Underwater Repairs to Ekofisk structures
Authors: Skipton J. , Headrick J. 
Published: October 2008

The paper indicates the extreme complexity that may be involved in underwater repairs, and emphasizes the necessity for very careful and detailed planning.

Although many methods are available for repairing underwater damage, a selected repair system will depend upon the combination of conditions specific to the damaged platform.

The case histories cited, cover various repair methods that have been effectively used in the Norwegian North Sea.

INTRODUCTION

The primary purpose of this paper is to present case histories of underwater repairs that have been successfully carried out on steel template type structures in the North Sea - specifically in the Phillips (1)Ekofisk Field.

The Ekofisk project includes a central complex, two outlying production platforms in the Ekofisk field, and several outlying fields with pipe line connections to the central complex. The central complex consists of a one million barrel concrete tank; Platform "P", which contains pumps at the initiating end of the 34 inch pipe line to Teesside, England; a compressor platform; a field terminal platform; and other auxiliary platforms, all extending for approximately 3000 feet.

Those of you involved in platform construction and operation will be fully aware that repairs and/or modifications to offshore structures are continuously required for one reason or another. It may be necessary to modify a structure to accommodate a variation in a process, or to comply with a new requirement by a certifying agent, or to repair members that have been accidentally damaged.

Although damage to a platform may occur at any time, and may involve almost any member, it has been found that the members most susceptible to damage are those located at, or passing thru the water line. All operations during the construction, and life of a platform have potential to some degree, for causing damage. Probably the most serious damage sustained by any platform has been attributable to either the installation or drilling operations. The most numerous cases of platform damage have resulted from loading and unloading supplies during marginal weather conditions.

Damage, when discovered, normally requires a complete investigation of the members involved, to determine any member misalignment, denting or flattening, and the integrity of welded connections. Depending upon the-extent and location of the damage, repair systems may include gouging and rewelding, sleeving damaged areas, or even replacing a defective member.

Damage occurring during the installation phase often necessitates major-repairs. For instance, it has been necessary to repair members at elevation minus 230 ft LAT, and it has also been necessary to replace a corner jacket leg and piling upwards from elevation minus 65 f t LAT.

Major Underwater repairs require a great deal of forethought and preparation.

Primarily the damaged area and all members and member ends in the near vicinity should be inspected visually by divers, and if possible, video tape recordings of all the damaged parts should be made and retained for reference during the repair design.