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Pressure Vessel Design Query

  1. Sep 3, 2013 #1
    Design a railway cistern for 120,000 kg of Liquid. It has to be a cylindrical shell on two supports.

    The cistern is
    18 m long
    3 m in diameter (inner).
    It is made of steel with the yield strength of SY= 240MPa.
    Safety factor of FY= 1.9;
    Total corrosion allowance, c= 3.0 mm;
    Welded joint efficiency = 0.85
    Shell thickness, t - 32mm

    Check whether this thickness is sufficient to withstand combined action of the internal pressure, t
    he weight of liquid, and the action of longitudinal external forces (tensile or compressive) .
    Assume the mass of the train as m= 12 x 10^6kg, deceleration during braking of a = 3m/sec
    , and during climbing uphill assume the inclination angle of 10 degrees


    I assume there will be 3 design cases for this problem:
    Case 1 Internal Pressure+ Weight of Liquid
    Case 2Internal Pressure+ Weight of Liquid + Inertia during breaking of the railway cistern
    Case 3 Forces acting on the pressure vessel: Internal Pressure + Weight of liquid+ inertia of breaking + inclination angle (locomotive applied to the first cistern in the train)

    Wondering if I am going about this correctly?
     
  2. jcsd
  3. Sep 3, 2013 #2
    I don't see any problem with your method of reasoning, but my question is why a railway cistern needs to be pressurized. AFAIK, a cistern just a big container to hold water or some other liquid, isn't it?
     
  4. Sep 3, 2013 #3
    So for each case I work out the total longitudinal stress?

    For case three I am unsure if I am going about it correctly:

    Determine mgsinx and Ff(friction).
    mgsinx pushes block down the incline and Ff(friction) opposes this.

    Write the equation
    Fnet = mgsinx - FfSince Ff=uFn and we know Fn=mgcosx and we also know Fnet=ma, we write

    ma = mgsinx- u(mgcosx)

    Divide by m throughout, so we don't need mass a=gsinx - ugcosx

    How would I work out u ?
     
  5. Sep 4, 2013 #4
    I think in your equations, "u" is really mu, the coefficient of friction. You should just look it up or experimentally determine it.
     
  6. Sep 4, 2013 #5

    AlephZero

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    Homework Helper

    The liquid exerts a hydrostatic pressure on ALL the surface of the container. That is different from a truck containing a solid. For example a liquid would exert a force on the ends of the cylinder when the train was horizontal, but a solid would not.
     
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