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Steel pipe coating


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GENERAL PRESENTATION
Different system concepts and different range of products
In the last years, multi-layer polyolefin coatings for external pipe protection has significantly grown and this industry has shift away from single-layer polyethylene to three-layer polyolefin pipe coating systems. Table 1 show the main advantages of some of the various types of coatings adopted by pipeline industry.

The three layer system (see fig. 1) provide excellent overall performances as they are the best compromise between the anti-corrosion properties of the epoxy primer and the high mechanical and thermal protection of the polyolefin top coat. The copolymer adhesive layer is applied between the two layers to ensure a total bond of the overall coating system.

LDPE was the main coating for years. But this application is becoming more and more demanding, often pipelines must perform higher operating temperatures and better mechanical requirements, thus MDPE and HDPE have also been developed.

As an answer to the increasing demand of performances Polypropylene system has also been introduced over the past decade. Polypropylene is the solution for pipeline operating at very high temperature (see table 2).

Although little has been published about the operational performance of three-layer systems, experience to date indicates that insignificant corrosion has occurred where polyolefin outer top-coats have remained undamaged.