Oil pipe lines connect points by straight lines as near as possible, and are usually laid below frost line, two or three feet under the surface of the ground, the undulations of which they follow throughout their entire course. They are constructed of wrought-iron pipes four to eighth inches in diameter and are provided with bends at regular intervals to take up the ex pansion and contraction due to varying tem peratures. Pumping stations and storage tanks are placed at intervals of 30 miles, or they are located at central points in the valleys along the lines, to pump the oil over the intervening hills and mountains. High pressure compound con densing pumps are used, working under a head depending upon the topography of the country through which the line is laid Lnd upon the friction due to the diameter of the pipe and the length of the line. The plugging up of the pipes by sedimentary deposits is prevented by occasionally running a "go devil" scraper through the pipes, which is forced along from station to station with the oil by the pressure of the pumps, and scrapes off the paraffin in crustations.
Pipe for conducting natural gas vary in construction being made from wrought-iron piping two or three inches in diameter, large cast-iron pipes, or from riveted steel-plate tubes, ranging from 15 to 25 inches in diameter. In the United States the use of natural gas followed the general development of the petroleum industry. Numerous gas-pipe lines were established in the various gas pro ducing areas, some of which are in operation at the present time, while many have been aban doned upon the exhaustion of the wells. Each of the main lines is about 50 miles in length and originally conducted gas at pressures rang ing from 200 to 1,200 pounds per square inch. In late years, however, these pressures have de creased enormously, being now but a small fraction of what they were, and necessitating the employment of pumps to maintain a de livery pressure ranging from 10 to 50 pounds per square inch. See GAS, NATURAL; STANDARD