We had an urgent call out this week to fix a leaking 250,000 litre silo. Now a food grade silo this big is an expensive bit of equipment, but unfortunately they are simply and easily catastrophically damaged.
So this silo is 4250mm diameter and has an overall height of 21,135 to the top of the handrail.
What really complicates things is that it is 40m away from anywhere a boom lift, truck mounted cherry picker or a crane can set up and therefore that distance rules out the first 2 and left only a crane which had to be a 90 tonne crane with a man box to access the side of the tank
What damaged the tank was a standard food industry process where the tank is washed with hot caustic solution, and then spray rinsed with cold water. The temperature differential is substantial and creates an instant vacuum if the vent is not adequate.
In this case the vent would normally be adequate, but because of a procedure that happened prior to the cold rinse in that the vent was reduced down so any hot caustic coming down the vent line was fitted with a reducer, reducing the diameter back to 1/3 and being directed back into tank through the side entry manway.
So full marks for eliminating hot caustic going over the factory floor, but by close coupling the vent to a much smaller diameter was an accident waiting to happen.
The fact that the guys had successfully CIPed the tank for 20 years without incident wasn’t enough
What should have been fitted was a cone under the vent line with that cone then reduced to return back into the tank. This would have provided a completely unrestricted venting of the tank and there would never have been a problem.
