Water authorities in the EU and UK write “GLS tank to EN ISO 28765” into their specifications. The same product is called GFS in North America and “enamel bolted tank” in many catalogs. The name changes; the compliance paperwork does not. If your tank must carry WRAS, KIWA or DWI Regulation 31 approval to win the job, the coating is only half the story.
This page explains what a glass lined steel (GLS) tank actually is, which approvals unlock a tender, and the line you should put in every RFQ so you receive bolted storage panels built to a real standard rather than a look-alike vessel.
What a glass lined steel tank is
A glass lined steel tank is assembled from factory-enamelled steel panels. Each panel carries a vitreous enamel layer fired at 820–930°C, so the glass bonds to the steel at the molecular level. The outcome is a surface that is inert, impermeable and smooth on both faces of the plate.
In EN ISO 28765 the product is named “vitreous enamelled bolted steel tank for the storage or treatment of water or municipal and industrial effluents.” In AWWA D103 the same panel is called “glass-fused-to-steel.” One product, two standard families. The firing, the coating thickness and the holiday test are identical; only the design code and the approvals trail differ.
Standards and approvals that clear a tender
The coating performs in the field. The certificates clear the desk. These are the documents a European or UK buyer is normally asked to show:
- EN ISO 28765 — the European design and finish standard for bolted enamel tanks in water and wastewater. It covers structural design and coating quality together.
- AWWA D103 — the North American factory-coated bolted steel tank standard, used when the spec originates from a US-style EPC.
- NSF/ANSI 61 — confirms the coating is safe for potable water contact, with nothing leaching into the stored liquid.
- WRAS — UK approval for products in contact with the public water supply.
- KIWA — Dutch and Benelux certification, frequently required in the Netherlands and Belgium.
- DWI Regulation 31 — England and Wales approval of products used in public water supply.
- BS 6920 — the test for non-metallic materials in contact with water: taste, odour, growth and metallic-ion release.
- NFPA 22 — the fire-protection tank standard, applied when the GLS tank serves as a fire-water reserve.
Ask for the certificate number and the exact model scope. “ISO 28765 compliant” printed on a brochure is not the same as a third-party audited listing. A supplier who can show WRAS or KIWA against a specific panel model clears the tender faster than one who quotes a generic line.
Why specifiers choose GLS over concrete and welded steel
The numbers below are not marketing claims. They describe what a buyer faces over a 30-year asset life.
| Factor | Glass lined steel (GLS) | Reinforced concrete | Welded carbon steel |
|---|---|---|---|
| Behaviour in H₂S and acidic effluent | Inert, unaffected | Crown corrosion risk | Needs coating, recoat cycle |
| Potable approval route | NSF 61, WRAS, BS 6920 | Depends on internal liner | Epoxy lining plus re-certification |
| Build time on site | Days to weeks (bolted) | Weeks to months (curing) | Weeks (field welding) |
| Relocate or expand later | Yes, add rings or move | No | No |
| Maintenance at 30 years | Minimal | Crack repair | Recurrent recoating |
| Compliance evidence | Standard certificate pack | Site-specific | Site-specific |
Concrete and welded steel are not wrong. They are simply fixed assets. A GLS tank is a bolted asset you can extend, dismantle and re-site, which changes how finance treats it.
What the panel data means for your duty
| Firing temperature | 820–930°C, molecular bond of glass to steel |
| Coating thickness | 0.25–0.4 mm, double coat for durable grades |
| Adhesion to substrate | 3,450 N/cm, so the layer tracks thermal movement without lifting |
| Surface hardness | 6.0 Mohs, resists abrasion from sludge and flow |
| Elasticity | ~500 kN/mm, matching the steel plate |
| Chemical envelope | pH standard 3–11, special grade 1–14 |
| Holiday test | Every panel, 700–1500 V by coating grade, before dispatch |
| Service life | Over 30 years with routine inspection |
| Capacity range | 20–18,000 m³ as a bolted modular system |
| Plate thickness | 3–12 mm, graded to height and load |
| Design standards | EN ISO 28765, AWWA D103, NSF/ANSI 61, WRAS, KIWA, DWI Reg 31, BS 6920, NFPA 22 |
The holiday test is the one buyers under-rate. A 1500 V spark across every panel before it leaves the factory means you receive coated steel that is already proven continuous. You are not paying to find a pinhole on site.
Where GLS tanks are specified
Potable water
Municipal reservoirs, rural supplies and emergency reserves. The coating path runs through NSF/ANSI 61, with WRAS and DWI Reg 31 for the UK and KIWA for the Benelux.
Food and beverage process water
BS 6920 confirms the surface adds no taste, odour or metallic ion. That is the test a food-grade buyer actually reads.
Anaerobic digestion and biogas
The inert surface shrugs off hydrogen sulphide, and the bolted seal stays airtight. This is why GLS is the default digester shell in biogas plants.
Industrial effluent and landfill leachate
The pH 1–14 envelope covers aggressive cocktails that strip epoxy and rot concrete.
Fire-water reserve
When the tank feeds a fire system, it is built and documented to NFPA 22.
Agriculture
Slurry, silage effluent and irrigation water, where easy cleaning and corrosion immunity matter more than appearance.
Frequently asked questions
Is GLS the same as GFS?
Yes, in industrial storage they describe the same fired-enamel panel technology. GLS is the EN ISO 28765 and European term; GFS (glass-fused-to-steel) is the AWWA and process term. The trap is the other “glass lined” product: pharmaceutical and chemical reactors. They are pressure vessels on a different code. State the standard in your RFQ and you remove the ambiguity.
Yes, in industrial storage they describe the same fired-enamel panel technology. GLS is the EN ISO 28765 and European term; GFS (glass-fused-to-steel) is the AWWA and process term. The trap is the other “glass lined” product: pharmaceutical and chemical reactors. They are pressure vessels on a different code. State the standard in your RFQ and you remove the ambiguity.
Which approvals do I need for a UK potable tank?
For England and Wales you normally need WRAS approval and DWI Regulation 31 acceptance, backed by BS 6920 material testing. NSF/ANSI 61 is also widely accepted. The decisive point is that the supplier holds these for the exact panel model you are buying, not for a sister product in the same catalogue.
For England and Wales you normally need WRAS approval and DWI Regulation 31 acceptance, backed by BS 6920 material testing. NSF/ANSI 61 is also widely accepted. The decisive point is that the supplier holds these for the exact panel model you are buying, not for a sister product in the same catalogue.
Can a glass lined steel tank be buried?
Generally no. It is an above-ground bolted vessel. Below-grade installation needs a separate engineered concrete encasement and is not a standard configuration. If the site plan calls for buried storage, say so in the RFQ so the supplier prices the right solution.
Generally no. It is an above-ground bolted vessel. Below-grade installation needs a separate engineered concrete encasement and is not a standard configuration. If the site plan calls for buried storage, say so in the RFQ so the supplier prices the right solution.
How long does a GLS tank take to install?
After the foundation is ready, bolted panel assembly runs from a few days to a few weeks depending on capacity and roof type. That is the time concrete needs just to cure, before any tank exists. The factory does the coating; the site only bolts.
After the foundation is ready, bolted panel assembly runs from a few days to a few weeks depending on capacity and roof type. That is the time concrete needs just to cure, before any tank exists. The factory does the coating; the site only bolts.
What should I put in an RFQ to avoid non-compliant bids?
State the design standard (EN ISO 28765 or AWWA D103), the required approvals (WRAS, KIWA, NSF/ANSI 61 as applicable), the stored liquid and its pH, the capacity, the site wind and seismic loads, and any roof or accessory needs. Bids that miss any one of these are the ones that fail compliance later.
State the design standard (EN ISO 28765 or AWWA D103), the required approvals (WRAS, KIWA, NSF/ANSI 61 as applicable), the stored liquid and its pH, the capacity, the site wind and seismic loads, and any roof or accessory needs. Bids that miss any one of these are the ones that fail compliance later.
Sizing a glass lined steel tank against your specification?
Send us the standard, the approvals your tender requires, the liquid and the site loads. We will return a sized proposal with coating grade, certificate scope and a delivered quote. Reply by email or reach us on WhatsApp and we will respond the same working day.
Email richie@scmondes.com WhatsApp +86 159 0282 5209Related: GFS tank (the AWWA-side name for the same technology) · Enamel bolted tank for the coating-science view · FBE bolted tank for a lower-cost epoxy alternative · Double membrane gas holder for biogas storage.
