During the last 15 years multilayer polypropylene coating systems have been developed and used as external coating for subsea pipelines in the offshore industry. There is now an increasing interest in the offshore steel pipe coating market for deep-water fields with a depth exceeding 1000 meters. It is important to have strong bonds between the different polymer layers in a multilayer concept, so the coating sticks to the pipe. To ensure anti-corrosion of the full-length flowlines, it is also important to have good fusion between the field joint (connecting point) and the line pipe coating. The first layer is Fusion Bonded Epoxy (FBE) which is applied to the steel pipe, as the corrosion protective coating. The second layer is a PP based adhesive. This is a grafted polypropylene, which via chemical and physical bonds functions as the glue between the FBE and the third layer, a solid PP. In the second extrusion step foamed PP is applied to the ready made 3 layer PP coating, followed by a solid PP as a top coating. The PP foam provides thermal insulation and the outer layer UV and mechanical protection. As an integral part of the pipe system, the field joint form a part of the uniform thermal insulation coating over the total length of the pipeline. The development trend for polypropylene (PP) materials is towards stiffer PP. The new Generation of stiff PP copolymers has generated the significant advance seen in the PP foam used as thermal insulation in a multilayer pipe coating system for offshore usage. In addition to the stiff PP copolymer, HMS-PP based polymers can be added to further improve pipe insulation, increasing both compression strength and thermal insulation capacity. The new PP foam with its increased stiffness enables the cell structure to withstand a much greater hydrodynamic pressure without risk of undesirable structure changes in the foam (i.e. collapse) thus altering the thermal insulation performance. The major resulting advantage is that PP foam thermal insulated pipes can be introduced for use at significantly greater water depths.
Polypropylene multilayer coating systems for the offshore pipeline industry
2001
10 Seiten, 8 Bilder, 1 Tabelle, 6 Quellen
Conference paper
English
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