In addition to increased capacity provided by the portable pumping units, other engineering improvements and new methods devised entirely within the company have increased capacity by 40,000 barrels a day, or 13 per cent.

RESTRAINED LINE: A NEW CONCEPT

Years ago, during the building of Tapline, the basic pipe used marked an industry first: the 30 and 31 inch diameter sizes were the largest yet attempted in a crude oil pipeline. At a quarter of an inch in thickness for more than half of its length, it also was the thinnest wall large-diameter pipe ever built, making possible substantial savings in the amount of steel needed. And by nesting the 30-inch diameter pipe inside the 31 -inch during shipment to the Middle East, transportation costs were halved.

A technique completely new to the pipeline industry was the installation of nearly half the line above ground, without expansion bends. This type of construction, used over the level, rocky plains of northwestern Saudi Arabia, avoided the need for excavating in solid rock, thereby saving time and reducing costs. The above-ground line is held in place in steel rings set in concrete supports 20 meters apart.

This original concept was followed by the subsequent successful application of bold new theories of operating at unusually high pressures. For years, pipelines everywhere were operated at pressures not exceeding 65 per cent of the "yield" strength of the steel (the stress point at which the metal begins to stretch more rapidly). This conservative practice had been adopted by the industry to assure safe operation because of the difficulty of calculating the combined effects of all the stresses to which a pipeline is subjected : those due to internal pressure, those caused by changes in temperature of the steel, and those caused by bending of the pipe. Tapline engineers

were convinced that it should be possible to operate at higher pressures by carefully calculating the effect of all these combined stresses, using modern theories of the causes of metal failure. The development of these theories was followed by an extensive program of pressure testing, which confirmed the theories and permitted increasing maximum operating pressures to 80 per cent of "yield".

Broad application of the combined stress theory and pressure test program has permitted Tapline to increase its capacity by 30,000 barrels a day without a single new facility or additional equipment. Further increases in pipeline capacity will be made possible by boosting the available horsepower at the pump stations.

Operating at such high pressures demands great care to assure that safe limits are not exceeded. For example, Tapline has had to solve unusual problems in the control of surges within the pipeline. If one of the intermediate remotely- controlled pumping units suddenly shuts down, a high pressure surge wave travels back toward the main pump station. If uncontrolled, it could rupture the pipeline. This unique problem was solved through a system that, upon shutdown of an intermediate unit, sends a radio signal from it back to the main station and automatically reduces the main station discharge pressure. The reduced pressure out of the main station offsets the surge from the remotely-controlled unit ahead and permits the line to continue to operate safely.

At Tapline's modern terminal south of Sidon, the world's largest supertankers can be loaded with crude oil at rates up to 60,000 barrels an hour.