Home / Tank materials / Double-wall tanks
Tank Solutions – FuelDouble-wall tanks
How a tank inside a tank contains a leak and shows it, which of our underground and above-ground tanks are built this way, and when a single-wall tank is enough.
Get a price
Tell us roughly what you need. A sales engineer for your state replies within 2 business days.
Have drawings or a full spec? Use the detailed quote form, or call NSW +61 2 4964 8270 or WA +61 8 9434 1707.
What a double-wall tank is
A double-wall tank has a primary wall that holds the fuel and a secondary wall around it. The gap between the two is the interstitial space.
If the primary wall ever leaks, the outer wall holds the fuel in the interstitial space instead of letting it reach soil, drains or groundwater. Monitoring that space shows the leak.
We build double-wall tanks in fibreglass (FRP), in steel, and in Glasteel® II, which puts a steel tank inside an FRP outer wall.
Why choose double wall
A single-wall tank relies on one wall, plus a bund above ground. A double-wall tank carries its own containment, and lets you check it.
360° secondary containment
On double-wall FRP the outer wall completely surrounds the primary wall, so a leak is held in the tank instead of reaching groundwater.
Leaks you can see
Where the interstitial space is monitored, a leak in the primary wall shows up before product reaches the ground.
No civil bund above ground
On a self-bunded tank the outer steel wall is the bund. There is no concrete bund to build and no rainwater to catch and dispose of.
Relocatable
Self-bunded and Fireguard® 4-hour tanks are self-contained, so they can be moved as the site changes. A relocated self-bunded tank needs recertifying to keep the warranty.
Meets containment rules
AS 4897 calls for secondary containment on underground petroleum storage systems. Under AS 1940 a bund generally needs to hold at least 110% of the largest tank, and on a self-bunded tank the outer wall is that containment.
A path for older sites
If your site still runs an older single-wall steel tank, a double-wall replacement adds secondary containment and leak monitoring.
Double-wall construction across our range
The idea is the same in each tank. The materials, the monitoring and where the tank goes are what change.
| Tank | Installed | Inner wall | Outer wall | Leak monitoring |
|---|---|---|---|---|
| Double-wall FRP | Underground | FRP with integral ribs | FRP, full 360° | Truchek® hydrostatic |
| Glasteel® II | Underground | Welded mild steel | FRP, fully enclosing the steel | Factory-fitted vacuum gauge |
| Self-bunded | Above-ground | Steel | Steel wrap bund | See datasheet |
| Fireguard® 4-hour | Above-ground | Steel | Steel, with insulation between the walls | See datasheet |
| Flameshield® 2-hour | Above-ground | Steel | Steel | Interstitial monitoring |
Underground
- Double-wall FRP is fibreglass inside and out, from 2,000L to 150,000L, with 1 to 4 compartments. Fibreglass doesn’t rust, inside or out.
- Glasteel® II puts a welded steel tank inside an FRP outer wall, so the steel never touches soil or groundwater and needs no cathodic protection. See how Glasteel® II works.
- Both are installed by an accredited installer.
Above-ground
- Self-bunded tanks hold up to 110,000L of diesel or 55,000L of petrol per tank, with no concrete bund.
- Fireguard® adds insulation between the walls and is rated to the SwRI 4-hour fire test. See how fire-rated tanks work.
- Flameshield® is accredited to a 2-hour fire test and comes horizontal or vertical, cylindrical or rectangular.
Interstitial monitoring
Containment holds a leak. Monitoring tells you it happened. Our underground tanks use two methods.
Hydrostatic, on double-wall FRP
Truchek® keeps the interstitial space filled with brine, and a reservoir on top of the tank holds it at a set level. It gives continuous leak detection, lets the owner do a visual tank tightness test and meets EPA requirements. See how Truchek® works.
Vacuum, on Glasteel® II
The interstitial space is put under vacuum at the factory and fitted with a vacuum gauge. A break in the inner or outer wall causes a loss of vacuum, so a regular check of the gauge confirms the tank’s integrity.
When single wall is enough
Underground, where secondary containment isn’t needed, such as water or some AdBlue installs, a single-wall FRP tank is lighter, delivered complete and quick to install.
Above ground, a single-wall horizontal tank sits in a simple concrete bund. It suits fuel farms and sites with an existing bund, at up to 150,000L per tank, with tanks side by side and manifolded.
Standards
| AS 4897 | Underground petroleum storage systems, including secondary containment |
|---|---|
| AS 1940 | Storage and handling of flammable and combustible liquids, including bunding. See our AS 1940 guide |
| AS 1692 | Steel tanks: Glasteel® II, self-bunded and Flameshield® 2-hour |
| UL 1316 | Fibreglass underground tanks: double-wall FRP |
| UL 58 | Steel underground tanks: Glasteel® II |
| UL 142 | Steel above-ground tanks: Flameshield® 2-hour |
General information only, not legal advice. Your state EPA or regulator and your site engineer set what applies to your site.
Our double-wall tanks
Each product page has sizes, construction details, datasheets and a quote form.
Double-wall fibreglass fuel tanks
Double-wall FRP tank with 360-degree secondary containment.
Glasteel® II underground fuel tanks
A welded mild steel tank with an FRP outer layer that provides secondary containment, leak protection and corrosion resistance.
Self-bunded diesel & fuel tanks
Relocatable double-wall steel tank that needs no on-site bund.
Fireguard® 4-hour fire-rated tanks
Insulated double-wall steel tank rated to the SwRI 4-hour fire test.
Service station fuel tanks
Double-wall FRP underground fuel tanks for new service stations, upgrades and replacements, with full 360-degree secondary containment.
Flameshield® 2-hour fire-rated tanks
Double-wall steel tank with interstitial monitoring, 2-hour fire rated.
Calculators and quizzes on containment
Free to use, with a PDF report and a quote request filled in from your answers. All calculators and quizzes
Fuel leak cost
What one leak from a single-wall tank would cost your site, beside the price of a double-wall replacement.
Cost a leakIs your old single-wall tank a risk?
Which of the published reasons for replacing an underground fuel tank apply to yours.
Check your tankIs your fuel storage AS 1940-ready?
A self-check against the main topics of AS 1940: bunding, separation, construction, overfill and approvals.
Run the self-checkCommon questions
Can’t see yours? Call NSW +61 2 4964 8270 or WA +61 8 9434 1707.