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Diffusers and other elements of the PE underwater pipelines

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Floating with the help of the “stinger”

Such method used a ship (or a pontoon) with an extensible ramp (“stinger”) in an “S” shape. The “stinger” is adjusted to the depth of the seabed, so it is placed the closer to the seabed and it is useful to discharge the sections of the pipe up to the seabed.

Like advantages of such method it is highlighted the reduction of the bending movements and the elimination of the “dent” risk, avoiding the bending both by the smoothness of the curves of the ramp, like the external pressure in the pipe, once the water level within the pipe reaches the sea level and then, it will not be necessary to use compressed air or the application of traction axial forces.

The disadvantage of the method is translated in the slowness of the process and its dependency in the favourable meteorological and sea conditions. Besides, the cost of this method is very high, if we take into account the used means.

Joins of the sections

Most of the pipelines are constituted by multiple sections of pipe of different length, anchored in a sequential way and then, they are joined together with flange adaptors + flanges. The joins could be performed in the surface or in the seabed.

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In some cases, especially when it is used big diameters, it is joined two sections in the seabed by using a pipe section of reduced length (“reel”). Such piece is placed between the two sections and its connexion is performed through a flange and flange adaptors.

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Diffusers

The liquids transported by the pipeline are discharged through diffusers which are placed at the end of the final section. From the hydraulic/sanitarian point of view, the diffusers are the most important elements of the deposition of any liquid in the aquatic environment. Its design and characteristics must follow the environmental recommendations.

Mechanism of the diffusers

The diffusers are normally constituted by a series of round outlets, placed at the final part of the pipeline and outlets, on the top generator of the pipe.

Like the main functions, the diffusers will must have the capacity of maximum discharge with the as low as possible loss of load and impede as far as possible the entrance of sea elements- like sediments and organisms (animals and plants). Such elements can reduce the flow of the pipeline due to the accumulation in the final part and it can make it difficult the cleaning. On the other hand, as long as there is a decrease of the flow of the pipeline, there can be intrusions of salty water in the internal part of the pipeline, affecting the initial capacity of dilution.

To minimize such effects, it is being more and more used some valves called duckbill valves, which are made of elastomeric materials reinforced with nylon or polyester, through a process similar to the tyres for cars and they are very resistant and flexible.

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Its main advantage is the opening and closing in a gradual and constant way, according to the increase or decrease of the flow, guaranteeing an efficient dilution and without intrusion of sea water.

Besides the duckbill valves type diffusers it is also used the diffusers executed with PE reduced tees. A more simple solution for diffusers is to make holes in the superior half of the pipeline for the dilution of the dumping. In this case, the pipeline can be installed in a trench and it must be supported in the seabed.

The advantages of this type of diffusers are the reduced execution costs and the control that can be done along the time, by increasing the number of holes in the case of increasing the flow. The main inconvenient is that the sea water can enter easily in the pipeline and the consequent formation of sediments and sea organisms.

Installation of sections with diffusers

The installation of the sections of the diffusers must not be performed in the same way as the rest of the pipeline. According to the type of the used diffuser will be reduced as much as possible the curvature of the section not to introduce tensions in the outlets of the diffusers which can damage to whole set.

Sometimes, it is used metal structures which provide rigidity to the section of the diffusers and so they can be flooded without producing curvatures, according to the following sequence.

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Reparation in underwater pipelines

The defects or failures in underwater pipelines are produced, for the most part, due to deficiencies of the project and/or construction/execution. They can also have an origin in the external factors (boat anchors, dredges, fishing appliances, etc.) or defected situations like seismic phenomena.

In the case it is necessary to perform reparation it must be taken into account the particularities of the pipeline and as welding can’t be performed under water. The reparation works consist in the use of metal clamps which comprise an elastomeric material band (EPDM), neoprene- against the ends of the pipes to be repaired.

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>>> The underwater pipelines are manufactured with PE 80 or PE 100 material and the pipes are manufactured according to the normative EN 12201. The colour of the pipes must be black or back with brown stripes. Leave a comment.

 

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