Dear All,
Hello Everybody!

I am designing a HP Heater with construction code as ASME section VIII, Div.2.
For cylindrical shell thickness formula is, t = D/2(exp(P/SE)-1) Part 4, equation 4.3.1, Can anybody explain how it is derived,based on which theory this formula is derived..??, and why the eponential is added in this formula..?
Also,
For the same material of construction (Sa266 Gr.2,Allowable stresses are same for Div1& 2 @ particular design temp),why thickness required for internal pressure of hemispherical dish end come more than same as per Div1...???..

Dear
1. please find an attachment of derivation of ASME SEC VIII Div-2 shell thickness equation. I tried to make it as simple it can be.

2. thickness comes out different in div-1 & div-2. as both division uses the different theory of failure. hope i attempted best to clarify up to maximum extend possible. however, expert's comments are always welcome!!