INTERNAL & EXTERNAL COATING OF POLYETHYLENE
ON M.S. PIPES

SCAN INDIA have developed a powder coating process where 3 layer polyethylene can be applied both internally and externally on Mild Steel Pipes.
 

This system provides excellent adhesion to the pipe surface with inherent shear resistance properties, impact and cathodic disbondment resistance and very low moisture permeability. The selected materials allow for operating temperatures up to 85^oC and installation temperatures down to -50^oC.
 

In typical three-layer systems, the polyethylene layer is applied by side extrusion for large diameter pipes and by crosshead extrusion for smaller diameter pipes. However, the problem with extrusion  on large diameter pipes with raised spiral or longitudinal welds is poor coverage of the welds especially where the profile is pronounced. There is the tendency  to form voids at the welds neck area  which produces pinholes and entraps water  during the cooling stage. Rollers have been used to compress the molten polyethylene around the weld seam with some success in longitudinal welds.

There is also a reduction of coating thickness at the top of the weld, which results in increased material usage to achieve the minimum required coating thickness. Powder coating avoids these problems.

SCAN Multi-layer  coatings offer

(i) optimization by combining favourable properties of different coating materials, and
(ii)  functional separation of performance such as corrosion protection and protection against mechanical damage.

Three layer pipeline coatings utilize a layer of FBE, a polyolefin outer layer and an adhesive tie layer. FBE is selected  because of its excellent adhesion to steel and their cathodic disbondment resistance. This is achieved because of the strong polar molecular structure, which is also responsible for its high moisture absorption. Polyolefins  are very non-polar, and thus have low moisture absorption and good electrical insulation properties. Interlayer adhesion is attained with a chemically modified polyolefin material with polar end groups, which can form linkages  between the non-polar polyolefin and the polar FBE, "The Polyolifin Adhesive and Polyethylene are similar to each other and intermingle easily to provide excellent adhesion and inherritent shear resistance properties". Thus multi-layer system can offer excellent  adhesion and corrosion properties as well as resistance to mechanical damage.

Typical Product Properties
 

Product Application Process

for
INTERNAL & EXTERNAL COATING OF POLYETHYLENE ON M.S.PIPES