slack flow is 2 phase flow
pressure of liquids drops below vapour pressure, liquid evaporates and forms vapour pockets in pipe
higher flow rate would result in greater friction hence greater pressure drop
pressure difference between peak and downstream would be less if there is a high flow rate
higher flow rate desired to avoid vapour pockets
vapour pockets form when elevation drops severely, pressure downstream increases due to elevation gain
slack flow disrupts pipe flow reducing transmission efficiency and increasing batch interface mixing sizes
damage to pipe interior could occur if vapour pocket suddenly collapses
design considerations --> minimum pressure- hydraulic calculations for flow rates- smaller pipe size- pressure reducing station
pipeline in hot environment--> temperature can increase due to pump inefficiency, frictional heating, surrounding soil
increase in T--> decrease in viscosity and density--> increase in vapour pressure--> decrease in pressure drop
increase in vapour pressure means pipeline pressure can drop below vapour pressure unless pump discharges at higher pressure
increase in vapour pressure increases evaporation in liquid pipelines and storage tanks
cooling facilities required
best locations are near water where line temperatures are low
ground permanently frozen --> permafrost
operating temperature is critical
considerations in cold climates --> slide 4
low temp steel pipes to control fracture
ground frozen--> installed above ground
pipeline shutdown --> crude may congeal
batching
densities and viscosities are different, pressure gradients are different and so are pipeline capacities
capacity depends on --> slide 5
fluid with largest density and viscosity and highest vapour pressure is picked for calculations in batching
pressure drop can be averaged if batch sizes are small, load factor is low, or batches similar in densities and viscosities
high vapour pressure products--> vapour pressure at 38 deg C exceeds 110 kPa
high vapour pressure products have low density, low viscosities, and require high operating pressure to maintain single phase
high vapour pressure products are highly flammable and heavier than air in gaseous form
leaks could lead to explosion
very sensitive to changes in Temperature, must be calculated carefully
governing design parameters for high vapour pressure products are maximum temperature and vapour pressure
heavy crude don't flow easily under normal operating temperature due to high viscosity and high pour point
methods for handling heavy or waxy crude--> slide 8
critical design parameters for heavy crude are viscosity and pour point
non newtonian flow near pour point requires additional pressure
no problem of pumping below pour point as long as fluid is in motion
shutdown --> gelled state--> more pressure required to pump
restart pressure less in a heavy HC shutdown but above pour point
design for heavy HC should include temperature behaviour of environment and effect on fluid properties and temperature effects on shutdown and restart
operating temperature also affects mechanical design and design for operations like shutdown and restart
hydraulic design and operation problems for heavy crude --> slide 10
temperature for heavy crude --> slide 11
heat duty --> slide 12
maximum allowable operating pressure can't be violated downstream of a pump
each station has the same differential head
flat terrain -->slide 14

	Created by nada.h.aly over 8 years ago

Normal-level (N-level) Oil & Gas Transmission & Storage Note on 3D Liquid Pipeline Design, created by nada.h.aly on 28/10/2015.