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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