The Utilization of Plastic Pipe for Submarine Outfalls – State of the Art
During the last 25 years, a great number of submarine pipelines have been built in Scandinavia. They are all a result of intensive activity in the field of environmental control, the consequence of which has often been that the last purification step in the wastewater treatment process has been considered to be the dilution of the residual waste into the ocean. Efforts have been made to develop a new piping technology which would allow great depths and points situated far off-shore to be reached, where the risk of problems due to floatable materials flowing back to the shore is insignificant. It has been regarded as especially essential to find a technique which would enable a cheap and rapid procedure for pipe submersion even far off-shore and in heavy sea conditions. The reason for this is that a major proportion of the cost of a submarine pipeline relates to submersion work. Additional requirements were that the pipe material should withstand sudden and even exceptional wave forces and also permit uneven settlements as well as movement of sediment on the sea bed. Thus, the aim has been to develop a highly flexible pipe. The paper presents the state of the art by referring to a submarine outfall project implemented in Sweden 1985. Some need for further development is also discussed.