ABSTRACT

Antifouling sheathings can be applied to offshore structures either during the onshore obstruction phase or by retrofitting to existing structures in situ. This paper examines attachment techniques and indicates the effects of the attachment methods on antifouling performance after three years of field testing.

INTRODUCTION

Marine befouling of platforms and other offshore structures penalizes offshore operators in at least three areas: design, fabrication, mad in-service inspection.

  1. During design, beefed-up platform members and piles are required to resist the increased wave-loading forces resulting from larine growth. The growth effectively increases member diameter and surface roughness as well as adding weight.

  2. Higher fabrication costs result from; he necessity of welding thicker sections and Providing post-weld heat treatment for some of these thicker sections.

  3. Conventional in-service underwater section of welded joints cannot be carried out mess the marine growth covering the welds is removed. This necessitates expensive underwater: leaning operations.

Marine growth on ships and mobile structures last traditionally been retarded by the use of misfiling paints and other coatings. These typically contain copper or tin additives and endure for a maximum of five years, usually less. Copper metal, itself, in the form of sheathing last occasionally been used very successfully on small boat hulls, but until the last seven or eight years, there was little experience with coating of large offshore structures.

In 1982, Exxon Production Research Company initiated a test program to Study various copy alloy Shea lining devices to determine if they would provide effective protection for a 40-year platform design life. One of the objectives of the study was to identify efficient techniques of both installing the sheathing on new construction and retrofitting it to existing structures. In all cases, the alloy to be utilized as the sheathing material was required to be 90 percent copper and 10 percent nickel (90 Cu/10 Ni). In addition, it had to be electrically isolated from the steel substrate by blastomeric materials.

TEST PROGRAM

The test program can best be described chronologically.

1983

  • Several hundred antifouling markers were banded and adhesively bonded to a Gulf of Mexico platform under construction in a fabrication yard.

  • Copper-nickel sheathing from three different manufacturers was Installed on a small steel jacket intended as a boat landing for a platform off the California coast. One product had been factory-installed by autoclaving (hot bonding) to a diagonal member.

The second was also hot-bonded in a factory. These two were welded into and clamped onto the structure, respectively, during jacket construction. The third product was retrofit- installed by divers after the jacket had been in the water for a few weeks. The retrofit product was held in place by adhesive and by bolted clamps. All three products were installed horizontally just below the water line

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