In the autumn of 1993 an incident occurred with a diving support vessel, whereby a live pipeline from a NAM gas production platform, situated in the Dutch sector of the North Sea, was considerably displaced. Key element in the repair of the line was to identify potential hazards involved in various remedial scenarios and to manage the associated risks.
During anchoring-up of a diving support vessel an incident took place. Bolt ends of a flange connection near platform L5 were hooked by one of the four anchor wires. This resulted in a horizontal displacement of 4 to 5 meters of the pipeline. The identification and management of risks inherent to the arisen situation as a result of this incident and the subsequent repair is the subject of this paper. This will be illustrated firstly by a brief description of the pipeline system and a review of the pre-incident period. Thereafter the incident will be described particularly in the light of the existing operational procedures Special attention will be paid to the risk trade-off of the repair scenario's and the selected recovery scheme. The identification of the uncertainties inherent to the selected method of repair will be discussed by a brief description of the integrated engineering and inspection program. Finally the execution of the work offshore and recommissioning of the pipeline is briefly presented.
NAM and Elf Petroland are operating five platforms along the 24/36 inch Northern Gas Transport Pipeline (NOGAT) in the Dutch sector of the North Sea (See attachment 1, which shows the relevant part of the Dutch sector of the North Sea). The particular platform of interest for this paper is the gas producing platform L5, installed in 1992 in a water depth of 40 meter.