The Substrate of Glass-Fused-to-Steel Storage Tanks

While steel, aluminum, cast iron, copper or brass may all serve as a substrate for glass coating, steel is used for porcelain enameled tanks. The type of steel is generally determined by the requirements of the size of the tank. High-strength low-carbon (<0.10 C) interstitial-free (to permit ageing and bake hardening) steel is used for tank walls.

It is well known that the fish scale can shorten the service life of tanks,   at present the tank manufacturers in the market usually use special low-carbon steel (such as titanium alloy steel) as substrate to avoid the fish scale, Fortunately our company has already developed our own patented anti fish scale enamel for bolted tank which can achieve ZERO fish scale. It is suitable for all kinds of steel plate regardless of the carbon content.

Porcelain enamel raw materials ingredient: frit,   pigments, clays and mill additions.

Frit used in porcelain enameling is a ceramic composition formulated from borosilicate. This is a type of glass known for having very low coefficients of thermal expansion, thus making it resistant to thermal shock and less subject to thermal stress. After fusing in a special furnace the material is quenched to form a glass. Quenching or high-pressure cooling consists of high-pressure air blasts to the surface of the glass that cools the outer surface more quickly than the center. As the center of the glass cools it remains in tension while the outer surfaces go into compression—thus giving the glass strength.

According to different types of steel plates and application fields we have already developed three series of anti fish scale enamel frit:

Holiday Testing

Holiday testing, or more accurately termed “discontinuity detection,” is a separate test from coating thickness easurement.   This crucial process is to check for the presence and locations of discontinuities, near voids or thin spots, entrapped contaminates and insufficient bubble structure in an otherwise non-conductive surface.   Holiday testing is performed by generating a DC voltage potential or difference between the glass surface and the steel (or other conductive) substrate, and then detecting any current flow that occurs between the two surfaces.

Holiday testing must be recreated for each and every sheet tested.   One leading manufacturer re-blasts any sheet found with any interior holidays.

The causes of fish scaling of enamels for sheet iron and steel.

Fish scales are steel-related defects which are half-moon shaped cracks in ground or cover coats. They occur after the firing operation with a typical size of 1-5 mm in diameters. They are the result of hydrogen diffusion through the steel and into the enamel layer. The hydrogen formed at the steel surface during firing according to the reaction.

Fe + H2O → FeO + H2

H2 is dissolved in atomic form and remains in the steel as supersaturated solution after cooling. The separation of hydrogen from the steel takes place by recombination to molecules at the steel/enamel phase boundary, When the pressure of hydrogen is large enough, it will break through the enamel layer and cause fish-scale. Generally tank manufacturers have to use special enameled steel plate (< 0.1% C)

Surface with fish scales are shown in Photo.

The solution of fish scaling

Our anti fish scale enamel frit can completely control the fish scaling which is suitable for all kinds of steel plate regardless of the carbon content. We have provided the qualified products to the customers at least 15 years with ZERO fish scale.

According to the feedback from our customers the enamel frit is used in the fields of enameled tank, aerospace, chemical industry.

Process Flow of Porcelain Enameled Storage Tanks

Complete Enameling Plants

Enamel production line   in China