ASME 8 Div-1 tmin thickness basis for thick cylinder

[NovaStark]

Good day all,

From ASME 8 Div 1 for a cylindrical tube under internal pressure, the minimum thickness is based off the simple hoop stress equation:

S = PD/2t once the cylinder is considered thin for a particular range of t/D.

Now if the thickness exceeds that or the pressure is greater than some calculated value, the code gives a different equation:

t = R[exp(P/SE)-1]

What stress is this based on? It does not seem to fit the Lame model for thick cylinders due to the exponential function.

 

[pdiculous963]

ASME PTB-1 has this equation derived in section 4.3.3. Per PTB-1, it is based on limit analysis theory using the tresca yield criterion.

 

[NovaStark]

Much thanks.

For the Div.1 formula, any idea on why 0.6P is taken away from SE ?