Severe Underfloor Corrosion-Hot Cone Up Tank

[LurmClaxton]

I've dealt with a few of these small condensate tanks now which have been completely chewed out from underside corrosion in annular ring area. They are typically holing about 4-6years as an estimate with 10mm (3/8") annulars

Can anyone describe the machanism by which this damage is occuring and suggest ways to stop it. I'm assuming its to do with some kind of condensation cycle under the hot (80ºC/175ºF) tank floor.

Currently base is bitumen sand under the annulars and dirt grade in the middle (i think). Generall conditions are pretty damp in the area with poor drainage.

Any suggestions gratefully acceptaded.

Lurmy

 

[Duwe6]

Your mechanism is 'CUI' - corrosion under insulation. The bitumen sand is providing insulation effect, and is also trapping water. Then, at 80°C, the water is vaporizing and refluxing, and keeping the bottom bathed in a thin layer of well-oxygenated water. We've got the same problem on a bunch of small tanks.

Run the existing floor to failure, and then replace it with stainless steel. Unless you can imrove the drainage to the place that your floors stay dry almost all the time, a stainless floor is your best option. IMHO.

 

[Ripz]

Install a cathodic protection system.