On Sun, 17 May 2009 17:36:54 -0500, "Karl Townsend"
wrote:

"The Kid" is on a rolling layoff, so I'm hiring him to do the fabrication on
my 6' by 10' plasma cutter. We're building a water tank 16" high by 6' by
10'. Our question, how thick a steel do we need to prevent the water
pressure from severely deforming the tank. The main issue is, of course, the
bottom and it would be no big deal to put in a reinforcing angle iron every
two feet.

"The Kid" thinks 0.070" or 14 gauge should be enough. I'm leaning toward
0.100" or 11guage to be sure. Any way to know?

Second question, if we weld every inch of every seam it will warp for sure.
I'd like to just stitch weld it and then use some sort of sealer/filler to
prevent leaks. What would work here?



Karl

It depends on your structural design. You have two requirements: one
is a water-impervious "skin" that will contain water, the other is a
structure that supports the weight of the water at desired height from
ground. Both of these requirements can be accomplished by one entity,
but they don't necessarily have to be. Example: a structure made of
lumber and plywood with a thin water-impervious rubber skin.

16" deep water weighs 83.2 lb per square foot. That will be the
pressure at the bottom of the tank, both on the bottom and on the
sides.

If it is to be at some height above floor or ground, then the bottom
structure needs to be a platform capable of supporting 83.2 lb per
square foot. The sides will be in tension due to water pressure, but
even very thin steel could handle this. A PET (plastic) soda bottle
can handle over 100 PSI which is 14,400 lb/ft^2.

For structural ideas, look at some trailers. A 4' x 8' trailer rated
for (and loaded with) 2662 lb would have 83.2 lb per square ft, and
so on.