A Buckeye Fabricating Company manufacturers pressure vessel
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A Buckeye Fabricating Company manufacturers pressure vessel

QUESTION 2

A Buckeye Fabricating Company manufacturers pressure vessel for submarine applications to store the fuel as shown in Figure 1. The main objective of the work is to select a suitable material for the outer wall of the pressure vessel. When the pressure vessel is fully assembled it resemble as a cylindrical shape having an internal pressure of 'p. The design of the outer wall of the cylindrical pressure tank and the selected material should resist the internal pressure. The radius of the pressure tank is 40 m. The outer wall containing the pressure, 'p' should not fail either by yielding, buckling or by fast fracture. The size of the possible largest crack contained in the outer wall is ac.

Most of the pressure vessels are made of high strength alloy steel, and they are heavy. You are asked to explore the potential of alternative materials for lighter pressure vessels, recognizing there must be a trade-off between mass and cost - if it is too expensive, the manufacturing company will not want it even if it is lighter.


In order to translate the right material selection for the fuel storage tank application into a real engineering problem you need to answer the following questions:

a) What is the function of the submarine pressure vessels?

b) What is the objective of the submarine pressure vessels?

c) What are the constraints of the submarine pressure vessels?

d) What are the free variables in the design of the submarine pressure vessels? Discuss the implication of the free variables for the optimal choice of the material selection.

e) Calculate the mass and cost of the outer wall of the submarine pressure vessels as a function of material properties to minimise the possibility of failure by material yielding.

f) What is the performance material index for failure due to yielding?

g) Calculate the mass and cost of the outer wall of the submarine pressure vessels as a function of material properties to minimise the possibility of failure by fast fracture mechanism.

h) What is the performance material index for failure due to fast fracture?

i) Calculate the mass and cost of the outer wall of the submarine pressure vessels as a function of material properties to minimise the possibility of failure by buckling.

j) What is the performance material index for failure due to buckling?

k) Show that the mass and material cost of the pressure vessel relative to one made of high strength alloy steel is given by


where p is the density, sigma y the yield strength and Cm the cost per kg of the material, and the subscript"o" indicates values for high strength alloy steel.

(Hint) Use the ratio for new material over the steel.

m/mo = mass relative to high strength alloy steel

and c/co= cost relative to high strength alloy steel.

Materials properties that are available for ranking materials are: density (p): Yield strength (sigma y); Critical stress intensity factor or fracture toughness of the material (KIC); The surface area of a cylindrical wall is given as As = 2 pi (R+h). The volume of material can be evaluated with respect to the surface area and the thickness of the cylindrical outer wall.


Hint
Management"The submarines that we use in modern days are needed to be well equipped and technically updated because they have to face the worst environmental conditions. As the working area of submarines is deep under the ocean surface, so the biggest problem that it can face is the pressure of water pushing inward. To keep the submarine going we have a submarine pressure vessel whose objecti...

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