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## Main Question or Discussion Point

Hello,

First, please understand that I'm lacking fundamentals in physics and engineering.

I'm trying to find the maximum pressure a submarine hull can resist. For the sake of simplicity I'm just considering a tube closed with magical caps that keep a different pressure inside and outside.

After much research and a few calculations, I think I've gone wrong somewhere, because I'm getting that a 2m diameter, 2m long steel tube 1cm thick will plastically deform under the pressure at 114m depth only.

From here (http://www.calctool.org/CALC/other/games/depth_press) I'm getting that the pressure at 114m depth is 1.24723 MPa = 1,247,230 Pascals or Newtons/square meter

My magical hull is a tube 2.02m outer diameter and 2m long, again without caps, and keeping the pressure difference, and I guess the inner pressure would be zero. So its surface area should be: D x pi x height = 2.02 x 3.14 x 2 = 12.69m2

That'd mean it's getting a total force exertion of 1,247,230 x 12.69 = 15,827,349 Newtons / 9.8 = 1,615,035 Kg = 1,615 metric tons. (Which seems ridiculously high)

Then I'm calculating the yield moment using this (http://en.wikipedia.org/wiki/Section_modulus#Elastic_section_modulus):

S =

pi x (oD^4 - iD^4)

-----------------------

32 x oD

pi x (2.02^4 - 2^4)

-----------------------

32 x 2.02

3.14 x (16.64 - 16)

------------------------

64.64

S= 0.031

If my hull is made of structural steel its got a yield strength of about 250MPa = 250,000,000 Newtons/square meter

Yield moment = S x yield strength = 0.031 x 250,000,000 = 7,893,642 Newtons/meter / 9.8 = 805,474 Kg/meter

Since my hull is 2m long, it should be able to withstand 1,610,947 Kg before plastic deformation occurs.

Where did I go wrong? And please remember that I have little physics/engineering background, so explain as you would to a child.

Thanks!

P.S.: Sorry for the format, but I can't bother to learn Latex or whatever it's used for writing equations just for one question.

First, please understand that I'm lacking fundamentals in physics and engineering.

I'm trying to find the maximum pressure a submarine hull can resist. For the sake of simplicity I'm just considering a tube closed with magical caps that keep a different pressure inside and outside.

After much research and a few calculations, I think I've gone wrong somewhere, because I'm getting that a 2m diameter, 2m long steel tube 1cm thick will plastically deform under the pressure at 114m depth only.

From here (http://www.calctool.org/CALC/other/games/depth_press) I'm getting that the pressure at 114m depth is 1.24723 MPa = 1,247,230 Pascals or Newtons/square meter

My magical hull is a tube 2.02m outer diameter and 2m long, again without caps, and keeping the pressure difference, and I guess the inner pressure would be zero. So its surface area should be: D x pi x height = 2.02 x 3.14 x 2 = 12.69m2

That'd mean it's getting a total force exertion of 1,247,230 x 12.69 = 15,827,349 Newtons / 9.8 = 1,615,035 Kg = 1,615 metric tons. (Which seems ridiculously high)

Then I'm calculating the yield moment using this (http://en.wikipedia.org/wiki/Section_modulus#Elastic_section_modulus):

S =

pi x (oD^4 - iD^4)

-----------------------

32 x oD

pi x (2.02^4 - 2^4)

-----------------------

32 x 2.02

3.14 x (16.64 - 16)

------------------------

64.64

S= 0.031

If my hull is made of structural steel its got a yield strength of about 250MPa = 250,000,000 Newtons/square meter

Yield moment = S x yield strength = 0.031 x 250,000,000 = 7,893,642 Newtons/meter / 9.8 = 805,474 Kg/meter

Since my hull is 2m long, it should be able to withstand 1,610,947 Kg before plastic deformation occurs.

Where did I go wrong? And please remember that I have little physics/engineering background, so explain as you would to a child.

Thanks!

P.S.: Sorry for the format, but I can't bother to learn Latex or whatever it's used for writing equations just for one question.