Device for joining of pipelines

In a pipeline used for transporting oil and gas undersea, said pipeline having a Y-connector for joining two branch pipelines (2, 2') to a main pipeline (1) where said main pipeline and said two branched pipelines have similar internal diameter, the improvement in said Y-connector comprising:

• (a) a main pipeline connector (III) having a hollow internal area similar in shape to a truncated cone, said main pipeline connector having an inlet corresponding to the base of said cone and an outlet corresponding to the top of said cone;
• (b) two branch-pipeline-connectors, each one having an inlet and an outlet, and each one having an internal diameter increasing in size from the inlet to the outlet;
• and
• (c) a middle section (II) having an inlet joined to the outlet of each of said two branch-pipeline-connectors and an outlet joined to the inlet of said main pipeline connector, said middle section having two branch-pipeline conduits merge together, the branch-pipeline conduits having circular cross sections which increasingly overlap each other in a central portion between said two branch-pipeline conduits as said two branch-pipeline conduits merge towards the outlet of said middle section, whereby part-circular envelopes remaining outside the overlapped portion of the circular cross-sections always are greater than 180.degree. thereby forming a pair of ridges through said middle section, and whereby the diameters of the overlapping cross sections are greater than the internal diameters of the branch-pipelines and the main pipeline, said Y-connector allowing a pig to pass from either one of said two branch pipelines to said main pipeline thereby following the flow of fluid in said pipeline.