Line Sizing Instruct Uwo by ilicaifengba

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									Where We Go Wrong
In Line Sizing
 Dick Hawrelak

 Presented to ES317Y in 1999 at UWO
Introduction
n   31% of large property damage
    losses are caused by failures in
    piping systems.
n   Some lines reach 60 inches in
    diameter - larger than many
    equipment items.
Mass and Energy Balances
n   MB & EB balances must include:
n   Normal mass balance - base case.
n   Start-up, shut down or upset dev’n.
n   Recycle of off-spec products.
n   Equipment bypass conditions.
n   MB for flare, fire water, sewers,
    steam, condensate and CTW
    headers.
Poor Line Sizing
Guidelines
n   Limiting line velocities not known
    or ignored.
n   Velocity greater than 15 fps in CS
    pipe can cause erosion.
n   Low velocities (< 3 fps) can cause
    entrained solids to settle and plug
    lines.
Poor Line Sizing
Engineering Discipline

n   Poor record keeping during Phase 3
    prevents detailed follow-up in Phase
    4 design stage.
n   PSV lines need to be checked in
    Phase 4.
n   Pump lines need to be checked in
    Phase 4.
Poor Pipe Selection
n   Corrosiveness of fluid unknown.
n   At high temps, degradation may
    produce acidic components. (La.
    HumbleTherm example).
n   Pipe not suitable for unexpected
    cold temperatures.
n   Pipe not suitable for unexpected
    extreme high temperatures.
Choked Flow Of
Compressible Fluids

n   Compressible fluid flow not well
    understood by process engineers.
n   Flows at Mach 1 (Sonic Flow) can
    be destructive.
Choked Flow Example 1
Choked Flow Example 2
Two-Phase Flow

n   Two Phase Flow not well
    understood by process engineers.
n   Horizontal Flow - Baker Chart.
n   Vertical Down Flow.
n   Vertical Up Flow.
Baker Chart
Horizontal, Two Phase Flow
    Two-Phase Flow In
    Vertical Down Flow
    Piping

n   Siphons may form readily
n   May have damaging pulsating flow
Vertical Down Flow
Piping
Two-Phase Flow In
Vertical Up Flow Piping

n   May have damaging pulsating flow
n   4 ft. dia. Cooling tower inlet pipe
    experiences severe vibration, fails
    & floods plant
Vertical Up Flow Piping
Two-Phase Flow
Pressure Drop

n   Two phase flow pressure drops
    may be higher than expected and
    thereby limit performance.
Two-Phase Flashing
Fluids

n   Flashing liquids often not
    considered during process design.

n   Two phase flow can be a complex,
    transient problem.
Two-Phase Flow In PSV
Systems

n   PSVs are usually sized for single
    phase flow.
n   Two phase flow can occur when
    vessels operated above maximum
    fill limit.
n   Two phase flow can occur when
    flows are higher than expected.
Vortex Problems
n   Draining water from KO Pot to
    open sewer during rain storm.
n   Flammable vapor entrained due to
    formation of liquid vortex.
n   Lightning strikes near plant ISBL.
n   Sewer explodes, wrecks cold box
    in Ammonia Plant.
n   One operator killed.
      Maldistribution

n   Flow in reactor manifolds.
n   Flows in branched piping.
n   Flows in shell-side of exchangers.
     Water Hammer

n   System or vessel design pressures
    exceeded when EBV suddenly
    stops flow.
n   EO transfer example.
n   See computer spreadsheet design
    program.
Water Hammer Results
Typical Exam Problems

n   Which flow regime should you
    avoid for horizontal, two phase
    flow?
n   If a liquid vortex forms on draining
    from a vessel, what safety
    problems can this create?
n   When can a PSV which is sized for
    single phase flow experience two
    phase flow?
Put Your Money Where
Your Mouth is!

								
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