Pipe-laying operations

Seismic surveys Pipe laying operations Equipment recovery Rig positioning Hazard location. 

During pipe-laying operations, a system failure in the hydraulic pipe handling system caused two quadmple joints being handled at the same time in two different areas of the tower to drop suddenly. Each piece of pipe was 50 m long with a diameter of 24 inches and weighed approximately 20 tons. 

Just prior to the incident the pipe-laying operation had been stopped. Operators reported a system failure and that the hydraulic power had been lost. Such an occurrence was not particularly unusual and, in line with company procedures, this was investigated immediately. A team of technicians led by the chief electrician tried without success to resolve the problems. After these attempts, a more in-depth analysis was made. It was decided, on the basis of input from the system diagnostics, to perform a memory reset. Following this the system appeared to be running correctly. This was the first time that a full memory reset was requested by the internal diagnostics of the control system during a project operational phase. 

Despite their simplicity, pipelines are highly capital intensive. Not only is pipe laying costly, the cost is split roughly evenly between materials and labour, but provision of compression stations - necessary for mass transport over long distances - can contribute 40% of finally installed capital. Once established, the operations of a pipeline system can cost 5% of the fixed capital per annum. 

In 2008, a fatal accident was reported when a pipe-laying ship dropped a 20 tonne section of pipe onto operations personnel [3]. The location of the accident was not reported but is presumed to be outside UK territorial waters. 

In New Zealand trenches over 5 ft (1-6 m) are invariably dug by machine. The movable shoring devices referred to in 15 and known as shields are being accepted as necessary components in the excavation operation. The shields are used to protect workmen either while timbering is being placed or while pipe laying or other work in the trench is being done. Four basic types of shield have been developed. 

In Fig. 1 the lay-out of electric heaters and thermal insulation on sodium piping is shown. The heaters have 100% reserve. Earthing of the main and stand-by heaters is continuously monitored. Leaking sodium creates an electric contact between the heater and the pipe wall. Simultaneous failure of both the operating and stand-by heaters is indicative of a sodium leak. Such systems have been installed at all our fast reactors. Their operation experience has shown high reliability and sensitivity of such systems. 

Pipe repair options include (1) external repairs, such as circumferential posttensioning, replacement, external steel or CFRP bands, or encasement of the distressed pipe, or (2) internal repairs, such as installing a steel liner or slip-lining with fiberglass or steel pipes, or lining with hand lay-up CFRP. Selecting the best option depends on access, acceptable duration of construction, impact on operation, the expected cost of repair, and reliability of the repaired pipeline. 

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