ISO 28765 Glass-Fused-To-Steel Tank: Design Standard And Specification
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ISO 28765 Glass-Fused-To-Steel Tank: Design Standard And Specification
ISO 28765 is a design and manufacturing standard for glass-fused-to-steel, vitreous-enamel-coated, tanks, covering the steel substrate, the fused glass coating, the shell and roof design, the firing and bonding of the enamel, and the factory tests that prove it. It is not a certification. The same construction is a D103 bolted tank with the glass system in North America and an EN 15079 tank in Europe.
Introduction
If you are specifying a glass-fused-to-steel tank, ISO 28765 is the standard you will most often be asked to cite, and it is also the one most often misread as a certification. It is not. It is a design and manufacturing standard for vitreous-enamel-coated tanks, and the value it gives you is a single referenced basis for the shell, the coating and the records that prove the bond between glass and steel.
This article works through what ISO 28765 actually controls and what it deliberately leaves to the engineer and to the site. It covers the scope and the tank types, the design and calculation requirements, the steel and glass materials, the production step that fuses the coating, and the factory testing that verifies it. It then maps the standard onto a purchase specification and explains how it relates to AWWA D103 and EN 15079.
One convention matters throughout: a standard is not a listing. Nothing in ISO 28765 certifies a tank or a supplier, so every conformance claim has to point at the design calculation and the factory test records, not at a certificate.
What ISO 28765 is and is not
ISO 28765 is an International Organization for Standardization standard that sets the requirements for the design and manufacture of vitreous-enamel-coated tanks, the glass-fused-to-steel, GFS, tanks used for water and other liquid storage. It is a design and manufacturing standard, not a certification. It defines what a conforming GFS tank and its panels must satisfy, and it points to the verification that proves a delivered tank meets those requirements.
It is not a listing scheme: there is no ISO 28765 certificate that a supplier holds in the way a product is listed under a third-party program, and the standard does not grade a tank as approved. What it does is give the engineer a single, referenced basis for specifying a GFS tank and for checking the submittal against defined design and production rules. The conformance is demonstrated, never assumed.
Scope and the tank types it covers
The standard covers cylindrical, flat-bottomed, vitreous-enamel-coated steel tanks built from factory-coated panels, with the coating fused to the steel at high temperature. The scope is the tank itself, shell, roof, floor and the coated panels, and the design of those elements for the stored liquid, including hydrostatic loads, wind and the seismic actions defined by the adopted site code.
It is written for liquid storage, and potable water is the most common duty. It does not extend to every bolted tank: a galvanized or thermoset-coated bolted tank is a different coating system and falls under a different basis, and a welded steel tank is outside its scope entirely. The point for you is to confirm the tank you are buying is a GFS tank before you cite ISO 28765, because the standard only governs the glass-fused-to-steel construction.
Design and calculation requirements
A GFS tank designed to ISO 28765 is checked for the same structural actions as any other steel liquid tank: the hydrostatic pressure of the liquid at each course, the wind moment on the shell and any supported roof, and the seismic overturning and shell actions from the site-specific parameters.
The shell courses are sized for the hoop stress the liquid head produces, with the roof and any ring beam providing the top restraint the wall needs. Because the panels are thin and bolted, the standard's design method addresses the bolted joint and the panel stiffness, and the anchorage is resolved with the foundation designer under the adopted building code. The calculation you receive should show the head used, the load combinations, the course thicknesses and the seismic basis, so the design can be reconciled with the approved drawings.
Materials, glass and steel grades
The two materials at the heart of the standard are the steel substrate and the vitreous enamel. The steel panel is selected for the strength and formability the shell course needs, and the grade is stated in the design so the thickness can be checked. The vitreous enamel is a glass formulation fused to the steel in a firing step, and the standard controls the enamel composition, the coating weight and the fired quality so the film is continuous and adherent.
The steel and the glass have different thermal expansion, which is why the fusion step and the enamel formulation matter: a good bond resists the differential movement the tank sees in service. The sealant at the bolted joints is a separate material and is specified and verified on its own, because the joint, not the panel, is where the wetted seal lives.
Production and the bond between glass and steel
The defining production step is the fusion of the glass to the steel, and ISO 28765 controls how that bond is made and proved. Panels are prepared, coated with the enamel slip and fired so the glass fuses to the steel surface into a single adherent layer; the standard sets the preparation, the application and the firing quality, and it requires the bond to be verified rather than assumed.
Holiday testing of the fired surface finds discontinuities in the coating, and the steel substrate thickness is verified before and after firing because the process removes no structural material but must not hide a deficient panel. The joint sealant is then applied at erection, and the production records, enamel batch, firing parameters, holiday test and thickness checks, are what let you trace a delivered panel back to the process that made it.
Testing and quality control
Quality control under ISO 28765 runs at the factory, because the coating is applied there, not in the field. The enamel adherence is tested so the fused layer will not lift in service, and the fired surface is holiday-tested for continuity before the panel leaves the plant.
Panel dimensions and the steel thickness are checked against the design, and the enamel formulation is controlled by batch so a change in the glass is a controlled, recorded event. What the standard does not do is replace the site acceptance and the owner's inspection programme; those follow at erection and over the tank's life. The deliverable you file is the factory test record tied to the panel numbers, so a panel on site can be matched to the test that qualified it.
Translating the standard into a specification
To specify against ISO 28765, write the standard and its edition into the tank requirement, name the duty and the design liquid level, and require the design calculation showing head, wind, seismic basis and course thicknesses. Require the material statements, steel grade and the enamel formulation, and the production records: holiday test, adherence test, panel dimensions and thickness checks, and the enamel batch identification.
State that the joint sealant is a specified, verified wetted material, and require the factory test records tied to panel numbers. Then separate the structural acceptance at site, the foundation design by the engineer of record, and the owner's inspection programme as distinct obligations. A specification that names the standard without asking for the records leaves the conformance unverifiable at the gate.
How ISO 28765 relates to AWWA D103
AWWA D103 is the AWWA standard for factory-coated bolted carbon steel tanks and it permits four factory coating systems: galvanized, glass, glass fused to steel, thermoset liquid suspension and thermoset powder. So a GFS tank in the AWWA market is a bolted tank built to D103 with the glass coating system selected, while in the international market the same construction is described as a tank built to ISO 28765.
The two standards are not competitors; they are different regional bases for the same glass-fused-to-steel construction, and a supplier working in both cites the one the project adopts. EN 15079 sits alongside them as the European vitreous-enamel-coated steel tank standard for potable water. You choose the designation the authority and the contract name, and you keep the coating system and the test records consistent with it.
ISO 28765 In Scope Versus Left To The Engineer
Aspect | Covered By ISO 28765 | Resolved Elsewhere |
Tank construction | Glass-fused-to-steel panels, shell, roof, floor | Erection sequencing and site acceptance |
Design actions | Hydrostatic head, wind, seismic actions | Site-specific seismic parameters and code edition |
Materials | Steel substrate grade, vitreous enamel formulation | Joint sealant specified and verified separately |
Production | Surface prep, enamel application, firing, bond | Field joint sealing at erection |
Testing | Adherence, holiday, thickness, batch control | Owner inspection programme over the tank life |
Conformance | Demonstrated by design and factory records | Authority acceptance of the installed tank |
Clause-To-Specification Mapping: What To Require
Standard Element | Specify | Demand As Evidence |
Design | Head, wind, seismic basis, course thicknesses | Design calculation tied to approved drawings |
Materials | Steel grade and enamel formulation named | Material statements and batch identification |
Production | Firing quality and bond verification | Holiday and adherence test records |
Panels | Dimensions and steel thickness per course | Dimensional and thickness inspection records |
Joints | Specified, verified wetted sealant | Sealant listing and application record |
Traceability | Panel numbers linked to tests | Factory test records tied to panel numbers |
Project Reference
The verified project library includes a large-diameter water storage project in Namibia, completed in 2021, referenced here to illustrate the boundaries of the standard's scope rather than as a conforming example. The source record does not state the application for this installation, and the recorded duty differs from the glass-fused-to-steel topic of this article, so the project is not presented as built to ISO 28765. No case identifier is used. Tank dimensions are stated in the source record and are published as recorded.
Location | Service | Total Storage Volume | Year |
Namibia | application not stated in source | volume not stated in source | 2021 |
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 does ISO 28765 specify?
It specifies the design and manufacture of vitreous-enamel-coated, glass-fused-to-steel, tanks for liquid storage: the steel substrate and the fused glass coating, the shell and roof design for hydrostatic, wind and seismic actions, the production and firing of the enamel, and the factory tests, adherence, holiday and thickness, that prove the bond. It is a design and manufacturing standard, not a listing scheme, and it gives the engineer a referenced basis for specifying and checking a GFS tank.
Is ISO 28765 a certification?
No. It is a design and manufacturing standard, not a certification or a listing. There is no third-party product listing that certifies a tank to ISO 28765 as a branded item; conformance is demonstrated through the design calculation and the factory production and test records the supplier provides. A claim that a tank is built to ISO 28765 should be verified with the design and the test documentation, not with a certificate.
What tank types does ISO 28765 cover?
It covers cylindrical, flat-bottomed, vitreous-enamel-coated steel tanks assembled from factory-coated panels, the glass-fused-to-steel construction. The scope is the tank itself for liquid storage, with potable water the common duty. It does not cover galvanized or thermoset-coated bolted tanks, which use different coating systems, and it does not cover welded steel tanks. Confirm the tank you are buying is a GFS tank before citing ISO 28765, because the standard only governs the glass-fused-to-steel build.
What does the standard require for production quality control?
The coating is applied and fired at the factory, so quality control is factory-based: the enamel adherence is tested, the fired surface is holiday-tested for continuity, panel dimensions and steel thickness are checked, and the enamel formulation is controlled by batch. The records, holiday test, adherence test, dimensions, thickness and batch ID, are tied to panel numbers so a delivered panel can be traced to the process that qualified it. Site acceptance and the owner's inspection programme follow separately.
How does ISO 28765 differ from AWWA D103?
AWWA D103 is the AWWA standard for factory-coated bolted carbon steel tanks and it permits glass fused to steel as one of four factory coating systems, so a GFS tank in the North American market is a D103 bolted tank with the glass system selected. ISO 28765 is the international design-and-manufacture standard for the same glass-fused-to-steel construction. They are different regional bases for the same build; a supplier cites the one the contract and authority name, keeping coating and test records consistent.
What should a supplier document against ISO 28765?
The design calculation showing head, wind, seismic basis and course thicknesses; the material statements for steel grade and enamel formulation; and the factory production records, holiday test, adherence test, panel dimensions, thickness checks and enamel batch identification, tied to panel numbers. Also require the specified joint sealant to be a verified wetted material. The documents let you reconcile the delivered panels with the approved design and the process that made them.
Which parties are responsible for what under the standard?
The tank manufacturer designs and produces the GFS panels and supplies the design and factory test records. The engineer of record designs the foundation and anchorage to the adopted code using the loads the manufacturer provides. The erector assembles the panels and applies the joint sealant. The authority having jurisdiction reviews the submittal and accepts the tank. Each party's obligation is distinct, and the standard's conformance is demonstrated by the manufacturer's records, not by a single certificate.
Conclusion
ISO 28765 gives the engineer a complete, referenced basis for a glass-fused-to-steel tank: the steel and the fused glass coating, the shell and roof design for liquid, wind and seismic actions, the firing that makes the bond, and the factory tests that prove it. Its strength is that the conformance is demonstrable from records, adherence, holiday, thickness and batch, tied to panel numbers, not asserted.
When you specify against it, name the standard and its edition, require the design calculation and the production records, and keep the structural acceptance, the foundation design and the owner's inspection programme as separate obligations. Send us the duty, the design level, the site seismic data and the adopted code, and we will return a GFS tank specification built to ISO 28765 with the glass formulation, the joint sealant and the factory test records defined.
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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