natural gas submarine pipeline maintenance is quite complicated. After the leak, it was not as many people imagined. As long as the gas transmission is stopped, the loss can be avoided. Because the natural gas pipeline is laid on the seabed and is surrounded by seawater, once the pressure inside the pipeline is lost, the seawater will immediately flow backwards and damage the pipeline. So the general approach is to keep the pipeline at a slight positive pressure, which is why Gazette did not stop gas transmission immediately after the Nordic pipeline ruptured.
Due to the flammable and explosive nature of natural gas, helium will be input into the pipeline to replace the remaining natural gas. As an inert gas, helium can prevent deflagation and explosion on the one hand, and on the other hand, it can protect the pipeline from corrosion by sea water backflow .
Generally speaking, small leak points can be solved by attaching a bushing outside, but the Beixi accident was obviously artificially damaged, and the leak points may be very large. Therefore, the bushing cannot be used, and the repair can only be done by replacing damaged pipes.
There are three ways to replace damaged pipelines:
This method is suitable for situations where the water depth is shallow and the pipeline is damaged on a large area, and production needs to be stopped for pipeline replacement. The specific method is to first cut off the damaged pipeline from both ends, then use a flat pipe to lift the damaged pipeline, and then install the replaced pipeline on the original pipeline through a flange (seals and fixtures installed at both ends of the replacement pipeline, at the circle of the drawing below). This method is suitable for seabeds with relatively straight terrain.
This method is suitable for seabeds with relatively complex terrain. First cut off the damaged pipe, then install a mechanical connector on both ends of the cutting surface, and finally place the replaced pipe on the mechanical connector. This maintenance method is suitable for repair operations within 200 meters of shallow seas.
. Dry cabin maintenance method
Dry cabin maintenance method is to first drill fixed piles around the damaged pipeline under the sea, then sink the dry maintenance warehouse to the seabed and fix it on the fixed pile, and the dry cabin covers the pipeline that needs maintenance. Then drain the sea water in the dry cabin, and the diver takes diving clock to enter the dry cabin to repair and replace the damaged pipeline.
replace and repair the natural gas pipelines on the seabed, and also face complex problems such as sea conditions, whether nearby are busy routes, and whether they are fishery production areas.
Nordic stream pipeline is located in Baltic Sea . The Baltic Sea is located in the transition zone between temperate marine climate and continental climate. It is prevalent throughout the year, and storms often occur in autumn and winter. Because the North Atlantic warm current in the North Atlantic is difficult to enter the Baltic Sea, the sea water is not regulated, resulting in a relatively low temperature in winter.
The subsea survey and measurement of damaged pipelines, mud blowing exposure, cold cutting, lifting, replacement and installation, etc., all need to be carried out under stable sea conditions. There are many storms in the Baltic Sea in winter, which will have adverse effects on all aspects of pipeline maintenance.
At the same time, the direction of pipelines No. 1 and No. 2 near Bornholm Island will pass through multiple busy routes, which will have an adverse impact on Russia's pipeline maintenance.
This time, the Beixi pipeline has a large range of bubbles formed on the sea surface, and the estimated damage range is also large, so it is likely that the problem of seawater backflow has occurred. After the pipeline maintenance is completed, the seawater entering the pipeline must be drained and dried and inert after the pressure test is completed. Otherwise, the entire pipeline and even the pressurized turbine will be damaged, so the maintenance time will be relatively long.
Currently, Russia estimates that it will take several months to repair the damaged pipeline, which is also a normal estimate. It also depends on the sea conditions of the Baltic Sea this winter. The global climate is changing dramatically this year, and I don’t know what will happen in winter.
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