Where We Go Wrong In Line Sizing

1
Where We Go Wrong In Line Sizing

• Dick Hawrelak
• Presented to ES317Y in 1999 at UWO

2
Introduction

• 31 of large property damage losses are caused by
  failures in piping systems.
• Some lines reach 60 inches in diameter - larger
  than many equipment items.

3
Mass and Energy Balances

• MB EB balances must include
• Normal mass balance - base case.
• Start-up, shut down or upset devn.
• Recycle of off-spec products.
• Equipment bypass conditions.
• MB for flare, fire water, sewers, steam,
  condensate and CTW headers.

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Poor Line Sizing Guidelines

• Limiting line velocities not known or ignored.
• Velocity greater than 15 fps in CS pipe can cause
  erosion.
• Low velocities (lt 3 fps) can cause entrained
  solids to settle and plug lines.

5
Poor Line Sizing Engineering Discipline

• Poor record keeping during Phase 3 prevents
  detailed follow-up in Phase 4 design stage.
• PSV lines need to be checked in Phase 4.
• Pump lines need to be checked in Phase 4.

6
Poor Pipe Selection

• Corrosiveness of fluid unknown.
• At high temps, degradation may produce acidic
  components. (La. HumbleTherm example).
• Pipe not suitable for unexpected cold
  temperatures.
• Pipe not suitable for unexpected extreme high
  temperatures.

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Choked Flow Of Compressible Fluids

• Compressible fluid flow not well understood by
  process engineers.
• Flows at Mach 1 (Sonic Flow) can be destructive.

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Choked Flow Example 1
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Choked Flow Example 2
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Two-Phase Flow

• Two Phase Flow not well understood by process
  engineers.
• Horizontal Flow - Baker Chart.
• Vertical Down Flow.
• Vertical Up Flow.

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Baker Chart Horizontal, Two Phase Flow
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Two-Phase Flow In Vertical Down Flow Piping

• Siphons may form readily
• May have damaging pulsating flow

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Vertical Down Flow Piping
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Two-Phase Flow In Vertical Up Flow Piping

• May have damaging pulsating flow
• 4 ft. dia. Cooling tower inlet pipe experiences
  severe vibration, fails floods plant

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Vertical Up Flow Piping
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Two-Phase Flow Pressure Drop

• Two phase flow pressure drops may be higher than
  expected and thereby limit performance.

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Two-Phase Flashing Fluids

• Flashing liquids often not considered during
  process design.
• Two phase flow can be a complex, transient
  problem.

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Two-Phase Flow In PSV Systems

• PSVs are usually sized for single phase flow.
• Two phase flow can occur when vessels operated
  above maximum fill limit.
• Two phase flow can occur when flows are higher
  than expected.

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Vortex Problems

• Draining water from KO Pot to open sewer during
  rain storm.
• Flammable vapor entrained due to formation of
  liquid vortex.
• Lightning strikes near plant ISBL.
• Sewer explodes, wrecks cold box in Ammonia Plant.
• One operator killed.

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Maldistribution

• Flow in reactor manifolds.
• Flows in branched piping.
• Flows in shell-side of exchangers.

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Water Hammer

• System or vessel design pressures exceeded when
  EBV suddenly stops flow.
• EO transfer example.
• See computer spreadsheet design program.

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Water Hammer Results
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Typical Exam Problems

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

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Put Your Money Where Your Mouth is!