Vitreous variety - developments in enamelling

Materials World magazine
,
2 Jan 2014

How is the vitreous enamel industry doing? Eoin Redahan asked Saqlain Ali, coatings specialist at tank and silo manufacturer Permastore, in Suffolk, UK.

What are the most exciting recent developments in vitreous enamel from a materials performance perspective?
Research in the field has been diverse in recent years. Substantial focus has been placed on both the enamel materials and the metallic substrates used in the production of vitreous enamel (VE) goods. The recent introduction of the EU’s Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) regulations and other environmental legislation changes have driven enamel material development programmes to deliver more environmentally friendly products.

There have been developments in electrically conductive enamels, and these materials have been applied to electrostatic filters for the biomass burning process. Enamels have also been developed to deliver antibacterial properties in applications where surface cleanliness properties are important.

Other new applications include the design and manufacture of thick film heating technology, where electrical tracks are printed onto enamelled surfaces. This technology offers substantial benefits over conventional heating element technology in areas such as speed of heating and design freedom.

Finally, there have been developments in the metallic substrate materials used in the VE industry, particularly in steels for enamelling. These have focused on performance enhancements in the mechanical and chemical properties of enamel products.

The economic downturn hit the industry hard. In what areas have companies managed to maintain success?
Surviving companies have focused on some key areas of the VE process such as energy efficiency. There has also been an acceptance of VE technology as a science rather than its historic perception as a black art (a less scientific trial-and-error approach). Companies have improved knowledge as a result of long-running investment programmes and partnerships with key VE constituent material suppliers. The willingness to challenge perceived views has resulted in a philosophy where traditional views are only accepted when they are shown to be effective in scientific terms.

In what areas and markets is vitreous enamel prominent?
The excellent properties of VE allow the material to be used in a variety of applications. While conventional products such as enamelled jewellery, cookware and white goods are still produced, other products are also manufactured using enamel materials. The chemical resistance properties of the material are used in the production of storage tanks and silos, often to store and treat aggressive products. These enamelled storage vessels are employed in many industrial applications, including biofuel storage and anaerobic digesters.

Chemical reaction vessels and their associated pipework and valves are frequently produced with industrial enamel finishes for the chemical and pharmaceutical industries. Heat exchanger parts are also manufactured with enamel surface coatings. These products have extended service life as a direct consequence of the properties of the enamel coating. More recently, new applications include the use of VE in flow-through heaters, which are used for the instant heating of water. It is also extensively used in signage applications, and is one of Transport for London’s materials of choice due to its fire safety properties. Other uses include architectural panels for building cladding, tunnel linings and the production of interactive whiteboards.

In what environments are your formulations used?
Our enamel formulations have been tailored for the storage of industrial and municipal liquids and dry bulk solid products in a modular bolted tank concept. The VE formulations must be suitable for a range of stored contents for chemical, temperature and pH resistance. They are designed for various applications, from the hygienic inert requirements of drinking water storage, to the aggressive, hightemperature applications of anaerobic digestion.

The formulations are fused to the high strength, low alloy steels used in the manufacture of tanks and silo panels. The combination of VE and the strength and flexibility of the steel results in a corrosion resistant, durable and colourfast glass-fused-to-steel finish on the internal and external surfaces.

The finish provides resistance to cold environmental temperatures where alternative materials such as concrete or epoxy coating may be affected over time. Similarly, the inert, inorganic VE finish is UV stable and colourfast, making the product suitable for high-temperature regions. Due to the tank wall structure of the steel substrate and the insulation properties of the glass coating finish, the thermal transfer properties are relatively low, minimising the effect on the stored contents.

How do you use vitreous enamel in your anaerobic digestion facilities?
The finishes and modular design of our tanks allow coatings to be tailored to the different parts of anaerobic digesters. For example, the top sludge level within an anaerobic digester usually remains constant. The gaseous zone above this top sludge level offers an onerous environment with higher temperatures and the presence of aggressive elements, such as hydrogen sulphide and sulphuric acids. For this zone, we use the glass-fused-to-steel finish.

The zone below the top sludge level is less onerous. While the gases and condensates associated with the gaseous zone may not have the same effect, there are other aspects to consider, such as pH, chlorides, electrolytes, bacterial corrosion and abrasion resistance. For this zone, we apply a secure finish grade of vitreous enamel.

How are you looking to develop this technology further?
Most recently, the technology has been used in mineral mine processes, demineralised water storage for power stations and in biofuel storage. We are looking to develop the technology further by creating a microbiological surface to aid future contamination requirements. Permastore has co-ordinated an EU Commission Seventh Framework project that focuses on developing farm and agriculture-stabilised thermophilic anaerobic digestion. Further details of this project are available at www.smartank.eu

What makes VE so useful in storage applications
Vitreous enamel allows us to use the structural properties of steel – the strength and flexibility of the steel substrate – with the corrosion protection of the enamel surface. So, when we put the two together in a composite, it delivers excellent performance.

VE in bridges
As you drive along the motorway, you see bridges with rusty streaks in some areas, where they need repair and maintenance. That is a consequence of steel rebar corrosion within the concrete. Research is taking place to see whether it is feasible to create VE-coated rebar, which would reinforce the concrete with the added benefit of having sectional corrosion resistance.

Ali on…
Saqlain Ali is the Quality, Health, Safety and Environment and Coatings Technology Manager of Permastore and is a board member of the UK Vitreous Enamellers’ Society, which is part of IOM3. For more information, visit www.vitreousenamellers.org.uk