Article: When Tanks Fail Due To Ratholes

Failure is something that no one wants to hear about. The consequences can be disastrous. One type of problem that may produce a dire result is the rathole in a tank or silo filled with powder. The Rathole” does not come about from a furry rodent, as you might suspect, burrowing or eating its way through the material stored inside. It happens when a cylindrical column of powder suddenly falls out of place from the middle of the tank, completely discharging out the bottom, and leaving behind a significant void inside the tank. Shows damage that resulted in a pressurized silo which dramatically collapsed in on itself as the powder discharged during the sudden formation of rathole.

How can powders do this? Is it commonplace? The answer is "yes", but not usually as dramatic as the damage shown. But the consequences of ratholes are still problematical, because the powder that remains in the tank may not discharge easily or at all. The challenge is to break or overcome the "hoop stress" that holds the remaining powder in place within the tank. Sometimes this requires going into the tank from the top and using makeshift means to dislodge the powder. The potential danger to the person charged with this mission is the sudden collapse of the powder which could accidentally suck them into the middle.