PIPE-LINE CONSTRUCTION In pipe-line construction, as in railroad construction, the topog raphy must be studied and lines of least resistance followed. Curves are avoided wherever possible.
The friction factor is an important one. If the friction due to curves is greater than that due to climbing grades then, if prac ticable, the pipe line must go upgrade.
Pipe lines are built to run in as nearly straight lines as possible. This may necessitate crossing numerous hills. Pumps are re quired to make the first lift to carry the oil to the top of a hill, but once up the hill gravity carries the oil down. Only sufficient pressure to overcome friction in the line is necessary after the first lift.
Main gathering lines should be located in valleys so that "feeders" will flow into the valley by gravity. Short curves should be avoided wherever possible as greater friction results.
The laying of pipe lines across streams calls for no great engineering skill, but for common-sense methods based on practice.
In some cases derricks are erected and pipe lines are suspended across a stream. In other cases pipe lines are laid on river bottoms. This is done in deep streams by floating a pontoon across the stream with the pipe line upon it, and then lowering the pipe overboard; or sometimes, simply by connecting the pipe together, and then pulling it across the stream by barge.
In Mexico the Pearson interests laid their offshore lines by building tracks into the Gulf, running the pipe out on trucks and then dropping it off the trucks.
The quality of oil determines largely the rapidity of flow and also the question of pump pressure needed. Heavy viscous oils, like those of California, flow slowly through a pipe line and require greater pressures to drive them through the line than are required by light oils, like those of Pennsylvania and the Mid-Continent.
Heavy oils must sometimes be heated to facilitate the flow. Light oils flow quite freely in warm weather but require heating in the winter: Steepness of Grade.—The steepness of grade is a factor to be considered. If the pipe line is down hill all the way, a gravity flow may be possible. If on the level, comparatively long
breaks between relay stations may be permissible. However, in an area of high hills considerable pressure may be necessary to lift the oil up the grades.
Pipe Specifications.—Pipe-lines are built of hydraulic steel pipe. Such pipe is light, as the pump pressures rarely exceed 600 to 800 lbs. It is tested at from 1000 to 1200 lbs.
Pipe weighs as follows; 6 in. — 19.37 lbs. 8 in. — 29 . 20 lbs. 10 in. — 41.60 lbs. 12 in. — 50.90 lbs.
Pump Stations.—Pumping stations (see Fig. 67) 12 to 25 miles apart are designed to deliver on a 6-in. line 600 bbls. per hour with 600 lbs. line pressure. An 8-in..line would carry 1200 bbls. per hour against a 1200-line pressure.
Pumping stations are placed at intervals of 1;- to 90 miles apart. A heavy oil of high viscosity, like the heavy California crude oil requires stations 14 miles apart. The oil must be heated to reduce viscosity and will retain sufficient heat at this interval. The oil is heated at the pump stations to 130 to 150°F. in heater drums 5 ft. in diameter, 21 ft. long. These drums are much like a water-tube boiler and the oil circulates through them. Heat is supplied by exhaust steam from the pumps. With light oils of 40936., and low viscosity it is not necessary to heat the oil in the lines. With such oils, stations are placed 25 to 40 miles apart, depending upon local conditions.
Different grades of oil are often pumped through a pipe line at the same time. A light oil is started through the line. Later a hundred thousand barrels of heavy oil may be pumped through the line. Then a hundred thousand barrels of light oil may be pumped through the line following the heavy oil. The two different oils mix slightly at their junction but the amount of mixing is not great—say a few hundred barrels or a thousand barrels of oil may be affected. Where the two oils are very differ ent in character it may be necessary to put through a small batch of "buffer" oil or oil of a grade intermediate between the two main batches.