At my workplace I am transporting Petrol/Diesel/Kerosene by pumping these products through a 18" dia pipeline and for a distance of 1150 kilometers.
My question is that do I need to carry out internal roughness measurement.
If Yes, then how to decrease this roughness.
i would say YES if it is feasible to do so.
In any flow, gaseous or liquid, a boundary layer occurs at the surface. If the surface is smooth then less energy is required from the pumps to produce the flow because the boundary layer is thin. In a rough pipe the boundary layer is thicker, the flow becomes more "turbulent" and more energy is required from the pumps; else the flow is reduced. For distances of 1150 km it may be cheaper, in the long run, to do a roughness check. BUT if the roughness can be smoothed; what will the cost be for a pipe that is already installed? an exercise in cost effectiveness.
Measurement should be done only if actual pressure drop is considerably more than predicted for the flow rate by standard methods. The actual average roughness can be calculated by the same methods. In an 18" pipe the roughness is usually small compared to the diameter, unless the pipe is old or badly corroded. High sulfur diesel can cause corrosion, removing carbon from steel, and making it weak unless a low carbon alloy is used.
Velocity in the pipe is important to keep it clean. Usually 3 feet per second is the minimum for liquids. Petrol often has a residue from cross linking of unsaturated bonds, like benzene, toluene, and xylene. Usually a velocity is specified around 5 feet per second and pumping stations are provided along the route to deliver the necessary head and flow. The maximum is usually 7 feet per second, above which the pipe might be over pressured or eroded by the high velocity. Exception is asphalt pipe where 15 feet per second is sometimes required to keep the pipe clean.
For a short time a higher velocity or a powder slurry may be used to clean a pipe and lower the roughness, within limitations of pressure ratings of the pipe. Flushing with a citric acid solution is also done in many places to clean and lower roughness. Too much of this makes the pipe thin and rated for less head and flow.
Plastic and rubber devices, sometimes called pigs, are commonly used to empty and clean a pipe when it must change from one liquid product to another. Stations are provided to launch and recover the devices. Many styles of devices are available. For best use the pipe should be originally constructed to facilitate the passage of the devices. On other pipes they are still used, but not always recovered intact or where expected. When the devices are used routinely then roughness is not usually a problem. If it is, then a different style device might be considered.
Your question probably relates to the measurement of pipe 'hydraulic equivalent roughness' (not the geometric roughness of pipe internal surface, which can be defined in different ways, varies from point to point and hardly serves any practical purpose for a pipeline in operation) ?
The pipe hydraulic equivalent roughness should be an appropriate roughness parameter for pipeline transportation, and is the 'epsilon' parameter in the friction factor formulation which serves to calculate pressure drop along the line, and so can be directly derived from pressure drop measurements between 2 points along the pipeline for given flowrates - assuming of course that the pipeline is clean from debris and deposits which would reduce the internal cross-section (the pressure drop equation is a function of pipe internal diameter).
my sincerely t.hanks to Nicholas Sion , Jerry Decker & Yves Friedmann
you can gauge roughness by pressure drops in the flow. the method suggested by Jerry Decker is a valid approach and should be adopted.
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