A Unique Approach to the Design and Installation of a Cathodic Protection System for a Cook Inlet Platform
Authors: Tibbetts Owen D. 
Published: December 2007

This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Las Vegas, Nev., Sept. 30-Oct. 3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

The difficulties encountered in the cathodic protection of Cook Inlet platforms are well known. The high driving voltages and high electrical currents required for protection together with the harsh protection together with the harsh environmental conditions make this a most challenging job.

After initial attempts at cathodic protection failed, twenty-five 8-ton anode protection failed, twenty-five 8-ton anode sleds were installed on the sea bottom near the Dolly Varden platform to provide the impressed current required for protection. Each anode was supplied with current by an armored cable connected to rectifiers on deck. A unique conduit system was constructed for these cables. It was attached externally to the platform leg and extended 155 feet from the Inlet bottom to above high tide. It was installed as one integral unit complete with a triangular prism-shaped ice breaker affording protection from ice floes throughout the tidal zone.

The design considerations and the installation of this system are discussed. The system's performance after nearly two years of operation has been satisfactory, pointing to the success of this design. pointing to the success of this design. it is also believed that this design and installation technique could find application in the offshore arctic and sub-arctic environment where the need for external pipe risers exists.

Introduction

Initial attempts to protect the early Cook Inlet platforms were nearly all inadequate. The inadequacies centered around the problem of maintaining polarization of the submerged metal surfaces of the structure because of the continual abrasive effect of strong tidal currents laden with glacial silt. This effect results in large electrical current requirements, typically 2000 amps or more, depending on the amount of submerged surface area. The problem is further compounded by the high driving potentials which are required as a result of the high resistivity caused by low temperatures, low salinity and the presence of glacial silt. These factors all presence of glacial silt. These factors all combine to make cathodic protection of these structures a most challenging job.

The platform that will be referred to in this study is the Dolly Varden and is the largest structure in the Inlet.