- bringing life to the desert -
By Corrie Johnstone, Corrintec limited

The Great Man Made River project was one of the most ambitious projects in the history of water engineering and had the aim of transforming large expanses of Libyan desert into fertile land for agriculture.

This vast and intricate scheme involved extracting ancient water from beneath the Sahara and distributing it through a complex system of pipelines and reservoirs. Because of the unique conditions found in the desert, problems of corrosion presented a risk to the structural integrity of the pipelines and therefore a key section of the pipeline has been safeguarded by equipment from Corrintec Limited, the British specialists in cathodic protection.

Corrintec's involvement in the project focused on the Benghazi end of the scheme where water accumulated into one of several reservoirs. Here, Corrintec designed and installed a sacrificial anode system that protects a 2 kilometer by-pass pipeline measuring 4.2 meters in diameter, as well as all the associated ductile iron inlet/outlet pipework at the reservoir.

A sacrificial anode cathodic protection system utilizes the concept that dissimilar metals which are electrically coupled, generate a DC current between the two through the electrolyte. A current will flow from the more reactive metal (anode) to the less reactive metal (cathode) and this is why corrosion occurs.

By connecting a more reactive metal (zinc) to a less reactive metal (steel), the structure becomes the non-consumable cathode while the reactive metal is consumed as the anode. This is the basis upon which sacrificial anodes prevent corrosion.

The Great Man Made River project began in 1989 when Corrintec carried out an initial soil resistivity survey for Enka Construction & Industries Inc. who were subcontracted for this section of the scheme by Dong Ah Construction of Korea.

"At some point in history, the desert had been a sea bed and at depths of over 3 meters we discovered low resistivity soil with a high salt content which obviously increases rates of corrosion for steel," said David Moran, Corrintec's Senior Technical & Development Consultant Engineer.

These factors were taken into consideration in the design of the cathodic protection system which used packaged zinc anodes weighing over 58 kilos to protect the buried pipeline which had been constructed from pre-stressed concrete.

Along its length, the pipeline is protected by four groundbeds of 15-30 zinc anodes, sited at intervals to provide the maximum spread of current to eliminate any naturally occurring corrosion in the steel reinforcement.

"The system has a design life of 50 years and therefore particular care had to be taken over the quality and integrity of the materials used, bearing in mind the desert's unique conditions" David Moran commented.
In the desert environment, equipment is vulnerable to wind blown sand and therefore test stations and bonding systems had to be sealed against the elements and were located in areas where they were least at risk.

When the scheme was finalized in 1995, Corrintec provided a training program for the Libyan engineers who are responsible for the maintenance of the pipeline to ensure that it continues to give the required levels of protection. The success of this project was due to the experience of the Corrintec engineers involved and their ability to design a sacrificial system, which had to take into account the unique and hostile desert conditions found in this part of the world.

Corrintec's experience in cathodic protection has been developed over a period of 35 years. In the Middle East, projects have involved the design and installation of impressed current and sacrificial anode systems for underground pumping stations in the desert as well as harbor protection systems along the Gulf of Suez. Internationally, the company provides expertise in all aspects of cathodic protection for underground and sub-sea pipelines, gas, sewerage and water mains, industrial plants and offshore structures, as well as the hulls of military and commercial vessels.