The Last Five Years' Experience in Steel Platform Repairs

ABSTRACT The purpose of this paper is to describe recent repair and strengthening projects on steel offshore platforms with particular reference to the cause of damage and the selected repair method. The data are used to update a detailed survey carried out in 1981. This update stems from the authors own involvement in the repair of thirty-nine structures worldwide during the period since 1981. The knowledge provided in this paper has worldwide application in the assessment of the likelihood of damage to offshore installations, the extent of damage from different causes and the most cost effective and frequently selected repair methods. The review shows that, wherever practical there is a general preference for welded repairs provided the extent of repair is limited to replacement of the original structure. However when strengthening, as opposed to repair, is required and whenever time and physical constraints (e.g. reduced diving windows, deep water, splash zone areas) apply, the use of mechanical and grouted clamping and bracing schemes is preferred. Observations are made on the typical timescale and resource requirements for different repair schemes through three case histories. INTRODUCTION On a worldwide basis, the requirements for subsea structural repairs is increasing as a result of increased numbers and ageing of platforms. It is increasingly important for platform operators to recognize the merits and disadvantages of various repair schemes and for cost effective and rapidly installable schemes to be selected. There is wide acceptance of mechanical and clamped repairs in the North Sea and increasingly in other locations, confirming significant financial savings to operators using these techniques. This paper will greatly assist those responsible for the general upkeep of any offshore installation. REVIEW OF REPAIRS In 1981 the author was responsible for a detailed review of repairs to permanent offshore platforms which was undertaken by UEG (1). This review was primarily concerned with North Sea structures and was undertaken by interviewing representatives of most of the operators of North Sea fixed platforms. The primary objectives were to establish the extent to which repairs were being carried out the causes of .the damage and the way in which the damage was discovered. In addition, the method of repair was noted. Sixty-one cases were recorded and detailed case histories are given in Reference 1 for twenty-four of these cases. Since publication of Reference 1, there have been a considerable number of repairs to offshore platforms throughout the world, and particularly in areas with severe offshore environments similar to the North Sea. The author has personally been involved in thirty-nine repairs in such areas. These thirty-nine cases represent a significant extension to the database and it is possible to detect significant trends in the causes of damage and in the selection of repair and strengthening methods. These trends are identified below.