3B - Design Process

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