Finding thickness of a cast iron cylinder

[joe465]

Homework Statement

A cast-iron cylinder of 300mm bore carries a pressure of 30 Newtons per square
millimetre; what should be its thickness for a unit working stress of 25 Newtons per
square millimetre?

Homework Equations

ó1 = pd/2t

t=pd/2tó1

The Attempt at a Solution

t=pd/2tó1

t= 30*300/2*25

=180mm

Its got to be wrong as its way too big but I am unsure on where I am going wrong, any help would be much appreciated.

'Edit'

ó1/pd=2t

25/(30*3000) = 2t

2t = 0.00277778

t= 0.0014mm (4dp)

Maybes this one, I am not sure.

Thanks, Joe

 

[rock.freak667]

Your first one should be correct. Considering that the pressure is 30 MPa.