Double Coating Gfs Tank Factory Center Enamels Two Coat Enamel System
Created on 09.02
Double Coating Gfs Tank Factory Center Enamels Two Coat Enamel System
A double coating GFS tank factory applies the enamel system in two coats, a ground or primer coat that bonds to the steel and a top or cover coat that forms the finished glass surface, then fires both at 820 to 930 °C so the layers fuse into the panel as one body. The finished enamel layer runs 0.25 to 0.45 mm, is rated above 3,450 N/cm², and is spark tested at 1500 V DC on every panel before shipment. For procurement, the acceptance evidence that matters is the per panel spark test record, the material test report, the gasket and bolt certification, and a written fire schedule that shows the two coats were cured in the right order.
Procurement teams selecting a glass-fused-to-steel supplier tend to compare thickness numbers and prices, and then discover at commissioning that the coating system they bought was a single thin coat over a poorly prepared substrate. The phrase two coat enamel system describes the standard manufacturing route: a first coat keys into the prepared steel, and a second coat gives the chemical resistant, low roughness surface. When you visit or audit a double coating GFS tank factory, the questions that distinguish a credible supplier are about furnace control, panel preparation, and the paperwork that travels with each panel. This article sets out the process, the acceptance documentation, the realistic lead time and the site checks that close out the order. The supplier under review is a double coating GFS tank factory Center Enamels two coat enamel system, and the furnace schedule is where the claim is either proved or dropped.
What the two coat system actually does
Two coats are a defect strategy, not a marketing phrase. The ground coat carries the mechanical bond to the steel and flows into the micro-roughness of the prepared surface, sealing the panel against pinhole formation at the metal side. The top coat then provides the finished glass layer with the chemical resistance and the surface finish the fluid sees. In a furnace running from 820 to 930 °C the two coats are fired into a single composite with the steel, so the boundary that fails in an organic lining, the interface under the coating, does not exist here. The enamel layer ends up 0.25 to 0.45 mm thick and rated above 3,450 N/cm² against bending and compressive load, and the resulting surface is glass with a roughness below Ra 0.8 µm, which is why the same lining is accepted for potable water and food contact grades.
The practical consequence for the buyer is that pinholes and thin spots are found in the factory, not in your tank. Each panel is spark tested at 1500 V DC before it is packed, and a panel that shows a defect is reworked or rejected there. That single document, the spark test record keyed to the panel number, is the backbone of the whole acceptance file.
What a factory audit should verify
Process control is verifiable in four places. First, panel preparation: chemical cleaning and surface treatment before the first coat, because a bond failure shows up as delamination much later. Second, the furnace: recorded firing temperature and the zone profile, since a coat fired below or above the window changes flow and thickness. Third, the coating line itself: the specified enamel powder, the layer build measured per panel, and the thickness of the finished enamel layer inside the 0.25 to 0.45 mm range. Fourth, the inspection station: the spark test voltage, the repair procedure for small defects, and how repairs are logged.
Plant scale is part of the audit too. A supplier running roughly 300,000 enamel-coated steel plates a year with close to 200 enamel-related patents and a new 150,000 m² production base can hold a furnace schedule when several projects are in the shop at once, which is exactly when a smaller workshop slips. Single tanks are supplied up to 60,000 m³, so the press, the furnace and the packing line have to handle large panels without distortion.
Technical Specification
Parameter | Typical Value / Range | Note |
Coating system | two coats: ground coat plus top coat | Fused into the steel panel |
Firing temperature | 820–930 °C | Furnace schedule record kept per batch |
Enamel layer thickness | 0.25–0.45 mm | Total fired enamel build per panel |
Enamel layer strength | above 3,450 N/cm² | Bending and compressive resistance |
Surface roughness | Ra < 0.8 µm | Easy clean, potable and food contact grade |
Spark test | 1500 V DC | Per panel, before packing |
pH tolerance | 1–14 | Wide chemistry envelope |
Design life | 30 years or more | Atmospheric storage service |
Panel and bolts | ~1.2 m panels, 8.8-grade bolts | EPDM gasketed flange joints |
Procurement file: what to demand before payment
Write the document list into the purchase specification and measure the supplier against it. The minimum for a bolted enamel tank is a material test report for the steel panel including the grade and the thickness, the enamel schedule describing the two coats and the firing window, the per panel spark test record with panel numbering, a coating thickness record, the gasket and bolt certification, the welding or cutting edge treatment description, the dimensional drawing of the assembled tank, the foundation load drawing, the assembly and bolt torque procedure, the coating repair procedure, and the certificate of conformity for the product certification the project requires. Where the stored fluid is drinking water, the lining should carry the relevant drinking water contact certification such as NSF/ANSI 61 or WRAS; where the project is in Europe, CE to EN 1090 and ISO 28765 are the usual references, and the manufacturing quality system is ISO 9001 with ISO 45001 for the shop.
Lead time is a function of the furnace queue, not of the order size alone. A realistic procurement plan asks the supplier for the furnace booking, the panel production plan by week, the shipping method and departure date, and the site assembly or supervision window. Panels ship as containers or breakbulk, so the shipping plan has to be confirmed against the destination port and the interior transport route to a site that may be hundreds of kilometres inland.
Acceptance on site
Two acceptance stages matter. The factory acceptance stage closes with the document pack and, where possible, a video or third party witness of the spark test on representative panels. The site stage closes with the assembly and the leak test: panels are unloaded and checked for transport damage, the tank is assembled ring by ring with the specified gasket and 8.8-grade bolts to the recorded torque, the ground edge of each panel is protected, and the completed tank is tested at atmospheric pressure with water before it is put into service. Any weeping joint is repaired at that point while access is still easy.
Two large deliveries illustrate the format well. A big diameter potable water tank of 44,900 m³ was supplied in Namibia, and a fire water tank programme of 8,930 m³, two units at φ19.87 × 14.4 m, was supplied in Sichuan. In both cases the scope included the enamelled panels, the bolt and gasket set, the site supervision, and the documentation pack used for mechanical completion.
Project Case
Project | Location | Product | Capacity | Scope |
Large diameter potable water storage | Namibia | GFS tank | 44,900 m³ | supply + supervision, two coat enamel system |
Fire water tank, two units | Sichuan, China | GFS tank | 8,930 m³ | supply + supervision, φ19.87 × 14.4 m × 2 |
Municipal effluent tank programme | Sichuan, China | GFS tank | 17,420 m³ | supply, 10 tanks |
Center Enamel Engineering Capability
Center Enamel (Shijiazhuang Zhengzhong Technology Co., Ltd) has designed and fabricated bolted storage tanks since 2008. As the first glass-fused-to-steel (GFS) tank manufacturer in China, the company holds close to 200 enamel-related patents, produces roughly 300,000 enamel-coated steel plates a year, has completed more than 30,000 installed projects and supplies its tanks to over 100 countries. The new 150,000 m² production base was added to raise output capacity, and single tanks are supplied up to 60,000 m³. Manufacturing runs under ISO 9001 and ISO 45001, with product certification including NSF/ANSI 61, WRAS, FDA, LFGB, CE (EN 1090), ISO 28765, FM, BSCI and EUROCODE, and design referenced to AWWA D103-09, AWWA C550 and NFPA where the application requires it.
For procurement review this means the furnace schedule, the two coat enamel build and the per panel 1500 V spark test record are all documented for each shipment, and the site acceptance scope is fixed in the contract before the panels are released.
Frequently Asked Questions
Q1: What does a two coat enamel system mean versus a single coat?
A1: The ground coat bonds to the prepared steel and the top coat forms the chemical resistant glass surface, both fired at 820 to 930 °C so they fuse with the panel as one body. A single thin coat over steel is more exposed to pinhole and thin spot development.
Q2: How thick is the finished enamel layer?
A2: The fired enamel build typically runs 0.25 to 0.45 mm per panel, which is the number to put in your specification rather than a generic coating thickness.
Q3: What is the spark test and why is 1500 V important?
A3: It is a 1500 V DC check applied to every panel before packing to find pinholes and thin areas in the fired glass. The per panel record is the key factory acceptance document for the coating.
Q4: Which certifications come with the tank?
A4: Manufacturing under ISO 9001 and ISO 45001, with product certification including NSF/ANSI 61, WRAS, FDA, LFGB, CE (EN 1090), ISO 28765, FM, BSCI and EUROCODE, and design referenced to AWWA D103-09, AWWA C550 and NFPA where the application requires it.
Q5: What is the typical lead time?
A5: It depends on the furnace queue and the panel count rather than the order value alone. Ask for the furnace booking date, the weekly panel production plan and the shipping departure date in writing at tender stage.
Q6: How is the tank shipped to an overseas site?
A6: Panels travel in containers or as breakbulk to the destination port, then move overland to site. Confirm the route, the bridge and tunnel restrictions, and the crane capacity at site before fixing the diameter.
Q7: What happens if a panel is damaged in transport?
A7: It is identified at unloading against the packing list, set aside, and either replaced or repaired under the documented coating repair procedure before assembly continues.
Buying a glass-fused-to-steel tank is buying a documented manufacturing process. The two coat enamel system fired at 820 to 930 °C, the 0.25 to 0.45 mm finished layer, the 3,450 N/cm² rating, the Ra below 0.8 µm surface and the 1500 V per panel spark test are the technical core; the furnace schedule, the material test reports and the spark test record are the proof. Fix those in the specification, ask for the production plan by week, and the lead time stops being a surprise. Send the capacity, the fluid and the site data to our commercial desk and you will receive the selection suggestion and the full document package including the coating schedule and acceptance list.
Talk to an Engineer
Send the tank data for review: required capacity and diameter limits, stored fluid and its pH range and temperature, potable or non potable, site coordinates, soil and foundation condition, crane capacity and preferred port of entry. Our team will return the coating system recommendation, the panel count and production sequence, the factory document pack list including the spark test record, the shipping plan and the site acceptance procedure. Engineering review and documents first, sales follow only if you proceed.
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