3B - Design Process

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Data required for steady state pressure and temperature profiles:

flow rates

fluid properties ( density, viscosity, bulk modulus, thermal expansion coefficient, heat capacity, vapor pressure, pour point)

pipe grade, pipe size, wall thickness and roughness

pipe length and elevation profile

injection and delivery locations

delivery pressure

injection and ground temperature

depth of burial and soil conductivity

operating data such as operating and ground temperatures

design is a plan according to given set of parameters

parameters are physical properties that affect behaviour of system

criteria are conditions and guidelines for design

optimal design optimises these factors

restraints imposed by codes and standards

prime consideration in design is safety

standards become codes when they are incorporated into a set of government regulations

need for a pipeline needs to exist before pipeline is built

pipeline could be new or an increase in capacity of existing pipeline according to demand and volume specified in request

optimal design should account for pipeline system growth

determine supply and demand and respective locations

seasonal variations should be taken into account for design

cost,timing and environmental impact are the major considerations of design

right of way affects construction and land acquisition cost

elevation profile affects hydraulics, pumping requirement and costs

depth of burial affects hydraulics due to heat of conduction, pipe integrity and construction cost

soil types affect construction cost and heat conduction

water crossings affect construction costs

geotechnical considerations like slope stability, earthquakes, ...etc

operating parameters include operating flow range, operating pressures and temperatures, fluid properties, ambient conditions

design does not only predict future growth, it also takes into account daily maximums and minimums and annual throughputs

optimum pipe diameter is a balance between material costs and pumping costs

low viscosity fluids (less than 10 cSt) --> use charts with recommended velocities ( slide 9)

high viscosity fluids (more than 10 cSt) use lower velocities, not purely economic factors, rather keeping pressure drop to an acceptable limit

minimum and maximum pressures for pipeline operations

maximum operating pressures constrained by pipe yield strength, pipe diameter and wall thickness, fluid density and elevation of the lowest point of the pipe

minimum pressures determined by vapour pressures of liquids

temperature affects density, viscosity and specific heat.

high temperature is beneficial because it lowers density, viscosity and hence the pressure drop

cooling non newtonian fluids leads to increase in viscosity which causes a very high pressure drop

to reduce pipe cooling, pipe can be insulated and or operated at a high temperature

it can also be blended with lighter HCs

temperature along pipeline is very hard to control because it depends on variable soil thermal conductivity and and ambient temperature

max temperature for buried pipe determined by: 1. ground conditions 2. stress before buckling 3. economics of pipe flow

minimum temperature limit determined by metallurgical properties of pipe and by ground conditions

higher density--> higher pressure drop due to friction

compressibility for controlling surges ( not important for pipeline design

viscosity is important in calculating size, hydraulics and pumping requirement

vapor pressure determines minimum pressure in pipeline, must be high to avoid 2 phase flow and pump cavitation

pour point is the lowest temp at which fluid flows and beyond which will start behaving like a non newtonian fluid

specific heat affects heat transfer rate through conduction process

ambient conditions play critical role in design especially in extreme environments such as deserts or the arctic

in permafrost fluid has to be chilled to avoid melting surrounding soil

air temp affects turbine driver thermodynamics and affects fluid properties due to conduction

burial advantages slide 11

greater depth of burial--> lower rate of heat transfer

effect of soil thermal conductivity depends on differential temperature between soil and fluid

soil colder--> fluid temp drops--> increase in viscosity --> higher pressure drop

parameters required to determine temperature profile --> slide 11

profitability of pipeline directly related to volume

pipe grade, diameter and wall thickness most important factors in determining capacity, and also affect pressures

large diameter--> more volume, smaller pressure drop per unit length

thickness determines steel, CAPEX and operating pressure

pipe grade determines steel strength and operating pressure

pipe roughness affects pressure drop and pigging operations

pipe coating protects from corrosion

nominal pipe size (NPS) indicates outer diameter of pipe (mm or inches)

design pressure (barlow equation)--> slide 13

effective pipe roughness affects frictional pressure drop and pipeline efficiency

higher roughness--> higher friction--> higher pressure loss

roughness reduced by coating inside of pipe or by pigging

maximum allowable pressure proportional to pipe strength

maximum pressure allowed for steady state pipeline operations

maximum allowable pressure is sum of pressure required to overcome friction loss, static head pressure, back pressures or delivery pressures

values of MAOP vary with elevation changes

hydrostatic test used to test integrity of pipeline

divided to multiple segments tested individually

hydrostatic test--> slide 15

pipe wall thickness requires an allowance of 10% over internal design pressure, 80% of minimum yield strength

allowance takes into account surges and changes in pressure

thickness increased and decreased according to local transient pressure requirement or decreased to reduce pipe cost

pipe thickness larger in river crossings or deep valleys, smaller in highest elevations

components designed to withstand maximum pressure differential between internal and external design pressures

external surface loading requires extra pipeline thickness

factors affecting cost: (slide 17)

mechanical ( pipe grade, size, and wall thickness, pipeline route and depth of cover)

capacity (operating parameters, station spacing anf pumping costs)

reliability (valve spacing, other valve related costs)

phases of design: conceptual design, system planning, detailed engineering

conceptual design --> product properties, flow profile, pipeline length and route, macro economic data ( may include hydraulic and economic studies)

hydraulic design procedure --> slide 19-20