STI-P3® Cathodically Protected Underground Tanks
Engineered and fabricated in Suwanee, GA by Metal Products Company. STI-P3® underground steel storage tanks combine heavy-gauge UL 58 structural strength with triple-layer UL 1746 Part 1 corrosion defense—protecting retail fuel stations, municipal fleets, and industrial depots across the United States.
STI-P3® Engineering & UL 1746 Specifications
Every STI-P3® tank manufactured by Metal Products Company undergoes Holiday dielectric spark testing, air-soap seam testing, and STI quality certification prior to shipment.
Triple Corrosion Protection (P3)
- 1. Dielectric Coating: High-build polyurethane or coal-tar epoxy shields the grit-blasted steel shell from soil moisture.
- 2. Electrical Isolation: Nylon bushings on all NPT bungs and flanges block stray electrical currents from connected piping.
- 3. Sacrificial Anodes: Weld-attached zinc or magnesium anodes provide continuous galvanic cathodic protection.
Compare with ACT-100® Composite USTs
Installing in high-corrosivity or stray-current soil? Explore our ACT-100® & ACT-100-U® Composite Underground Tanks.
Call Engineering Sales: (770) 945-8383Frequently Asked Questions: STI-P3® Underground Tanks
What are the three corrosion protection mechanisms in an STI-P3® tank?
The 'P3' in STI-P3® stands for three integrated layers of subsurface corrosion defense: (1) a high-build dielectric exterior coating applied over commercial grit-blasted steel, (2) factory-installed nylon bushings that electrically isolate the tank from connected steel piping so stray currents cannot enter, and (3) weld-attached zinc or magnesium sacrificial anodes that provide continuous galvanic cathodic protection.
How is an STI-P3® tank monitored for compliance after burial?
Double-wall STI-P3® tanks include a dedicated interstitial monitoring riser port between the inner and outer steel shells, enabling continuous electronic liquid sensing, vacuum monitoring, or hydrostatic brine monitoring under EPA 40 CFR Part 280. Cathodic potential can also be verified at grade using a standard reference electrode.
When should I choose STI-P3® vs. ACT-100® composite underground tanks?
STI-P3® is the industry benchmark for standard commercial and retail fueling soils where verifiable galvanic cathodic protection is desired at a highly competitive price point. ACT-100® (100-mil FRP composite cladding) is preferred in high stray-current zones (such as near electric rail lines) or corrosive soils where owners want to eliminate periodic cathodic anode testing.
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