On Sat, 26 Jun 2010 07:47:41 -0700, Winston
wrote:

On 6/26/2010 5:00 AM, J. D. Slocomb wrote:
On Fri, 25 Jun 2010 22:48:29 -0700,
wrote:

Here's what I was on about:

Envision a barrel 22" diameter by 35" high. Let's agree I pressurized
that barrel to 10 PSIG.

Let's arbitrarily say that all seams measure 0.05" in width.
We have a total seam length of ~173" (Two circumferences plus the side
seam). So 173" of seam length x 0.05" of seam width is 8.66 square inches
of total seam area. If we multiply that by our 10 PSIG we get
a force of 86.6 lbs acting against all the seams collectively.
If we divide that force by the seam length, we decide that the force
per inch of seam is about 0.5 lb, yes?

Envision that same barrel only this time, we now have two side
seams and four circumferential seams (instead of just two).
Our new total seam length is now 346.5" for a total seam area
of ~17.3 sq. inches. If we multiply that by our 10 PSIG we get
a force of ~173.2 lbs acting against all the seams collectively.
If we divide that force by the seam length, we decide that the force
per inch of seam is about 0.5 lb, yes?



Where did I go wrong?


--Winston-- I mean, concerning 'seam pressure'.

In a closed cylinder pressure is applied to all surfaces equally. so
you have an area of 2,419 sq. inches with a pressure of 10 PSIG =
24,190 pounds of force applied to the inside the vessel.

How much of this force is trying to rip the seams apart?

I agree the problem is more complicated than my arithmetic
suggests because I did not consider the most important aspect
and that is the leverage against the top and bottom seams
by the bowed flat surfaces.

The point of my arithmetic was to discover how much normal
force was placed on a seam of a given length and how that
force changed as seam length increased. Apparently it's
linear (for the side seam anyway!)

--Winston


I was only trying to illustrate that the force trying to separate the
seam is not simply the force applied to the seam itself by the 10 PSI.

Years ago, in the USAF I watched some fuel cell guys build a box of
several cubic feet with a circular cut-out in one side. They mounted a
pressure relief valve in one cut-out side of the box and screwed an
air fitting in the other. I asked them what they were doing and they
said that they needed to actually see the valve operate when pressure
was only a few inches of water pressure high. I wouldn't let them use
my air system to do it so they went over to an unused hanger and set
up there.

A bit later the Sergeant in charge of the test came back and said,
"well I didn't believe you but you made so much noise about it that we
put the box out in the middle of the hanger and all went outside.
Reached around the door and started to open the air valve, just a tiny
bit. the box blew up before the air gage even started to wiggle.

Low PSI in big boxes (or cylinders) is sometimes more potent then it
appears simply from looking at the gage.

Cheers,

John D. Slocomb
(jdslocombatgmail)