Shell thickness of a pressure vessel required subjected to a cyclic pressure

[electric_head_uk]

I was wondering if anyone could help me with the following question, please:

A thin walled pressure vessel is to be used as a pressure accumulator in a number of situations all involving a number of different operation conditions some of which create cyclic stresses. The dimentions of the vessel are 600mm long (not including end caps) and a shell outside diameter of 60mm. The material which the vessel is made from is pressure vessel steel, with a yield of 510 MPa. A failure stress of 630 MPa and an Endurance stress of 400 MPa. Static stressing has shown that the vessel is safe for all the stress situations proposed and it must now be determined if the vessel is safe from fatigue failure for the following situations:

1. If the vessel is subjected to cyclic pressure of 0 and 400 bar, determine the minimum shell thickness of the vessel to give infinit life.

2. If the vessel is subjected to cyclic pressure of 50 to 600 bar, determine the minimum shell thickness of the vessel to give infinit life.

 

[minger]

Show us an attempt and we can steer you in the right direction.

 

[electric_head_uk]

For the first part, I thought of using Hopp stress equestion σ = p d / 2 t and taking Endurance stress (400 MPa) as the value for σ since in the cyclic pressure is 400 bar which less that Endurance stress, thus:

4 x 10^8 = [(4 x 10^7)(60x10^-3 - t)] / 2t

t = 0.003 m

 

[electric_head_uk]

Anybody goin to "steer me in the right direction" now ?