line sizing
Post on 14-Oct-2015
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Where We Go Wrong In Line Sizing
Dick Hawrelak
Presented to ES317Y in 1999 at UWO
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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.
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Mass and Energy BalancesMB & 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 (< 3 fps) can cause entrained solids to settle and plug lines.
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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.
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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 readilyMay 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 flow4 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!
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