameter • Equates to ~264,000 gallons • Shell thickness less than ½ inch and bottom thickness equal to ¼ inch AST Type and Capacity Category 1 Category 2 Category 3 Field-erected AST P, E(5), I (10) P, E&L (5), I (10) P, E&L (5), I (10)
- 11. 11 STI SPOO1 Inspection Frequency Risk Based Hierarchy Inspection Matrix AST Type and Size (Us Gallons) Category 1 Category 2 Category 3 Shop / Fabricated ASTs 0 – 1100 gal. P P P, E & L (10) 1101 – 5000 gal. P P, E & L (10) [P, E & L (5), I (10)] OR [P, L (2), E (5)] 5001 – 30,000 gal. P, E (20) [P, E (10), I (20)] OR [P, E (5), L (10)] [P, E & L (5), I (10)] OR [P, L (1), E (5)] 30,001 – 75,000 gal. P, E (20) P, E & L (5), I (15) [P, E & L (5), I (10)] Portable Containers P P P** R I S K R I S K
- 12. 12 STI SPOO1 Definitions Continuous Release Detection Method (CRDM) • Inherent design - passive • Liquid releases are detected visually • Release prevention barrier (RPB) • Secondary containment AST, including double-wall AST or double-bottom AST • Elevated AST, with or without release prevention barrier Release Prevention Barrier (RPB) • Liquid containment barrier under the AST • Steel (as in steel double bottom tanks) • Concrete foundation pad or dike floor • Elastomeric liners or other suitable materials Spill Control = Secondary Containment • Dike (concrete, earth, steel) • Double-walled • Remote Impoundment Overfill Prevention Procedures or devices used to prevent liquid in ASTs from running over or spilling out of the AST during the filling process
- 13. 13 AST Category Chart (from STI SP001 Table A2.2): Tank Configuration Tank has Spill Control? Tank has CRDM? AST Category Single wall vertical AST in contact with ground and no spill control No No 3 Single wall vertical AST in contact with ground in an earthen dike Yes No 2 Single wall vertical AST in concrete dike with concrete floor. Concrete floor extends under tank completely Yes Yes 1 Single wall vertical AST in dike with elastomeric liner. Liner extends under tank completely Yes Yes 1 Single wall vertical AST installed on gravel and no spill control No No 3 Single wall vertical AST installed on gravel in an earthen dike Yes No 2 Elevated AST with spill control Yes Yes 1 Elevated AST without spill control No Yes 3 AST with double-bottom and spill control Yes Yes 1 Double-wall AST with overfill prevention Yes Yes 1 Double-wall AST without overfill prevention No Yes 3 Concrete exterior AST with overfill prevention Yes Yes 1 Concrete exterior AST without overfill prevention No Yes 3
- 14. 14 STI SPOO1 Inspection Types P- Periodic AST Inspection – owner’s inspector knowledgeable in the tank operation – Monthly and Annual frequency E- Formal External Inspection (FEI) by certified STI inspector I-Formal Internal Inspection (FII) by certified STI inspector L-Leak test by owner or owner’s designee (#) indicates maximum inspection interval in years. For example, E(20) indicates formal external inspection every 20 years
- 15. 15 STI SPOO1 Inspection Frequency Risk Based Hierarchy Inspection Matrix AST Type and Size (Us Gallons) Category 1 Category 2 Category 3 Shop / Fabricated ASTs 0 – 1100 gal. P P P, E & L (10) 1101 – 5000 gal. P P, E & L (10) [P, E & L (5), I (10)] OR [P, L (2), E (5)] 5001 – 30,000 gal. P, E (20) [P, E (10), I (20)] OR [P, E (5), L (10)] [P, E & L (5), I (10)] OR [P, L (1), E (5)] 30,001 – 75,000 gal. P, E (20) P, E & L (5), I (15) [P, E & L (5), I (10)] Portable Containers P P P** R I S K R I S K
- 16. 16 API 653 Standard (5th Edition, November 2014) Steel storage tanks built to API 650 or older API 12C. Minimum requirements for maintaining the integrity of tanks after placed in service Addresses inspection, repair, alteration, relocation, and reconstruction of ASTs. • Assess suitability for continued use • Assess Brittle Fracture Risk • Recognizes fitness-for-service assessment concepts
- 17. 17 API 653 Inspection Components • Tank Foundation • Bottom – flaw and thickness detection • Shell – flaw and thickness detection • Brittle Fracture/Failure Assessment • Structure • Roof • Attached Appurtenances • Nozzles to face of 1st flange, 1st threaded joint, or 1st welding-end connection Example Inspection Checklist provided in Standard
- 18. 18 Field-Erected AST Applicability • Capacity greater than 75,000 gallons • Size greater than 50 feet in height and 30 feet in diameter • Welded or Riveted How to determine if you have a Field-Erected AST? • Manufacturer Tank Plate • Standard Certification Plate • Capacity • No Lifting Lugs • Rounded Stairway • Tank Specifications • Owner Purchase Records
- 19. 19 API 653 Inspection Frequency Routine In-Service Inspections • Owner personnel knowledgeable in tank system and operation • Monthly External Inspections • Authorized API 653 Inspector • In service • Ultrasonic thickness inspection • Every 5 years Internal Inspections • Authorized API 653 Inspector • Out of service • Assessment of tank bottom condition • Calculated according the API 653, Section 6.4.2 (corrosion rate determination)
- 20. 20 API 653 Inspection Frequency Initial Internal Inspections Intervals • 10 years from date of initial service, or • According to Risk-Based Inspection (RBI) Assessment criteria Tank Safeguard Max. Initial Interval i) Original nominal bottom thickness 5/16 in. or greater 12 years ii) Cathodic protection of the soil-side of the primary tank bottom per Note 1 12 years iii) Thin-film lining of the product-side of the tank bottom per Note 2 12 years iv) Fiberglass-reinforced lining of the product-side of the tank bottom per Note 2 13 years v) Cathodic protection plus thin-film lining 14 years vi) Cathodic protection plus fiberglass-reinforced lining 15 years vii) Release prevention barrier per Note 3 (when similar service assessment performed) 20 years viii) Release prevention barrier per Note 3 (when RBI assessment performed) 25 years NOTE 1 For the purposes of 6.4.2.1, effective cathodic protection of the soil-side of the primary tank bottom means a system installed and maintained in accordance with API 651. NOTE 2 For purposes of 6.4.2.1, lining of the product-side of the tank bottom means a lining installed, maintained and inspected in accordance with API 652. NOTE 3 For purposes of 6.4.2.1, a release prevention barrier means an under-bottom leak detection and containment system designed in accordance with API 650, Appendix I.
- 21. 21 API 653 Inspection Frequency Subsequent Internal Inspection Intervals • Determined in accordance with corrosion rate procedure calculations • RBI procedures • Not to exceed maximum intervals Procedure Used Max. Interval i) Corrosion rate procedures in 6.4.2.3 20 years ii) RBI assessment per 6.4.2.4 25 years iii) RBI assessment per 6.4.2.4 and a release prevention barrier per Note 30 years NOTE For purposes of 6.4.2.2, a release prevention barrier means an under-bottom leak detection and containment system designed in accordance with API 650, Appendix I.
- 22. 22 Comparison STI SP001 vs. API 653 Regulatory Compliance • Both Standards provide compliance for tank integrity inspection for SPCC and local environmental regulations Risk Based Benefit • Both Standards provide reduction in inspection frequency for use of release prevention barrier for reduced spill risk Applicability • STI SP001 – All configurations of shop-built tanks and smaller field-erected tanks. • API 653 - Field-erected tanks (welded or riveted). Also includes guidance for repair, alteration, relocation. Cost • STI SP001 - $700 to $2,000 depending upon tank configuration, insulation, economy of scale • API 653 - $3,500 to $5,500 depending upon tank configuration and economy of scale
- 23. 23 Overview of STI SP001 vs. API 653 Questions? Gary Diewald, P.E. Gary.Diewald@anteagroup.com