Aboveground tank inspection: STI SP001 monthly and annual checklists
If your site needs an SPCC plan, each aboveground tank has to be inspected or tested on a regular schedule following an industry standard. For shop-built tanks, that's usually STI SP001: a monthly and an annual visual inspection you can do yourself, plus a formal inspection by a certified inspector on larger tanks. (40 CFR 112.8(c)(6); EPA)
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What the SPCC rule requires
The rule says to "test or inspect each aboveground container for integrity on a regular schedule and whenever you make material repairs" (40 CFR 112.8(c)(6)). It also requires you to:
- Set the inspector qualifications, frequency, and type of testing following industry standards, based on the tank's size and design: shop-built, skid-mounted, elevated, double-walled, and so on
- Inspect the tank's supports and foundations
- Frequently inspect the outside of the tank for deterioration, leaks, or oil collecting in the dike
- Keep comparison records; records kept as usual business practice count
EPA points to STI SP001 as a standard that may be used for shop-built tanks. Its scope covers shop-fabricated tanks, small field-erected tanks, portable containers, and their secondary containment (EPA). Not sure you need a plan? See Do I need an SPCC plan?
Who inspects, and how often
Monthly and annual inspections are visual checks by the owner's inspector; no certification needed (STI SP001 checklist). Larger tanks also get a formal external inspection by a certified inspector. Wisconsin's state guidance lays out the SP001 intervals like this (Wisconsin DATCP):
| Tank capacity | Monthly | Annual | Formal inspection every 20 years |
|---|---|---|---|
| Up to 5,000 gallons | Yes | Yes | No |
| 5,001–50,000 gallons | Yes | Yes | Yes |
- Formal inspections are done by an STI SP001 certified inspector, or an API 653 inspector with the SP001 adjunct certification (Wisconsin DATCP).
- The schedule depends on the tank's category, not just its size. SP001 looks at whether the tank has spill control and a continuous way to detect a leak. If an inspection finds those compromised, the tank's category and inspection timetable should be re-evaluated (STI SP001 monthly checklist).
- Seasonal tanks: Wisconsin doesn't require monthly inspections while a seasonal tank is empty (Wisconsin DATCP).
Field note: I'm a certified inspector, and I do these inspections for customers.
The monthly checklist
STI's monthly checklist covers the tank, the equipment on it, and the containment. In summary (STI SP001 monthly checklist, 7th edition):
- Tank and piping: no visible leaks from the tank or piping connections; the level gauge is readable and working; no signs of leakage around the tank; no soil, vegetation, or water piled against the tank bottom
- Water: the primary tank is free of water (see water in your diesel tank)
- Double-wall tanks: interstitial monitoring works, and the space between the walls is free of liquid. If it's product, investigate a possible leak
- Overfill equipment: test buttons sound the horn or light; mechanical tests work; batteries replaced as needed
- Spill container: empty, no leaks, in good condition
- Containment: free of excess liquid, debris, cracks, and corrosion; dike drain valves closed and working (see secondary containment)
- Ladders and platforms secure
After severe weather such as snow, ice, or wind storms, or after maintenance like coating, inspect critical components such as normal and emergency vents and valves as soon as it's safe (STI SP001 monthly checklist).
The annual checklist
Once a year, a deeper look, in addition to the monthly checks (STI SP001 annual checklist, 7th edition):
- Foundation and supports: no settling or washout; pad free of cracks; supports sound; water drains away; grounding strap in good shape
- Shell: no coating failure, distortion, buckling, denting, or bulging; labels legible
- Piping: joints, manway covers, gaskets, and bolts tight; supports in good condition; leak detection on underground piping done and documented if required
- Vents: normal and emergency vents free of obstructions; emergency vent working and moving freely (see fuel tank vents)
- Gauges and alarms checked for operability
- Valves: anti-siphon, check, isolation, solenoid, fire, and shear valves free of leaks and damage (see anti-siphon valves)
- Filters and strainers clean; wiring sound; cathodic protection tested if the tank has it
Field note: On tank inspections I find all of it: water, leaking fittings, bad gauges, and containment problems.
STI's checklists are models; a locally developed checklist is acceptable if it's substantially equivalent (STI SP001 annual checklist). Download them free: monthly, annual.
Records and problems
- Keep completed checklists at least 36 months (STI SP001 annual checklist).
- Remove water promptly from the tank, containment, interstice, or spill container, check it for product, and dispose of it properly (STI SP001 annual checklist).
- Problems that affect tank or containment integrity need evaluation by an engineer experienced in tank design, a certified inspector, or the tank maker, who decides the fix (STI SP001 annual checklist).
- Changes that may affect your SPCC plan should be evaluated by a Professional Engineer (STI SP001 annual checklist).
FAQ
Do I need a certified inspector for monthly and annual checks?
No. STI says the periodic inspection is a visual inspection that doesn't require a Certified Inspector; it's done by the owner's inspector (STI SP001 monthly checklist). Certified inspectors do the formal external inspections on larger tanks.
Is SP001 required by law?
The SPCC rule requires inspections "in accordance with industry standards" (40 CFR 112.8(c)(6)), and EPA says SP001 may be used for shop-built tanks (EPA). Some states require it directly; Wisconsin does for shop-built metal tanks of 5,000 gallons or more, with farm and heating oil tanks excepted (Wisconsin DATCP).
What if I find fuel between the walls of a double-wall tank?
Treat it as a possible leak and investigate (STI SP001 monthly checklist). Wisconsin, for example, requires deliveries to stop right away and a vacuum or pressure test or closure within 10 business days (Wisconsin DATCP).
Sources
- 40 CFR 112.8, including (c)(6) integrity testing (Cornell LII)
- EPA: Tank inspections
- Steel Tank Institute: SP001 monthly inspection checklist, 7th edition (2024)
- Steel Tank Institute: SP001 annual inspection checklist, 7th edition (2024)
- Wisconsin DATCP: STI SP001 inspection requirements for aboveground storage tanks (2025)
This guide summarizes STI's checklists; it doesn't replace the SP001 standard. Your SPCC plan and state rules set what's required at your site.