If you’re weighing steel against fiberglass underground storage tanks for a new fuel system, a tank replacement, or a facility upgrade, the material you choose shapes almost everything else about the project — how much ongoing maintenance the tank needs, how well it holds up to today’s fuel blends, and how long it lasts before you’re looking at replacement again.
Quick answer: Fiberglass tanks resist corrosion by nature, since fiberglass-reinforced plastic (FRP) doesn’t rust. Steel tanks are strong and still widely used, but they need active corrosion protection — a coating, cathodic protection, or a composite design — to meet federal requirements. For most new fuel storage projects, that difference is why fiberglass has become the default choice, though steel and steel-fiberglass composite tanks still have a solid place in the industry.
Below, we’ll walk through how each type works, what the regulations actually require, and how to decide which one fits your project.
Steel vs. Fiberglass
| Fiberglass (FRP) | Steel | |
|---|---|---|
| Corrosion resistance | Built into the material — it doesn’t rust | Needs added protection (coating, cathodic protection, or composite shell) |
| Weight | Lighter, easier to handle on site | Heavier, needs larger equipment to set |
| Ongoing corrosion testing | Not required | Cathodic protection systems must be tested on a set schedule |
| Fuel compatibility | Naturally suited to ethanol and biodiesel blends | Compatible, but corrosion risk rises with some biofuels |
| Best fit | New installations, corrosive soils, low-maintenance goals | Specific design requirements, matching existing infrastructure |
What Are Fiberglass Underground Storage Tanks?
Fiberglass underground storage tanks are built from fiberglass-reinforced plastic (FRP) instead of metal. Because the tank wall itself isn’t metal, it simply can’t rust or corrode the way a steel tank can.
Federal regulations recognize this directly. Under 40 CFR 280.20, a new tank meets EPA’s corrosion protection standard automatically if it’s built and listed to UL 1316, the Underwriters Laboratories standard for glass-fiber-reinforced plastic tanks. No coating, no cathodic protection system, and no ongoing corrosion testing required.
That’s a big part of why fiberglass has become the standard material for new gas station and fuel storage installations over the past few decades. For more background on how these systems are classified and regulated in general, our guide on what counts as an underground storage tank and how the rules apply is a good starting point.
Tex Tanks builds these to spec as the UL 1316 double-wall fiberglass fuel tank, available in 8, 10, and 12-foot diameters up to 50,000 gallons, backed by a 30-year limited warranty.
What Are Steel Underground Storage Tanks?
Steel tanks are exactly what they sound like: a tank shell built from steel plate. They’ve been the traditional material for underground fuel storage for decades and are still manufactured and installed today, often as part of a composite design.
Because steel corrodes when it’s in contact with soil and moisture, the same EPA rule requires steel tanks to use one of a few recognized corrosion-protection methods: coated and cathodically protected steel, a Steel Tank Institute STI-P3 tank, a UL 58 tank, or a steel tank wrapped in an outer fiberglass or composite shell — the approach behind composite designs like Tex Tanks’ Elutron®, which pairs a steel primary tank with a corrosion-resistant fiberglass exterior.
In short, “steel” and “corrosion-proof” aren’t the same thing underground — steel needs a system layered on top of it to get there.
Corrosion Protection and Regulatory Compliance
This is where the two materials diverge the most.
Fiberglass: No cathodic protection system to install, monitor, or test. Corrosion resistance is part of the tank, not an add-on.
Steel: If a steel tank relies on cathodic protection, federal rules require that system to be tested within 6 months of installation and at least every 3 years after that. Tanks using impressed current systems also need a check every 60 days to confirm the equipment is running properly.
Both materials, regardless of which one you pick, are also subject to a newer requirement: tanks and piping installed or replaced after April 2016 must include secondary containment with interstitial monitoring, a change EPA finalized in 2015 specifically to catch leaks before they reach soil or groundwater.
Lifespan and Maintenance
Federal rules don’t assign a fixed number of years to a tank’s lifespan. Instead, the corrosion protection system has to be designed to prevent releases for as long as the tank is in service — which puts the real burden on the corrosion protection method itself.
For fiberglass, that mostly means the tank keeps performing with minimal upkeep. That’s why Tex Tanks backs its UL 1316 fiberglass tanks with a 30-year limited warranty.
For steel, staying protected means keeping up with the cathodic protection testing schedule above, plus periodic tank tightness testing and, for internally lined tanks, inspection of the lining. Miss a testing cycle, and you’re not just out of compliance — you’re also increasing the odds of an undetected corrosion problem.
Installation Process and Timeline
The broad steps look similar for either material:
- Site assessment and permitting — soil conditions, groundwater depth, and required setback distances all factor in.
- Excavation — sized to the tank plus required clearance and backfill material.
- Tank setting and anchoring — including anti-flotation measures if groundwater is a concern.
- Backfill, piping, and leak detection installation.
- Precommissioning testing — a tightness test before the tank goes into service.
- Regulatory notification — owners must notify their state or local implementing agency that the tank exists within 30 days of bringing it into use.
Fiberglass tanks are lighter than steel, which can simplify handling on tight sites, but it doesn’t fundamentally change this sequence. The real timeline driver on most projects is permitting and site prep, not the tank material itself.
Cost Considerations
We’re intentionally not throwing out a per-gallon price here — costs vary too much by tank size, site conditions, and local permitting to give a number that would hold up across projects. A few things are worth knowing directionally:
- Material and installation: Fiberglass tanks are lighter, which can reduce the equipment and labor needed to set them, partly offsetting any difference in upfront material cost.
- Ongoing compliance: Steel tanks relying on cathodic protection carry a recurring cost for the testing cycle described above. Fiberglass tanks don’t have that line item.
- Long-term risk: A corrosion-related failure — and the cleanup that can follow — is hard to predict but expensive to absorb, which is worth weighing alongside sticker price.
For a number specific to your site and tank size, requesting a quote is the fastest way to get an accurate estimate.
Risks and Failure Points
Steel tanks: The main long-term risk is corrosion, particularly if a cathodic protection system fails or slips out of its testing cycle unnoticed. That’s exactly why the testing intervals above exist — corrosion rarely announces itself until there’s a leak.
Fiberglass tanks: Corrosion isn’t a concern, but the material can be damaged if it’s mishandled during shipping or installed with improper bedding and backfill. Fiberglass tanks are also engineered for specific load ratings (H-20 for vehicle traffic, for example), so setting one under a driveway or parking area without matching the right load rating is a real risk to plan around.
When to Choose Steel vs. Fiberglass
- Choose fiberglass if: you want to avoid ongoing cathodic protection testing, you’re storing ethanol or biodiesel blends, your soil is known to be corrosive, or you’re installing a new tank from scratch.
- Choose steel (or a steel-fiberglass composite) if: a specific design requirement calls for it, you’re matching existing steel infrastructure, or your project calls for a composite design like Elutron®, which pairs a steel primary tank with a corrosion-resistant fiberglass shell.
Many projects land on fiberglass simply because it removes an entire category of ongoing compliance work. Tex Tanks manufactures both, including our double-wall fiberglass tank built to UL 1316 for straightforward, corrosion-free storage.
FAQ
Do fiberglass underground storage tanks need cathodic protection? No. Because FRP doesn’t corrode, tanks built and listed to UL 1316 meet EPA’s corrosion protection standard without cathodic protection or a coating system.
Can fiberglass tanks store ethanol and biodiesel blends? Yes. Fiberglass is naturally compatible with common fuel blends, including higher-ethanol fuels, without the corrosion concerns that can come up with steel and certain biofuels.
Do steel underground storage tanks still meet current regulations? Yes, as long as they’re built and protected to one of the recognized standards — STI-P3, UL 58, or a composite design — and the corrosion protection system is tested on schedule.
How long do underground storage tanks last? There’s no fixed number in the regulations. Tanks are required to prevent corrosion-related releases for their entire operational life, so warranty terms are the more practical benchmark — Tex Tanks backs its fiberglass tanks with a 30-year limited warranty.