What Is ISO 28765? A Plain Explanation Of The Glass-Fused-To-Steel Tank Standard
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What Is ISO 28765? A Plain Explanation Of The Glass-Fused-To-Steel Tank Standard
ISO 28765 is the international design and manufacturing standard for vitreous-enamel-coated (glass-fused-to-steel) tanks. It controls the enamel and steel combination, the panel design, the sealant and the bolted assembly so the tank performs as a unit. It is a design standard, not a certification, and it leaves site-specific structural and seismic design to the engineer using the adopted code.
Introduction
ISO 28765 is the international standard for the design and manufacture of vitreous-enamel-coated steel tanks - the tanks most often called glass-fused-to-steel, or GFS. If you are meeting this standard for the first time, the useful first step is to stop reading it as a product name and start reading it as a design basis: it sets how the enamel-coated steel panels, the sealant and the structural assembly are designed and made, so that the finished tank performs as a unit. This article explains in plain terms what the standard requires and why it exists, without assuming you have the document open.
The short version is that a GFS tank is a bolted steel tank whose panels carry a vitreous enamel layer fused to the steel at high temperature. The glass gives the tank its corrosion resistance and cleanable surface; the steel gives it strength; the bolted assembly gives it transportability and a controlled factory finish. ISO 28765 is the rulebook that keeps those three facts consistent across designers and manufacturers. The sections below separate what the standard controls from what it deliberately leaves to the engineer on the project.
What the standard is
ISO 28765, full title Design and Manufacture of Vitreous-Enamel-Coated (GFS) Tanks, is an international standard that sets the requirements for tanks built from steel panels to which a vitreous enamel coating has been fused. It is a design and manufacturing standard, not a marketing label, and it applies to the tank as a product: the panel, the enamel, the sealant at the joints and the way the panels are assembled into a tank.
The standard exists so that a GFS tank from one supplier can be judged against the same criteria as one from another. It works alongside, but does not replace, the construction and coating standards that govern other tank types.
What glass-fused-to-steel actually means
Glass-fused-to-steel describes a panel made of two materials that behave as one. The base is a carbon-steel plate; the surface is a vitreous enamel - essentially glass - applied as a slip and fired so that it bonds to the steel.
The result is a panel that combines the tensile strength of steel with the chemical inertness of glass, which is why GFS tanks are used for water and process liquids that would attack bare steel. The term is descriptive of the product, not a claim about any single property; the standard is what defines how the combination must be made and checked. When you see GFS, read it as 'enamel-coated steel panel assembled into a bolted tank.'
Why the glass is fused rather than painted on
The enamel is fused, not painted, because the two materials are brought to a temperature where the glass melts and bonds chemically and mechanically to the steel, forming a continuous, non-porous layer.
A paint sits on the surface and can undercut or delaminate; a fused enamel becomes part of the panel face. That continuity is what gives the corrosion resistance and the cleanable surface, and it is why the standard controls the firing and the enamel quality rather than only the appearance. The trade-off is that the panel must survive the firing process without distortion, so the steel grade and the enamel formulation are matched by the manufacturer and verified, not chosen independently by the buyer.
What the standard controls
The standard controls the things that make the enamel-and-steel panel a repeatable product: the steel substrate and its preparation, the enamel composition and application, the firing that fuses the two, the dimensional and flatness tolerances of the finished panel, the sealant used at the joints, and the bolted assembly including the panel arrangement and the fasteners.
It sets acceptance criteria for the enamel surface - continuity, adhesion and freedom from defects - and for the assembled tank's integrity. In short, it controls the manufactured item and its documented quality, so that what is designed is what is delivered. These are the points a reviewer checks against the manufacturer's records.
What the standard does not control
ISO 28765 does not perform the site-specific structural or seismic design of the tank; that is left to the engineer of record using the adopted building code and the site parameters, because the ground, the wind and the seismic demand are project-specific.
It does not set the foundation, the anchorage or the piping outside the tank, and it does not decide the tank's capacity for a given duty - that comes from the process design. It also does not grant a health-effects certification for potable contact; where the wetted surface must meet a contact-material standard, that is handled separately, for example by evaluating the enamel under NSF/ANSI 61. The standard gives the product; the project gives the installation.
The structural basis that the standard leaves out is substantial: the wind and seismic actions come from the adopted code such as ASCE 7 and the local building code, applied with the site class and risk category, and the foundation is designed by the engineer of record for those loads. A GFS tank therefore arrives as a verified product that still needs a site-specific structural and seismic calculation before it is approved, which is why the standard and the project design must be reconciled rather than assumed equivalent.
How it relates to the other tank standards
A GFS tank is a bolted steel tank, so ISO 28765 relates closely to AWWA D103, the construction standard for factory-coated bolted carbon steel tanks, which permits glass fused to steel as one of its four factory coating systems.
In European and some international programmes, EN 15079 covers vitreous-enamel-coated steel tanks for potable water storage and is a parallel reference. The relationship is that the construction standard may reference the enamel system, while ISO 28765 defines that system in detail. For a welded steel tank the relevant standard is instead AWWA D100. Knowing which standard is primary for your tank type prevents specifying the wrong basis.
EN 15079 and ISO 28765 overlap on the enamel system but differ in programme: EN 15079 is written into European and UK potable-water practice and addresses design, fabrication and site assembly of vitreous-enamel-coated steel tanks, while ISO 28765 is the international design-and-manufacture reference. A project that cites one should name the edition and note where the other is referenced, so the reviewer sees a single primary standard rather than two partly overlapping ones.
What a buyer should ask for
Ask the supplier for the panel and enamel documentation: the steel grade and preparation, the enamel formulation and the firing records, and the acceptance results for surface continuity and adhesion.
Ask for the sealant specification and the bolted-assembly details, including fastener type and panel arrangement. Ask how the site-specific structural and seismic design will be done and who signs it, because that is outside the standard. Ask whether the wetted surface meets the relevant contact-material requirement for your duty. The answers should be documents, not adjectives; a tank 'built to ISO 28765' is demonstrated by the manufacturer's records mapped to the standard's clauses.
When a project specifies ISO 28765
A project specifies ISO 28765 when the duty calls for a factory-enameled, bolted steel tank - common for water storage, wastewater treatment and many industrial liquids where a cleanable, corrosion-resistant wetted surface matters and site welding is impractical.
The specification names the standard as the design and manufacturing basis, then layers the project requirements on top: capacity, site structural and seismic design, foundation, appurtenances and any contact-material requirement. The standard is the starting point, not the whole specification. When you write it, name ISO 28765 for the product and the adopted code for the site, and require the manufacturer's records that prove the two were reconciled.
What ISO 28765 Controls Versus What It Leaves To The Engineer
Parameter | Controlled by ISO 28765 | Left to the engineer / project |
Steel substrate and preparation | Grade and surface preparation specified | Plate thickness from capacity design |
Vitreous enamel | Composition, application and firing controlled | Colour and cosmetic appearance |
Panel tolerances | Dimensional and flatness tolerances set | Tank diameter and height from layout |
Sealant and bolts | Joint sealant and fasteners specified | Joint loads from site design |
Structural and seismic | Product integrity criteria | Site design to adopted code |
Potable contact | Enamel as a product | Contact-material listing (e.g. NSF/ANSI 61) |
ISO 28765 In Relation To Other Tank Standards
Standard | Scope | Relationship to GFS |
ISO 28765 | Design and manufacture of GFS tanks | Primary product standard for GFS |
AWWA D103 | Factory-coated bolted carbon steel tanks | Permits GFS as one of four coating systems |
EN 15079 | Vitreous-enamel steel tanks for potable water | Parallel European reference |
AWWA D100 | Welded steel water-storage tanks | Applies to welded, not bolted, GFS-type tanks |
Project Reference
The project reference records a multi-tank water storage project in Maputo, Mozambique, completed in 2019 (match level C). It is used here as a worked example of what ISO 28765 governs; the recorded application differs from this article's topic, and the source does not state the application or the volume, so neither is published as a figure. Dimensions are stated in the source record and are published as recorded. The reference is included for the type of construction in service, not as evidence of compliance with any standard, because no such statement is on record.
Location | Service | Total Storage Volume | Year |
Maputo, Mozambique | application not stated in source | volume not stated in source | 2019 |
About Center Enamel
Center Enamel (Shijiazhuang Zhengzhong Technology Co., Ltd.) designs and fabricates bolted steel storage tanks, welded steel tanks, fusion-bonded epoxy tanks, galvanized tanks, stainless steel vessels, pressure vessels, aluminum geodesic dome roofs and floating roofs. The company has more than 30 years of production experience and has supplied equipment to projects in more than 100 countries. Aluminum geodesic dome roofs are designed and fabricated to API 650 Appendix G, AWWA D108, the Aluminum Design Manual, ASCE 7 and IBC, and the company developed and exported a 72 m diameter aluminum dome roof in 2023. Engineering, fabrication, coating, quality control and site service are handled as one scope, which is why the drawings, the calculation basis and the delivered hardware can be reconciled against each other.
Frequently Asked Questions
What is ISO 28765 in simple terms?
ISO 28765 is the international standard that defines how glass-fused-to-steel tanks are designed and made. A GFS tank is built from steel panels whose surface carries a vitreous enamel fused to the steel, and the standard sets the requirements for the steel, the enamel, the firing, the sealant and the bolted assembly. It is a design and manufacturing rule for the product, so that panels from a supplier can be judged against consistent criteria. It is not a product name and not a certification; it is the basis a specification references when it calls for a GFS tank.
Is ISO 28765 a certification or a design standard?
It is a design and manufacturing standard, not a certification. It sets the requirements a GFS tank must meet and the records that demonstrate them; it does not issue a certificate to a tank or a manufacturer. Calling a tank 'certified to ISO 28765' misuses the term - the correct phrasing is a tank built to ISO 28765, demonstrated by the manufacturer's records. Third-party product listings are a separate mechanism under a separate body, and any such claim should point at a specific listed product, not at the standard itself.
Why is glass fused to steel instead of painted?
Because fusion bonds the enamel to the steel at high temperature, forming a continuous, non-porous layer that becomes part of the panel, whereas a paint sits on the surface and can undercut or delaminate. The fused layer gives the corrosion resistance and the cleanable surface that make GFS suitable for water and process liquids. The firing must not distort the panel, so the steel grade and enamel are matched by the manufacturer and verified. The standard controls the firing and enamel quality precisely because the bond, not the appearance, is what performs.
What does the standard leave to the engineer?
ISO 28765 leaves the site-specific structural and seismic design to the engineer of record, using the adopted building code and the site parameters, because ground, wind and seismic demand are project-specific. It also leaves the foundation, the anchorage, the external piping and the capacity for the duty, which come from the process and civil design. It does not grant a potable contact-material certification; that is handled separately where required, for example by evaluating the enamel under NSF/ANSI 61. The standard defines the product; the project defines the installation around it.
How does ISO 28765 relate to AWWA D103 and EN 15079?
A GFS tank is a bolted steel tank, so ISO 28765 relates to AWWA D103, the construction standard for factory-coated bolted carbon steel tanks, which lists glass fused to steel as one of its four permitted factory coating systems. EN 15079 is a parallel European reference for vitreous-enamel-coated steel tanks for potable water storage. The construction standard may reference the enamel system while ISO 28765 defines it in detail. For a welded steel tank the relevant standard is instead AWWA D100, so the primary standard follows the tank type.
What should a buyer ask for against ISO 28765?
Ask for the panel and enamel documentation: steel grade and preparation, enamel formulation and firing records, and the acceptance results for surface continuity and adhesion. Ask for the sealant specification and the bolted-assembly details, including fastener type and panel arrangement. Ask how the site-specific structural and seismic design is done and who signs it, since that is outside the standard. Ask whether the wetted surface meets the contact-material requirement for the duty. The answers should be documents mapped to the standard's clauses, not general claims about the tank.
What happens if a tank is not built to ISO 28765?
A tank not built to ISO 28765 is simply built to a different basis, which may be acceptable if another standard applies, but it will not carry the consistency the standard provides for enamel quality, panel tolerances and assembly. The risk is that the enamel-to-steel bond, the sealant and the fasteners are not verified to a common criterion, so performance depends on the supplier's internal practice rather than a shared rule. If your specification names ISO 28765, require the manufacturer's records that demonstrate it; without those records, the name in the specification is not evidence the tank was actually built to it.
ISO 28765 is most usefully read as the definition of a product: a bolted steel tank whose panels carry a vitreous enamel fused to the steel, made and checked to a consistent international rule. It controls the enamel, the steel, the sealant and the assembly, and it leaves the site-specific structural and seismic design to the engineer using the adopted code. Reading it that way keeps the standard in its proper place beside, not above, the project design.
When you specify a GFS tank, name ISO 28765 as the manufacturing basis and require the manufacturer's records that map to it, then add the capacity, the site design, the foundation and the contact-material requirement for your duty. Send us the liquid, the volume and the site constraints, and we will return a specification that places the standard where it belongs and ties it to documents a reviewer can check.
Talk To Our Engineering Team
Send the duty, the volume basis, the governing code and the site constraints, and our engineering team will come back with a specification that a supplier can price and a reviewer can approve. We will also tell you plainly when a different tank type or a different scope is the better answer.
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