Castoro Dieci.. Sealing of Pipes
Before being laid on the seabed the pipes are welded and sealed on the pipelay vessel. Once the weld is confirmed acceptable, a corrosion-resistant, heat-shrink sleeve is applied around its entire circumference. Then, polyurethane foam is poured into a mould surrounding the weld area. The foam hardens, providing further protection to the weld.
Source for the image and text, is owned by Nord Stream AG