What is glass fused to steel tanks?

Growing use of glass-fused-to-steel tanks for wastewater applications

Glass tankage systems are easily adapted to a wide variety of complex internal requirements that could include clarifier mechanisms, aeration systems, mixers, media support structures, weir troughs, baffles and many other specialized requirements.

Tanks are delivered to site, flat packed, for easy transport and site handling. The prime components of the kit are the glass-fused-to-steel panels, ready for bolting together and complete with any special cut-outs for nozzles and/or manways or other appurtenances as required. The panels overlap and are bolted together and sealed with a high performance seal, chosen to suit the material being stored.

At the top and bottom of the tank, a galvanized steel anchor provides dimensional stability. The bottom angle is leveled on shims and secured to the concrete base, with anchor bolts. The rebate is then filled with concrete and a perimeter seal to ensure a bubble tight interface. Sectional tank designs can be carried out in a wide variety of national codes, including AWWA, DIN, NSF61 and local building codes.

Panel joining is an important feature worthy of closer examination. The sealant (mastic) is applied to the overlap sheet surface and is allowed to dry and cure. Mastic has the benefit of forming an adhesive bond with the glass on the panel. It is also flexible and has high cohesion strength. This means that, as the tank flexes, the seal can move with the tank and remain intact, an improvement over gasket seals.

All the bolt heads are plastic-capped to provide corrosion protection in the process environment. Mastic squeezes out between the panels and the bolt head seals the shank and protects it from contact with process fluids.

Construction with jacks is cost-effective and particularly beneficial for taller tanks. A trained and experienced crew of three people can easily install twenty sheets per day. An example of this efficient construction procedure is the Regional Municipality of Niagara – Garner Road biosolids storage where the third tank (106′ diameter x 33′ sidewall complete with geodesic domes) was erected in less than two weeks!

Technical benefits

There are a number of unique benefits to the end user for sectional bolted steel tanks:

Expandability. Systems are easily expandable to suit future requirements. A simple procedure of breaking the seal at the concrete foundation, jacking the tank and adding additional rings can in crease the capacity for a remarkably low cost.

Relocating tanks. Due to the high corrosion resistance of the glass surfaces, the tankage system, after 20 or 30 years or even longer, can have considerable life left. It is a simple matter of disassembling the tank, cleaning the mastic from the sheets, relocating, and re-erecting the tank in another area. This again, could be done at low cost.

Final Disposition of Asset. If, at some time in the future, the tankage is no longer required, it is a simple matter of disassembling the system and removing the tankage. This compares favourably to the costs of removing a concrete, in-ground vessel and restoring the property by back-filling the excavation. In addition, the glass-fused-to-steel tank has significant value even after 30 plus years of service. Many consulting engineers are now calculating the final disposition of tankage in the life cycle analysis.

Anaerobic digesters and covers

An exceptional application for the inert corrosion-resistant glass-fused-tosteel technology is anaerobic digester tanks and/or covers. Problems related to corrosion in anaerobic  digesters simply have not been solved by the equipment manufacturers, or the engineering profession, to this point in time. Preventative maintenance to minimize corrosion will help, however, there are many covers that need replacing as a result of this aggressive off gas environment which is unique to anaerobic digestion.

The wastewater industry has recognized the significant increase in hydrogen sulphide gas over the past 15 – 20 years. This is primarily a function of the reduction of heavy metal at source, which frees a much higher percentage of sulphide ion, thus producing hydrogen sulphide gas and subsequently, sulphuric acid. Corrosion on all types of tankage, including concrete and steel, has become a concern for the wastewater industry at large. The inert corrosion-resistant capability of glass-fused-to-steel technology eliminates this problem. More and more, municipalities, owners and engineers are looking at long-term solutions to the elimination of corrosion.

The glass-fused-to-steel technology is basically a design-build approach in virtually every application. The manufacturer is responsible for site preparation, foundation design and placement, as well as design, erection and testing of the tank and cover. There is an excellent opportunity for the consulting engineering profession to partner with the tank manufacturers to reduce engineering costs to benefit owners.

The tremendous increase in the popularity of this technology is principally a function of a more thorough approach to life cycle costs, including elimination of corrosion, cleaning of the tank surfaces, expandability, as well as the ability to relocate at a very low cost. One of the most intriguing aspects of this technology is the asset value of the tankage system at some point in time in the future. Whether it be 20 or 30 years, the tank could still have significant value if it is no longer required for service.