ABSTRACT

The object of this review is to present to those engaged in the design of offshore structures, and those charged with their maintenance, information concerning the manner in which testing often is performed as well as the performance of a variety of teel compositions which led to the development of several new proprietary steels. New data are presented concerning the long-term performance of protective coatings on steel. In addition, new data are presented concerning the long-term performance of thermally applied or moralized coatings on steel. Selected case histories are cited for the insight they provide toward the effective use of steel in offshore structures. By including an extensive bibliography, many useful data are brought to the attention of the practicing engineer so that the concepts involved in the discussion become understandable. It is the intent that attention be called to the need to consider simultaneously the principles of corrosion as well as the principles of structural.. design at the planning stage, because one without the other could be self-defeating.

INTRODUCTION

Man's experience with the marine environment has taught him that its aggressive action on materials of construction is a continuous and insidious one. The application of galvanic protection was recognized by Faraday and the principles of corrosion theory began to be established in the early part of the 19th century. The systematic approach toward understanding the corrosion mechanism and the development of corrosion resistant steels began in the first quarter of the 20th century. Assistance was rendered by the formation of the American Society for Testing and Materials (ASTM) which pioneered the establishment of the outdoor test site where joint effort involving the exposure of various materials to different types of environments such as marine, industrial and rural, as well as the conduct of immersion tests in brackish and saline waters, led to the development of much useful data. With the creation of the electrochemical theory of corrosion came a better understanding of how metals and alloys could be used more effectively by means of design and the avoidance of conditions which accelerate corrosion.

The use of relatively small test specimens (under one square foot in area) made it economically possible to develop useful information for comparing compositions as well as calibrating the corrosively of a particular environment and supplying an insight into the annual variations individual environments undergo from time to time. Following in the path of ASTM, The International Nickel Company, Inc. (INCO), established a marine test station at Harbor Island, Wrightsville Beach, North Carolina, and an atmospheric exposure site at Kure Beach, North Carolina. The station has pioneered many useful studies basic to the understanding of factors significant in both atmospheric and seawater corrosion. Figure 1 shows the 800-ft. atmospheric test lot at Kure Beach.

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