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Factors affecting pipeline performance

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    Factors affecting pipeline performance

    MASS & WEIGHT
    Mass and weight are not the same thing.
    Mass is defined as the
    amount of matter an object contains
    . The standard unit of mass is
    the pound (lb
    m) kilograms (kg).

    Weight
    is the measure of gravitational force exerted upon an object
    .
    Weight is measured in a unit called the pound-force (lb
    f) Newton (N),
    which describes the mass of an object multiplied by the acceleration
    due to gravity:
    Gravitational Force = mass [lb
    m] ´ acceleration due to gravity [ft/s2]
    = mass
    [kg] ´ acceleration due to gravity [m/s2]

    W =m

    [g]
    [lbm] [ft]
    =
    [kg
    m]
    = [N]

    [g
    c] [s2] [s2]

    where
    m =lb
    m

    (mass)
    =
    kg (mass)
    g = acceleration due to gravity (32.174 ft/s
    2)
    = acceleration due to gravity
    (9.8 m/s2)

    g
    c = conversion factor
    32.174 lb
    m ft/s2

    lb
    f

    As a matter of convenience, the mass of an object on the earth’s
    surface is equated to the object’s weight, so that the measure of an
    object’s mass and the measure of an object’s weight are often used
    interchangeably. When we move off the earth’s surface, the difference
    between mass and weight is more apparent. Consider a person
    whose mass is 119 lb
    m (54 kg) on the surface of the earth. If that
    person goes to the moon, where the gravitational force is 1/6 as much
    as it is on earth, his mass will not change. A person with a mass of
    119 lb
    m (54 kg) weighs 119 lbf (529.5 N) on earth, where the acceleration
    due to gravity is 32.174 ft/s
    2 (9.8 m/s2) (at sea level and
    45º latitude):
    Gravitational force
    (weight) = mass
    ´ acceleration
    = 119 lb
    m ´ (32.174 ft/s2) ´ 1 lbf

    32.174 lb
    m ft/s2

    =
    54 kg ´ (9.8 m/s2)

    = 119 lb
    f

    =
    529.2 N
    On the moon, where the acceleration due to gravity is 5.25 ft/s
    2

    (1.6 m/s
    2), the same person with a mass of 119 lbm (54 kg) weighs
    19.4 lb
    f (86.4 N):
    Gravitational force (weight) = mass
    ´ acceleration
    = 119 lb
    m ´ (5.25 ft/s2) 1 lbf

    32.174 lb
    m ft/s2

    =
    54 kg ´ 1.6 m/s2

    = 19.4 lb
    f
    =
    86.4 N

    On a daily basis, density and viscosity are the most important factors
    affecting line operation. They account for most line pressure changes
    and, subsequently, for most of the operators’ actions to control the
    movement of liquid in the pipeline.
    VISCOSITY
    On a daily basis, density and viscosity are the most important factors
    affecting line operation. They account for most line pressure changes
    and, subsequently, for most of the operators’ actions to control the
    movement of liquid in the pipeline.
    Viscosity
    is defined as the property of a liquid which describes its
    resistance to flow, or as the measure of a liquid’s internal friction
    .
    A liquid with high viscosity will not flow or pour as easily as a liquid
    with low viscosity. Honey, for example, has a much higher viscosity
    than water. Because honey has a higher viscosity than water, honey
    tends to change shape much less easily and flow much more slowly
    than water.
    Viscosity and density are not related. Two liquids may have the same
    density but very different measures of viscosity. For example,
    mercury is quite dense but has low viscosity. The energy needed to
    overcome pipeline friction is one of the most significant costs in
    operating a pipeline.
    When liquid moves down the pipeline there is friction between the
    liquid at the pipe wall and the pipe wall itself. This friction slows
    down the liquid along the pipe wall. The higher a liquid’s viscosity,

    the more friction there will be against the pipe wall.
    Fluidity is the opposite of viscosity. While viscosity is the property of
    a liquid which describes its resistance to flow,
    fluidity is the capacity
    of a liquid to flow
    . A liquid with high viscosity can also be said to
    have a low fluidity; conversely, a liquid with low viscosity can also be

    said to have a high fluidity.
    the line pressure between two pump stations, A
    and B. The initial pressure at A is dictated by the required suction
    pressure at B and depends on the density of the liquid. Pressure is lost
    between the two stations in overcoming the frictional resistance to
    flow.


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    DENSITY
    Density
    is defined as the mass of a substance with respect to volume,

    and is designated by the Greek symbol,
    r (rho). To calculate density
    use the following equation:
    Density (
    r) =
    mass (M)
    ´ [lbm]
    volume (V) [ft
    3]
    =
    mass (M)
    ´ [kg]

    volume (V)
    [m3]

    Water at 39.2°F
    (4ºC), for example, has a density of 62.43 lbm/ft3

    (1000 kg/m
    3). This means that at 39.2°F (4ºC), a volume of 1 ft3

    (1 m
    3) of water has a mass of 62.43 lbm (1000 kg):

    r
    =
    mass
    ´ [lbm]
    volume [ft
    3]
    =
    mass
    ´ [kg]

    volume
    [m3]

    r
    =
    62.43 lb
    m

    1 ft
    3

    =
    1000 kg
    1 m
    3

    r
    = 62.43 lbm/ft3

    = 1000 kg/m3
    Suppose there is a tank containing 141 ft
    3 (4 m3) of a diesel fuel with
    a mass of 6076 lb
    m (2756 kg). The density, then, is:

    r
    = mass ´ [lbm]
    volume [ft
    3]
    = mass
    ´ [kg]

    volume
    [m3]

    r
    =
    6076 lb
    m

    141 ft
    3

    =
    2756 kg
    4 m
    3

    r
    = 43.1 lbm/ft3

    =
    689 kg/m3

    When people say that lead is “heavier” than water, or talk about
    “light” and “heavy” fuels, they are talking about the density of the
    substances. To illustrate density, imagine having two containers of
    equal volume. The first container is filled with water and the second
    container is filled with lead. Lead has a higher density than water,
    which means that the container of lead has more mass than the
    container of water.
    SPECIFIC GRAVITY
    17
    LIQUID PROPERTIES
    The terms density and specific gravity are often used interchangeably
    but they do not have the same meaning. Density is mass per unit
    volume.
    Specific Gravity (SG) compares the density of any liquid to
    the density of water, with each at the same reference temperature of
    60ºF
    (15ºC)
    . Operators must understand the relationship between
    density and specific gravity because it is often necessary to convert
    one to the other.
    Again, density is the mass of a substance divided by its volume. If the
    volume of a medium crude oil such as a sweet hydrocarbon is
    706.4 ft
    3 (20 m3) and the mass is 36 861 lbm (16 720 kg), the density
    of the hydrocarbon is 36 861 lb
    m /706.4 ft3 = 52.2 lbm/ft3

    (16 720/20) = 836 kg/m
    3). The standard temperature used in the
    petroleum industry is 60ºF
    (15ºC) at atmospheric pressure (14.7 psi or
    1 atmosphere). The density of pure water at 60ºF
    (15ºC) is
    62.4 lb
    m/ft3 (999.1 kg/m3). The specific gravity of the hydrocarbon
    with respect to water at 60ºF
    (15ºC) would be:
    SG = density of hydrocarbon at 60ºF
    (15ºC)

    density of water at 60ºF
    (15ºC)

    = 52.2 lb
    m/ft3

    62.4 lb
    m/ft3

    = 836 kg/m
    3

    999.1 kg/m
    3

    = 0.836
    In many applications, it is necessary to express density in terms of
    API gravity (for more information, see the module titled D
    ENSITY &
    S
    PECIFIC GRAVITY). To convert Specific Gravity to API gravity, use
    the following formula:
    API = 141.5 - 131.5
    SG
    For the above example,
    API = 141.5 - 131.5
    SG
    API = 141.5 - 131.5
    0.836

    API = 37.8



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    REVIEW
    INTRODUCTION TO FLUID BEHAVIOR
    1. Mass is defined as the __________.
    a) measure of gravitational force exerted upon an object
    b) density of an object
    c) amount of matter in an object
    d) total amount of space an object takes up
    2. Weight is defined as the __________.
    a) measure of gravitational force exerted upon an object
    b) density of an object
    c) amount of matter in an object
    d) total amount of space an object takes up
    3. Density is the mass of a substance with respect to __________.
    a) volume
    b) weight
    c) viscosity
    d) specific gravity
    4. The term viscosity refers to the capacity of a liquid
    to __________.
    a) expand
    b) dissolve
    c) vaporize
    d) resist flow
    5. A product with high fluidity has a __________.
    a) low resistance to flow
    b) high density
    c) low volume
    d) high resistance to flow
    6. The term specific gravity refers to __________.
    a) the density of a substance at 32ºF
    (0ºC)

    b) the density of a liquid at 60ºF
    (15ºC) compared to the density
    of water at 60ºF
    (15ºC)

    c) the volume of a liquid at 60ºF
    (15ºC) compared to the volume
    of an equal mass of water at 60ºF
    (15ºC)

    d) the density of a substance at 60ºF
    (15ºC)

    7. If a product at 60ºF
    (15ºC) has a density of 57.2 lbm/ft3

    (916 kg/m
    3), the product’s specific gravity is __________.

    a) 0.350
    b) 3.50
    c) 7.01
    d) 0.917
    8. How does the mass of a substance on the moon compare to
    its mass on the earth?
    a) It is greater on the moon.
    b) It is greater on the earth.
    c) It is the same.
    d) It depends on the substance.
    9. A tank containing 352.9 ft
    3 (10 m3) of heavy hydrocarbon with
    a mass of 20 040 lb
    m (9090 kg) has a density of __________.

    a) 31.2 lb
    m/ft3 (500 kg/m3)

    b) 50.2 lb
    m/ft3 (804 kg/m3)

    c) 56.8 lb
    m/ft3 (909 kg/m3)

    d) 32.8 lb
    m/ft3 (525 kg/m3)

    10. A liquid with high viscosity will __________.
    a) have a high density
    b) change shape readily

    d) flow slowly c) have high fluidity



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