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 ?

 

[DeeNos]

I would approach this question by first considering the factors that contribute to fatigue failure in a pressure vessel. These include the material properties, the applied cyclic pressure, and the geometry of the vessel.

Based on the given information, the material used for the vessel is pressure vessel steel with a yield strength of 510 MPa, a failure stress of 630 MPa, and an endurance stress of 400 MPa. This means that the vessel can withstand a maximum stress of 630 MPa before failure, but it is recommended to keep the stress below 400 MPa for extended periods to avoid fatigue failure.

Next, I would analyze the applied cyclic pressure in each situation. In the first situation, the vessel is subjected to a cyclic pressure of 0 and 400 bar. This means that the pressure alternates between 0 bar (no pressure) and 400 bar (maximum pressure). In the second situation, the pressure ranges from 50 to 600 bar. This is a wider range of pressure and may cause more stress on the vessel.

To determine the minimum shell thickness of the vessel for infinite life, I would use the ASME Boiler and Pressure Vessel Code, specifically Section VIII Division 2 for pressure vessels subjected to cyclic loading. This code provides equations for calculating the required shell thickness based on the material properties, applied pressure, and geometry of the vessel.

Using these equations, I would calculate the minimum shell thickness for each situation and compare it to the current thickness of the vessel. If the calculated thickness is greater than the current thickness, then the vessel is safe for infinite life. If not, modifications may need to be made to the vessel to ensure its safety.

In addition, I would also consider other factors such as weld quality, surface finish, and any potential stress concentrations in the vessel design. These can also affect the fatigue life of the vessel and should be taken into account in the analysis.

Overall, with proper analysis and consideration of all factors, it is possible to determine the minimum shell thickness required for a pressure vessel to withstand cyclic pressure without fatigue failure.