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Is there long term experience with the vitrified (enameled) steel in this application? My experience is that it starts out very nice but eventually the vitrified layer cracks and fails and then the steel beneath rusts rapidly. For example, I have a gas barbecue grill which uses vitrified steel plates as heat deflectors - these are tent shaped pieces of metal that cover the gas burners so that food drippings from the grill above do not clog them. The underside where the plates are in contact only with the hot gases appear shiny and new but the top side (where the acidic food juices drip) are terribly pockmarked and rusted thru. These deflectors are not very big (maybe 10cm x 30 cm) so for a few pennies more they could (and should) have done them in stainless steel but I can imagine that for a large tank the difference in cost between stainless and vitrified is considerable. But not if the stainless tank outlasts the vitrified by some order of magnitude. Would concrete work in this application (perhaps with the tank being partially/fully underground)?K
I had my doubt when this tank was built, but after five years it stands as new. More I cannot say.
The other application that comes to mind are domestic hot water heaters (tank storage type - in the US these are almost universal and on demand type is rare). Almost all are vitrified steel. These inevitably fail at the seams when their sacrificial anode rods are consumed, sometimes as little as 5 years. K
J, would it be possible to make the tanks out of Cor-ten?
I believe weathering steel has to be exposed to the air to be effective. If it is immersed (as in the inside of a tank) it will rust thru.K
I am not familiar with the subject.
What really stands out about the British built tank is that it is held together using rivets and not welds.
I don't think you can weld enameled steel in the field (i.e. after it has been vitrified). You can only weld bare metal to bare metal. So rivets are the only alternative. Once upon a time rivets were the normal joining technique for bridges, skyscrapers, etc. - a large structure would have many thousands. The riveting actually goes quite fast if you have a skilled and experienced crew .K
I mentioned the rivets because they struck me as obsolete. Rivets are no longer used in bridges because they must be regularly checked and replaced as needed when they fail individually. A couple of miles from where I live there is a large diesel tank for a quarry and since it looks too big to be hauled by truck I assume that it was welded together onsite and painted inside and out. Granted, fuel is a lot less corrosive than either water or fermenting sewage, but I thought a welded tank would have been the first option. After a tank is welded together onsite it can then be painted inside to prevent corrosion.
Baked on Porcelain enamel on steel is far superior to any paint coating. You are literally coating the steel with a layer of molten glass. Think of a domestic hot water heater - if all they did was just paint the steel interior of the tanks then these heaters would fail even faster than they do. In the US , these reactors are often in the form of mostly underground concrete lined pits (like a swimming pool). I don't know why this tank had to be above ground.K
In a Wastewater treatment plant the flow must be gravitational, so there is advantage in height. Also building underground is much more expensive.
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