INTRODUCTION
Abstract

The paper describes the condition survey methodology, design and installation of a cathodic protection (C.P.) system for a large reinforced concrete reservoir and sea water intake structure. The structure is critical for the supply of cooling water for a 2.4 million metric ton steel plant. The C.P. System consisting of mixed metal oxide coating on titanium mesh type anodes and automatic voltage/current controlled rectifiers was successfully installed and has been operating within design guidelines for the past 15 months.

Saudi Basic Industries Corporation (SABIC) is one of Saudi Arabia''s leading industrial conglomerate, producing more than 20 million metric tons per year of petrochemicals and chemicals, fertilizers, plastics, metals and industrial gases.

Saudi Iron & Steel Company (HADEED) affiliate of the conglomerate was established in 1979 in the city of Jubail in Saudi Arabia. The integrated Iron and Steel Complex came on stream in 1983. The original design capacity was 850,000 metric tons per year, which was increased through technical enhancements and expansions to 2.4 million tons per year.

The infrastructure in the industrial city of Jubail has been designed and constructed by the Royal Commission (RC) with the needs of large scale industrial units in mind. Special attention has been paid to the provision of utilities. Cooling water is provided by a network of open canals carrying sea water to and from the Gulf. Each of the fifteen complexes draw cooling water from this system. Large and massive reinforced concrete reservoirs and intake structures are built in each of the complexes for this purpose. Several of these structures which are now a little more than 10 years old are showing signs of distress. As these structures are extremely important for the continued operation of the plants, special attention has been paid for the repair and rehabilitation of these structures by the plants as well as the R&D management.

WATER STRUCTURE
SEA

The structure was showing early signs of concrete distress. This was manifested as cracking and spalling generally above the water level. While not severe, it was evident that chloride intrusion had progressed to a significant degree. Below the water level the structures were found in good condition as they were cathodically protected from the very beginning. However, the intake structure is very large and complex and the below water structures form only a fraction of the overall structure. Since this structure was critical to the plant usage, short term repair strategies were not considered due to their disruptive actions and the frequency of repairs. A decision was taken to implement a long term repair and rehabilitation strategy. A combination of C.P. System using impressed current anodes and overlay in areas subject to contact with sea water and a conventional repair in areas subject to water spillage was used. This was applied to the internal and external as well as vertical and horizontal surfaces of the entire structure.

The corrosion status prior to installation was determined physically and electrochemically.

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