Abstract: The present invention provides subsea seawater filtration and treatment system, comprising a filtration assembly (1,3) for filtering out particles and detritus from the seawater; a first pump (5) comprising an inlet in fluid communication with the filtration assembly (1,3) and an outlet; a sulphate removal unit (6) comprising an inlet in fluid communication with the outlet of the first pump (5), a first fraction outlet for sulphate depleted seawater and a second fraction outlet for sulphate enriched seawater; at least one second pump (7) comprising an inlet in fluid communication with the first fraction outlet, and an outlet for the sulphate depleted seawater; wherein the second fraction outlet is in fluid communication with the filtration assembly (1,3), such that the sulphate enriched seawater may be used for backwashing at least a part of the filtration assembly during use.

Abstract: An optical cable unit has a metal tube with a longitudinal laser-welded seam and at least one optical waveguide in the interior of the metal tube. The metal tube has a first inner layer and a second outer layer, where the first inner layer is made from copper and the second outer layer is made from austenitic steel. The longitudinal seam of both layers is laser welded and the seams of the layers are in superimposed alignment, where the laser welding is perfromed by a CO2 laser.